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A Review of Enhanced Methods for Oil Recovery from Sediment Void Oil Storage in Underground Salt Caverns

Xinxing Wei

^1,2

Xilin Shi

^1,2,*

Yinping Li

^1,2,3,

Peng Li

^1,2

Mingnan Xu

^1,2,

Yashuai Huang

^1,2 and

Yang Hong

^1,2

State Key Laboratory of Geomechanics and Geotechnical Engineering Safety, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China

University of Chinese Academy of Sciences, Beijing 100049, China

Hubei Key Laboratory of Geo-Environmental Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China

Author to whom correspondence should be addressed.

Energies 2025, 18(2), 360; https://doi.org/10.3390/en18020360 (registering DOI)

Submission received: 30 December 2024 / Revised: 10 January 2025 / Accepted: 13 January 2025 / Published: 16 January 2025

(This article belongs to the Special Issue Enhanced Oil Recovery: Numerical Simulation and Deep Machine Learning)

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Abstract

Salt caverns are recognized as an excellent medium for energy storage. However, due to the unique characteristics of China’s bedded salt formations, which contain numerous salt layers and a high concentration of insoluble impurities, significant accumulation at the bottom of salt caverns occurs, leading to the formation of extensive sediment voids. These sediment voids offer a potential space for underground oil storage, referred to as sediment void oil storage (SVOS). Oil recovery process from these sediment voids is a critical process. This paper summarizes the oil recovery technologies for SVOS and identifies four key factors—geological evaluation, stability evaluation, tightness evaluation, and oil storage capacity—all of which influence enhance oil recovery from sediment voids. This paper also outlines the overall oil recovery process, presents oil recovery experiments, and discusses oil recovery methods for enhancing oil recovery from sediment void. Additionally, it addresses the challenges of oil recovery in SVOS and explores its potential advantages and applications. The findings suggest that salt cavern sediment voids, as a promising storage space, provide a new approach to realize oil recovery and can overcome the limitations associated with cavern construction in high-impurity salt mines. The oil recovery from the sediment void is feasible, and China has rich rock salt and other convenient conditions to develop SVOS technology.

Keywords:

underground energy storage; salt cavern; sediment void oil storage; insoluble sediment particles; oil recovery process

1. Introduction

The outbreak of the Russia–Ukraine war and the destruction of surface oil storage tanks have accelerated the strategic arrangements for underground oil storage in various countries [1,2]. Additionally, the instability of the international oil market, along with the influence of external political factors on oil-exporting countries, has made the oil import situation increasingly concerning for many nations [3]. Establishing adequate oil reserves is crucial for the development of national economies and energy security [4,5]. Underground salt cavern energy storage, as the safest and most economical method, has already gained significant momentum in the underground gas storage sector [6,7]. Moreover, salt caverns are also used for the storage of liquid hydrocarbons such as crude oil, petroleum products, diesel, fuel oil, gas oil, kerosene, heavy fuel oil, liquefied petroleum gases (ethane, propane, butane, ethylene, propylene), and 1,2-dichloroethane (DEC) [8]. Salt cavern oil storage is increasingly recognized as an excellent solution for underground oil reserves due to its high safety, low cost, and low risk of leakage [9,10]. The United States, France, and Germany have all established large-scale underground salt cavern oil reserves [11]. China, with its resource profile of abundant coal but limited oil, has become a major oil-importing country [12,13]. In 2020, China’s oil imports reached 542 million tons, and although there was a slight decline in 2021, imports still remained above 500 million tons [12], as shown in Figure 1a. Analysis indicates that China’s oil and gas reserves can only last for about one month, far below the international safety standard of three months [14]. With the growing instability in international affairs and the rise of anti-globalization trends, it has become urgent to accelerate the construction of underground oil reserves to fill the gap in China’s underground oil energy storage [15]. China’s dependence on foreign oil has exceeded 50% for four consecutive years [16], as shown in Figure 1b.

Furthermore, the uneven global distribution of oil resources has amplified the importance of oil storage [18], as shown in Figure 2. Countries such as Iran, Saudi Arabia, and the United States hold oil reserves exceeding 50 billion barrels [19]. Therefore, establishing large-scale underground energy storage facilities in China is crucial for stabilizing the oil supply [15]. Salt caverns, as the optimal medium for underground storage, have already been implemented in numerous engineering projects abroad [20,21,22,23,24], but China has yet to develop salt cavern oil storage facilities [25]. In contrast to the marine-type salt layers found abroad, China’s salt layers are lacustrine in origin, characterized by many interlayers of salt rock and a high content of insoluble impurities [26]. The cavern creation process often generates significant amounts of insoluble particulate sediment. These sediment particles drastically reduce the available storage space within the salt caverns, and the voids between the sediment particles can account for up to 40% of the total sediment accumulation. Utilizing the voids within the sediment particles for oil storage is an effective way to enhance the oil storage capacity of salt caverns [27]. Oil recovery from sediment voids plays a crucial role in the operation of the SVOS. Utilizing sediment voids for oil storage can significantly advance global salt cavern energy storage technology, providing an ideal underground space for this purpose.

Research on oil storage in sediment voids within salt caverns is limited both domestically and internationally. These sediment voids, located within the cavern, follow a similar oil storage process to that of conventional salt cavern storage. Consequently, it is essential to first analyze traditional salt cavern oil storage methods and then investigate strategies for enabling oil recovery from the sediment voids. Regarding the oil storage process in salt caverns, Wang et al. [25] analyzed the cooling process of oil recovery from the salt cavern, and they proved the effectiveness of the heat exchanger. From the perspective of salt cavern oil storage modeling and numerical analysis, the scholars focused on operation stability evaluation [29], allowable salt pillars [30], salt cavern model construction [31], proper cavern shape construction [32], wellbore damage and oil leakage [33,34], geomechanical simulations of a salt cavern model [35], oil injection analysis [36], and oil casing construction [37,38,39]. In terms of safety and stability, Wang [40] established an evaluation method for the stability of salt cavern oil storage, from the acquisition of geological parameters to the establishment of stability indicators and subsequent simulation. This method provides a comprehensive evaluation approach for salt cavern oil storage stability. Wei et al. [41] studied the oil recovery process from sediment voids, demonstrating that the average oil recovery rate could reach up to 90%. Liu [42] studied two-phase flow in single channels and investigated the effect of wall surface roughness on the flow. In summary, SVOS technology is evolving, but research on oil recovery methods, particularly from sediment voids, remains limited. The feasibility of oil recovery is critical for evaluating SVOS, and it serves as the primary focus of this paper. This study aims to explore the oil recovery process from salt cavern sediment voids, considering various influencing factors. The findings could contribute to the large-scale development of salt cavern oil storage in high-impurity salt mines. The novelty of this paper lies in integrating traditional salt cavern oil storage technology with the proposed sediment void oil storage approach. The oil recovery process is examined from theoretical, experimental, and field application perspectives. The structure of the paper is as follows: Section 2 analyzes the development of oil recovery technologies for SVOS in both China and other countries, identifying key influencing factors such as geological evolution, stability, tightness, and oil storage capacity. Section 3 evaluates the oil recovery process and methods for SVOS, proposing oil recovery techniques. Section 4 addresses four major challenges in oil recovery: oil loss, oil flow behavior, recovery simulation, and cavern construction. Finally, Section 5 discusses the potential advantages and applications of oil recovery in SVOS.

2. The Development of Oil Recovery from Sediment Void

2.1. Oil Recovery Technologies Worldwide

Ever since the concept of underground salt cavern energy storage was first proposed by German scientist Erdöl in 1916, significant progress has been made [43]. In 1959, the Soviet Union established the world’s first salt cavern gas storage facility [44]. Since then, large-scale salt cavern energy storage has continued to develop, with more than 2000 salt caverns worldwide now used for storing various underground energy resources [45,46,47]. Oil, as a major form of underground energy, was first stored in salt caverns abroad in the 1950s [48]. In the United States, all of the country’s oil reserves are stored in underground salt formations, primarily around the Gulf of Mexico [49]. This setup facilitates the transfer of offshore oil. Additionally, countries such as France, Germany, and Canada have also established underground salt cavern oil storage facilities [50]. According to incomplete statistics, the United States has a strategic oil reserve in salt caverns amounting to 103 million tons, while Germany, France, and Canada have approximately 10 million cubic meters of oil storage capacity in salt caverns. Notably, Germany’s Etzel salt dome, located in Wilhelmshaven, has an oil storage capacity of 13 million cubic meters [51]. Canada has also established a salt cavern ethane storage facility in Alberta’s Saskatchewan region [52], as shown in Figure 3.

In addition, salt cavern oil storage is also highly cost-effective. As shown in Table 1, the storage cost per barrel of oil in underground salt caverns is approximately USD 5.50. This is about one-third the cost of underground rock cavern storage and one-seventh the cost of surface tank storage, highlighting a significant cost advantage. Therefore, when underground salt rock resources are accessible, using salt caverns for oil storage offers an excellent solution for large-scale underground oil storage.

Although there are high-impurity salt layers abroad, their utilization of the sediment void of salt cavern is relatively limited due to the high level of rock salt exits. As a result, the oil injection and recovery processes are carried out within the clean space of the salt cavern. The oil injection and recovery process in foreign salt caverns is shown in Figure 4. During oil injection, the oil is pumped through the annular space of the wellbore and injected into the cavern, while brine is discharged through the central pipe, completing the oil storage process in the salt cavern.

The specific oil recovery process involves injecting saturated brine through the central pipe, with oil being discharged from the annular space of the casing. Since brine is denser than oil, the injected brine displaces the oil inside the salt cavern, thereby completing the extraction process. In this process, the losses due to the adhesion of oil to the salt cavern walls and casing, as well as the micro-leakage of oil through the salt cavern, are neglected. As a result, most of the oil can be effectively extracted from the cavern. The extracted oil is then processed and refined, and once it meets the required quality standards, it can be used in factories or at petrol stations.

2.2. Oil Recovery Technology in China

China has yet to establish any salt cavern oil storage facilities. A comparison of five oil storage methods, considering domestic salt resources and oil reserves (see Table 2), reveals that the majority of the country’s oil reserves rely on surface and semi-surface tanks, with only one underground rock cavern storage facility in operation. Among these methods, salt cavern oil storage is the most cost-effective option. China has abundant salt resources, with a long history of salt mining. However, the development of salt cavern energy storage is hindered by the accumulation of insoluble impurities within the caverns, which reduces available storage space. To address this challenge, the concept of using sediment voids for oil storage has been proposed, along with a new oil recovery process for these voids.

To analyze the oil recovery process from the sediment void, it is crucial to determine the resources of sediment particles. Understanding the properties of sediment particles is crucial for analyzing the oil recovery process. Figure 5a illustrates a salt-dome-type salt rock, where after the water dissolution cavern creation process, there is little to no sediment at the bottom of the cavern. Figure 5b shows a typical stratified salt rock, where numerous interlayers exist between salt layers. These interlayers are primarily composed of insoluble rocks such as anhydrite or mudstone. During the solution mining process, methods like the oil cushion technique or nitrogen injection are used to control the dissolution of freshwater along the cavern’s sidewalls. This promotes the collapse of the interlayers, which enhances the cavern’s storage capacity. The collapsed interlayers, influenced by gravity, fracture and accumulate at the bottom of the cavern. Additionally, insoluble impurity particles from the salt rock settle at the cavern’s base. Sediment particles in these caverns have a much larger particle size compared to traditional oil reservoir storage, and the void spaces within them are abundant. These voids can be utilized for storing oil [41], natural gas [62], and other energy resources. Using sediment voids for energy storage is an important method for expanding the storage capacity of underground salt caverns. Field experiments on salt caverns have demonstrated that the internal voids of sediment also exhibit good connectivity with minimal resistance [63].

For oil storage in salt cavern sediment voids, we propose corresponding oil injection and recovery processes. Figure 6a illustrates the oil injection process for SVOS, where the oil injection and brine discharge lines are fully separated. Oil is injected through the oil injection line and gradually enters the sediment, starting from the upper part of the sediment pile. Meanwhile, brine is displaced and gradually exits from the lower part of the sediment pile, ultimately being expelled through the brine discharge line. As oil continues to be injected, the void spaces within the sediment particles fill with oil, while brine is progressively expelled from the sediment voids.

For oil recovery in SVOS, brine is injected through the brine injection string, while oil is extracted via both the injection and production strings. As brine is injected, oil within the sediment voids is gradually extracted, as shown in Figure 6b. The recovered oil may contain small sediment particles, which can be removed through surface settling and impurity removal processes, ensuring that oil quality is not affected. Compared to traditional salt cavern oil storage in the net space, the oil recovery rate may be lower. During the oil recovery process, some oil will adhere to the sediment particles, particularly for oils with higher viscosity, where the adhesion forces are stronger and brine cannot fully displace the oil. The pores inside the sediment will absorb some of the oil; however, this absorption effect is weak, as gypsum and mudstone sediments are hydrophilic, and the existing saturated brine environment fills most of the sediment’s pores with brine. Additionally, oil in disconnected or blind-ended voids, as well as in blocked or clogged pores, cannot be recovered.

Figure 7a illustrates the novel sediment void oil recovery process, while Figure 7b depicts the traditional salt cavern oil recovery process. SVOS offers a significantly larger oil storage capacity compared to traditional salt cavern storage. The oil recovery efficiency of SVOS is crucial for evaluating its feasibility.

2.3. Oil Recovery Influencing Factors Analysis from Sediment Void

2.3.1. Geological Evaluation of Sediment Void Oil Storage

The oil recovery of SVOS is closely linked to geological conditions. Geological feasibility evaluation plays a crucial role in utilizing sediment voids within salt caverns for oil storage, requiring an in-depth analysis of factors such as the fault system, regional seismic characteristics, sedimentary features of the strata, regional structural characteristics, interlayer integrity, and composition of interlayers. The impact of geological conditions on the oil recovery process can be divided into three key aspects, as shown in Figure 8.

Firstly, the thickness and purity of the salt layers, as well as the presence of interlayers, affect both the quantity of sediment deposits and the void spaces within the sediment. The content of sediment at the bottom of the cavern is typically determined by analyzing the solubility of the salt layers involved in the cavern creation. If the interlayer quantity is low and the salt layers contain a high amount of insoluble impurities, the sediment at the cavern bottom will be fragmented, and the connectivity of the voids within the sediment will be poor. Conversely, if the number of interlayers is high and the sediment particles formed by the collapse of these interlayers are larger than those created by insoluble impurities in the salt layers, the voids within the sediment will be larger. The size of these sediment voids directly affects the ease of oil recovery.

Secondly, the rock properties of the salt strata influence the connectivity within the sediment voids, which in turn impacts the oil recovery process. If the interlayers and the majority of the salt layers consist of anhydrite, the accumulated anhydrite sediment will have weak water absorption and expansion capabilities, leading to better connectivity of the sediment voids. By contrast, if the sediment consists of clay-rich particles, such as mudstone containing expansive minerals like montmorillonite or bentonite, the water absorption and expansion ability of the sediment will exceed that of the anhydrite, leading to particle clogging and negatively affecting oil recovery efficiency. Thus, the geological evaluation results will influence the sediment void connectivity and the oil recovery process. In more detail, if the interlayer within the salt layer is thick and strong, there is a higher likelihood of overall collapse during the water-soluble cavern construction process, which leads to better connectivity of the sediment voids at the bottom of the salt cavern. On the other hand, if the interlayer is thin and weak, the connectivity of the resulting sediment voids is poorer. Additionally, the overall solubility of the salt layer, as assessed in the geological evaluation, influences the height of the sediment accumulation. The higher the content of insoluble materials in the salt layer, the more sediment accumulation will be formed.

Additionally, geological conditions also impact the stability and sealing properties of the SVOS. During the oil recovery process from the sediment void, changes in cavern operation pressure can occur. If faults or other adverse geological conditions are present, there is a risk of cavern roof collapse, which could lead to oil leakage. The stability and sealing characteristics during the oil recovery process will be analyzed separately in the following sections.

2.3.2. Stability Evaluation of Sediment Void Oil Storage

The oil recovery of SVOS is also related to the stability of the salt cavern. The sediment voids in salt caverns may be influenced by factors such as geological movements and pressure variations, making it essential to evaluate the stability of these sediment voids. Long-term oil storage and extraction can lead to changes in the shape of sediment voids, which in turn may affect the efficiency of oil recovery. The chemical stability of the sediment voids also plays a crucial role in determining the success and efficiency of the oil extraction process [64]. The stability of oil recovery in SVOS can be analyzed from three key aspects. From a chemical perspective, before initiating oil extraction, experimental studies should be conducted to analyze the chemical reactions between the sediment particles and the stored oil. It is also important to evaluate the stability of the sediment particles under varying external conditions, such as temperature and pressure, throughout the storage process. In an ideal scenario, the sediment particles should act as stabilizers for the oil, preventing any changes in the oil’s quality and appearance during storage, thereby ensuring the stability of the oil storage. The key to this process is measuring the total acid value of the stored oil to determine whether any chemical reactions occur between the sediment particles and the oil [65]. The chemical reaction between oil and sediment particles occurs as follows: naphthenic acid in the oil phase reacts with calcium sulfate to form calcium naphthenate, which then dissolves in the oil. This reaction is enhanced by high temperatures. To model the deterioration of stored oil quality, detailed laboratory experiments are needed.

C_{n} H_{2 n - 1} C O O^{-} + C a^{2 +} \to {(C_{n} H_{2 n - 1} C O O)}_{2} C a

(1)

In addition, the overall stability of the salt cavern during the oil recovery process is critical. As brine gradually displaces the oil, the internal pressure of the cavern changes, which can affect the cavern’s structural stability. If the cavern becomes unstable and fractures occur, the oil recovery process will be interrupted, and the ability to extract oil from the sediment voids will be significantly reduced. To assess the stability of the salt cavern during oil recovery, the following methods should be employed, as shown in Figure 9.

From a microscopic perspective, the stability of sediment particle morphological changes during long-term injection and production processes is also crucial [66]. If, during oil recovery, the morphology of sediment particles changes, the original sediment void channels may become blocked. Therefore, analyzing the morphological changes in particles during the oil recovery process is an important aspect of assessing the stability of the extraction process. This can be performed using particle simulation software such as PFC 6.0 (Particle Flow Code) to study the behavior of sediment particles and predict potential blockages, providing valuable insights into the overall stability of the oil recovery operation.

2.3.3. Tightness Evaluation of Sediment Void Oil Storage

The tightness during the sediment oil recovery process is crucial for ensuring the smooth execution of oil extraction. This tightness involves several key components: the caprock tightness, interlayer tightness, and the overall cavern tightness [67]. The caprock, located directly above the salt cavern, serves as the first barrier to prevent oil leakage, while the secondary caprock, situated above the primary caprock, provides an additional layer of protection. The permeability and breakthrough pressure of these caprock layers are critical indicators of their tightness, and both should be measured to ensure the stability and reliability of the seal. Additionally, the tightness of interlayers is essential to prevent oil leakage through horizontal strata. Scanning electron microscopy (SEM) is commonly employed to assess the tightness of these interlayers, which is vital for the successful operation of oil storage in salt caverns. Interlayer tightness is a key factor in the selection of appropriate salt caverns for storage. As for the overall tightness of the cavern, ensuring airtightness is paramount to preventing oil leakage, which is a fundamental aspect of the facility’s construction and operation. Two primary methods are employed for detecting cavern tightness, gas leakage testing (API method) and liquid leakage testing (Geostock method) [68], as shown in Table 3. While both methods are applicable, liquid leakage testing is generally preferred for oil storage due to its higher sensitivity to airtightness requirements. The two main approaches for evaluating cavern airtightness include monitoring the leakage rate over time, which should gradually decrease and eventually stabilize, and assessing the gas–brine interface to ensure that changes are minimal, typically less than 1%, during the monitoring period [69].

Currently, the most suitable method for evaluating the tightness of salt caverns is the field liquid leakage test, while indoor experiments and tightness simulations are considered auxiliary methods. Sediment particles tend to accumulate at the bottom of the salt cavern, which has minimal impact on the field liquid sealing test. The sediment voids exhibit great connectivity, allowing liquid to flow easily through them. In high-impurity salt formations, tightness challenges primarily arise from interlayer tightness failures, as the porosity and permeability of interlayers are higher than those of the rock salt layers. To address this issue, a cost-effective solution is to inject ultra-fine cement slurry into the interlayers to enhance tightness.

2.3.4. Oil Storage Capacity of Sediment Void Oil Storage

The oil storage capacity of sediment voids directly impacts their oil recovery potential, and different sediment voids with varying storage capacities may require different displacement mediums during the oil recovery process. If the sediment void has a large storage capacity and good connectivity, its oil recovery ability will also be stronger. There are two main methods for measuring oil storage capacity: sonar measurement and the salt dissolution volume method. Sonar measurement is the most commonly used method for determining the oil storage capacity of salt caverns [70]. It provides two-dimensional and three-dimensional images of the cavern [71]. Sonar equipment is lowered through the wellbore into the cavern, emitting sound waves of specific frequencies towards the surrounding cavern walls. The sonar device then receives the sound waves reflected by the cavern walls. By continuously descending and rotating, the sonar measures the distance between the surrounding walls at the same position at different heights. A three-dimensional model of the cavern is then created using computer simulations based on the sonar data [72], allowing for the detection of the cavern’s volume, as shown in Figure 10. However, sonar cannot measure the thickness of the sediment deposits or the extent of the sediment-covered areas.

The salt dissolution volume method relies on the principle of salt dissolution in water. By maintaining constant cavern pressure and using the concentration of saturated brine, the amount of dissolved salt can be calculated, and the dissolved volume of the cavern can be estimated. This method allows for a more accurate determination of the oil–water interface in the cavern, although it has relatively lower measurement precision. In addition to the two methods mentioned, geophysical techniques such as three-dimensional seismic surveys are also applied to assess the oil storage capacity of sediment voids. These methods gather seismic wave data to construct a three-dimensional image of the underground salt layers. Therefore, to determine the oil storage capacity of sediment voids, it is necessary to use a combination of sonar measurements, the salt dissolution volume method, and three-dimensional seismic surveys. This integrated approach will provide a comprehensive understanding of the height and depth of the sediment deposits and their potential for oil storage. In addition, the sediment void storage capacity can also be obtained by the brine injection method. This involves injecting brine into the sediment voids until the brine level matches the height of the sediment surface and then discharging the brine. The ratio of the volume of discharged brine to the total volume of the sediment deposit represents the internal porosity of the sediment, which also reflects the sediment’s storage capacity.

3. Oil Recovery Process and Method from Sediment Void

3.1. Oil Recovery Process of Sediment Void Oil Storage

The oil recovery process in salt cavern storage primarily involves three construction components: the brine injection station and pipeline network, the crude oil injection and extraction station with its pipeline network, and the crude oil export pipeline. Brine and crude oil are transported through a closed-loop pipeline system to achieve oil storage in the salt cavern. During oil recovery from sediment voids in salt caverns, oil viscosity causes the initial injected oil to adhere to sediment particles, lowering recovery efficiency. To address this issue, waste oil or lower-economic-value oil should first be injected to coat the particle surfaces, followed by high-value oil. The lower-quality oil should have similar properties to the high-value oil to simplify later purification processes. During storage, oil inevitably carries small rock particles due to sediment presence. Traditional filtration methods struggle with such particles because of oil viscosity, and filter wear is significant. To improve the purity of extracted oil, centrifugal separation can be used to effectively remove particles, followed by further separation through oil–water–sediment devices. As depicted in Figure 11, the brine is injected through the central brine pipe, while the oil is extracted through the production pipes on both sides. Pressure gauges are installed above the wellhead to monitor the brine injection pressure and oil extraction pressure.

In addition, safety concerns surrounding SVOS in salt caverns must be carefully addressed. Blowout incidents, such as the West Hackberry salt cavern blowout near the Gulf of Mexico in southern Louisiana, highlight the risks. This incident occurred due to packer failure, resulting in oil blowout and fire. A similar blowout involving particle-laden oil would cause even greater damage to the surrounding infrastructure and the environment. Therefore, ensuring reasonable and effective control of pressure variations during oil recovery is fundamental to the safe operation of SVOS in salt caverns. Wu [23] analyzed that a salt cavern can be viewed as a pressure vessel, with high-pressure fluids sealed within its surrounding layers. However, it differs significantly from a standard container. First, the oil storage cavity in a salt cavern can reach heights of up to 1000 m. At such a vertical difference, the pressure at the base, as described by the liquid pressure formula, shows that even small density differences can lead to substantial changes in the weight of the fluid column. Additionally, the cavern’s large volume—up to

1 \times 1 0^{6} m^{3}

—means that even a minor pressure drop can cause significant changes in the amount of material inside. This underscores the importance of considering the incompressibility of liquids, as neglecting this factor could result in negative pressure within the cavern. Storing oil in sediment voids helps to mitigate salt cavern shrinkage, as the sediment particles themselves act to stabilize the cavern, enhancing its overall stability.

The oil recovery process in salt cavern storage can be achieved using different displacement media, as shown in Table 4. The table compares four oil recovery methods for salt cavern sediment void storage: saturated brine displacement, freshwater displacement, compressed air displacement, and the pumping method. Saturated brine and freshwater displacement are mature techniques but require significant brine management. Compressed air displacement avoids water dependence but involves high equipment costs. The pumping method is simple and cost-effective but unsuitable for sediment void storage. Overall, saturated brine displacement is the most feasible, while freshwater and compressed air methods show potential under specific conditions.

Based on the aforementioned oil recovery factors and salt cavern construction methods, an integrated oil recovery process for SVOS is proposed, as illustrated in Figure 12. The process begins with site selection for SVOS, followed by the establishment of SVOS volume parameters and oil recovery volume parameters. Subsequently, the stability and integrity of both the salt cavern and sediment void are assessed. If the results of the stability and integrity evaluations fail to meet the required standards, the site selection process should be revisited. Following successful evaluation, cavern leaching, equipment installation, and oil injection into the sediment void are performed. When oil extraction is necessary, appropriate oil recovery mediums and methods are employed to achieve the desired oil recovery objectives.

3.2. Oil Recovery Experiments of Sediment Void Oil Storage

Oil recovery experiments in SVOS are a crucial step. Figure 13a illustrates the oil extraction setup, which includes five key components: a brine pump, debrining string with simulated salt cavern, oil tank, electrical balance, and data logging system. The brine pump ensures steady brine injection, displacing oil from the sediment void, while the debrining string and simulated cavern store the sediment particles and oil. The oil tank collects the extracted oil, and the electrical balance measures its weight. The process involves placing oil and sediment into the simulated cavern, connecting the components, checking system tightness, injecting brine, and monitoring the extraction rate. Figure 13b shows the extraction process in three stages: (1) oil is stored in the sediment void, (2) brine displaces the oil, with some remaining due to adhesion to particles, and (3) most of the oil is extracted, leaving the void filled with brine. The process highlights the importance of system tightness and addresses the challenge of oil adhering to sediment particles. The oil recovery experiments show that the maximum oil recovery rate can reach 90.0%.

Figure 14 presents the oil recovery results from the sediment void, with recovery rates of 92.7% for diesel at 25 °C, 93.6% for diesel at 50 °C, and 98.7% for petrolatum at 25 °C, all exceeding 90%. These results indicate that sediment voids are suitable for oil storage. The higher recovery rate for petrolatum (98.7%) compared to diesel (92.7%) suggests that lower-viscosity oils recover more effectively. Furthermore, diesel recovery improves at 50 °C, demonstrating that higher temperatures enhance recovery. The experimental results confirm that oil recovery from sediment voids is feasible, with oil viscosity and temperature influencing the recovery rate. However, due to the complexity of real-world conditions, laboratory results may not fully replicate actual field conditions. Therefore, field experimental studies on sediment void oil storage in salt caverns are necessary.

3.3. Oil Recovery Methods of Sediment Void Oil Storage

Utilizing the sediment voids in salt caverns for oil storage is an expansion of the original storage capacity. In traditional oil field development, the reservoir’s oil capacity is limited by the rock’s porosity and permeability. However, due to the unique structure of salt cavern sediment voids, they may potentially accommodate more oil. Therefore, the technology of using sediment voids for oil storage inherently oil recovery process. To further increase the recovery rate from these sediment voids, our research aims to maximize the extraction of oil stored within these voids. This can be achieved by employing appropriate techniques such as water injection, gas injection, and other reservoir management methods, which could help improve the flowability of the sediment voids and enhance the overall extraction efficiency.

For the oil recovery of SVOS, we proposed the following measures aimed to enhance the oil recovery. To begin with, it is important to consider that sediment particles tend to adhere to oil, with this adhesion being mostly a one-time occurrence. That is, when oil first comes into contact with the sediment, adhesion happens, but subsequent adhesion is minimal. Therefore, injecting low-quality oil initially allows it to thoroughly permeate the sediment particles, reducing the loss of high-quality oil when it is introduced later. Additionally, to minimize the impact of oil mixing on oil quality, it is advisable for a salt cavern to store the same type of oil consistently. If sediment voids experience clogging during the oil recovery process, brine can be injected through the oil injection well to flush out the clogging and restore connectivity within the sediment voids. This ensures the continuity of the sediment voids before continuing with oil extraction.

Furthermore, selecting an appropriate displacement medium can improve the oil recovery from sediment voids. The most common method is brine injection, which displaces the crude oil in the sediment voids, directing it toward the extraction well and improving recovery rates. When the connectivity of the sediment voids is good, most of the oil in the connected voids can be recovered. Injecting gases such as natural gas, carbon dioxide, or nitrogen can also assist in oil extraction from sediment voids. However, it is crucial to ensure that the injected gas does not react with the oil, as this could degrade its quality. Although gas injection for oil recovery has not yet been applied in salt cavern extraction, its feasibility should be analyzed, taking into account its potential impact on cavern stability, sealing, and the quality of the extracted oil. If gas injection proves feasible, using CO₂ to displace oil from the sediment voids could further oil recovery efficiency.

4. Problems of Oil Recovery from Sediment Void

4.1. Oil Loss Problem of Sediment Void Oil Storage

The oil loss in sediment void storage in salt caverns is relatively lower compared to surface storage tanks due to its good sealing and stability. However, the main factors contributing to oil loss include the leakage of oil due to issues with the sealing of the salt cavern, the adhesive effect of oil caused by its viscosity interacting with the salt cavern wall and sediment particles, degradation of oil caused by reactions between certain minerals in the salt rock and the oil, and oxidation and volatilization of oil caused by poor sealing at the casing. Most of these losses are due to engineering construction errors. To mitigate the adhesive effect, one solution is to inject waste oil first, followed by new oil. Additionally, the unavoidable losses from the adhesion of oil to sediment particles and the mixing of oils with different densities should not be overlooked. Furthermore, in deeply buried salt caverns, temperature-induced evaporation of oil can also contribute to oil loss. A different oil recovery medium leads to a different oil recovery rate, and it is necessary to carry out the proper oil recovery medium to reduce the oil loss in sediment voids.

4.2. Oil Flow Rule in Sediment Void

The flow mechanism of oil in the particle pore spaces is still not fully understood, especially in the oil extraction process from sediment voids, where the microscopic flow and displacement processes of brine and oil inside the sediment void need further investigation. Currently, most research focuses on the macroscopic level, lacking in-depth analysis of the microscopic flow behavior of oil and water phases in sediment voids. The changes in the oil–water interface within sediment voids, as well as the effects of brine injection rates and oil recovery efficiency, require further validation through experiments and simulations. The variation in the oil–brine interface directly affects oil recovery efficiency, particularly during the flow of oil and water. The complex structure and uneven pore distribution in sediment voids significantly impact the displacement efficiency of oil. Therefore, studying the effects of different brine injection rates, pressure gradients, and other factors on the oil–water interface is crucial to improving oil recovery efficiency. Existing research has not fully considered the impact of sediment pore structure, chemical reactions, and capillary effects on the distribution of oil and water. Future studies should use microfluidic models and advanced imaging technologies to better explore the mechanisms of oil–water phase exchange. In summary, further experimental and simulation research is essential to reveal the microscopic mechanisms of oil and water flow during oil extraction from sediment voids. This will help optimize extraction processes, improve oil recovery rates, and promote the sustainable development of sediment-based oil storage technology.

The efficiency of oil recovery from sediment voids in salt caverns is influenced by both microfluidic processes and geological and technological factors. Understanding the interaction between these elements is essential for optimizing the oil displacement process. Oil flow in sediment voids is a liquid–liquid two-phase flow, with recovery efficiency affected by factors such as interlayer thickness, void structure, oil viscosity, and brine injection pressure. Sediment primarily forms from the collapse of interlayers; the thicker and stronger the interlayer, the larger the sediment particles, which creates more void spaces between the sediment deposits. These void spaces facilitate easier oil recovery, as even high-viscosity oils can flow through the sediment voids, reducing the brine injection pressure required for extraction. The sediment void structure also plays a key role in recovery. In cases with complex void structures, some oil may remain trapped in the intricate internal voids during extraction. Therefore, complex void structures are better suited for storing low-viscosity oils, while simple void structures are more effective for high-viscosity oils.

4.3. Oil Recovery Simulation from Sediment Void

Currently, research on SVOS is relatively limited, making the development of relevant numerical simulation studies particularly important. Such research not only helps to deepen the understanding of the physical and chemical mechanisms involved in the SVOS process but also provides theoretical support for practical engineering applications. In numerical simulations of sediment oil storage, coupled simulations using PFC (Particle Flow Code) and FLAC (Fast Lagrangian Analysis of Continua) are widely used to study the stability of sediment oil storage. This method can accurately simulate the changes in the morphology of sediment particles and their interactions with brine and oil phases, thus providing essential data support for evaluating and optimizing the oil storage process.

Additionally, to address potential sealing issues during the sediment oil extraction process, simulation software such as COMSOL software 6.2 is used to analyze the sealing performance under different brine injection pressures. These simulations can optimize the sealing design during the sediment oil storage process, reduce the risk of leakage, and ensure the safe extraction of oil. To further improve oil extraction efficiency, the application of machine learning techniques, particularly large models such as neural networks, has become an important direction in current research. These technologies can help construct more accurate models for displacement fluids and key parameters such as displacement rates, thereby improving the oil recovery rate from sediment voids.

4.4. Sediment Void Oil Storage Construction Problem

The location of SVOS in salt caverns is influenced by natural conditions and requires precise geological exploration to ensure the stability of the salt rock and suitability for cavern formation. Advanced exploration techniques assess the salt layer’s thickness, fractures, and aquifers, supporting site selection. The project also necessitates new pipelines for oil and brine transport, with attention to pressure, corrosion, and long-term stability. Real-time cavern monitoring technologies, such as high-precision sensors, satellite remote sensing, and underground acoustic imaging, are essential to track cavern shape, pressure, and oil–gas distribution, preventing leaks or instability. Additionally, a sufficient brine supply is critical for cavern maintenance and oil extraction. A well-designed pipeline layout and surface oil–water separation facilities are key to efficient oil extraction, impacting oil purity and recovery rates. The entire system must integrate underground capacity, pipelines, monitoring, and separation technologies to ensure efficient, safe, and economical oil extraction [74].

Sediment void oil storage is more economically viable than traditional oil storage methods. With the same infrastructure investment, traditional salt caverns can only store oil in the net space above the sediment, whereas sediment void oil storage in salt caverns can utilize both the voids above the sediment and the gaps between the sediment particles. This reduces the cost of oil storage in salt caverns from a unit construction perspective. Environmentally, the sediment at the bottom of the salt cavern remains inside, without reaching the surface, which results in less environmental impact compared to traditional methods. The main environmental risk of sediment void oil storage arises from the potential extraction of small sediment particles during the recovery process. However, this can be managed by installing cooling and sedimentation devices on the surface to remove these particles, ensuring proper treatment to prevent environmental harm. From a risk perspective, while sediment void oil storage may result in slightly higher oil loss than traditional salt cavern storage, this risk can be controlled. Using low-viscosity oil in sediment void storage can minimize the risk of loss.

5. Advantages and Application of Oil Recovery from Sediment Void

5.1. Potential Advantages of Sediment Void Oil Storage

China is rich in salt rock resources, with large-scale underground salt mines distributed across regions such as East China, Northern Jiangsu, Southern Jiangsu, Huainan in Anhui, and Shandong [75]. This provides a solid foundation for the development of underground oil storage in salt caverns. Additionally, a salt cavern gas storage facility has been operational in Jintan, Jiangsu, offering valuable insights for the development of related salt cavern oil storage projects [76]. Furthermore, the process of oil recovery from sediment voids in salt caverns requires sufficient freshwater and brine disposal capacity. Freshwater enters from the surface, and after dissolving the salt, the brine is discharged through the brine drainpipe, allowing for the extraction of the salt layer. Once the salt is extracted, the cavern can be used for crude oil storage.

The geographical feature of China, with a high western region and a low eastern region, provides favorable conditions for water resources [77]. The water systems in the eastern region are well developed, with the Yangtze River’s tributaries and main rivers passing through the eastern provinces, providing abundant freshwater sources. Thus, the eastern region has sufficient water resources and salt rock resources for the development of water-soluble cavern creation, making it an ideal area for large-scale SVOS. Additionally, besides the oil pipeline developed in the northern region with Russia, most of China’s oil imports are transported via maritime routes. Therefore, salt-soluble caverns should be located near ports to reduce transportation costs and improve efficiency. For example, the majority of US oil reserves are concentrated around the Gulf of Mexico [78], which benefits oil storage and transportation, reducing transportation and intermediary losses. China’s long eastern coastline provides a clear advantage for establishing large-scale salt cavern SVOS bases.

Moreover, the vast consumption potential of the eastern region, especially for oil and other chemical products, means that oil storage reserves can also be used for actual consumption in industrial applications. In parallel, large-scale projects like the West-to-East Gas Transmission project have accelerated the development of salt cavern gas storage in the eastern region. The site of salt cavern oil storage projects shares many similarities with natural gas storage, and the location selection for oil storage can benefit from the experiences of gas storage site selection. China’s major salt mines are primarily located in the southern provinces such as Hubei, Yunnan, and Zhejiang, with significant distributions in Xinjiang and Qinghai. From the perspective of energy reserves and economic value, the utilization of salt mines in the southeastern region holds greater potential.

The feasibility of SVOS in eastern China is supported by favorable geological, infrastructural, and resource conditions. The region has abundant salt layers, a flat terrain, and a simple equipment layout, making construction easier. It also benefits from a dense railway network, strong port infrastructure, and sufficient water resources from the Yangtze River tributaries. Market conditions, such as concentrated industries and high energy consumption, align well with SVOS requirements. Additionally, the region’s talent concentration and easy technical development further enhance the feasibility of SVOS implementation. The successful construction of SVOS would strengthen national energy reserve capacity and promote the development of related industries, as shown in Figure 15.

5.2. Potential Application of Sediment Void Oil Storage

Figure 16 presents the present engineering salt cavern shape, indicating that the traditional oil storage volume of a salt cavern is only about

1.7 \times 10^{5} m^{3}

without considering the SVOS. The mining volume is about

1.66 \times 10^{6} m^{3}

based on the brine production data. This indicates that 90% of the cavern is filled with sediment void. During the oil recovery process, the oil is injected into the salt cavern by the C1-well and the C2-well, and the brine is discharged from the C3-well. The oil can be stored in the sediment void based on the above experimental results; the oil–brine interface can enter the inner sediment particles. If the sediment void utilization ratio can reach 40.0%, the oil storage volume can reach

7.7 \times 10^{5} m^{3}

. The SVOS technology can increase the oil storage capacity of salt caverns by 4.5 times compared to traditional SCOS technology.

6. Conclusions

Oil recovery is a key factor influencing the feasibility of salt cavern sediment void oil storage, yet existing research often overlooks the application of sediment void utilization. The goal of this research is to analyze the oil recovery process from sediment voids in the context of high-impurity salt mine construction. This study considered factors affecting oil recovery, the recovery process, and methods, as well as the applications, problems, and challenges associated with salt cavern sediment void oil storage through theoretical analysis, experimental studies, and potential field applications. Salt cavern sediment void oil storage has the potential to overcome limitations in high-impurity salt mines and contribute to large-scale underground oil storage. This novel oil recovery technology can enhance national energy storage capacity and contribute to global energy security. The major findings of the study are as follows:

The development of salt cavern oil storage technology was summarized, and the oil recovery technology of salt cavern sediment void oil storage was proposed. The sediment void oil storage method can broke the forbidden zone in cavern construction in high-impurity salt mines. The oil recovery process from salt cavern sediment void was proposed.
Four influencing factors that influence oil recovery from sediment void were proposed, which are geological evaluation, stability evaluation, tightness evaluation, and oil storage capacity. The geological evaluation results can influence the connectivity of sediment void and oil recovery ratio.
The oil recovery process of sediment void oil storage was proposed, and the corresponding oil recovery experiment was summarized. A series of techniques enhancing oil recovery methods for the sediment void oil extraction process were proposed. The overall oil recovery process of sediment void oil storage was proposed.
The four problems that influence the oil recovery of sediment void oil storage were proposed, which are oil loss in sediment void, oil flow rule in sediment void, oil recovery simulation in sediment void, and sediment void oil storage construction.
The potential advantages of sediment void oil storage construction in China were analyzed, and the potential application oil recovery in sediment void was analyzed. China has rich rock salt and other convenient conditions to develop SVOS.

In the future, it is necessary to conduct in situ tests for SVOS in China, and the in situ results could provide valuable data for verifying and improving SVOS applications under Chinese conditions. In addition, it is also crucial to explore the integration of SVOS with other energy storage technologies.

Author Contributions

X.W.: Investigation, Writing—original draft, Formal analysis. X.S.: Formal analysis, Writing—review and editing. Y.L.: Formal analysis, Methodology. P.L.: Data curation, Methodology. M.X.: Data curation, Methodology. Y.H. (Yashuai Huang): Validation. Y.H. (Yang Hong): Validation. All authors have read and agreed to the published version of the manuscript.

Funding

The authors wish to acknowledge the Excellent Young Scientists Fund Program of the National Natural Science Foundation of China (Grant No. 52122403), Natural Science Foundation of Wuhan (No. 2024040701010062), the Youth Innovation Promotion Association CAS (Grant No. Y2023089), and the National Natural Science Foundation of China (No. 52304069, No. 52374069).

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Crude oil imports and oil dependence in China [17]. (a) Oil import and growth rate from 2012 to 2022. (b) Oil dependency and growth rate from 2012 to 2022.

Figure 2. Distribution of oil reservoirs in the world [28].

Figure 3. Distribution of salt cavern oil storage projects in the world [53].

Figure 4. Operation mode of traditional salt cavern oil storage system [54].

Figure 5. Comparison of rock salt characteristics in the US and China. (a) Rock salt occurrence in the US. (b) Rock salt occurrence in the China.

Figure 6. The novel salt cavern sediment void oil storage utilization system [27]. (a) oil storage system of sediment void oil storage method. (b) Oil utilization system of sediment void oil storage method.

Figure 7. Comparison of novel sediment void oil storage technology and traditional salt cavern oil storage technology [41]. (a) The novel sediment void oil storage technology. (b) Traditional salt cavern oil storage technology.

Figure 8. Geological evaluation of oil recovery from sediment void.

Figure 9. Stability evaluation method of salt cavern sediment void oil recovery process.

Figure 10. The cavern shape and volume detection technology by sonar [73].

Figure 11. The oil recovery process from the salt cavern sediment void.

Figure 12. The overall oil recovery process in salt cavern sediment void.

Figure 13. The oil recovery experiment from the salt cavern sediment void [41]. (a) Oil recovery from sediment void equipment. (b) Oil recovery process from the sediment void.

Figure 14. The results of oil recovery from the salt cavern sediment void [41].

Figure 15. Feasibility evaluation of salt cavern sediment void oil storage in China.

Figure 16. The potential engineering applications of salt cavern sediment void oil storage [79].

Table 1. Comparison cost of different oil storage method.

Oil Storage Method	Total Cost for 100 Million Barrels/10⁸ Dollar	Cost per Barrel/Dollar	Annual Production Cost/10⁶ Dollar
Underground salt cavern	5.5	5.5	17.5
Underground rock cavern	15.4	15.4	8.8
Surface storage tank	35.0	35.0	——

Table 2. Comparison analysis of different oil storage methods.

Oil Storage Method	Construction Characteristics	Advantages	Disadvantages	Application
Aboveground oil tank storage [55,56]	Easy to build	Simple structure	Large area, oil leakage caused by tank rupture, high risk, low security	Inland refinery
Semi-underground oil tank storage [57]	The buried depth of the oil tank is greater than 50% of the tank height	Good fire safety performance	Covers a large area, easily leaking	Inland refinery
Underground rock cavern oil storage [58]	Excavate caves manually and seal oil through the pressure difference between groundwater and oil products	Good sealing property, not easy to destroy, not easily leaking, low risk	Difficult site selection	Good location of underground caverns
Underground salt cavern oil storage [59]	Using salt cavern formed by solution mining to store oil	Strong bearing capacity, impermeability	Difficult site selection; insoluble sediment particles take up oil storage space	An area with good salt rock strata
Offshore oil storage tank [60,61]	Floating tanks and bottom tanks	Not occupying land area; it can be rebuilt by abandoned tankers	Oil spills pollute the marine environment; poor security	Oil refinery along the river

Table 3. Tightness evaluation method of salt cavern sediment void oil storage.

Test Name	Currently Applied Area	Medium	Test Method
Gas leakage test method	North America	Nitrogen or air	Nitrogen or air is injected into the cavity, and the gas–water interface is monitored using logging instruments to evaluate the sealing performance of the cavern.
Liquid leakage test method	European region	Fuel oil	The integrity of the cavern’s seal can be evaluated by injecting fuel oil, monitoring the wellhead pressure, and recovering the fuel oil to compare the volume within the cavern.

Table 4. Comparison of oil recovery process flow of salt cavern sediment void oil storage.

Oil Storage and Recovery Technology of Salt Cavern	Oil Recovery Principle	Oil Recovery Process Flow	Related Ground Facilities	Applicability
Situated brine to displace oil	The saturated brine is injected into the salt cavern, displacing the oil towards the surface due to the difference in specific gravity between the brine and the oil.	Saturated brine storage tank → Brine injection system → Salt cavern sediment void → Oil extraction from sediment void → Oil storage tank	Brine storage tank, high-pressure injection and production pumps, water injection, oil injection pipelines, crude oil system, and supporting equipment.	The process is well established, but the demand for saturated brine is high.
Freshwater to displace oil	Freshwater is injected into the salt cavern, displacing the crude oil towards the surface due to the difference in specific gravity between the oil and the water.	Freshwater storage tank → Water injection system → Salt cavern sediment void → Oil extraction from sediment void → Oil storage tank	Freshwater storage tank, brine storage tank, and crude oil storage tank.	The process is mature, but the demand for saturated brine is substantial.
Compressed air to displace oil	Compressed gas is injected into the salt cavern via an air compressor, driving the oil towards the surface.	Compressed air injection system → Salt cavern sediment void → Oil extraction from sediment void → Oil storage tank	Air compressor and air compression system.	The high-capacity surface air compressors and the equipment are complex.
Pumping method to displace oil	A submersible pump is installed within the salt cavern to transport the oil from the cavern to the surface.	Submersible pump in salt cavern → Oil storage tank	Oil injection pump and crude oil storage tank.	Simple, cost-effective, low-investment, and suitable for emergency needs but not applicable for SVOS.

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Wei, X.; Shi, X.; Li, Y.; Li, P.; Xu, M.; Huang, Y.; Hong, Y. A Review of Enhanced Methods for Oil Recovery from Sediment Void Oil Storage in Underground Salt Caverns. Energies 2025, 18, 360. https://doi.org/10.3390/en18020360

AMA Style

Wei X, Shi X, Li Y, Li P, Xu M, Huang Y, Hong Y. A Review of Enhanced Methods for Oil Recovery from Sediment Void Oil Storage in Underground Salt Caverns. Energies. 2025; 18(2):360. https://doi.org/10.3390/en18020360

Chicago/Turabian Style

Wei, Xinxing, Xilin Shi, Yinping Li, Peng Li, Mingnan Xu, Yashuai Huang, and Yang Hong. 2025. "A Review of Enhanced Methods for Oil Recovery from Sediment Void Oil Storage in Underground Salt Caverns" Energies 18, no. 2: 360. https://doi.org/10.3390/en18020360

APA Style

Wei, X., Shi, X., Li, Y., Li, P., Xu, M., Huang, Y., & Hong, Y. (2025). A Review of Enhanced Methods for Oil Recovery from Sediment Void Oil Storage in Underground Salt Caverns. Energies, 18(2), 360. https://doi.org/10.3390/en18020360

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A Review of Enhanced Methods for Oil Recovery from Sediment Void Oil Storage in Underground Salt Caverns

Abstract

1. Introduction

2. The Development of Oil Recovery from Sediment Void

2.1. Oil Recovery Technologies Worldwide

2.2. Oil Recovery Technology in China

2.3. Oil Recovery Influencing Factors Analysis from Sediment Void

2.3.1. Geological Evaluation of Sediment Void Oil Storage

2.3.2. Stability Evaluation of Sediment Void Oil Storage

2.3.3. Tightness Evaluation of Sediment Void Oil Storage

2.3.4. Oil Storage Capacity of Sediment Void Oil Storage

3. Oil Recovery Process and Method from Sediment Void

3.1. Oil Recovery Process of Sediment Void Oil Storage

3.2. Oil Recovery Experiments of Sediment Void Oil Storage

3.3. Oil Recovery Methods of Sediment Void Oil Storage

4. Problems of Oil Recovery from Sediment Void

4.1. Oil Loss Problem of Sediment Void Oil Storage

4.2. Oil Flow Rule in Sediment Void

4.3. Oil Recovery Simulation from Sediment Void

4.4. Sediment Void Oil Storage Construction Problem

5. Advantages and Application of Oil Recovery from Sediment Void

5.1. Potential Advantages of Sediment Void Oil Storage

5.2. Potential Application of Sediment Void Oil Storage

6. Conclusions

Author Contributions

Funding

Data Availability Statement

Conflicts of Interest

References

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