CN112836442B - Method for determining liquid injection amount of hydraulic cracks of old well of shale oil well pattern - Google Patents

Abstract

The invention relates to a method for determining the liquid injection amount of a hydraulic fracture of an old well of a shale oil well pattern, which comprises the following steps: establishing an initial three-dimensional reservoir model and a three-dimensional geological model which comprise a horizontal well old well and an old well hydraulic fracture network, and calculating stratum defect and ground stress evolution caused by old well production by using a fluid-solid coupling method; the old well liquid injection mode is adopted to simulate the encrypted well crack control net and characterize the protection effect of the old well liquid injection on the encrypted well crack, the stratum defect filling amount and the ground stress recovery degree are taken as criteria, the inter-well interference effect is ensured not to induce the encrypted well crack to cause adverse damage to the old well crack of the horizontal well, and the old well crack protection liquid injection amount is optimized. The invention can analyze the ground stress deficiency and the ground stress evolution mode induced by the old well production, and perform the optimal analysis of the old well liquid injection quantity.

Description

A method for determining the fluid injection volume of hydraulic fractures in old wells in shale oil horizontal well pattern

technical field

The invention relates to the technical field of hydraulic fracturing reconstruction of shale oil reservoirs to increase production, in particular to a method for determining the optimal liquid volume for hydraulic fracture protection of old wells in a horizontal well pattern of shale oil.

Background technique

Against the backdrop of rising domestic dependence on foreign crude oil, unconventional shale oil resources are of great significance for increasing crude oil production due to their large proven reserves and good prospects for exploitation. Compared with conventional oil and gas reservoirs, the permeability of shale oil reservoirs is usually low, and it is difficult to form industrial oil flow naturally during the production process. It is often necessary to use infill horizontal well dense cutting and fracturing to improve reservoir permeability and form a The hydraulic fracture network connected to the wellbore of the horizontal well makes it easier for the crude oil in the low-permeability reservoir to flow to the wellbore to provide productivity.

The occurrence of hydraulic fracture network is the key to determining the productivity of shale oil, and the reservoir stress is an important main controlling factor affecting the propagation law of hydraulic fractures. In hydraulic fracturing, the direction of the minimum horizontal principal stress is critical to determine the fracture direction. Quantitatively characterizing the in-situ stress field state of reservoirs at each stage of shale oil fracturing and production and the corresponding hydraulic fracture initiation and propagation laws is an important means to improve shale oil production efficiency.

The significant difference between intensified horizontal wells and old horizontal wells is that the geomechanical environment in which the old horizontal wells were fractured was not affected by fracturing and production, while when the intensified horizontal wells were fractured, there were already one or more wells in the area. There are two horizontal wells and old wells. The formation pressure deficit and the time-space evolution of in-situ stress caused by the production of the old wells will greatly change the in-situ in-situ stress field of the reservoir, which will affect the fracturing effect of the infill well and induce the gap between the old well and the infill well. Interference between wells will damage the productivity of the well pattern. By injecting fluid into old wells, it can fill up the formation deficit and partially restore the stress state of the reservoir, suppress interwell interference induced by fracturing of infill wells, protect old well fractures and well pattern productivity, and quantitatively calculate the amount of fluid injection in old wells Method is the key to realize this technology. Therefore, it is necessary to propose a method for determining the optimum fluid volume for hydraulic fracture protection of old wells in shale oil horizontal well pattern.

Contents of the invention

Aiming at the deficiencies of the above-mentioned prior art, the present invention aims to provide an analysis method for the optimal injection volume of old well protection, so as to fill up the formation deficit and partially restore the stress state of the reservoir, and suppress the interwell interference induced by fracturing of infill wells phenomenon, protect old well fractures and well pattern productivity, and quantitatively calculate the injection volume of old wells.

The present invention proposes a method for determining the fluid injection volume of hydraulic fractures in old wells in a shale oil horizontal well pattern, said method comprising:

Establish the initial 3D reservoir model and 3D geological model including old horizontal wells and hydraulic fracture network of old wells, and use the fluid-solid coupling method to calculate formation deficit and in-situ stress evolution caused by production of old wells;

The old well fluid injection method is used to simulate the infill well fracturing network, and to characterize the protection effect of the old well fluid injection on the infill well fracturing, and to ensure that interwell interference will not induce In order to make infill well fracturing cause unfavorable damage to old well fractures of horizontal wells, the fluid injection volume for protection of old well fractures is optimized.

According to an embodiment of the present invention, when using the fluid-structure coupling method for calculation, the method further includes:

Fitting the calculated data of formation deficit and in-situ stress evolution caused by the production of the old well with the real data on site, and calibrating the analysis model of the fluid-solid coupling method.

According to an embodiment of the present invention, the method further includes, analyzing according to the analysis model of the fluid-solid coupling method, obtaining formation pressure deficit and in-situ stress changes under different production modes of old wells, and obtaining The respective three-dimensional formation pressure and three-dimensional stress field.

According to an embodiment of the present invention, in the case of obtaining the respective three-dimensional formation pressure and three-dimensional stress field of each time step, the following methods are also included:

Preliminary selection of infill horizontal well locations and hydraulic fracturing section cluster locations includes the following steps:

Firstly, a preliminary selection is made based on the parameters of porosity, permeability, saturation and brittleness index obtained from the integrated evaluation of geology and engineering, and the overlapping points of geological sweet spots and engineering sweet spots are prioritized;

Then, according to the determined range of formation pressure deficit and the range of in-situ stress evolution, the cluster interval of the hydraulic fracturing section of the intensified horizontal well is preliminarily determined.

According to an embodiment of the present invention, the method further includes simulating the fracturing of infill wells without using old well fluid injection, and characterizing the interaction and interference between old well fractures and infill well fractures; Simulating infill well fracturing under the condition of well injection includes the following steps:

In the preliminarily selected intensified horizontal wells and hydraulic fracturing section cluster intervals, select a section to perform multi-cluster hydraulic fracture initiation-propagation calculation based on fracture mechanics, and analyze hydraulic fractures in intensified horizontal wells under various section cluster conditions network occurrence, and obtain its interaction with old well fractures;

Continue to complete the subsequent calculation of the hydraulic fracture network occurrence of infill wells in all sections to be fractured, and obtain the interaction between fracture disturbance and communication between old wells and infill wells, and then determine the pressure of infill wells without using old well fluid injection protection. The degree of fracture interference and interwell interference.

According to an embodiment of the present invention, under the condition of not taking liquid injection in old wells, the method further includes:

In the candidate infill well position, the occurrence of the hydraulic fracture network is used to calculate, and the hydraulic fracture network between the corresponding infill well and the old well is obtained, and the fracture interaction is analyzed.

According to an embodiment of the present invention, when the old well injection method is adopted, the old well injection calculation is performed through the analysis model of the fluid-solid coupling method, and the influence of the old well injection volume and the injection method on the formation pressure deficit is analyzed. According to the filling effect and the recovery of ground stress, the ratio of the injection volume to the deficit volume is analyzed.

According to an embodiment of the present invention, when the old well injection method is adopted, the method further includes:

Referring to the hydraulic fracture network between the infill well and the old well under the condition of not using old well fluid injection, comprehensively analyze the connection and interaction characteristics of interwell fractures corresponding to the fluid injection volume of various old wells, and repeatedly optimize the old well fluid injection To determine the optimal injection volume and injection method that can effectively protect old wells.

According to an embodiment of the present invention, when establishing the three-dimensional reservoir model,

Based on geological data, wellbore structure data, fracturing segmented and clustered data, construction data, and microseismic data, a three-dimensional reservoir model including old horizontal wells and hydraulic fracture networks of old wells was established using unstructured grids.

According to an embodiment of the present invention, when establishing the three-dimensional geological model, on the basis of the three-dimensional reservoir model, the three-dimensional geological model is established according to the logging interpretation method of core experiments and rock mechanical parameters, so as to characterize Formation elastic characteristics and initial stress distribution characteristics.

The invention can analyze the in-situ stress deficiency and the in-situ stress evolution mode induced by the production of old wells, and on this basis, analyze the effect of filling the formation pressure deficiency and the in-situ stress recovery effect of different old well protection liquid injection volumes, and can combine the infill well pressure Calculation of fracture occurrence and optimal analysis of fluid injection volume for old wells provides an analysis method for optimal fluid injection volume for old well protection.

Description of drawings

Fig. 1 is a technical method flow chart of an embodiment of the present invention;

Fig. 2 is a schematic diagram of an old well and an unfractured infill well pattern of the present invention;

Fig. 3 is a schematic diagram of the interference effect of infill well fracturing on old well fractures when the old well fluid injection protection is not used in the implementation of the present invention;

Figure 4 is a schematic diagram of the effective protection of old well fractures from the interference of infill well fracturing after the old well is protected by fluid injection.

Detailed ways

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so as to better understand the purpose, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the present invention, but only to illustrate the essence of the technical solutions of the present invention.

At present, domestic shale oil is facing severe interwell fracturing interference between infill wells and old wells, and the corresponding protection measures for old wells are still insufficient. Effective optimization of fluid injection in old wells can protect old well fractures from adverse effects of interwell fracturing Interference and protection of the production capacity of horizontal well patterns meet the current demand for cost reduction and efficiency increase in domestic shale oil drilling and production. It is difficult to accurately and quantitatively evaluate the evolution of formation pore pressure and in-situ stress, and it is difficult to determine the effects of fluid injection in old wells on filling the formation deficit and restoring in-situ stress. The present invention solves the above problems, and can provide a method for determining the optimum liquid volume for hydraulic fracture protection of old wells in a shale oil horizontal well pattern.

The invention can analyze the in-situ stress deficiency and the in-situ stress evolution mode induced by the production of old wells, and on this basis, analyze the effect of filling the formation pressure deficiency and the in-situ stress recovery effect of different old well protection liquid injection volumes, and can combine the infill well pressure Calculate the occurrence of cracks, carry out the optimization analysis of the injection volume of old wells, and provide an analysis method for the optimal injection volume of old well protection.

The present invention relates to a method for determining the optimum liquid volume for hydraulic fracture protection of old wells in a horizontal well network. Firstly, the on-site seismic, geological, and horizontal well data are imported, an initial three-dimensional reservoir and geological model are established, and the fluid-solid coupling method is used for calculation. Formation deficit and in-situ stress evolution caused by production of old wells. Afterwards, the fracturing of infill wells was simulated without using old well fluid injection, and the interaction and interference between old well fractures and infill well fractures were characterized. Then use the old well fluid injection method to simulate the infill well fracture network, and characterize the protection effect of the old well fluid injection on the infill well fracturing, and optimize the old well fracture protection injection volume.

Specifically, according to one embodiment of the present invention, the present invention adopts the analysis technology of in-situ stress spatio-temporal evolution and the hydraulic fracture network analysis technology under the complex in-situ stress field to achieve the above-mentioned purpose, and the technical solution provided mainly includes the following steps:

Step 1: Based on geological data, wellbore structure data, fracturing segmented cluster data, construction data, microseismic data, etc., use unstructured grids to establish a 3D reservoir model including old horizontal wells and hydraulic fracture networks of old wells ;

Step 2: On the basis of the reservoir model, a three-dimensional geomechanical model is established according to core experiments, logging interpretation of rock mechanical parameters, etc., to characterize the elastic characteristics of the formation and the distribution characteristics of the initial in-situ stress;

Step 3: Based on the 3D reservoir model and 3D geomechanics model, using the fluid-solid coupling analysis method, calculate the formation pressure deficit and in-situ stress over time in the 3D space induced by the production of old wells;

Step 4: Fit the calculated old well production data (pressure drop, production, etc.) with the real data on site, and calibrate the fluid-solid coupling analysis model in step 3;

Step 5: According to the analysis results, the formation pressure deficit and ground stress changes under different production modes of old wells are obtained, and the respective 3D formation pressure and 3D ground stress fields of each historical time step are obtained;

Step 6: Under the respective 3D formation pressure and 3D in situ stress field at each time step, preliminarily select the location of the infill horizontal well and the location of the fracturing section cluster, which specifically includes the following two steps:

Step 6 (I): Firstly, according to the parameters such as porosity, permeability, saturation and brittleness index obtained by the integrated evaluation of geology and engineering, preliminary selection is made, and the overlapping points of geological sweet spot and engineering sweet spot are determined first;

Step 6 (II): According to the range of formation pressure deficit and the range of in-situ stress evolution determined in step 5, preliminarily determine the hydraulic fracturing segment cluster interval of the intensified horizontal well. Stress evolution has less influence

Step 7: As a control item, analyze the interaction between fractures in intensified horizontal wells and fractures in old wells when the old well fluid injection protection method is not adopted, specifically including the following two steps:

Step 7 (I): In step 6 initially selected intensified horizontal wells and hydraulic fracturing section cluster intervals, select a section to perform multi-cluster hydraulic fracture initiation-propagation calculation based on fracture mechanics, and analyze the fracture under various section cluster conditions. Intensify the occurrence of hydraulic fracture networks in horizontal wells, and obtain the interaction with fractures in old wells;

Step 7 (II): Continue to complete the calculation of the occurrence of hydraulic fractures in infill wells in all stages to be fractured, and obtain the interaction of fracture crossing and communication between old wells and infill wells, so that it can be determined that no old well injection fluid is used Infill well fracturing interference and interwell interference degree under protection;

Step 8: On the basis of step 6, calculate the liquid injection of old wells through the fluid-solid coupling model, analyze the filling effect of the liquid injection volume and injection mode of the old well on the formation pressure deficit and the recovery of in-situ stress, and analyze the relationship between the fluid injection volume and the injection method. The proportion of shortfall;

Step 9: Under the condition of not taking fluid injection in old wells, calculate the occurrence of hydraulic fractures in candidate infill wells using the same hydraulic fractures as in step 7, obtain the hydraulic fracture network between the corresponding infill wells and old wells, and analyze the fractures interactive situation;

Step 10: On the basis of step 9, comprehensively analyze the connection and interaction characteristics of interwell fractures corresponding to the fluid injection volumes of various old wells, and determine the optimal fluid injection volume and injection method that can effectively protect the old wells.

The present invention proposes a fluid-solid coupling and hydraulic fracturing numerical simulation process for the entire process of shale oil reservoir production and fracturing, and innovatively proposes a specific application of the process in the aspect of fluid injection protection for old wells.

The present invention characterizes formation deficit filling and in-situ stress recovery effects of fluid injection in old wells in recovery of unfavorable effects of in-situ stress evolution by modeling and simulating processes, and overcomes the deficiency that traditional calculation methods cannot characterize the process.

The present invention innovatively proposes a method for determining the optimum liquid volume for hydraulic fracture protection of old wells in a horizontal well pattern, and uses the amount of formation deficit filling and the degree of in-situ stress recovery as criteria to ensure that interwell interference will not induce infill wells Fracturing will cause unfavorable damage to the fractures of old wells in horizontal wells, and provide technical support for the efficient development of shale oil intensified well patterns.

Example

A method for determining the optimal liquid volume for hydraulic fracture protection of old wells in a shale oil horizontal well pattern, as shown in Figure 1, comprising the following steps:

1. Establish a three-dimensional reservoir model that can describe reservoir characteristics based on on-site reservoir and construction data. The model includes old wells, horizontal wells and old well fracture networks;

2. Establish a three-dimensional geomechanical model, which can represent the distribution of rock mechanical properties in three-dimensional space;

3. Carry out fluid-solid coupling simulation for old wells and horizontal wells, calculate the pore pressure field and in-situ stress evolution characteristics in three-dimensional space, and describe the formation deficit;

4. Historically match the simulation results in 3 with the on-site pressure drop and production data to improve the accuracy and reliability of the simulation results;

5. Based on the calibrated model in step 4, the quantitative calculation results of the pore pressure field and the in-situ stress field under different old well deficit degrees are obtained;

6. According to the geological and engineering survey documents, preliminarily select the location of the infill well, and characterize its positional relationship with the old well, as shown in Figure 2;

7. Obtain the fracturing results of infill wells in the control group that do not use fluid injection in old wells, as shown in Figure 3. Characterize the interference characteristics of infill well fractures on old well fractures;

8. Carry out fluid-solid coupling simulation of old well injection to obtain formation pressure deficit filling and in-situ stress recovery under various injection volume conditions;

9. Based on fluid-solid coupling simulation of old well injection, carry out infill well fracturing simulation at candidate well locations, obtain the characteristics of infill well fractures and old well fracture network under the old well fluid injection method, and judge whether the old well fluid injection is effective Protect its fractures from the disruption of infill well fracturing;

10. Based on the fluid-solid coupling simulation of old well injection, the fluid injection volume of old wells is repeatedly optimized, so that the fracturing fractures of infill wells will not interfere with the old well fractures, and finally the optimal fluid injection volume that can effectively protect the old well fractures is obtained, taking into account The cost of fluid injection and the effect of fracture protection in old wells are shown in Fig. 4.

The technical content not elaborated in the present invention belongs to the well-known technology of those skilled in the art.

It should be noted that, in this document, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate directions Or the positional relationship is based on the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation , and therefore should not be construed as limiting the invention; relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply There is no such actual relationship or order between these entities or operations. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or device. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

In addition, in the description of the present invention, it should be noted that unless otherwise specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a A detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediary, and it may be an internal communication between two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

The above-mentioned embodiments are only used to illustrate the present invention, and the components and devices of the embodiments can be changed, and the various implementation modes can be combined or deleted as required, and not all parts are necessary in the accompanying drawings. configuration, the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments described herein, and all equivalent transformations and improvements made on the basis of the technical solution of the present invention shall not be excluded from the protection scope of the present invention.

Claims (1)

1. The method for determining the liquid injection amount of the hydraulic fracture of the old well of the shale oil well pattern is characterized by comprising the following steps:

step 1: based on geological data, well structure data, fracturing segmentation clustering data, construction data and microseism data, using a non-structural grid to establish a three-dimensional reservoir model comprising a horizontal well old well and an old well hydraulic fracture network;

step 2: based on a reservoir model, a three-dimensional geomechanical model is established according to a core experiment and a logging interpretation method of rock mechanical parameters, and stratum elasticity characteristics and initial ground stress distribution characteristics are represented;

step 3: based on the three-dimensional reservoir model and the three-dimensional geomechanical model, calculating the formation pressure deficit and the change condition of ground stress along with time in the three-dimensional space induced by old well production by using a fluid-solid coupling analysis method;

step 4: fitting the calculated old well production data with field real data, and calibrating the fluid-solid coupling analysis model in the step 3;

step 5: according to the analysis result, the formation pressure defect condition and the ground stress change condition under different old well production modes are obtained, and the three-dimensional formation pressure and the three-dimensional ground stress field of each historical time step are obtained;

step 6: under the respective three-dimensional stratum pressure and three-dimensional ground stress field of each time step, preliminarily selecting the well position of the encrypted horizontal well and the position of the fracturing section cluster, and specifically comprising the following two steps:

step 6 (I): firstly, preliminarily selecting porosity, permeability, saturation and brittleness index parameters obtained according to geological engineering integrated evaluation, and determining the coincidence point of geological desserts and engineering desserts;

step 6 (II): and then according to the stratum pressure deficit range and the ground stress evolution sweep range determined in the step 5, preliminarily determining the hydraulic fracturing section cluster interval of the encrypted horizontal well, wherein the screening condition is that the stratum pressure deficit and the ground stress evolution sweep effect of the section cluster interval are small;

step 7: as a comparison item, when the method of old well injection protection is not adopted in analysis, the interaction condition of the horizontal well crack and the old well crack is encrypted, and the method specifically comprises the following two steps:

step 7 (I): in the preliminarily selected encrypted horizontal well and hydraulic fracturing section cluster interval in the step 6, selecting a section to perform multi-cluster hydraulic fracture initiation-expansion calculation based on fracture mechanics, analyzing the encrypted horizontal well hydraulic fracture network production under various section cluster conditions, and acquiring the interaction condition of the encrypted horizontal well hydraulic fracture network production with old well fractures;

step 7 (II): continuously completing calculation of the hydraulic fracture network production of the encrypted well of all the subsequent sections to be fractured, obtaining the interaction condition of fracture channeling and communication between the old well and the encrypted well, and determining the fracturing interference and the inter-well interference degree of the encrypted well under the condition of not using the injection protection of the old well;

step 8: on the basis of the step 6, old well injection calculation is carried out through a fluid-solid coupling model, the filling effect and the ground stress recovery condition of the old well injection amount and the injection mode on the stratum pressure deficit are analyzed, and the ratio of the injection amount to the deficit is analyzed;

step 9: under the condition that the old well is not adopted for liquid injection, adopting the hydraulic fracture occurrence calculation same as that in the step 7 on the candidate encryption well position to obtain the hydraulic fracture network situation between the corresponding encryption well and the old well, and analyzing the fracture interaction situation;

step 10: and 9, comprehensively analyzing the crack communication and interaction characteristics among wells corresponding to the injection amounts of the old wells, and determining the injection amounts and injection modes of the old wells.

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