CN112360410B - Method for improving water-drive oil displacement efficiency of low-permeability reservoir - Google Patents
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Abstract
The invention belongs to the technical field of improvement of oil and gas field development recovery efficiency, and particularly relates to a method for improving water-drive oil displacement efficiency of a low-permeability reservoir.
Description
Technical Field
The invention belongs to the technical field of improvement of oil and gas field exploitation and recovery efficiency, and particularly relates to a method for improving water-drive oil displacement efficiency of a low-permeability reservoir.
Background
Conventional reserves in the world are rapidly decreasing, and in order to meet oil and gas requirements, oil and gas resources in low-permeability oil reservoirs need to be developed. The low permeability reservoir refers to a general name of reservoirs with the average permeability of 0.1-50mD, and is subdivided into three subclasses according to the permeability, namely a general low permeability reservoir, an ultra-low permeability reservoir and an ultra-low permeability reservoir. Water flooding development is a development mode widely adopted by low-permeability oil reservoirs at home and abroad at present. Typically, the water flooding recovery is 10-40% by waterflood development, the lower the permeability, the lower the water flooding recovery. How to further develop 60-90% of residual oil resources after water flooding, improve the water flooding development effect and increase the recovery ratio becomes the focus of domestic and foreign research, wherein the increase of the oil displacement efficiency is one of two main directions for increasing the recovery ratio. The key for improving the water flooding efficiency is to definitely influence the main control of the water flooding efficiency.
At present, a method for researching influence factors of water flooding displacement efficiency mainly researches influences of injection parameters (including injection speed, injection pressure, water passing multiple and the like) and reservoir physical property parameters (including permeability, wettability, pore throat structure and the like) on displacement efficiency through an indoor core water flooding experiment. Although the considered parameters are more, the main control factors influencing the water flooding efficiency of different types of oil reservoirs are different, the relative influence degree of each parameter on the oil flooding efficiency is usually ignored, and the quantitative sequencing of the factors is not carried out, so that the selection of the oil flooding efficiency improvement method is lack of pertinence, and the oil flooding efficiency is not obviously improved.
Disclosure of Invention
The invention aims to provide a method for improving the water-drive oil displacement efficiency of a low-permeability reservoir, and the method can be used for overcoming the technical problems in the prior art.
Therefore, the technical scheme provided by the invention is as follows:
a method for improving the water-flooding oil displacement efficiency of a low-permeability reservoir comprises the following steps:
step 1) obtaining a plurality of target oil reservoir natural cores, processing the cores, obtaining permeability K and porosity phi by adopting a gas logging method, and obtaining water-drive displacement efficiency eta and irreducible water saturation S of each core by measuring through an unsteady state method wi Isoosmotic point saturation S we Isoosmotic point phase K re And residual oil-water phase permeability K rm ；
Step 2) determining permeability K, porosity phi and irreducible water saturation S wi Isoosmotic Point saturation S we Isotonic point infiltration K re And residual oil-water phase permeability K rm The primary and secondary sequence of the influence on the water flooding oil displacement efficiency eta;
and 3) selecting a method for improving the water flooding oil displacement efficiency according to the main control factors.
The number of the target oil deposit natural cores obtained in the step 1) is at least 20, the cores are drilled into cylinders with the diameter of 2.5cm or 3.8cm, the length of the cylinders is not less than 1.5 times of the diameter, and then cleaning and drying are carried out.
The primary and secondary sequential process for determining the influence of each parameter on the oil displacement efficiency in the step 2) is as follows: the oil displacement efficiency eta, the permeability K, the porosity phi and the saturation S of the bound water wi Isoosmotic point saturation S we Isotonic point infiltration K re And the residual oil-water phase permeability are expressed by a multiple linear regression method, the standard regression coefficients of all parameters are obtained by calculation respectively, the absolute values of the standard regression coefficients are sequenced, and the parameter with the largest absolute value is a main control factor.
In the step 3), when the permeability K or the porosity phi is determined as a main control factor, the method for improving the water-flooding oil displacement efficiency is reservoir transformation, wherein the reservoir transformation is acidizing or fracturing operation;
when the saturation degree S of the isotonic point is determined we When the main control factor is adopted, the method for improving the water-flooding oil displacement efficiency is to inject an oil displacement agent capable of improving the rock wettability;
when determining the isoosmotic point phase permeation K re When the main control factor is high, the method for improving the oil displacement efficiency of water flooding is to inject surfactant or natural gas and CO 2 A gas;
when the residual oil-water phase permeability K is determined rm When the main control factor is high, the method for improving the water flooding oil displacement efficiency is gas injection.
Step 2) water flooding oil displacement efficiency eta, permeability K, porosity phi and irreducible water saturation S wi Isoosmotic point saturation S we Isotonic point infiltration K re And residual oil-water phase permeability K rm The multiple linear regression method of (a) is represented as follows:
η＝b+a 1 K+a 2 φ+a 3 S wi +a 4 S we +a 5 K re +a 6 K rm
in the formula, a i (i =1,2,3,4,5,6) is the multiple linear regression coefficient, b is the intercept.
Standard regression coefficient
In the formula, a i (i =1,2,3,4,5,6) is a multiple linear regression coefficient; x s For different core permeability K, porosity phi and irreducible water saturation S wi Isoosmotic point saturation S we Isoosmotic point phase K re Or residual oil-water phase permeability K rm Standard deviation of (d); eta s The standard deviation of the water flooding oil displacement efficiency of different rock cores is shown.
The multiple linear regression coefficient a i The calculation formula is as follows:
wherein x is permeability K, porosity phi and irreducible water saturation S of different rock cores wi Isoosmotic Point saturation S we Isotonic point infiltration K re Or residual oil-water phase permeability K rm Experimental test values; y is the water flooding oil displacement efficiency of different rock cores; and n is the number of the tested natural rock cores.
Standard deviation of water flooding displacement efficiency of different rock cores
Wherein,
in the formula eta i Measured values of oil displacement efficiency of different rock cores,%;
the average value of the oil displacement efficiency of different rock cores is percent; and n is the number of the tested natural rock cores.
The invention has the beneficial effects that:
the method for improving the water-flooding oil displacement efficiency of the low-permeability reservoir provided by the invention utilizes a multivariate linear regression method, obtains standard regression coefficients of 6 parameters of oil displacement efficiency, permeability, porosity, bound water saturation, isoosmotic point phase permeability and residual oil-water phase permeability according to a large number of core water-flooding relative permeability test results of different blocks of the same type reservoir obtained through experiments, completes sequencing of the influence degree of different parameters on the oil displacement efficiency, determines the judgment of the main control factor of the oil displacement efficiency, provides a basis for selecting a subsequent method for improving the water-flooding oil displacement efficiency, and has strong pertinence and obvious improvement of the oil displacement effect.
The following will be described in further detail with reference to the accompanying drawings.
Drawings
FIG. 1 is a non-steady state process oil-water phase permeability curve.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the drawings are not intended to limit the present invention.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Example 1:
the embodiment provides a method for improving the water-flooding oil displacement efficiency of a low-permeability reservoir, which comprises the following steps of:
step 1) obtaining a plurality of target oil deposit natural cores, processing the cores, obtaining permeability K and porosity phi by adopting a gas measurement method, and measuring the water-drive displacement efficiency eta and the irreducible water saturation S of each core by adopting an unsteady state method wi Isoosmotic Point saturation S we Isotonic point infiltration K re And residual oil-water phase permeability K rm ；
Step 2) determining permeability K, porosity phi and irreducible water saturation S wi Isoosmotic Point saturation S we Isoosmotic point phase K re And residual oil-water phase permeability K rm The primary and secondary sequence of the influence on the water flooding oil displacement efficiency eta;
and 3) selecting a method for improving the water flooding oil displacement efficiency according to the main control factors.
According to a large number of core water-flooding relative permeability test results of different blocks of the same type of oil reservoir obtained through experiments, 6 phase permeability key parameters influencing the oil displacement efficiency are calculated by using a multivariate linear regression method, wherein the 6 phase permeability key parameters comprise permeability, porosity, irreducible water saturation, isoosmotic point relative permeability and residual oil-water phase permeability standard regression coefficients, and the relative influence degrees of different factors on the oil displacement efficiency are determined. By carrying out quantitative sorting, the main control factors of the oil displacement efficiency are further determined, and a basis is provided for selection of a method for subsequently improving the water flooding efficiency.
Example 2:
on the basis of embodiment 1, this embodiment provides a method for improving water-drive oil displacement efficiency of a low permeability reservoir, and in step 1), at least 20 natural cores of a target reservoir are obtained, cylinders with a diameter of 2.5cm or 3.8cm and a length of not less than 1.5 times of the diameter are drilled, and then cleaning and drying are performed.
Obtaining a target oil reservoir natural core, and drilling and washing the core according to a method in SY/T5345-2007 method for measuring relative permeability of two-phase fluid in rock 3.
Example 3:
on the basis of embodiment 1, this embodiment provides a method for improving the water flooding oil displacement efficiency of a low permeability reservoir, and the primary and secondary sequence process for determining the influence of each parameter on the oil displacement efficiency in step 2) is as follows: the oil displacement efficiency eta, the permeability K, the porosity phi and the saturation S of the bound water wi Isoosmotic Point saturation S we Isotonic point infiltration K re And residual oil-water phase permeability K rm Expressed by a multiple linear regression method, and each parameter is obtained by respectively calculatingThe standard regression coefficients are sorted according to the absolute value, and the parameter with the largest absolute value is a main control factor.
The method comprises three steps of testing an oil-water phase permeability curve by an unsteady state method, classifying data, calculating a standard regression coefficient and sorting factors by a multiple linear regression method, judging and identifying main control factors and selecting a method for improving the oil displacement efficiency. Firstly, selecting the core wells of the target low-permeability reservoir, obtaining the rock cores of different depths of oil layer sections of different core wells, and measuring the rock oil-water relative permeability curve according to the unsteady state method to obtain the oil displacement efficiency eta, the permeability K, the porosity phi and the irreducible water saturation S of different low-permeability rock core series wi Isoosmotic point saturation S we Isoosmotic point phase K re And residual oil-water phase permeability K rm 7 parameters; secondly, performing regression coefficient calculation and standard regression calculation on different core data according to a multiple linear regression method to obtain the influence directions and relative sizes of different parameters on the oil displacement efficiency, and performing factor sorting; and thirdly, determining the main control factor of the oil displacement efficiency, and integrating the phase permeability curves of different oil displacement agents to select the optimal oil displacement efficiency improvement method. The specific process is as follows:
1) And obtaining key 6 parameters of a phase-permeation curve and the oil displacement efficiency through testing an oil-water phase-permeation curve by an unsteady state method.
Obtaining a target oil reservoir natural core, firstly drilling and washing the core according to a method in SY/T5345-2007 determination method of relative permeability of two-phase fluid in rock 3, and obtaining gas logging permeability and porosity; then, according to an unsteady state method described in SY/T5345-2007 method for measuring relative permeability of two-phase fluid in rock 6.2, 7 parameters of oil-water relative permeability in rock cores, oil displacement efficiency, permeability, porosity, irreducible water saturation, isoosmotic point phase permeability and residual oil-water phase permeability of different rock cores are carried out, and the parameters are shown in table 1.
The oil-water phase permeability curve of the unsteady state method is shown in figure 1, wherein K ro Represents the relative permeability curve of the oil phase, K rw Representing the relative permeability curve of the water phase, and the abscissa of the intersection point of the two curves is the saturation degree S of the isotonic point we The ordinate is isoosmotic point facially osmotic K re (relative permeability at the point of isotonicity)。
TABLE 1 key parameter table of different core facies permeability curves
2) Calculating standard regression coefficient by multiple linear regression method
The oil displacement efficiency eta (dependent variable) and six phase permeability key parameters (independent variables) are expressed by a multivariate linear regression method by utilizing the multivariate linear regression method:
η＝b+a 1 K+a 2 φ+a 3 S wi +a 4 S we +a 5 K re +a 6 K rm
in the formula, a i (i =1,2,3,4,5,6) is the multiple linear regression coefficient and b is the intercept. The calculation process of each coefficient of the multiple linear regression is as follows,
in the formula, x is the experimental test value of 6 characteristic parameters of different rock cores, and y is the water flooding oil displacement efficiency of different rock cores. Coefficient a corresponding to K 1 For example, the calculation formula is as follows:
according to the method, linear regression coefficients a corresponding to other different characteristic parameters are respectively obtained i 。
In order to research the influence degree of different factors on the oil displacement efficiency, eliminate the difference of the dimension and the magnitude of the different factors, and carry out the calculation of a standard regression coefficient. Calculating the standard deviation of 7 phase permeability key parameters according to the following formula, taking the oil displacement efficiency as an example, and calculating according to the following formula:
In the above formula: eta s The standard deviation of the oil displacement efficiency of different rock cores is dimensionless; eta i Measured values of oil displacement efficiency of different rock cores,%;
the average value of the oil displacement efficiency of different rock cores is percent; and n is the number of the tested natural rock cores.
Permeability (K), porosity (phi), and irreducible water saturation (S) were calculated according to the same method wi ) Isoosmotic Point saturation (S) we ) Isotonic point infiltration K re Residual oil water phase permeability (K) rm ) Standard deviation of 6 parameters to obtain K s 、φ s 、S wis 、S wes 、K res 、K rms 。
Calculating the standard regression coefficient of K according to the formula, taking permeability as an example:
wherein A is 1 The standard regression coefficient is the absolute value of which reflects the influence degree of different parameters on the oil displacement efficiency.
Porosity (. Phi.) and irreducible water saturation (S) were calculated according to the above method wi ) Isoosmotic Point saturation (S) we ) Isoosmotic point phase K re Residual oil water phase permeability (K) rm ) Standard regression coefficients of the parameters.
And comparing and sorting the standard regression coefficients of different parameters according to the calculation result, wherein the larger the coefficient is, the larger the influence of the coefficient on the oil displacement efficiency is, and determining the coefficient as a main control factor.
3) Clear identification of main control factors of oil displacement efficiency and optimal oil displacement efficiency improvement method
When the main control factors of the oil displacement efficiency are the permeability and the porosity of the reservoir, the reservoir modification (acidification or fracturing operation) is proposed for improving the oil displacement efficiency; when the main control factor of the oil displacement efficiency is the isosmotic point saturation (reservoir wettability), an oil displacement agent which can improve the rock wettability such as a surfactant is recommended to be injected for improving the oil displacement efficiency; when the main control factor of the oil displacement efficiency is the isotonic point phase permeation, the surfactant or the gas (natural gas or CO) with better solubility with the crude oil is recommended to be injected for improving the oil displacement efficiency 2 A gas); when the main control factor of the oil displacement efficiency is the water phase permeability of residual oil, gas injection is suggested for improving the oil displacement efficiency, and the gas injection comprises nitrogen, natural gas and CO 2 And gases such as steam. The irreducible water saturation is a reservoir attribute parameter and is difficult to change artificially.
The method can be used for researching the oil displacement efficiency main control factors of different types of oil reservoirs, and provides a corresponding method for improving the water flooding efficiency in a targeted manner.
Example 4:
this embodiment takes a certain low-permeability reservoir as an example, and further details the method of the present invention. The process is as follows:
1) Completing the test of the physical property and the relative permeability curve of the rock core base to obtain key parameters
The table 2 shows the characteristic parameters of 40 core-phase permeability of a certain low-permeability reservoir core well and the oil displacement efficiency result.
TABLE 2 oil-water phase permeability characteristic parameters of different cores
(2) Calculating multiple linear regression coefficients of different parameters
Obtaining linear regression coefficient a of different variables by calculation according to least square method i
Different variable regression coefficient table
| Parameter(s) | Regression coefficient a i |
| Permeability rate of penetration | 6.456 |
| Porosity of | -1.113 |
| Irreducible water saturation | -0.323 |
| Water saturation of isotonic point | 1.475 |
| Relative permeability of oil and water at isosmotic point | -1.170 |
| Permeability of residual oil-water phase | 14.292 |
The oil displacement efficiency multiple linear regression formula is as follows:
η＝-12.12+6.456K-1.113φ-0.323S wi +1.475S we -1.17K re +14.292K rm
calculating the standard deviation of different parameters:
calculation results of standard deviation of different parameters
Calculating standard regression coefficients of different parameters, wherein the calculation formula is as follows:
regression coefficients of different parameters
| Parameter(s) | Standard regression coefficient A |
| Permeability rate of penetration | 0.4369 |
| Porosity of | -0.1494 |
| Irreducible water saturation | -0.1528 |
| Water saturation of isotonic point | 1.0126 |
| Relative permeability of oil and water at isotonic point | -0.7403 |
| Permeability of residual oil-water phase | 0.4118 |
Sorting the factors:
comparing absolute values of standard regression coefficients of different parameters, wherein the larger the absolute value is, the larger the influence degree of the parameter on the oil displacement efficiency is. For the water flooding reservoir, the influence factors of the oil displacement efficiency are sequenced as follows: the water saturation (wettability) of the isotonic point is more than the relative oil-water permeability of the isotonic point is more than the permeability of the residual oil-water phase is more than the saturation of the irreducible water is more than the porosity.
(3) Oil displacement efficiency improving method
The main control factors of the oil displacement efficiency are determined to be the water saturation of an isotonic point (reservoir wettability) and the oil-water relative permeability of the isotonic point, so that an oil displacement agent which can be subjected to rock wettability such as a surfactant is recommended to be injected to improve the oil displacement efficiency of the oil reservoir.
The above examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention, which is intended to be covered by the claims and any design similar or equivalent to the scope of the invention.
Claims (6)
1. A method for improving the water flooding oil displacement efficiency of a low permeability reservoir is characterized by comprising the following steps:
step 1) obtaining a plurality of target oil deposit natural cores, processing the cores, obtaining permeability K and porosity phi by adopting a gas measurement method, and measuring the water-drive displacement efficiency eta and the irreducible water saturation S of each core by adopting an unsteady state method wi Isoosmotic point saturation S we Isotonic point infiltration K re And residual oil-water phase permeability K rm ；
Step 2) determining permeability K, porosity phi and irreducible water saturation S wi Isoosmotic point saturation S we Isoosmotic point phase K re And residual oil-water phase permeability K rm The primary and secondary sequence of the influence on the water flooding oil displacement efficiency eta comprises the following processes: the water flooding displacement efficiency eta, the permeability K, the porosity phi and the irreducible water saturation S wi Isoosmotic point saturation S we Isoosmotic point phase K re And the residual oil-water phase permeability is expressed by a multiple linear regression method, the standard regression coefficients of all parameters are obtained by calculation respectively, the absolute values of the standard regression coefficients are sequenced, and the parameter with the largest absolute value is a main control factor;
step 3) selecting a method for improving the water flooding oil displacement efficiency according to the main control factors, which specifically comprises the following steps:
when the permeability K or the porosity phi is determined as a main control factor, the method for improving the water flooding oil displacement efficiency is reservoir transformation, wherein the reservoir transformation is acidizing or fracturing operation;
when the saturation degree S of the isotonic point is determined we When the main control factor is the water flooding efficiency, the method for improving the water flooding efficiency is to inject an oil displacement agent capable of improving the rock wettability;
when determining the isoosmotic point phase permeation K re When the main control factor is high, the method for improving the water-flooding oil displacement efficiency is to inject a surfactant or natural gas or CO 2 A gas;
when determining the residual oil-water phase permeability K rm When the main control factor is adopted, the method for improving the water flooding oil displacement efficiency is gas injection.
2. The method for improving the water-flooding oil displacement efficiency of the low permeability reservoir according to claim 1, wherein the number of the obtained target reservoir natural cores in the step 1) is at least 20, the obtained target reservoir natural cores are drilled into cylinders with the diameter of 2.5cm or 3.8cm and the length of the cylinders is not less than 1.5 times of the diameter, and then the cylinders are cleaned and dried.
3. The method for improving the water flooding efficiency of low permeability reservoirs according to claim 1, wherein: step 2) water flooding displacement efficiency eta, permeability K, porosity phi and irreducible water saturation S wi Isoosmotic point saturation S we Isoosmotic point phase K re And residual oil-water phase permeability K rm The multiple linear regression method of (a) is represented as follows:
η＝b+a 1 K+a 2 φ+a 3 S wi +a 4 S we +a 5 K re +a 6 K rm
in the formula, a i Is a multiple linear regression coefficient, i =1,2,3,4,5,6; b is the intercept.
4. The method for improving the water flooding efficiency of low permeability reservoirs according to claim 1, wherein: standard regression coefficient
In the formula, a i Is a multiple linear regression coefficient, i =1,2,3,4,5,6; x s For different core permeability K, porosity phi and irreducible water saturation S wi Isoosmotic point saturation S we Isoosmotic point phase K re Or residual oil-water phase permeability K rm Standard deviation of (d); eta s The standard deviation of the water flooding oil displacement efficiency of different rock cores is shown.
5. The method for improving the water flooding efficiency of low permeability reservoir according to claim 3 or 4, wherein the multiple linear regression coefficient a i The calculation formula is as follows:
wherein x is permeability K, porosity phi and irreducible water saturation S of different rock cores wi Isoosmotic Point saturation S we Isoosmotic point phase K re Or residual oil-water phase permeability K rm Experimental test values; y is the water-flooding oil displacement efficiency of different cores; and n is the number of the tested natural rock cores.
6. The method for improving the water flooding efficiency of low permeability reservoirs according to claim 4, wherein: standard deviation of water flooding displacement efficiency of different rock cores
Wherein,
in the formula eta i Measured values of water flooding oil displacement efficiency of different rock cores are percent;
average of water flooding displacement efficiency of different cores%(ii) a And n is the number of the tested natural rock cores.
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| CN106447644A (en) * | 2015-07-31 | 2017-02-22 | 中国石油化工股份有限公司 | New method for quantitative analysis of microscopic oil displacement experiment |
| WO2018213083A1 (en) * | 2017-05-15 | 2018-11-22 | University Of Houston System | Advanced technique for screening enhanced oil recovery and improved oil recovery methodologies for a petroleum reservoir |
| CN109339752A (en) * | 2018-11-19 | 2019-02-15 | 中国石油天然气股份有限公司大港油田分公司 | Oil reservoir development method based on the phlogisticated air displacement of reservoir oil |
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