Estimation method of fractured karst cave type oil reservoir geological reserves

Abstract

The invention belongs to the technical field of oil and gas reservoir exploration and development, and particularly relates to a method for estimating fractured karst cave type reservoir geological reserves. The method comprises the specific steps that the waste pressure of a target well is obtained according to production data of the target well and the relation, summarized through analysis, between permeability and a waste pressure coefficient, and then the accumulated oil production of the target well reaching the waste pressure is monitored through formation pressure monitoring data; the value of the natural energy recovery ratio is obtained according to the relation between the permeability and the natural energy recovery ratio and the permeability of the oil layer of the well, and then the geological reserves of the target well are dynamically estimated by combining the accumulated oil production of the well, so that the method is simple in calculation, convenient and practical, and the geological reserves of the target well can be calculated under the condition that the requirement for calculating the geological reserves by using a static method is not met. The method for estimating the geological reserves can be provided, and a material basis is provided for development deployment and productivity construction in the next step.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas reservoir exploration and development, and in particular relates to a method for estimating geological reserves of fracture-cavern type oil reservoirs. Background Art

[0002] The reserves of oil and gas reservoirs include geological reserves and recoverable reserves. They are important national resource figures and an important basis for the deployment of oil and gas reservoir development. Therefore, determining the reserves of oil and gas reservoirs in the field of oil and gas field exploration and development is a very important task. The methods for determining reserves mainly include static methods and dynamic methods. Among them, the static method uses the static geological parameters of oil and gas reservoirs to calculate the reserves according to the volume of pore space occupied by oil and gas fluids, also known as the volumetric method; the dynamic method uses the production dynamic parameters such as pressure, production, and cumulative production that change over time to calculate reserves, such as material balance method, water drive characteristic curve method, production decline method, and prediction model method. Correspondingly, the reserves calculated by the static method are geological reserves, which characterize the storage capacity of the reservoir; the dynamic method obtains dynamic recoverable reserves, which characterizes the size of reserves that can be recovered under certain technical and economic conditions.

[0003] Carbonate oil and gas reservoirs are an important part of oil and gas resources. Therefore, in recent years, carbonate reservoirs have become an important field of oil and gas exploration and development in my country. Carbonate reservoirs are highly heterogeneous, with a large number of fractures, dissolved pores and caves, making it very difficult to accurately calculate their geological reserves. At present, the calculation of geological reserves of carbonate reservoirs still mainly uses the volumetric method. The geological reserves of oil and gas reservoirs can be expressed as the product of parameters such as oil and gas area, effective thickness, effective porosity and oil and gas saturation.

[0004] For example, the Chinese invention patent with the authorization announcement number CN103293562B discloses a method and equipment for determining the geological reserves of carbonate reservoirs, which collects electrical imaging logging data and test well data of carbonate reservoirs; divides the carbonate reservoirs into four types of production capacity areas according to the electrical imaging logging data; determines the reservoir effectiveness coefficients of the production capacity areas according to the test well data; determines the geological reserves of the four types of production capacity areas according to the reservoir effectiveness coefficients; and determines the total geological reserves of the carbonate reservoir according to the geological reserves of the four types of production capacity areas. This invention patent uses the static method to calculate the sum of geological reserves of different production capacity areas based on the reservoir effectiveness coefficient, which has the following problems:

[0005] For carbonate fracture-cavity reservoirs with severe heterogeneity, the heterogeneity and spatial continuity of the reservoir space distribution are greatly different, and the volumetric method for calculating geological reserves based on static data of the formation around the wellbore is limited; for carbonate reservoirs with extremely strong heterogeneity of fracture-cavity development, it is difficult to determine the reserve calculation parameters such as porosity, and the volumetric method is difficult to calculate with low accuracy; when the volumetric method is used for calculation, the reserve parameters (oil and gas area, effective thickness, effective porosity, oil and gas saturation, etc.) are all calculated using the average value. The mean is used to express it, and the heterogeneity of the reservoir is not fully taken into account, which makes the reserve calculation less accurate. The oil and gas saturation distribution states in carbonate porous media vary greatly, and the different combinations of these reservoir spaces in three-dimensional space make the saturation of fluids in the same reservoir vary greatly. It is not possible to use a single reservoir space as a representative, nor is it possible to simply calculate its average value. Therefore, the volumetric method is mainly applicable to relatively homogeneous reservoirs. For carbonate fracture cave reservoirs with extremely strong heterogeneity, the volumetric method is obviously not applicable. Summary of the invention

[0006] The purpose of the present invention is to provide a method for estimating geological reserves of fracture-cavity type oil reservoirs, so as to solve the problem that the prior art uses a static method to calculate the geological reserves of oil reservoirs with extremely strong heterogeneity of fracture-cavity development, which results in great calculation difficulty and low calculation result accuracy.

[0007] In order to solve the above technical problems, the present invention provides a method for estimating the geological reserves of fractured cave oil reservoirs, wherein the permeability of the target well is obtained according to the logging or well testing parameters of the target well, the abandonment pressure coefficient of the well is obtained according to the relationship between the permeability and the abandonment pressure coefficient and the obtained oil layer permeability, and the abandonment pressure of the well is obtained by multiplying the obtained abandonment pressure coefficient by the saturation pressure of the well; the cumulative oil production of the well when the formation pressure drops from the initial pressure to the abandonment pressure is calculated according to the elastic yield of the well; the value of the natural energy recovery rate is obtained according to the relationship between the permeability and the natural energy recovery rate and the oil layer permeability of the well, and then combined with the cumulative oil production of the well, the geological reserves of the target well are calculated.

[0008] The beneficial effects are as follows: in order to solve the problem of great difficulty in calculation and low accuracy of calculation results when the existing technology uses the static method to calculate the geological reserves of oil reservoirs with extremely strong heterogeneity in fracture and cave development, the present invention obtains the abandonment pressure of the well through the production data of the target well and the relationship between the permeability and the abandonment pressure coefficient summarized by analysis, and then monitors the cumulative oil production of the target well to reach the abandonment pressure through the formation pressure monitoring data, so as to dynamically estimate the geological reserves of the target well. The present invention is simple in calculation, convenient and practical, and can provide a method for estimating geological reserves when the requirements for calculating geological reserves using the static method are not met, thereby providing a material basis for the next development deployment and capacity construction.

[0009] Furthermore, the specific relationship between the permeability and the abandonment pressure coefficient is: the permeability is less than or equal to 1mD, the abandonment pressure coefficient is 0.95; the permeability is greater than 1mD and less than 3mD, the abandonment pressure coefficient is 0.90; the permeability is greater than or equal to 3mD and less than 10mD, the abandonment pressure coefficient is 0.85; the permeability is greater than or equal to 10mD and less than 100mD, the abandonment pressure coefficient is 0.80; the permeability is greater than or equal to 100mD and less than 500mD, the abandonment pressure coefficient is 0.75; the permeability is greater than or equal to 500mD, the abandonment pressure coefficient is 0.70.

[0010] Furthermore, the natural energy recovery rate is positively correlated with the reservoir permeability, and the specific relationship is: when the permeability is less than or equal to 1mD, the natural energy recovery rate is 0.04; when the permeability is greater than 1mD and less than 3mD, the natural energy recovery rate is 0.055; when the permeability is greater than or equal to 3mD and less than 10mD, the natural energy recovery rate is 0.07; when the permeability is greater than or equal to 10mD and less than 100mD, the natural energy recovery rate is 0.085; when the permeability is greater than or equal to 100mD and less than 500mD, the natural energy recovery rate is 0.12; when the permeability is greater than or equal to 500mD, the natural energy recovery rate is 0.15.

[0011] Furthermore, the elastic yield of the target well is calculated based on the original formation pressure of the target well, the formation pressure after the production test, the oil production in the production test phase, and the oil production in the production test phase. The calculation formula is:

[0012]

[0013] Where β is the elastic yield; P i is the original formation pressure; P1 is the formation pressure after test production; N p1 is the oil production in the oil testing stage, N p2 This is the oil production during the trial production phase.

[0014] Furthermore, the specific means of calculating the cumulative oil production of the target well includes: adding the stage oil production when the formation pressure of the target well drops from the current pressure to the abandonment pressure calculated according to the elastic yield to the oil production of the target well in the oil test stage and the oil production in the test production stage to obtain the cumulative oil production of the target well. The calculation formula is:

[0015] N p =N p1 +N p2 +N p3

[0016] Among them, N p is the cumulative oil production of the target well; N p1 is the oil production in the oil testing stage; N p2 is the oil production in the trial production stage; N p3It is the oil production at the stage when the formation pressure drops from the current pressure to the abandonment pressure.

[0017] Furthermore, the stage oil production when the formation pressure of the target well drops from the current pressure to the abandoned pressure is calculated, and the calculation formula is:

[0018] N p3 =β(P1-P d )

[0019] Among them, N p3 is the stage oil production when the formation pressure drops from the current pressure to the abandoned pressure; β is the elastic yield; P1 is the formation pressure after trial production; P d To waste pressure.

[0020] Furthermore, the geological reserve calculation formula of the target well is:

[0021]

[0022] Among them, N p is the cumulative oil production of the target well; N p1 is the oil production in the oil testing stage; N p2 is the oil production in the trial production stage; N p3 E is the oil production when the formation pressure drops from the current pressure to the abandoned pressure; R is the natural energy recovery rate; N is the geological reserves. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention;

[0024] Figure 2 It is a relationship diagram between formation pressure and stage oil production of the present invention. DETAILED DESCRIPTION

[0025] The basic concept of the present invention is: according to the production data of the target well and the relationship between the permeability and the abandonment pressure coefficient analyzed and summarized, the abandonment pressure of the well is obtained, and then the cumulative oil production of the target well reaching the abandonment pressure is monitored through the formation pressure monitoring data, and the value of the natural energy recovery rate is obtained according to the relationship between the permeability and the natural energy recovery rate and the permeability of the oil layer of the well, and then combined with the cumulative oil production of the well, the geological reserves of the target well are dynamically estimated. Based on this concept, a method for estimating the geological reserves of fracture-cavern type oil reservoirs of the present invention can be realized.

[0026] The present invention will be described in detail below with reference to the accompanying drawings and method embodiments.

[0027] Method Example:

[0028] The method for estimating geological reserves of fractured cave oil reservoirs of the present invention is shown in the flow chart as follows: Figure 1 As shown, the specific implementation steps include:

[0029] Step 1: Obtain the original formation pressure, formation pressure after production test, saturation pressure, oil production during the production test phase, and oil production during the production test phase of the target well based on the production test;

[0030] Step 2: Calculate the elastic yield of the target well according to the original formation pressure, formation pressure after production trial, oil production in the production trial stage and oil production in the production trial stage of the target well obtained in step 1, and calculate the abandoned pressure of the elastic production stage of the target well according to the saturation pressure. The specific calculation formula is as follows:

[0031]

[0032] P d =αP b

[0033] Where β is the elastic yield, 10 4 t / MPα;P i is the original formation pressure, MPa; P1 is the formation pressure after test production, MPa; N p1 is the oil production in the oil testing phase, 10 4 t;N p2 is the oil production in the trial production stage, 10 4 t;

[0034] In the formula, p d is the abandoned pressure in the elastic oil production stage, MPa; p b is the saturation pressure, MPa; α is the waste pressure coefficient, decimal.

[0035] Step 3: According to the post-test production formation pressure of the target well obtained in step 1, combined with the elastic yield of the target well obtained in step 2, and the abandoned pressure in the elastic oil production stage, the oil production at the stage when the formation pressure value drops to the abandoned pressure value is calculated. The calculation formula is:

[0036] N p3 =β(P1-P d )

[0037] Where N p3 is the oil production when the formation pressure drops to the abandonment pressure, 10 4 t;

[0038] Step 4: Based on the oil production in the oil test stage and the oil production in the trial production stage obtained in step 1, combined with the stage oil production when the formation pressure drops to the abandonment pressure calculated in step 3, the cumulative oil production in the elastic oil production stage is calculated. The calculation formula is:

[0039] N p =Np1 +N p2 +N p3

[0040] Where N p is the cumulative oil production in the elastic oil production stage, 10 4 t;

[0041] Step 5: Based on the cumulative oil production in the elastic oil production stage obtained in step 4, combined with the natural energy recovery rate, the geological reserve estimation result is calculated. The specific calculation formula is:

[0042]

[0043] In the formula, E R is the natural energy recovery rate; N is the geological reserves.

[0044] The above-mentioned method for estimating geological reserves of oil reservoirs is used to estimate the geological reserves of a target well. The specific implementation process is as follows:

[0045] The cumulative loss of mud in a target well (M6) is 2202m 3 , M6 well depth 3958.01m, drilling tool emptying 3.26m, leakage rate 15.0m 3 / h, leakage 95m 3 , there is no backflow at the wellhead mud outlet; the well depth is 3975.55m, the drilling tool is emptied and the leakage rate is 30m 3 / h, leakage 2107m 3 There is no backflow at the wellhead mud outlet, the well depth is 3975.55-3978.55m, the drilling tools are emptied, and the overflow flame height is 8-10m. A naked eye test was conducted at 3957.74-3978.55m, and the daily oil production of 6mm oil nozzle is 211m 3 and natural gas 10.7×10 4 m 3 After 13 days, the oil production in the oil test phase was 0.076678×10 4 t and natural gas 48.62×10 4 m 3 .

[0046] 1) The original formation pressure P measured at the initial stage of the M6 ​​well oil test i =48.67MPa, oil production in the oil testing phase N p1 =0.076678×10 4 t, oil production during the trial production phase as of April 26, 2023 N p2 =1.06330×10 4 t, corresponding to the formation pressure after test production P1 = 38.0MPa, the data of M6 well is substituted into the formula The elastic yield of well M6 is β = 0.10684 × 10 4 t / MPa;

[0047] According to the statistical analysis of developed oil reservoirs, the abandonment pressure coefficient is related to the physical properties of the oil reservoir. The lower the permeability, the greater the seepage resistance, and the greater the abandonment pressure coefficient; the greater the permeability, the smaller the seepage resistance, and the smaller the abandonment pressure coefficient;

[0048] When the permeability is less than or equal to 1mD, the abandoned pressure coefficient is 0.95; when the permeability is greater than 1mD and less than 3mD, the abandoned pressure coefficient is 0.90; when the permeability is greater than or equal to 3mD and less than 10mD, the abandoned pressure coefficient is 0.85; when the permeability is greater than or equal to 10mD and less than 100mD, the abandoned pressure coefficient is 0.80; when the permeability is greater than or equal to 100mD and less than 500mD, the abandoned pressure coefficient is 0.75; when the permeability is greater than or equal to 500mD, the abandoned pressure coefficient is 0.70; According to the data of M6 well, the analysis shows that the permeability of its oil layer is relatively high, and the permeability of the oil layer emptied by drilling in the cave is at least several Darcy. Therefore, the abandoned pressure coefficient is α=0.70, combined with the saturation pressure P obtained in M6 well b =34.266MPa, substitute into the formula P d =αP b The abandoned pressure P of the elastic production stage of Well M6 is calculated. d =23.99MPa.

[0049] 2) The abandoned pressure P of the elastic production stage of M6 well d =23.99MPa, elastic yield β = 0.10684×10 4 t / MPa, and the formation pressure after the test mining P1=38.0MPa are substituted into the formula N p3 =β(P1-P d ), the stage oil production N of M6 well when the formation pressure drops to the abandonment pressure is calculated. p3 =1.49682×10 4 t.

[0050] 3) The calculated stage oil production N of Well M6 when the formation pressure drops to the abandonment pressure p3 =1.49682×10 4 t, and the oil production N of the M6 ​​well during the oil test phase p1 =0.076678×10 4 t and oil production during the trial production phase N p2 =1.06330×10 4 Substitute t into the formula N p =N p1 +N p2 +Np3 The cumulative oil production N of Well M6 during the elastic production stage is calculated. p =2.6368×10 4 t; From this, we can get the relationship between formation pressure and stage oil production, such as Figure 2 As shown in the figure, the horizontal axis is the formation pressure, and the vertical axis is the stage oil production. When the original formation pressure is 48.67 MPa, the oil production is 0 t; when the current pressure is 38.0 MPa, the cumulative oil production is 0.076678×10 4 t and oil production in the trial production stage 1.06330×10 4 t; when the formation pressure drops to the abandoned pressure of 23.99 MPa in the elastic stage, the cumulative oil production in the elastic production stage is 2.6368×10 4 t; the absolute value of the slope, i.e. the elastic yield (β) is 0.10684×10 4 t / MPa.

[0051] According to the statistical analysis of developed oil reservoirs, the natural energy recovery rate is related to the physical properties of the oil reservoir, and the natural energy recovery rate is positively correlated with the permeability of the oil reservoir. The specific relationship is: when the permeability is less than or equal to 1mD, the natural energy recovery rate is 0.04; when the permeability is greater than 1mD and less than 3mD, the natural energy recovery rate is 0.055; when the permeability is greater than or equal to 3mD and less than 10mD, the natural energy recovery rate is 0.07; when the permeability is greater than or equal to 10mD and less than 100mD, the natural energy recovery rate is 0.085; when the permeability is greater than or equal to 100mD and less than 500mD, the natural energy recovery rate is 0.12; when the permeability is greater than or equal to 500mD, the natural energy recovery rate is 0.15.

[0052] According to the data of M6 well, the permeability of its oil layer is relatively high. The permeability of the oil layer after drilling into the cave is at least several Darcy. Therefore, the natural energy recovery factor is E R =0.15, combined with N p =2.6368×10 4 t and put it into the formula The geological reserves are calculated to be N = 17.58 × 10 4 t; The geological reserve estimation results are shown in Table 1 below:

[0053] Table 1

[0054]

[0055] In order to accurately determine the geological reserves, the trial production time must be long enough when calculating the elastic yield, and the formation pressure must drop to a certain extent. The greater the drop in formation pressure, the more accurate the calculated elastic yield and the more reliable the estimated geological reserves. Otherwise, the error in the estimated geological reserves will be large.

[0056] The present invention provides a dynamic method for estimating geological reserves by using production data and formation pressure monitoring data. Different from conventional dynamic methods (water drive characteristic curve method, decline method, well test method), the present invention is simple in calculation, convenient and practical. When the requirements for calculating geological reserves by using static methods are not met, a method for estimating geological reserves can be provided, thus providing a material basis for the next development deployment and capacity construction.

Claims

1. A method for estimating geological reserves of fractured-cavern oil reservoirs, characterized in that: The permeability of the target well is obtained according to the logging or well testing parameters of the target well. The abandonment pressure coefficient of the well is obtained according to the relationship between the permeability and the abandonment pressure coefficient and the obtained oil layer permeability. The abandonment pressure of the well is obtained by multiplying the obtained abandonment pressure coefficient by the saturation pressure of the well. The cumulative oil production of the well when the formation pressure drops from the initial pressure to the abandonment pressure is calculated according to the elastic yield of the well. The value of the natural energy recovery rate is obtained according to the relationship between the permeability and the natural energy recovery rate and the oil layer permeability of the well, and then combined with the cumulative oil production of the well, the geological reserves of the target well are calculated.

2. The method for estimating geological reserves of fractured-cavern type oil reservoirs according to claim 1, characterized in that: The specific relationship between permeability and abandonment pressure coefficient is: when the permeability is less than or equal to 1mD, the abandonment pressure coefficient is 0.95; when the permeability is greater than 1mD and less than 3mD, the abandonment pressure coefficient is 0.90; when the permeability is greater than or equal to 3mD and less than 10mD, the abandonment pressure coefficient is 0.85; when the permeability is greater than or equal to 10mD and less than 100mD, the abandonment pressure coefficient is 0.80; when the permeability is greater than or equal to 100mD and less than 500mD, the abandonment pressure coefficient is 0.75; when the permeability is greater than or equal to 500mD, the abandonment pressure coefficient is 0.

70.

3. The method for estimating geological reserves of fractured-cavern oil reservoirs according to claim 1, characterized in that: The natural energy recovery rate is positively correlated with the reservoir permeability, and the specific relationship is: when the permeability is less than or equal to 1mD, the natural energy recovery rate is 0.04; when the permeability is greater than 1mD and less than 3mD, the natural energy recovery rate is 0.055; when the permeability is greater than or equal to 3mD and less than 10mD, the natural energy recovery rate is 0.07; when the permeability is greater than or equal to 10mD and less than 100mD, the natural energy recovery rate is 0.085; when the permeability is greater than or equal to 100mD and less than 500mD, the natural energy recovery rate is 0.12; when the permeability is greater than or equal to 500mD, the natural energy recovery rate is 0.

15.

4. The method for estimating geological reserves of fracture-cavern type oil reservoirs according to claim 1, characterized in that: The elastic yield of the target well is calculated based on the original formation pressure of the target well, the formation pressure after the test production, the oil production during the test production phase, and the oil production during the test production phase. The calculation formula is: Where β is the elastic yield; P i is the original formation pressure; P1 is the formation pressure after test production; N p1 is the oil production in the oil testing stage, N p2 This is the oil production during the trial production phase.

5. The method for estimating geological reserves of fracture-cavern type oil reservoirs according to claim 1, characterized in that: The specific means of calculating the cumulative oil production of the target well include: adding the stage oil production when the formation pressure of the target well drops from the current pressure to the abandoned pressure calculated according to the elastic yield to the oil production of the target well during the oil test stage and the oil production test stage to obtain the cumulative oil production of the target well. The calculation formula is: N p =N p1 +N p2 +N p3 Among them, N p is the cumulative oil production of the target well; N p1 is the oil production in the oil testing stage; N p2 is the oil production in the trial production stage; N p3 It is the oil production at the stage when the formation pressure drops from the current pressure to the abandonment pressure.

6. The method for estimating geological reserves of fracture-cavern type oil reservoirs according to claim 5, characterized in that: Calculate the stage oil production when the formation pressure of the target well drops from the current pressure to the abandoned pressure. The calculation formula is: N p3 =β(P1-P d ) Among them, N p3 is the stage oil production when the formation pressure drops from the current pressure to the abandoned pressure; β is the elastic yield; P1 is the formation pressure after trial production; P d To waste pressure.

7. The method for estimating geological reserves of fracture-cavern type oil reservoirs according to claim 1, characterized in that: The calculation formula for the geological reserves of the target well is: Among them, N p is the cumulative oil production of the target well; N p1 is the oil production in the oil testing stage; N p2 is the oil production in the trial production stage; N p3 E is the oil production when the formation pressure drops from the current pressure to the abandoned pressure; R is the natural energy recovery rate; N is the geological reserves.

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