Method for obtaining nuclear magnetic resonance porosity of shale oil reservoirs based on mineral analysis data

Abstract

The present invention relates to the technical field of reservoir nuclear magnetic porosity calculation method, which is a method for obtaining shale oil reservoir nuclear magnetic porosity based on mineral analysis data, which is calculated by the formula Ip=100*(K p *Pla+K c *Cal+K d *Dol+K) to calculate the nuclear magnetic porosity of shale oil reservoirs. The method of the present invention for obtaining the nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data only needs to use the rock cuttings collected by drilling logging with low cost for mineral analysis, and then apply the mineral content fitting to calculate the nuclear magnetic porosity; because the mineral content of the rock cuttings is measured, the measured value is not affected by the wellbore environment, the mineral content measurement accuracy is high, and thus the numerical accuracy of the calculated nuclear magnetic porosity is also high.

Description

Technical Field

[0001] The invention relates to the technical field of reservoir nuclear magnetic porosity calculation methods, and is a method for obtaining shale oil reservoir nuclear magnetic porosity based on mineral analysis data. Background Art

[0002] The problem faced in the shale oil blocks of Xinjiang Oilfield (such as the Jimsar shale oil block) is that nuclear magnetic resonance logging is usually carried out after each horizontal well is drilled to obtain nuclear magnetic resonance porosity parameters for reservoir evaluation; however, due to the high cost of nuclear magnetic resonance logging and the limitations of wellbore conditions, nuclear magnetic resonance logging cannot be carried out on some horizontal wells, resulting in the inability to obtain complete nuclear magnetic resonance porosity parameters for reservoir evaluation.

[0003] The Chinese patent document with the authorization publication number of 106443800 discloses a method for correcting the nuclear magnetic porosity of intermediate-basic volcanic rocks. The method includes: statistically analyzing the experimental data in combination with ECS logging, optimizing the sensitive mineral elements that affect the nuclear magnetic porosity of intermediate-basic volcanic rocks, establishing a correction model for nuclear magnetic porosity and ECS logging mineral element content, and determining the parameters in the model by the optimal fitting method; finally, using the correction model to correct the nuclear magnetic logging porosity to obtain a porosity curve that reflects the true situation of the formation. Based on the petrophysical experiment of volcanic rocks, the invention establishes a correction model for nuclear magnetic porosity according to ECS logging, realizes the continuous correction of the nuclear magnetic logging porosity of intermediate-basic volcanic rocks, and improves the calculation accuracy of the nuclear magnetic logging porosity.

[0004] The characteristics of shale oil reservoirs are obviously different from those of igneous rocks (volcanic rocks); igneous rock reservoirs have dual storage spaces of matrix pores and fractures, while shale oil reservoirs are mainly matrix pore storage spaces, in which dissolution pore types dominate, and the degree of dissolution pore development is closely related to the content of specific minerals; the igneous rock nuclear magnetic porosity correction method is to obtain a corrected nuclear magnetic porosity model based on the element content measured by ECS element logging, and then correct the nuclear magnetic porosity value. This method must first implement the ECS special logging project with higher cost in a single well to obtain the element content measurement value. Secondly, the accuracy of the element content measured by ECS element logging is easily affected by the wellbore environment, which in turn affects the final fitted calculated nuclear magnetic porosity value. Summary of the invention

[0005] The present invention provides a method for obtaining the nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problems that the existing nuclear magnetic porosity measurement method is relatively high in cost and the nuclear magnetic porosity calculation method of volcanic rock reservoirs is not suitable for the nuclear magnetic porosity calculation of shale oil reservoirs; at the same time, it can solve the problem that some horizontal wells cannot be subjected to nuclear magnetic logging due to limited wellbore conditions, thus making it difficult to obtain complete nuclear magnetic porosity data.

[0006] The technical solution of the present invention is achieved by the following measures: A method for obtaining the nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data is carried out as follows: the nuclear magnetic porosity of shale oil reservoirs is calculated according to formula 1,

[0007] Formula 1: Ip = 100*(K p *Pla+K c *Cal+K d *Dol+K)

[0008] Where, Ip is the nuclear magnetic porosity, %;

[0009] Pla is the plagioclase content, %;

[0010] Cal is the calcite content, %;

[0011] Dol is dolomite content, %;

[0012] K p , K c , K d , K is the coefficient related to the minerals of plagioclase, calcite and dolomite;

[0013] Substitute the content data of plagioclase, calcite and dolomite in the reservoir characteristic minerals of the test wells in the shale oil block and the corresponding logging nuclear magnetic porosity data into Formula 1 to obtain the corresponding K p , K c , K d , K value, K p , K c , K d After the K value is determined, the formula for determining the coefficient is obtained. The mineral analysis of the cuttings collected by logging while drilling in the shale oil block is carried out to obtain the mass percentage of plagioclase, calcite and dolomite minerals. The mass percentage of plagioclase, calcite and dolomite minerals is substituted into K p , K c , K d After the K value is determined, the nuclear magnetic porosity data of the corresponding well can be calculated in formula 1.

[0014] The following are further optimizations and / or improvements to the above technical solutions:

[0015] For the Jimusar shale oil block in Xinjiang Oilfield, K p =0.002, K c =0.004, K d =0.001, K = -0.016, and its nuclear magnetic porosity is calculated according to the following formula:

[0016] Ip=100*(0.002*Pla+0.004*Cal-0.001*Dol-0.016)

[0017] Where, Ip is the nuclear magnetic porosity, %;

[0018] Pla is the plagioclase content, %;

[0019] Cal is the calcite content, %;

[0020] Dol: dolomite content, %.

[0021] The method for obtaining the nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data described in the present invention only requires the use of low-cost rock cuttings collected by drilling logging to perform mineral analysis, and then apply mineral content fitting to calculate the nuclear magnetic porosity; since the mineral content of the rock cuttings is measured in kind, the measured value is not affected by the wellbore environment, the mineral content measurement accuracy is high, and thus the numerical accuracy of the calculated nuclear magnetic porosity is also high. DETAILED DESCRIPTION

[0022] The present invention is not limited by the following embodiments, and specific implementation methods can be determined according to the technical solution of the present invention and actual conditions. The percentages in the present invention are all mass percentages unless otherwise specified.

[0023] The present invention will be further described below in conjunction with embodiments:

[0024] Example 1: The method for obtaining the nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data is performed as follows: the nuclear magnetic porosity of the shale oil reservoir is calculated according to Formula 1:

[0025] Formula 1: Ip = 100*(K p *Pla+K c *Cal+K d *Dol+K)

[0026] Where, Ip is the nuclear magnetic porosity, %;

[0027] Pla is the plagioclase content, %;

[0028] Cal is the calcite content, %;

[0029] Dol is dolomite content, %;

[0030] K p , K c , K d , K are coefficients related to plagioclase, calcite and dolomite minerals, respectively;

[0031] Substitute the content data of plagioclase, calcite and dolomite in the reservoir characteristic minerals of the test wells in the shale oil block and the corresponding logging nuclear magnetic porosity data into Formula 1 to obtain the corresponding K p , K c , K d , K value, K p , K c , K d After the K value is determined, the formula for determining the coefficient is obtained. The mineral analysis of the cuttings collected by logging while drilling in the shale oil block is carried out to obtain the mass percentage of plagioclase, calcite and dolomite minerals. The mass percentage of plagioclase, calcite and dolomite minerals is substituted into K p , K c , K d After the K value is determined, the nuclear magnetic porosity data of the corresponding well can be calculated in formula 1.

[0032] Through correlation analysis of mineral analysis data and nuclear magnetic resonance logging data of a large number of shale oil horizontal well reservoirs, the sensitive mineral combination that affects the nuclear magnetic resonance porosity of shale oil reservoirs was found, namely the mineral combination of plagioclase, calcite and dolomite.

[0033] The shale oil reservoir characteristics of different blocks are different, so the corresponding K p , K c , K d , K are also different.

[0034] For a shale oil reservoir in a certain block, according to the method described in Example 1, the mineral composition content and nuclear magnetic porosity data of individual wells in the block are first substituted into the above formula to obtain the corresponding K p , K c , K d , K values, the NMR porosity calculation formula of the block can be obtained. For other wellbores in the block, there is no need for NMR logging. It is only necessary to conduct mineral analysis on the rock cuttings collected by drilling logging to obtain the mass percentage of plagioclase, calcite and dolomite minerals, and then calculate the NMR porosity at the wellbore. In this way, complete NMR porosity data of the block can be obtained to meet the evaluation needs of shale oil reservoirs.

[0035] The logging nuclear magnetic porosity of multiple horizontal wells was verified and compared with the nuclear magnetic porosity calculated by the method of the present invention. The accuracy of the nuclear magnetic porosity calculated by the method of the present invention reached more than 90%, which meets the needs of shale oil reservoir evaluation.

[0036] The method for obtaining the nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data of the present invention only needs to use the rock cuttings collected by drilling logging with low cost for mineral analysis, and then apply the mineral content fitting to calculate the nuclear magnetic porosity; because the mineral content is measured on the actual rock cuttings, the measured value is not affected by the wellbore environment, the mineral content measurement accuracy is high, and thus the numerical accuracy of the calculated nuclear magnetic porosity is also high.

[0037] Example 2: For the Jimusar shale oil block in Xinjiang Oilfield, K p =0.002, K c =0.004, K d =0.001, K = -0.016, and its nuclear magnetic porosity is calculated according to the following formula:

[0038] Ip=100*(0.002*Pla+0.004*Cal-0.001*Dol-0.016)

[0039] Where, Ip is the nuclear magnetic porosity, %;

[0040] Pla is the plagioclase content, %;

[0041] Cal is the calcite content, %;

[0042] Dol: dolomite content, %.

[0043] According to the above formula, it is only necessary to conduct mineral analysis on the rock cuttings collected by drilling logging in each wellbore of the Jimusar shale oil block in the Xinjiang Oilfield to obtain the mass percentage of plagioclase, calcite and dolomite minerals, and then calculate the nuclear magnetic porosity at the wellbore, and use this method to obtain complete nuclear magnetic porosity data for the block; compared with previous nuclear magnetic porosity acquisition methods (nuclear magnetic logging, etc.), this method can directly calculate the nuclear magnetic porosity of the Jimusar shale oil block in the Xinjiang Oilfield, and the calculation accuracy can reach more than 90%. The accuracy of the calculated nuclear magnetic porosity parameters can not only meet the needs of reservoir evaluation, but also reduce the cost of obtaining porosity parameters by more than 50% compared with nuclear magnetic logging.

[0044] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. A method for obtaining nuclear magnetic porosity of shale oil reservoirs based on mineral analysis data, characterized in that: Applied to shale oil blocks, the specific method is as follows: Calculate the nuclear magnetic porosity of the shale oil reservoir according to formula 1, Formula 1: Ip = 100*(K p *Pla+K c *Cal+K d *Dol+K) Where, Ip is the nuclear magnetic porosity, %; Pla is the plagioclase content, %; Cal is the calcite content, %; Dol is dolomite content, %; K p , K c , K d , K is the coefficient related to the minerals of plagioclase, calcite and dolomite and the geological characteristics of the block; Substitute the content data of plagioclase, calcite and dolomite in the reservoir characteristic minerals of the test wells in the shale oil block and the corresponding logging nuclear magnetic porosity data into Formula 1 to obtain the corresponding K p , K c , K d , K value, K p , K c , K d After the values ​​of K are determined, the formula for determining the coefficient is obtained. The mineral analysis of the cuttings collected by logging while drilling in the shale oil block is carried out to obtain the mass percentage of plagioclase, calcite and dolomite minerals. The mass percentage of plagioclase, calcite and dolomite minerals is substituted into K p , K c , K d After the K value is determined, the nuclear magnetic porosity data of the corresponding well can be calculated in formula 1; For the Jimusar shale oil block in Xinjiang Oilfield, K p =0.002, K c =0.004, K d =0.001, K=-0.016, and its nuclear magnetic porosity is calculated according to the following formula: Ip=100*(0.002*Pla+0.004*Cal-0.001*Dol-0.016) Dol: dolomite content, %.