Shale oil oil saturation correction method for conventional coring

Abstract

The invention discloses a shale oil oil saturation correction method for conventional coring. The method comprises the steps that S1, shale oil coring well selection work is carried out; s2, carrying out effective porosity and oil saturation determination on the conventional coring sample obtained in the step S1; s3, the mud invasion correction value of the conventional coring shale oil well is determined; s4, the oil loss correction value of the conventional coring shale oil well is determined; and S5, calculating the corrected oil saturation of the conventional coring shale oil well. According to the method, the original oil saturation under the formation condition can be obtained through conventional coring, parameters are convenient to obtain, a large amount of cost and time cost of closed coring and pressure-maintaining coring can be saved, the precision of the oil saturation of the shale subjected to conventional coring is effectively improved, and operability is high.

Description

TECHNICAL FIELD

[0001] The present application relates to a shale oil oil-bearing saturation correction method, more particularly to a shale oil oil-bearing saturation correction method for conventional coring. BACKGROUND

[0002] Oil-bearing saturation is an important parameter for shale oil reservoir oil-bearing evaluation and reserve estimation. Currently, it is mainly determined by core analysis and well logging interpretation. Well logging interpretation method needs core analysis and test data for calibration. Core analysis and test require sealed coring or pressure-maintaining coring data as the basis, and two-dimensional nuclear magnetic experiments or other core analysis methods are used for analysis. Sealed coring is to use a sealed coring tool and sealed liquid to take out a core that is basically not contaminated by drilling fluid and can truly reproduce the original conditions of the formation. Pressure-maintaining coring is to use a pressure-maintaining sealed coring tool and sealed liquid to drill a core that is not contaminated by drilling fluid and maintains the reservoir pressure under the then bottom-hole conditions. Such coring equipment and technology are more complex and more costly.

[0003] Conventional coring is the largest amount, most commonly used and most economical coring method in coring operations, but drilling fluid filtrate easily enters the core, causing changes in oil and water saturation, especially for shale with developed layering joints. Such invasion can cause large errors in core analysis saturation data. At the same time, oil and gas also escape to some extent during coring and drilling, causing the analyzed oil-bearing saturation to be further smaller. Therefore, it is urgent to establish a shale oil oil-bearing saturation correction method for conventional coring, so as to realize accurate calculation of conventional coring oil-bearing saturation, improve the reliability of water-based mud coring oil-bearing saturation, and also has important significance for shale oil reservoir oil-bearing evaluation and reserve estimation. SUMMARY

[0004] Therefore, it is necessary to provide a shale oil oil-bearing saturation correction method for conventional coring in view of the above technical problems.

[0005] In order to solve the above technical problems, the present application adopts the following technical solutions: A shale oil oil-bearing saturation correction method for conventional coring, comprising the following steps: Step S1, shale oil coring well selection work is carried out: determine the conventional coring shale oil well that needs to be corrected for oil-bearing saturation, take conventional coring samples from the conventional coring shale oil well, and analyze the conventional coring samples to meet the preset requirements for oil-bearing saturation determination, and select a sealed coring shale oil well around the conventional coring shale oil well; Step S2: The effective porosity and oil saturation of the conventional cored samples obtained in Step S1 are measured to obtain So', where So' is the oil saturation of the conventional cored shale oil well, in percentage (%). Step S3: Determine the mud invasion correction amount for conventional coring shale oil wells to obtain So filter, where So filter is the mud filtrate saturation, in percentage (%). Step S4: Determine the oil loss correction amount for conventional cored shale oil wells to obtain So_escape, where So_escape is the oil saturation of the loss, expressed as % (%). Step S5: Calculate the corrected oil saturation of conventional cored shale oil wells: So = So' + So_filter + So_escape, where So is the corrected oil saturation of conventional cored shale oil wells, in units of %.

[0006] In a preferred embodiment, in step S1, the geological conditions of the sealed coring shale oil well are similar to those of the conventional coring shale oil well.

[0007] In a preferred embodiment, in step S2, the effective porosity is determined by helium gas method or two-dimensional nuclear magnetic resonance (NMR) method, and the oil saturation is determined by distillation extraction method or two-dimensional NMR method.

[0008] In a preferred embodiment, in step S3, a two-dimensional nuclear magnetic resonance (NMR) experiment is performed on a conventionally cored sample. The inversion recovery method or the saturation recovery method is selected for the two-dimensional NMR T1-T2 measurement pulse sequence. The measurement system parameters and acquisition parameters are set and T1-T2 measurements are performed. The measurement results are processed to obtain the T1-T2 distribution. The amount of intruding mud filtrate is determined based on the distribution range and intensity of the mud filtrate signal, and the mud filtrate saturation is calculated based on the effective porosity.

[0009] In a preferred embodiment, in step S4, the conventional core sample is removed from the tube under sealed or pressurized conditions for two-dimensional NMR oil saturation measurement. The conventional core sample is then exposed to air for different times after being removed from the tube, and the oil saturation is measured sequentially to determine the oil saturation loss value at different exposure times.

[0010] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for correcting oil saturation in shale oil produced by conventional coring, effectively solving the problem of distorted oil saturation in shale produced by conventional coring. It obtains the original oil saturation under formation conditions by correcting the oil saturation of conventional cored wells using mud filtrate and oil dispersion. This invention allows for the acquisition of original oil saturation under formation conditions through conventional coring, facilitating parameter acquisition and saving significant costs and time associated with closed-loop and pressure-maintained coring. It effectively improves the accuracy of oil saturation in conventional cored shale, demonstrating strong operability and broad application prospects. The beneficial effects of this embodiment have been verified in the Qintong Depression of the Subei Basin. The oil saturation calculated using this method matches the well's trial production results and shows good consistency with well logging interpretation results, proving the reliability of the method. Attached Figure Description

[0011] To more clearly illustrate the solutions in this invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0012] Figure 1 This is a three-dimensional structural schematic diagram of the method for correcting the oil saturation of shale oil using conventional core sampling according to the present invention. Figure 2 This is a graph showing the oil saturation correction data in an embodiment of the present invention. Detailed Implementation

[0013] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0014] like Figure 1 As shown, this method for correcting the oil saturation of shale oil obtained from conventional core samples includes the following steps: Step S1: Conduct shale oil core well selection: Identify conventional cored shale oil wells that require oil saturation correction. Core samples are obtained from these conventional cored shale oil wells and analyzed to ensure they meet the preset requirements for oil saturation determination. A closed-loop cored shale oil well is selected near the conventional cored shale oil well. The core sample must be representative and effectively simulate oil dispersion. In other words, the geological conditions of the closed-loop cored shale oil well must meet the similarity criteria to those of the conventional cored shale oil well. Step S2: The effective porosity and oil saturation of the conventional cored samples obtained in Step S1 are measured to obtain So', where So' is the oil saturation of the conventional cored shale oil well, in percentage (%). Step S3: Determine the mud invasion correction amount for conventional coring shale oil wells to obtain So filter, where So filter is the mud filtrate saturation, in percentage (%). Step S4: Determine the oil loss correction amount for conventional cored shale oil wells to obtain So_escape, where So_escape is the oil saturation of the loss, expressed as % (%). Step S5: Calculate the corrected oil saturation of conventional cored shale oil wells: So = So' + So_filter + So_escape, where So is the corrected oil saturation of conventional cored shale oil wells, in units of %.

[0015] It should be noted that, in step S1, the geological conditions of the sealed coring shale oil well are similar to those of the conventional coring shale oil well.

[0016] In step S2, the effective porosity is determined by helium gas method or two-dimensional nuclear magnetic resonance (NMR) method, and the oil saturation is determined by distillation extraction method or two-dimensional NMR method.

[0017] Specifically, the main steps for determining oil saturation using the distillation extraction method are as follows: weigh the original rock sample, extract water using toluene and record the water volume; then wash the oil with chloroform, dry the rock sample after washing, and weigh it again, determining the oil mass by the mass difference; finally, calculate the pore volume based on the rock sample density and porosity, and then calculate the percentage content of water and oil in the total pore volume, thus obtaining the water saturation and oil saturation of the rock sample. The experiment follows the "Core Analysis Methods" (GB / T29172). Two-dimensional nuclear magnetic resonance (NMR) method identifies and quantifies reservoir fluids by measuring the relaxation decay signal of fluids in rock pores and based on the differences in the transverse relaxation time (T2) and longitudinal relaxation time (T1) properties of the fluid. The plate is generally determined through experiments such as centrifugation, drying, and saturation, or it can be determined by cluster analysis combined with experimental calibration. Different positions on the plate represent different fluid properties, pore space, and flowability. The experiment follows the "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples" (SY / T 6490).

[0018] In step S3, a two-dimensional nuclear magnetic resonance (NMR) experiment is performed on a conventional core sample. The inversion recovery method or the saturation recovery method is selected for the two-dimensional NMR T1-T2 measurement pulse sequence. The measurement system parameters and acquisition parameters are set and T1-T2 measurements are performed. The measurement results are processed to obtain the T1-T2 distribution. The amount of intruding mud filtrate is determined based on the distribution range and intensity of the mud filtrate signal, and the mud filtrate saturation is calculated based on the effective porosity.

[0019] In step S4, under sealed or pressurized conditions, the conventional core sample is removed from the tube and subjected to two-dimensional NMR oil saturation measurement. After being exposed to air for different times, the oil saturation of the conventional core sample is measured sequentially to determine the oil saturation loss value at different exposure times.

[0020] The working mode of the shale oil oil saturation correction method for conventional coring is specifically described below.

[0021] In this embodiment, the shale oil reservoir of the second member of the Funing Formation in Well QY1, a conventional coring well in the Qintong Sag of the Subei Basin, is taken as an example. Conventional systematic coring has been carried out in the second member of the Funing Formation, and oil saturation measurements have been carried out using methods such as distillation extraction and two-dimensional nuclear magnetic method, and the basic data is complete.

[0022] This embodiment provides a shale oil oil saturation correction method for conventional coring wells, including the following steps: Step S1: Select wells for shale oil coring.

[0023] Determine the conventional coring shale oil well QY1 that needs to perform oil saturation correction. The coring and sample conditions of this well meet the relevant requirements for oil saturation determination; select the sealed coring shale oil well QY8 with similar geological conditions around this well. The core of this well is representative and can effectively simulate the experiment of oil dissipation.

[0024] Step S2: Measure the effective porosity and oil saturation of conventional coring samples.

[0025] Measure the effective porosity of the conventional coring samples in Well QY1 by the helium method and measure the oil saturation by the distillation extraction method. The oil saturation So' in the test oil interval is 25.5% - 48.8%, with an average value of 36.1%, which is significantly low.

[0026] Step S3: Determine the mud invasion correction amount of the conventional coring well.

[0027] Perform two-dimensional nuclear magnetic experiments on the conventional coring samples in Well QY1. Identification charts of capillary bound water, bound oil, movable oil, movable water, etc. are determined through experiments such as centrifugation, drying, and saturation. Analyze the T1-T2 distribution of the samples in Well QY1's conventional coring well, and determine the mud filtrate identification standard as 0.5 < T1 / T2 < 2 and T2 ≥ 6 ms. Based on this, the mud filtrate saturation So filter is determined to be 1.5% - 45.5%, with an average value of 17.5%. The correction amounts of different samples show that the better the electrical properties of the reservoir, the greater the amount of mud filtrate, indicating that the better the physical properties, the greater the mud invasion amount and the greater the impact on oil saturation.

[0028] Step S4: Determine the oil dissipation correction amount of the conventional coring well.

[0029] The exposure time for conventional core samples from well QY1 before oil saturation analysis was one day. For sealed core samples from well Q8, two-dimensional NMR oil saturation measurement was performed immediately after removal from the core, followed by one day of exposure to air before further oil saturation measurement. The difference in oil saturation between the two measurements determined the oil saturation loss due to diffusion. Ultimately, the diffusion-induced oil saturation loss (So) ranged from 3.0% to 13.4%, with an average of 7.0%.

[0030] Step 5: Calculate the corrected oil saturation of conventional core wells.

[0031] The corrected oil saturation So of the conventional cored well QY1 was calculated by correcting for mud intrusion and oil escape. Using the formula So=So'+Sofilter+Soescape, the corrected oil saturation So of the conventional cored shale oil well was found to be 45.9% to 75.9%, with an average of 60.6%.

[0032] The beneficial effects of this embodiment have been verified in the Qintong Depression of the Subei Basin. The oil saturation calculated using the method of this invention matches the well's trial production results and shows good consistency with the well logging interpretation results, proving the reliability of the method.

[0033] This invention provides a method for correcting oil saturation in shale oil using conventional coring, effectively solving the problem of distorted oil saturation in shale oil obtained through conventional coring. It obtains the original oil saturation under formation conditions by correcting the oil saturation of conventional cored wells using mud filtrate and oil dispersion. This invention allows for the acquisition of original oil saturation under formation conditions through conventional coring, facilitating parameter acquisition and saving significant costs and time associated with closed-loop and pressure-maintained coring. It effectively improves the accuracy of oil saturation in conventional cored shale oil, demonstrating strong operability and broad application prospects. The beneficial effects of this embodiment have been verified in the Qintong Depression of the Subei Basin. The oil saturation calculated using this method matches the well's trial production results and shows good consistency with well logging interpretation results, proving the reliability of the method.

[0034] Obviously, the embodiments described above are only some embodiments of this application, and not all embodiments. The accompanying drawings show preferred embodiments of this application, but do not limit the patent scope of this application.

Claims

1. A method for correcting oil saturation in shale oil obtained through conventional coring, comprising the following steps: Step S1: Conduct shale oil core well selection: Identify conventional core shale oil wells that require oil saturation correction, obtain conventional core samples from the conventional core shale oil wells, analyze the conventional core samples to ensure they meet the preset requirements for oil saturation determination, and select a closed core shale oil well around the conventional core shale oil wells. Step S2: The effective porosity and oil saturation of the conventionally cored samples obtained in Step S1 are measured to obtain S... o ',in, S o 'This represents the oil saturation of a conventionally cored shale oil well, expressed in %'. Step S3: Determine the mud invasion correction amount for conventional coring shale oil wells, and obtain S. o滤， Among them, S o滤 The saturation of the mud filtrate is expressed as % (%). Step S4: Determine the oil dispersion correction amount for conventional coring shale oil wells, and obtain S. o逸， Among them, S o逸 The percentage of oil saturation lost due to evaporation is expressed as %. Step S5: Calculate the corrected oil saturation of conventional cored shale oil wells: S o =S o '+S o滤 +S o逸 Among them, S o The corrected oil saturation of conventionally cored shale oil wells is expressed in percent.

2. The method for correcting oil saturation in shale oil obtained through conventional core sampling according to claim 1, characterized in that, In step S1, the geological conditions of the sealed coring shale oil well are similar to those of the conventional coring shale oil well.

3. The method for correcting oil saturation in shale oil obtained through conventional core sampling according to claim 1, characterized in that, In step S2, the effective porosity is determined by helium gas method or two-dimensional nuclear magnetic resonance (NMR) method, and the oil saturation is determined by distillation extraction method or two-dimensional NMR method.

4. The method for correcting oil saturation in shale oil obtained through conventional core sampling according to claim 1, characterized in that, In step S3, a two-dimensional nuclear magnetic resonance (NMR) experiment is performed on a conventional core sample. The inversion recovery method or the saturation recovery method is selected for the two-dimensional NMR T1-T2 measurement pulse sequence. The measurement system parameters and acquisition parameters are set and T1-T2 measurements are performed. The measurement results are processed to obtain the T1-T2 distribution. The amount of intruding mud filtrate is determined based on the distribution range and intensity of the mud filtrate signal, and the mud filtrate saturation is calculated based on the effective porosity.

5. The method for correcting oil saturation in shale oil obtained through conventional core sampling according to claim 1, characterized in that, In step S4, under sealed or pressurized conditions, the conventional core sample is removed from the tube and subjected to two-dimensional NMR oil saturation measurement. After being exposed to air for different times, the oil saturation of the conventional core sample is measured sequentially to determine the oil saturation loss value at different exposure times.

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