A method for determining the distribution of remaining oil in shale oil production by water injection

Abstract

The present invention relates to a method for determining the remaining oil distribution in shale oil production by water injection, which includes: selecting a core, determining the cumulative distribution curve of the core pore volume, the NMR T2 spectrum D corresponding to the distribution of distilled water filled in the core saturated with distilled water wr and D wr of the porosity cumulative curve, the relationship between the T2 of oil and the pore throat radius r, and the relationship between the T2 of water and r; drying the core again to a constant weight, performing NMR T2 spectrum testing on the dry core sample to determine the T2 spectrum D of the dry core sample g ; saturating the core with oil, performing NMR T2 spectrum testing on the oil-saturated core to determine the T2 spectrum D of the oil-saturated core oi ; using the oil-saturated core to carry out a simulation experiment on water-based medium huff and puff imbibition oil production, and performing NMR T2 spectrum testing on the core after the experiment to determine the T2 spectrum D of the core after oil production ow ; calculating the remaining oil distribution in the core. The present invention ensures a reasonable simulation of the oil production process and reliable results of the corresponding oil production mechanism analysis, and reduces the experimental cost.

Description

Technical Field:

[0001] The present invention relates to the field of research on the distribution of remaining oil after shale reservoir exploitation in petroleum engineering, specifically to a method for determining the microscopic remaining oil distribution in pores of different scales after imbibition enhanced oil recovery by water-based matrix soaking in shale oil reservoir cores. Background Art:

[0002] China is rich in shale oil resources. Accelerating the exploration and development of shale oil is one of the realistic ways to ensure China's energy security. The matrix of shale oil reservoirs is rich in micro-nano scale pores and has a high clay content, with extremely low permeability. Imbibition displacement is an important mechanism for crude oil production in shale matrix. At present, the development of shale oil in China is still in the exploration stage. Achieving efficient exploitation of shale oil still faces many challenges, and the research and optimization of imbibition agents are one of the key issues that need to be solved urgently. Based on indoor oil production experiments to analyze the microscopic remaining oil distribution in cores under different imbibition agent conditions and clarify the oil production mechanism of imbibition agents is the basis for the optimization and research of imbibition agents. Since shale oil reservoir cores simultaneously develop nano-scale matrix pores, micro-scale bedding fractures and natural fractures, with a multi-scale pore structure, methods and techniques suitable for characterizing the microscopic remaining oil distribution in conventional sandstones, such as CT scanning, fluorescence thin section analysis, and laser confocal microscopy, are difficult to apply to shale. Nuclear magnetic resonance (NMR) testing is widely used in shale microscopic remaining oil characterization because of its non-destructive nature to rocks and wide characterization scale.

[0003] Currently, the characterization of microscopic remaining oil distribution in shale is generally achieved based on the analysis of NMR T1-T2 spectra or NMR T2 spectra. The main problems are as follows: The testing accuracy of NMR T1-T2 spectra is low, and there is no unified understanding of the division criteria for oil and water in different types of pores in shale. Therefore, it is difficult to accurately characterize the microscopic remaining oil distribution in shale; The testing accuracy of NMR T2 spectra is high, but since the NMR signals of oil and water overlap and cannot be distinguished, only heavy water that does not generate NMR signals can be used to replace experimental water, or fluorinated oil that does not generate NMR signals can be used to replace crude oil, or a paramagnetic ion solution that can reduce the relaxation time of the water phase can be added to the experimental water to carry out oil production simulation experiments. However, imbibition displacement is closely related to the interactions between liquid-liquid and solid-liquid. The fluorinated oil, heavy water, and experimental water after adding paramagnetic ion solution have different properties from actual oil and water, which will affect the imbibition displacement oil production process and then affect the remaining oil distribution characteristics, resulting in the remaining oil distribution characteristics obtained from experimental simulations not matching the true remaining oil distribution characteristics. At the same time, the use of heavy water, fluorinated oil, and paramagnetic ion solutions also increases the experimental cost. Therefore, the existing methods for determining the microscopic remaining oil distribution of imbibition enhanced oil recovery in shale cores based on NMR testing still need to be improved. Summary of the Invention:

[0004] The object of the present invention is to provide a method for determining the remaining oil distribution in shale oil production by water injection, which is used to solve the problem that the existing method for determining the microscopic remaining oil distribution in shale huff and puff imbibition oil production based on T2 spectrum analysis needs to carry out oil production simulation experiments using heavy water, fluorinated oil or paramagnetic ion solution, resulting in high experimental costs and the difference in the properties between the experimental fluid and the actual fluid, which makes it impossible to truly simulate the imbibition agent imbibition oil production process and affects the research results of the remaining oil distribution in huff and puff imbibition oil production.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows: This method for determining the remaining oil distribution in shale oil production by water injection includes the following steps:

[0006] Step 1: Select a core, the core is a shale core, and determine the cumulative distribution curve S of the core pore volume a , the NMR T2 spectrum D corresponding to the distribution of distilled water filled in the core saturated with distilled water wr and D wr of the porosity cumulative curve S wr , the relationship R between T2 of oil and pore throat radius r o , the relationship R between T2 of water and r w ;

[0007] Step 2: Dry the core again to a constant weight, conduct NMR T2 spectrum testing on the dry core sample, and determine the T2 spectrum D of the dry core sample g ;

[0008] Step 3: Saturate the core with oil, conduct NMR T2 spectrum testing on the core saturated with oil, and determine the T2 spectrum D of the core saturated with oil oi ;

[0009] Step 4: Use the core saturated with oil to carry out a water-based medium huff and puff imbibition oil production simulation experiment. After the experiment, conduct NMR T2 spectrum testing on the core to determine the T2 spectrum D of the core after oil production ow ;

[0010] Step 5: Calculate the remaining oil distribution in the core.

[0011] In the above solution, Step 5 is specifically as follows:

[0012] ① Subtract D oi from D g , select the part where T2 ≥ 0.2 ms in the obtained T2 spectrum to obtain the NMR T2 spectrum D corresponding to the distribution of oil filled in the core saturated with oil oir and D oir of the porosity cumulative curve S oir , subtract D ow from D g, select the part where T2 ≥ 0.2 ms in the obtained T2 spectrum to obtain the nuclear magnetic T2 spectrum D corresponding to the distribution of injected oil and water-based medium in the core after oil production owr and D owr 's porosity cumulative curve S owr ;

[0013] ② Read the minimum T2 value t with a signal intensity greater than 0 from D wr , and convert t wmin to the pore throat radius r according to R w , read the minimum T2 value t with a signal intensity greater than 0 from D wmin , and convert t wmin to the pore throat radius r according to R oir , take the smaller value of r omin and r o as r omin , and convert r omin to the T2 value t of the oil phase according to R wmin , and convert t omin to the pore throat radius r according to R min , and convert t o to the pore throat radius r according to R min , and convert t l to the pore throat radius r according to R w , and convert t l to the pore throat radius r according to R l ;

[0014] ③ Read the maximum T2 value t with a signal intensity greater than 0 from D oir , read the maximum T2 value t with a signal intensity greater than 0 from D o (1), read the maximum T2 value t with a signal intensity greater than 0 from D wr , and convert t wm to the pore throat radius r according to R w , read the minimum T2 value t greater than t wm and with a signal intensity of 0 from D max , read the minimum T2 value t greater than t wr and with a signal intensity of 0 from D wm , read the minimum T2 value t greater than t o (2), read the cumulative porosity values s oir corresponding to t o (1), t o (2) from S oir , read the cumulative porosity values s oir (1), s owr corresponding to t o (1), t o (2) from S owr , read the cumulative porosity values s owr (1), s o corresponding to t o (1), t o(2) is converted into pore throat radii r(1) and r(2), where r(1) > r(2). Then, the initial oil content Δs in the pore throats with radii from r(2) to r(1) oir (1) = s oir (1) - s oir (2), and the remaining oil content Δs ro (1) = s owr (1) - s owr (2). The crude oil recovery factor k(1) = 1 - Δs ro (1) / Δs oir (1);

[0015] ④ From R w determine the T2 values t w (1) and t w (2) of the aqueous phase corresponding to r(1) and r(2) respectively. From R o determine the pore throat radii r(3) and r(4) corresponding to t w (1) and t w (2) respectively, where r(3) > r(4). Read the cumulative porosity values s oir from S corresponding to t w (1) and t w (2). Then, the initial oil content Δs in the pore throats with radii from r(4) to r(3) oir (3) = s oir (3) - s oir (4); Read the cumulative porosity values s oir (3) and s oir (4) from S corresponding to t owr (1) and t w (2). Read the cumulative porosity values s w (3) and s owr (4) from S corresponding to t owr (1) and t a from S. Read the cumulative porosity values s a (1) and s a (2) corresponding to r(1) and r(2). Then, the remaining oil content Δs in the pore throats with radii from r(4) to r(3) ro (3) = s owr (3) - s owr (4) - [s a (1) - s a (2) - Δs ro (1)], and the crude oil recovery factor k(3) = 1 - Δs ro (3) / Δs oir (3);

[0016] ⑤ The initial oil content Δs in the pore throats with radii from r(3) to r(2) oir (2) = |soir (2)-s oir (3)|; determined by R w Determine t o (2) corresponding pore throat radius r(0), r(1) > r max , then the remaining oil content Δs in the pore throats with radius r(3) to r(2) ro (2) = s owr (3)-s owr (2); if r(1) ≤ r max , read r from S a The corresponding cumulative porosity value s max , then the remaining oil content Δs in the pore throats with radius r(3) to r(2) am (2) = s ro (2)-s owr (3)-[s owr (3)-[s am -s a (1)], the oil recovery rate k(2) = 1 - Δs ro (2) / Δs oir (2);

[0017] ⑥ Calculate the initial oil content, remaining oil content and oil recovery rate in the pore throats with radius r(2q + 2) to r(2q + 1) and r(2q + 1) to r(2q) (q = 2, 3, 4...) in turn, the method is as follows: determined by R w Determine the T2 values t w (2q - 1), t w (2q) of the aqueous phase corresponding to r(2q - 1) and r(2q) respectively, determined by R o Determine t w (2q - 1), t w (2q) of the pore throat radii r(2q + 1) and r(2q + 2) respectively corresponding to them, r(2q + 1) > r(2q + 2), read t from S oir The cumulative porosity values s w (2q - 1), t w (2q) corresponding to them, then the initial oil content in the pore throats with radius r(2q + 2) to r(2q + 1) is Δs oir (2q + 1) = s oir (2q + 1)-s oir (2q + 2); read t from S oir (2q - 1), t oir (2q) corresponding to them, the cumulative porosity values s owr (2q + 1), s w (2q) corresponding to them, then the initial oil content in the pore throats with radius r(2q + 2) to r(2q + 1) is Δs w (2q + 1) = s owr (2q + 1)-s owr(2q + 2), read from S a the cumulative porosity values s corresponding to r(2q - 1) and r(2q) a (2q - 1), s a (2q), then the remaining oil content Δs in the pore throats with radii from r(2q + 2) to r(2q + 1) ro (2q + 1) = s owr (2q + 1) - s owr (2q + 2) - [s a (2q - 1) - s a (2q) - Δs ro (2q - 1)], the oil recovery factor k(2q + 1) = 1 - Δs ro (2q + 1) / Δs oir (2q + 1). The initial oil content Δs in the pore throats with radii from r(2q + 1) to r(2q) oir (2q) = |s oir (2q) - s oir (2q + 1)|, the remaining oil content Δs ro (2q) = |s owr (2q) - s owr (2q + 1)| - [|s a (2q - 2) - s a (2q - 1)| - Δs ro (2q - 2)], the oil recovery factor k(2q) = 1 - Δs ro (2q) / Δs oir (2q);

[0018] If r(2q + 2) = r min , the calculation ends; if r(2q + 2) < r min and r(2q + 1) ≥ r min , then let r(2q + 2) = r min , t xl = t w (2q), t w (2q) = t l , r xl = r(2q), r(2q) = r l , read from S oir the cumulative porosity values s corresponding to t w (2q - 1), t w (2q) oir (2q + 1), s oir (2q + 2), then the initial oil content in the pore throats with radii from r(2q + 2) to r(2q + 1) is Δs oir (2q + 1) = s oir (2q + 1) - soir (2q + 2); read t from S owr and t xl 、t w (2q - 1), t w and the cumulative porosity value s corresponding to (2q) owrxl 、s owr (2q + 1), s owr (2q + 2), read r from S a and r xl and the cumulative porosity value s corresponding to r(2q - 1) a (2q), s a (2q - 1), then the remaining oil content Δs in the pore throats with radii from r(2q + 2) to r(2q + 1) ro (2q + 1) = s owr (2q + 1) - s owr (2q + 2) - [s a (2q - 1) - s a (2q) - Δs ro (2q - 1) - s owr (2q + 2) + s owrxl , and the oil recovery rate k(2q + 1) = 1 - Δs ro (2q + 1) / Δs oir (2q + 1); the initial oil content Δs in the pore throats with radii from r(2q + 1) to r(2q) oir (2q) = |s oir (2q) - s oir (2q + 1)|, and the remaining oil content Δs ro (2q) = |s owr (2q) - s owr (2q + 1)| - [|s a (2q - 2) - s a (2q - 1)| - Δs ro (2q - 2)], and the oil recovery rate k(2q) = 1 - Δs ro (2q) / Δs oir (2q), calculation ends; if r(2q + 1) < r min , then let r(2q + 1) = r min , t xl = t w (2q - 1), t w (2q - 1) = t l , r xl = r(2q - 1), r(2q - 1) = r l , read t from S oir and the cumulative porosity value s corresponding to t w (2q - 1) oir(2q + 1), read t from S owr and the cumulative porosity value s corresponding to t xl 、t w (2q - 1) owrxl 、s owr (2q + 1), then the initial oil content Δs in the pore throats with radii r(2q + 1) to r(2q) oir (2q) = s oir (2q) - s oir (2q + 1), read r a from S xl and the cumulative porosity value s corresponding to it a (2q - 1), then the remaining oil content Δs ro (2q) = s owr (2q) - s owr (2q + 1) - [s a (2q - 2) - s a (2q - 1) - Δs ro (2q - 2) - s owr (2q + 1) + s owrxl , and the oil recovery rate k(2q) = 1 - Δs ro (2q) / Δs oir (2q), where Δs ro (2q - 2) has been obtained in the previous step, and the calculation ends; otherwise, let q = q + 1 and repeat step ⑥.

[0019] Beneficial effects:

[0020] Based on the fact that the T2 value of crude oil is greater than that of water in the pore space of the same size, and the T2 value has a positive correlation with the pore throat radius, therefore, in the T2 spectrum of the core after oil production, the interval greater than the T2 value of water corresponding to the maximum pore throat radius and the interval less than the T2 value of oil corresponding to the minimum pore throat radius are single-phase intervals. Also, in the pore space of a certain size, the T2 values of crude oil and water are fixed and the volume of the pore space of a certain size remains unchanged before and after oil production, that is, the total volume of the fluids contained therein remains unchanged. At the same time, considering that shale is rich in bedding and microfractures, the imbibition agent can reach the nano-scale small pores, and the imbibition displacement oil production effect in the smaller pores in shale is more significant. Also, due to the mixed wettability of shale, the pore throats that can be entered by oil and water in shale are different. The present invention establishes a method for determining the remaining oil distribution in shale water injection oil production, which has higher accuracy than the method based on two-dimensional T1-T2 spectrum analysis, and avoids the problem that there is no unified understanding of the division standard of oil and water in different types of pores in current shale. At the same time, using this method to determine the microscopic remaining oil distribution in shale cores does not require using other liquids to replace water or oil in the oil production simulation experiment, nor adding other solutions, avoiding the influence of non-formation fluids on the oil production process, ensuring the rationality of the oil production process simulation and the reliability of the corresponding oil production mechanism analysis results, and also reducing the experimental cost. Brief Description of the Drawings:

[0021] Figure 1 For shale saturated with water (D wr 、S wr ), saturated with oil (D oir 、S oir ), and after oil production (D owr 、S owr ), the nuclear magnetic T2 spectrum and porosity cumulative curve corresponding to the fluid distribution and the schematic diagram of the parameter values for calculating the remaining oil.

[0022] Figure 2 Schematic diagram of the pore throat radius distribution of shale and the parameter values for calculating the remaining oil. Detailed Embodiment:

[0023] The following further describes the present invention:

[0024] This method for determining the remaining oil distribution in shale water injection oil production includes the following steps.

[0025] I. Select a shale core sample, select the most typical single-component hydrocarbon as the experimental oil according to the actual shale oil component test results, and determine the full pore size distribution B of the core according to the Chinese invention patent ZL202310657387.7 "Method for Determining the Full Pore Size Distribution of Shale Oil Reservoir Cores Based on Nuclear Magnetic T2 Spectrum", and calculate the cumulative distribution curve S of the core pore volume by accumulating B a, take the relationship R between the T2 of the oil finally determined in the process of measuring B and the pore throat radius r o , the relationship R between the T2 of water and r w , take the nuclear magnetic T2 spectrum D corresponding to the distribution of distilled water filled in the core saturated with distilled water obtained in the process of measuring B wr , from D wr Cumulatively calculate to determine D wr of the porosity cumulative curve S wr ;

[0026] Second, dry the core again at 110 °C until it reaches a constant weight, and carry out NMR T2 spectrum test on the dry core sample of the core according to the standard "SY / T6490-2014 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples" to determine the T2 spectrum D of the dry core sample of the core g ;

[0027] Third, saturate the core with oil according to the standard "GB / T29172-2012 Core Analysis Method", weigh the core after saturation with oil, and carry out NMR T2 spectrum test according to the standard "SY / T6490-2014 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples" to determine the T2 spectrum D of the core saturated with oil oi ;

[0028] Fourth, carry out a simulation experiment on water-based medium huff and puff imbibition oil recovery on the core saturated with oil with reference to the standard "GB / T29172-2012 Core Analysis Method". After the experiment, carry out NMR T2 spectrum test on the core according to the standard "SY / T6490-2014 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples" to determine the T2 spectrum D of the core after oil recovery ow ;

[0029] Fifth, calculate the remaining oil distribution of the core based on the experimental data. The specific calculation method is:

[0030] ① Subtract D oi from D g , select the part where T2≥0.2ms in the obtained T2 spectrum to obtain the nuclear magnetic T2 spectrum D corresponding to the distribution of oil filled in the core saturated with oil oir and D oir of the porosity cumulative curve S oir , subtract D ow from D g , select the part where T2≥0.2ms in the obtained T2 spectrum to obtain the nuclear magnetic T2 spectrum D corresponding to the distribution of oil and water-based medium filled in the core after oil recovery owr and D owr of the porosity cumulative curve S owr ;

[0031] ② Read the minimum T2 value (t wr with a signal volume greater than 0 from D wmin),According to R w Convert t wmin to the pore throat radius r wmin , read the minimum T2 value (t oir ) with a signal volume greater than 0 from D omin , According to R o Convert t omin to the pore throat radius r omin , take the smaller value of r wmin and r omin as r min , According to R o Convert r min to the T2 value t of the oil phase l , According to R w Convert t l to the pore throat radius r l (see attachment Figure 1 );

[0032] ③ Read the maximum T2 value (t oir ) with a signal volume greater than 0 from D o (1)), read the maximum T2 value (t wr ) with a signal volume greater than 0 from D wm , According to R w Convert t wm to the pore throat radius r max , read the minimum T2 value (t wr ) greater than t wm and with a signal volume of 0 from D o (2)), According to R o Convert t o (1), t o (2) to the pore throat radii r(1), r(2) (r(1)>r(2)), then D oir and D owr the t in o (2)~t o (1) corresponding signal is the signal of oil in the pore throats with radii from r(2) to r(1), and the signals in the interval of t o (2)~t o (1) are all signals of oil. Read the cumulative porosity values s oir corresponding to t o (1), t o (2) from S oir (1), s oir (2), read the cumulative porosity values s owr corresponding to t o (1), t o (2) from S owr (1), s owr (2)(see attachmentFigure 1 ), then the initial oil content Δs in the pore throats with radii from r(2) to r(1) oir (1) = s oir (1) - s oir (2), and the remaining oil content Δs ro (1) = s owr (1) - s owr (2), and the oil recovery factor k(1) = 1 - Δs ro (1) / Δs oir (1);

[0033] ④ Determine the T2 values t w (1) and t w (2) of the aqueous phase corresponding to r(1) and r(2) respectively from R w , and determine the pore throat radii r(3) and r(4) (r(3) > r(4)) corresponding to t o (1) and t w (2) respectively from R w . Then the signal in D oir corresponding to t w (2) to t w (1) is the oil signal in the pore throats with radii from r(4) to r(3), and the signal in D owr corresponding to t w (2) to t w (1) is the superposition of the water signal in the pore throats with radii from r(2) to r(1) and the oil signal in the pore throats with radii from r(4) to r(3). Read the cumulative porosity values s oir (3) and s w (4) corresponding to t w (1) and t oir (2) from S oir . Then the initial oil content Δs oir (3) = s oir (3) - s oir (4). Read the cumulative porosity values s owr (3) and s w (4) corresponding to t w (1) and t owr (2) from S owr (see Appendix Figure 1 ), and read the cumulative porosity values s a (1) and s a (2) corresponding to r(1) and r(2) from S a (see Appendix Figure 2 ). Then the water content in the pore throats with radii from r(2) to r(1) is s a (1) - s a (2) - Δsro (1), the remaining oil content Δs in the pore throats with radii from r(4) to r(3) ro (3) = s owr (3) - s owr (4) - [s a (1) - s a (2) - Δs ro (1)], and the oil recovery factor k(3) = 1 - Δs ro (3) / Δs oir (3), where Δs ro (1) has been obtained in the previous step;

[0034] ⑤D oir where t w (1) to t o (2) correspond to the oil signal in the pore throats with radii from r(3) to r(2), then the initial oil content Δs in the pore throats with radii from r(3) to r(2) oir (2) = |s oir (2) - s oir (3)|. D owr where t w (1) to t o (2) correspond to the superposition of the water signal in the pore throats with radii from r(1) to r(0) and the oil signal in the pore throats with radii from r(3) to r(2), where r(0) is obtained by converting t o (2) based on R w The T2 value t w (0) = t o (2) > t wm (see appendix Figure 1 ). If r(1) > r max , then the water signal in the pore throats from r(1) to r(0) is 0, and the remaining oil content Δs in the pore throats with radii from r(3) to r(2) ro (2) = s owr (3) - s owr (2). If r(1) ≤ r max , then the water signal in the pore throats from r(1) to r(0) is equal to the water signal in the pore throats from r(1) to r max and the T2 value t max corresponding to the oil signal of r omax ≥ t o (1), that is, there is no oil signal in the pore throats from r(1) to r max , and there is only water in this part of the pore throats, and the volume of water is equal to the volume of the pore throats. Read the cumulative porosity value s a corresponding to r max from S am, then the remaining oil content Δs in the pore throats with radii from r(3) to r(2) ro (2) = s owr (2) - s owr (3) - [s am - s a (1)], and the oil recovery factor k(2) = 1 - Δs ro (2) / Δs oir (2);

[0035] ⑥ Calculate the initial oil content, remaining oil content, and oil recovery factor in the pore throats with radii from r(2q + 2) to r(2q + 1) and from r(2q + 1) to r(2q) (q = 2, 3, 4...) in sequence. The method is as follows: Determine the T2 values t w of the aqueous phase corresponding to r(2q - 1) and r(2q) respectively as t w (2q - 1) and t w (2q), and determine the pore throat radii r(2q + 1) and r(2q + 2) (r(2q + 1) > r(2q + 2)) corresponding to t o (2q - 1) and t w (2q) respectively by R. Then, the signal corresponding to t w (2q) to t oir (2q - 1) in D is the oil signal in the pore throats with radii from r(2q + 2) to r(2q + 1). The signal corresponding to t w (2q) to t w (2q - 1) in D is the superposition of the water signal in the pore throats with radii from r(2q) to r(2q - 1) and the oil signal in the pore throats with radii from r(2q + 2) to r(2q + 1). Read the cumulative porosity values s owr corresponding to t w (2q - 1) and t w (2q) from S as s oir (2q + 1) and s w (2q + 2). Then, the initial oil content in the pore throats with radii from r(2q + 2) to r(2q + 1) is Δs w (2q + 1) = s oir (2q + 1) - s oir (2q + 2). Read the cumulative porosity values s oir (2q + 1) and s oir (2q + 2) corresponding to t oir (2q - 1) and t owr (2q) from S, and read the cumulative porosity values s w (2q + 1) and s w (2q + 2) corresponding to t owr (2q - 1) and t owr (2q) from S. Read the cumulative porosity values s a corresponding to r(2q - 1) and r(2q) from S as s a(2q - 1), s a If it is (2q), then the water content in the pore throats with radius r(2q) to r(2q - 1) is s a (2q - 1) - s a (2q) - Δs ro (2q - 1), the remaining oil content Δs in the pore throats with radius r(2q + 2) to r(2q + 1) ro (2q + 1) = s owr (2q + 1) - s owr (2q + 2) - [s a (2q - 1) - s a (2q) - Δs ro (2q - 1)], the oil recovery factor k(2q + 1) = 1 - Δs ro (2q + 1) / Δs oir (2q + 1). D oir Among them, t w (2q - 1) to t w (2q - 2) corresponds to the oil signal in the pore throats with radius r(2q + 1) to r(2q), D owr Among them, t w (2q - 1) to t w (2q - 2) corresponds to the superposition of the water signal in the pore throats with radius r(2q - 1) to r(2q - 2) and the oil signal in the pore throats with radius r(2q + 1) to r(2q). Then the initial oil content Δs in the pore throats with radius r(2q + 1) to r(2q) oir (2q) = |s oir (2q) - s oir (2q + 1)|, the water content in the pore throats with radius r(2q - 1) to r(2q - 2) is |s a (2q - 2) - s a (2q - 1)| - Δs ro (2q - 2), the remaining oil content Δs in the pore throats with radius r(2q + 1) to r(2q) ro (2q) = |s owr (2q) - s owr (2q + 1)| - [|s a (2q - 2) - s a (2q - 1)| - Δs ro (2q - 2)], the oil recovery factor k(2q) = 1 - Δs ro (2q) / Δs oir (2q), where Δs ro (2q - 1), Δs ro (2q - 2) have been obtained in the previous steps.

[0036] If r(2q + 2) = r min , the calculation ends; if r(2q + 2) < r min and r(2q + 1) ≥ r min , then let r(2q + 2) = r min , t xl = t w (2q), t w (2q) = t l , r xl = r(2q), r(2q) = r l , then the signal corresponding to t oir (2q) to t w (2q - 1) in D w is the oil signal in the pore throats with radii from r(2q + 2) / r min to r(2q + 1), and the signal corresponding to t owr (2q) to t w (2q - 1) in D w is the superposition of the water phase signal in the pore throats with radii from r(2q) / r l to r(2q - 1) and the oil signal in the pore throats with radii from r(2q + 2) / r min to r(2q + 1). Read the cumulative porosity values s oir (2q - 1), s w (2q), s w (2q + 1), s oir (2q + 2) from S oir , then the initial oil content in the pore throats with radii from r(2q + 2) to r(2q + 1) is Δs oir (2q + 1) = s oir (2q + 1) - s oir (2q + 2). The water phase signal in the pore throats with radii from r l to r(2q - 1) is equal to the water phase signal in the pore throats with radii from r xl to r(2q - 1) minus the water phase signal in the pore throats with radii from r xl to r l . Since there is no oil signal in the range of t xl < t l , t xl to t l , read the cumulative porosity values s owr , s xl , s w (2q - 1), s w (2q) / t l from S owrxl , s owr (2q + 1), s owr (2q + 2), then the radius is from r xl~r l The water-based medium content in the pore throat is s owr (2q + 2) - s owrxl , from S a Read r xl , the cumulative porosity value s corresponding to r(2q - 1) a (2q), s a (2q - 1), then the radius is r xl ~r(2q - 1) The water-based medium content in the pore throat is s a (2q - 1) - s a (2q) - Δs ro (2q - 1), the radius is r l ~r(2q - 1) The water-based medium content in the pore throat is s a (2q - 1) - s a (2q) - Δs ro (2q - 1) - [s owr (2q + 2) - s owrxl , then the remaining oil content Δs in the pore throat with a radius of r(2q + 2) ~ r(2q + 1) ro (2q + 1) = s owr (2q + 1) - s owr (2q + 2) - [s a (2q - 1) - s a (2q) - Δs ro (2q - 1) - s owr (2q + 2) + s owrxl , the oil recovery rate k(2q + 1) = 1 - Δs ro (2q + 1) / Δs oir (2q + 1). As mentioned above (step ⑥), the initial oil content Δs in the pore throat with a radius of r(2q + 1) ~ r(2q) oir (2q) = |s oir (2q) - s oir (2q + 1)|, the remaining oil content Δs ro (2q) = |s owr (2q) - s owr (2q + 1)| - [|s a (2q - 2) - s a (2q - 1)| - Δs ro (2q - 2)], the oil recovery rate k(2q) = 1 - Δs ro (2q) / Δs oir (2q), where Δs ro (2q - 1), Δs ro (2q - 2) has been obtained in the previous steps, and the calculation ends; if r(2q + 1) < r min, then let \(r(2q + 1)=r\) min , \(t\) xl \(=t\) w (2q - 1), \(t\) w (2q - 1)=t l , \(r\) xl \(=r(2q - 1), r(2q - 1)=r\) l , then \(D\) oir the \(t\) in w (2q - 1)~\(t\) w (2q - 2) corresponds to a signal of oil in pore throats with a radius from \(r(2q + 1) / r\) min ~\(r(2q)\). The \(t\) in \(D\) owr the \(t\) in w (2q - 1)~\(t\) w (2q - 2) corresponds to a signal which is the superposition of the water - phase signal in pore throats with a radius from \(r(2q - 1) / r\) l ~\(r(2q - 2)\) and the oil signal in pore throats with a radius from \(r(2q + 1) / r\) min ~\(r(2q)\). Reading the cumulative porosity value \(s\) oir corresponding to \(t\) w (2q - 1) from \(S\) oir , then the initial oil content \(\Delta s\) in pore throats with a radius from \(r(2q + 1)\) to \(r(2q)\) oir (2q)=s oir (2q)-s oir (2q + 1). The water - phase signal in pore throats with a radius from \(r\) l ~\(r(2q - 2)\) is equal to the water - phase signal in pore throats with a radius from \(r\) xl ~\(r(2q - 2)\) minus the water - phase signal in pore throats with a radius from \(r\) xl ~\(r\) l . Since there is no oil signal in the \(t\) xl ~\(t\) l interval, reading the cumulative porosity values \(s\) owr corresponding to \(t\) xl , \(t\) w (2q - 1) and \(s\) owrxl , \(s\) owr (2q + 1) from \(S\), then the water - based medium content in pore throats with a radius from \(r\) xl ~\(r\) l is \(s\) owr (2q + 1)-s owrxl . Reading the cumulative porosity value \(s\) a corresponding to \(r\) xl from \(S\), then the water - based medium content in pore throats with a radius from \(r\) a (2q - 1) is \(s\) xl ~\(r(2q - 2)\) a (2q - 2)-s a(2q - 1)-Δs ro (2q - 2), with a radius of r l ~r(2q - 2) the water-based medium content in the pore throats is s a (2q - 2)-s a (2q - 1)-Δs ro (2q - 2)-[s owr (2q + 1)-s owrxl , then the remaining oil content Δs in the pore throats with a radius of r(2q + 1)~r(2q) ro (2q)=s owr (2q)-s owr (2q + 1)-[s a (2q - 2)-s a (2q - 1)-Δs ro (2q - 2)-s owr (2q + 1)+s owrxl , the crude oil recovery factor k(2q)=1 - Δs ro (2q) / Δs oir (2q), where Δs ro (2q - 2) has been obtained in the previous step, the calculation ends; otherwise, let q = q + 1 and repeat step ⑥.

Claims

1. A method for determining the distribution of remaining oil in shale oil production by water injection, characterized in that Including the following steps: Step 1: Select a core, which is a shale core, and determine the cumulative distribution curve S of the core pore volume a , the nuclear magnetic T2 spectrum D corresponding to the distribution of distilled water filled in the core saturated with distilled water wr and D wr porosity cumulative curve S wr , the relationship R between the T2 of oil and the pore throat radius r o , the relationship R between the T2 of water and r w ; Step 2: Dry the core again until it reaches a constant weight, and conduct NMR T2 spectrum tests on the dry core sample to determine the T2 spectrum D of the dry core sample g ; Step 3: Saturate the core with oil, conduct NMR T2 spectrum tests on the oil-saturated core, and determine the T2 spectrum D of the oil-saturated core oi ; Step 4. Conduct a water-based medium huff and puff imbibition oil production simulation experiment using cores saturated with oil. After the experiment, conduct NMR T2 spectrum tests on the cores to determine the T2 spectrum D of the cores after oil production ow ; Step Five: Calculate the remaining oil distribution in the core: ① Subtract D oi from D g , select the part where T2≥0.2ms in the obtained T2 spectrum to obtain the nuclear magnetic T2 spectrum D corresponding to the distribution of the injected oil in the saturated oil core oir and the porosity cumulative curve S of D oir ; subtract D oir from D ow , select the part where T2≥0.2ms in the obtained T2 spectrum to obtain the nuclear magnetic T2 spectrum D corresponding to the distribution of the injected oil and water-based medium in the core after oil production g and the porosity cumulative curve S of D owr and D owr ; owr ; ② Read the minimum T2 value t with a signal volume greater than 0 from D wr and convert t wmin to the pore throat radius r w according to R wmin ; read the minimum T2 value t with a signal volume greater than 0 from D wmin and convert t oir to the pore throat radius r omin according to R o ; take the smaller value between r omin and r omin as r wmin and convert r omin to the T2 value t of the oil phase min according to R o ; convert t min to the pore throat radius r l according to R w ; l l ;​ ③ Read the maximum T2 value t with a semaphore greater than 0 from D oir (1), read the maximum T2 value t with a semaphore greater than 0 from D o (1), read the maximum T2 value t with a semaphore greater than 0 from D wr Convert t wm to the pore throat radius r according to R w (1), read from D wm the minimum T2 value t greater than t max and with a semaphore of 0 wr (2), read t wm (1) and the corresponding cumulative porosity value s o (2) from S oir (1), read t o (1), t o (2) and the corresponding cumulative porosity value s oir (1), s oir (2) from S owr (1), read t o (1), t o (2) and the corresponding cumulative porosity value s owr (1), s owr (2) from S o (1), convert t o (1), t o (2) to the pore throat radii r(1), r(2), where r(1)>r(2), then the initial oil content Δs oir (1) in the pore throats with radii from r(2) to r(1) is s oir (1)-s oir (2), the remaining oil content Δs ro (1) is s owr (1)-s owr (2), and the crude oil recovery factor k(1)=1-Δs ro (1) / Δs oir (1); ④Determined by R w to determine the T2 values t(1) and t(2) of the aqueous phases corresponding to r(1) and r(2) respectively w (1) and t w (2), determined by R o to determine t w (1) and t w (2) corresponding to the pore throat radii r(3) and r(4) respectively, where r(3) > r(4). Read t oir (1) and t w (2) corresponding cumulative porosity values s w (3) and s oir (4), then the initial oil content Δs oir (3) in the pore throats with radii from r(4) to r(3) is s oir (3) = s oir (3) - s oir (4); Read t owr (1) and t w (2) corresponding cumulative porosity values s w (3) and s owr (4), read from S owr the cumulative porosity values s a (1) and s a (2) corresponding to r(1) and r(2), then the remaining oil content Δs a (3) in the pore throats with radii from r(4) to r(3) is s ro (3) = s owr (3) - s owr (4) - [s a (1) - s a (2) - Δs ro (1)], and the oil recovery factor k(3) = 1 - Δs ro (3) / Δs oir (3); ⑤Initial oil content Δs in pore throats with radii from r(3) to r(2) oir (2) = |s oir (2) - s oir (3)|; Determine t w from the pore throat radius r(0) corresponding to R o (2), where r(0), r(1) > r max , then the remaining oil content Δs in pore throats with radii from r(3) to r(2) ro (2) = s owr (3) - s owr (2); If r(1) ≤ r max , read the cumulative porosity value s a corresponding to r max from S am , then the remaining oil content Δs in pore throats with radii from r(3) to r(2) ro (2) = s owr (2) - s owr (3) - [s am - s a (1)], and the oil recovery factor k(2) = 1 - Δs ro (2) / Δs oir (2); ⑥Calculate the initial oil content, remaining oil content and oil recovery rate in the pore throats with radii from r(2q + 2) to r(2q + 1) and from r(2q + 1) to r(2q) (q = 2, 3, 4...) in sequence. The method is as follows: From R w Determine the T2 values t w (2q - 1) and t w (2q) of the aqueous phase corresponding to r(2q - 1) and r(2q) respectively. From R o Determine the pore throat radii r(2q + 1) and r(2q + 2) corresponding to t w (2q - 1) and t w (2q) respectively, where r(2q + 1) > r(2q + 2). Read the cumulative porosity values s oir (2q + 1) and s w (2q + 2) corresponding to t w (2q - 1) and t oir (2q) from S oir . Then the initial oil content in the pore throats with radius from r(2q + 2) to r(2q + 1) is Δs oir (2q + 1) = s oir (2q + 1) - s oir (2q + 2); Read the cumulative porosity values s owr (2q + 1) and s w (2q + 2) corresponding to t w (2q - 1) and t owr (2q) from S owr . Read the cumulative porosity values s a (2q - 1) and s a (2q) corresponding to r(2q - 1) and r(2q) from S a . Then the remaining oil content Δs ro (2q + 1) = s owr (2q + 1) - s owr (2q + 2) - [s a (2q - 1) - s a (2q) - Δs ro (2q - 1)], and the oil recovery rate k(2q + 1) = 1 - Δs ro (2q + 1) / Δs oir (2q + 1); The initial oil content Δs oir (2q) = |s oir (2q) - s oir (2q + 1)|, and the remaining oil content Δs ro (2q) = |s owr (2q) - s owr (2q + 1)|-[|s a (2q - 2)-s a (2q - 1)|-Δs ro (2q - 2)], the crude oil recovery rate k(2q) = 1 - Δs ro (2q) / Δs oir (2q); If r(2q + 2) = r min , the calculation ends; if r(2q + 2) < r min and r(2q + 1) ≥ r min , then let r(2q + 2) = r min , t xl = t w (2q), t w (2q) = t l , r xl = r(2q), r(2q) = r l , read t oir from S w (2q - 1), t w (2q) corresponding cumulative porosity values s oir (2q + 1), s oir (2q + 2), then the initial oil content in the pore throats with radius r(2q + 2) to r(2q + 1) is Δs oir (2q + 1) = s oir (2q + 1) - s oir (2q + 2); read t owr from S xl , t w (2q - 1), t w (2q) corresponding cumulative porosity values s owrxl , s owr (2q + 1), s owr (2q + 2), read r a from S xl , r(2q - 1) corresponding cumulative porosity values s a (2q), s a (2q - 1), then the remaining oil content Δs ro (2q + 1) = s owr (2q + 1) - s owr (2q + 2) - [s a (2q - 1) - s a (2q) - Δs ro (2q - 1) - s owr (2q + 2) + s owrxl , the crude oil recovery rate k(2q + 1) = 1 - Δs ro (2q + 1) / Δs oir (2q + 1); the initial oil content Δs oir (2q) = |s oir (2q) - s oir (2q + 1)|, the remaining oil content Δs ro (2q) = |s owr (2q) - s owr (2q + 1)| - [|s a (2q - 2) - s a (2q - 1)| - Δs ro (2q - 2)], the oil recovery factor k(2q) = 1 - Δs ro (2q) / Δs oir (2q), calculation ends; if r(2q + 1) < r min , then let r(2q + 1) = r min , t xl = t w (2q - 1), t w (2q - 1) = t l , r xl = r(2q - 1), r(2q - 1) = r l , from S oir read t w (2q - 1) corresponding cumulative porosity value s oir (2q + 1), from S owr read t xl , t w (2q - 1) corresponding cumulative porosity value s owrxl , s owr (2q + 1), then the initial oil content Δs in the pore throats with radius r(2q + 1) to r(2q) oir (2q) = s oir (2q) - s oir (2q + 1), from S a read r xl corresponding cumulative porosity value s a (2q - 1), then the remaining oil content Δs ro (2q) = s owr (2q) - s owr (2q + 1) - [s a (2q - 2) - s a (2q - 1) - Δs ro (2q - 2) - s owr (2q + 1) + s owrxl , the oil recovery factor k(2q) = 1 - Δs ro (2q) / Δs oir (2q), where Δs ro (2q - 2) has been obtained in the previous steps, calculation ends; Otherwise, let q = q + 1 and repeat Step Six.

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