A method for evaluating oil saturation based on the self-sealing ability of tight reservoirs

Abstract

This invention discloses a method for evaluating oil saturation based on the self-sealing capacity of tight reservoirs, relating to the field of petroleum exploration and development technology. First, this invention fits an acoustic transit time-depth trend line based on conventional logging data, and uses the Eaton method to calculate the total overpressure and separate hydrocarbon generation pressurization. Second, through high-pressure mercury injection experiments and conversion of charging characteristics, the relationship between pore throat radius and oil saturation is determined. Then, based on the capillary pressure formula and hydrocarbon generation pressurization intensity, the critical charging pore throat radius is determined. Based on mechanical equilibrium relationships, the upper limit of the self-sealing pore throat radius is determined. Finally, the effective reservoir pore throat range is defined, and oil saturation is calculated. This method overcomes the technical shortcomings of traditional methods that neglect the dynamic coupling relationship between hydrocarbon generation pressurization, pore throat charging, and self-sealing capacity during tight oil accumulation, resulting in large evaluation errors.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration and development, and more specifically, to a method for evaluating oil saturation based on the self-sealing capability of tight reservoirs. Background Technology

[0002] Tight oil, as an important component of unconventional oil and gas resources, boasts abundant reserves and enormous development potential, making it a key area for global oil and gas exploration and development. Oil saturation is a core parameter for tight oil reservoir evaluation, reserve calculation, and development planning, directly determining the economic value of the reservoir.

[0003] Traditional methods for evaluating the oil saturation of tight oil reservoirs are mostly based on well logging curve interpretation models or conventional core experimental analysis, such as resistivity methods and neutron porosity methods. However, tight oil reservoirs are characterized by low porosity, low permeability, and complex pore-throat structures. The fluid occurrence state and seepage patterns in these reservoirs differ significantly from those in conventional oil and gas reservoirs, leading to substantial errors in the evaluation results obtained using traditional methods, making it difficult to accurately reflect the true oil content of the reservoir. Summary of the Invention

[0004] The purpose of this application is to provide an oil saturation evaluation method based on the self-sealing capacity of tight reservoirs. This method solves the problem that conventional methods ignore the coupling relationship between crude oil charging behavior caused by hydrocarbon generation and pressurization during the formation of tight oil reservoirs and the self-sealing capacity of reservoir pores and throats, which leads to large errors in the evaluation results and makes it difficult to accurately reflect the true oil content of the reservoir.

[0005] To solve the above-mentioned technical problems, the solution adopted in this application is as follows:

[0006] A method for evaluating oil saturation based on the self-sealing capability of tight reservoirs, the implementation of which includes the following process:

[0007] Step S100: Based on conventional logging response data, perform hydrocarbon generation pressurization recovery in tight reservoirs to obtain the hydrocarbon generation pressurization intensity Phydrocarbon.

[0008] Step S200: Based on the mercury injection test data, the pore throat radius is transformed as a function of oil content to obtain the curve.

[0009] Step S300: Determine the critical charging pore throat radius in tight reservoirs based on hydrocarbon generation and pressurization intensity; determine the upper limit of the self-sealing pore throat radius in tight reservoirs based on the principle of mechanical equilibrium;

[0010] Step S400: Based on the curve of pore throat radius changing with oil content, critical filling pore throat radius and upper limit of self-sealing pore throat radius, define the effective self-sealing pore throat range, determine the effective self-sealing pore porosity, and calculate the proportion of effective self-sealing pore volume to total porosity in this range, which is the oil saturation.

[0011] As a preferred technical solution, the specific implementation process of step S100 is as follows:

[0012] Step 101: Using sonic transit time data from shallow, normally compacted mudstone sections, fit an exponential compaction trend line based on the exponential compaction law to show the variation of sonic transit time with depth:

[0013] ;

[0014] in, This represents the normal compaction acoustic transit time at depth H; C represents the initial acoustic transit time at the surface; C is the mudstone compaction coefficient. For burial depth.

[0015] Step 102: Based on the exponential compaction trend line obtained in Step 101, and combined with the measured logging data of the tight reservoir section, the formation pore pressure is calculated using the Eaton method. To determine the formation overpressure .

[0016] ;

[0017] ;

[0018] ;

[0019] ;

[0020] in, Formation pore pressure; This represents the total pressure of the overlying strata. Normal pore pressure; This is the normal compaction acoustic time difference; This is the measured time difference of acoustic waves in the formation; Eaton Index; average density of the formation; The hydrostatic pressure gradient; This is the acceleration due to gravity.

[0021] Step 103: Based on the logging data, calculate the effective stress and sonic velocity, and draw the intersection diagram of effective stress and sonic velocity and the overpressure line; measure the angle between the hydrocarbon generation pressurization horizontal line and the overpressure line. The pressure increase due to hydrocarbon generation is calculated, which is the hydrocarbon generation pressure increase intensity.

[0022] ;

[0023] Wherein, P represents the hydrocarbon generation pressure increase intensity; This is due to formation overpressure. The angle between the hydrocarbon generation pressurization horizontal line and the overpressure line.

[0024] Specifically, the measured effective stress It represents the degree of contact between rock particles; the greater the effective stress, the more tightly the particles are compressed.

[0025] speed of sound It reflects the porosity and density of rocks. Generally, the higher the velocity, the denser the rock; the lower the velocity, the looser the rock or the higher the pore pressure.

[0026] In the cross-plot, the horizontal axis represents the measured effective stress, and the vertical axis represents the acoustic velocity. For each depth point in the target layer, the measured effective stress and acoustic velocity can be calculated from the collected data. Plotting these points in a Cartesian coordinate system yields the cross-plot of effective stress and acoustic velocity. Due to the heterogeneity of underground lithology and the diverse causes of overpressure, these points typically do not form perfect straight lines but are scattered within a certain area. The trend line obtained by mathematically fitting these points represents the overpressure line for that layer.

[0027] The hydrocarbon generation pressurization level is a theoretical reference line representing an ideal end-member condition—the rock physical response caused solely by hydrocarbon generation under conditions where the effective stress remains essentially constant. It can be obtained through rock physical experiments or artificially defined based on geological knowledge; this is existing technology and will not be elaborated upon further in this invention.

[0028] As a preferred technical solution, the specific implementation process of step S200 is as follows:

[0029] Step S201: Mercury-driven capillary pressure obtained from high-pressure mercury intrusion experiments Mercury saturation The relationship between changes; combining the differences in interfacial tension and contact angle between oil-water and mercury-air, the capillary pressure of mercury displacement is considered. Converted to oil-driven capillary pressure Thus, the oil-driven capillary pressure is obtained. Mercury saturation Change relationship;

[0030] Mercury-driven capillary pressure With oil-driven capillary pressure The conversion relationship between them is as follows:

[0031]

[0032] in, For oil-driven capillary pressure; For oil-water interfacial tension; The contact angle between oil / water and rock; The interfacial tension between mercury and air; The contact angle between mercury and rock; Mercury-driven capillary pressure.

[0033] Step S202: Based on the capillary pressure formula, adjust the oil-driven capillary pressure according to the mercury saturation. The relationship changes to mercury saturation. Curve showing variation with throat radius;

[0034] The orifice radius as a function of capillary pressure in oil-driven capillary tubes is obtained based on the capillary pressure formula. The relationships of change are as follows:

[0035] ;

[0036] in, For oil-water interfacial tension; The contact angle between oil / water and rock; Let be the radius of the throat.

[0037] In this step, the oil-driven capillary pressure obtained in step S201 will be used. Substituting into the capillary pressure formula, the corresponding pore throat radius was calculated, thus obtaining the pore throat radius as a function of mercury saturation. Variation curve. Orifice throat radius as a function of mercury saturation. The variation curve shows that, since the conversion from mercury to oil filling characteristics has been completed throughout the process, the orifice throat radius changes with the mercury saturation. Change curve (r) is equivalent to the curve of the pore throat radius changing with oil content.

[0038] It is worth noting that high-pressure mercury intrusion porosimetry is an existing experimental method in this field. In mercury intrusion porosimetry, the mercury saturation is... This represents the percentage of pore volume into which mercury has entered under a certain pressure, relative to the total pore volume. It is calculated after the mercury is driven through the capillary pressure. Converted to oil-driven capillary pressure After being further converted into the pore throat radius, the mercury saturation is... This is equivalent to the oil saturation in the response radius voids. Therefore, the oil content at different pore throat radii is equivalent to the mercury ingress saturation corresponding to each radius interval on the pore throat radius distribution curve. Increment.

[0039] In some specific implementation schemes, step S300 is implemented as follows:

[0040] Step S301: Based on the hydrocarbon generation and pressurization intensity, determine the critical capillary pressure value for crude oil injection, and calculate the corresponding orifice throat radius, which is the critical injection orifice throat radius. ;

[0041] Specifically, when the capillary pressure of the oil-driven pipeline is greater than the hydrocarbon generation pressure, the corresponding pore throat radius is smaller than the critical filling pore throat radius, which is an ineffective pore that is difficult to fill; otherwise, it is an effective pore.

[0042] Specifically, based on the capillary pressure formula, the calculated pore throat radius is obtained by substituting the hydrocarbon generation pressure into the calculated pore throat radius, which is the pore throat radius limit, i.e., the critical filling pore throat radius. Pores with a throat radius greater than the critical filling throat radius are considered effective pores because crude oil can overcome capillary resistance to enter. Pores with a throat radius smaller than the critical filling throat radius are considered ineffective pores because crude oil cannot overcome capillary resistance to enter and does not contribute to oil saturation.

[0043] Step S302: Calculate the capillary force in the tight reservoir The correspondence between the orifice throat radius and the orifice throat radius;

[0044] ;

[0045] In the formula, For oil-water interfacial tension, The contact angle between oil / water and rock. Where is the throat radius, This refers to the pore size.

[0046] Step S303: Calculate the buoyancy at different dip angles of the strata;

[0047]

[0048] In the formula, Pore ​​size; Density of formation water; Density of crude oil; It is the acceleration due to gravity; The dip angle of the strata.

[0049] Step S304: Obtain the relationship between capillary force, buoyancy, and pore throat radius in tight reservoirs. When capillary force and buoyancy reach equilibrium, the corresponding pore throat radius is the upper limit of the self-sealing pore throat radius. greater than The holes are effective unobstructed holes, and the crude oil in these holes will continue to move under the action of buoyancy.

[0050] The specific implementation process of step S400 is as follows:

[0051] Step S401: Combine the pore throat radius with mercury saturation Change curve (r) Determine the porosity of ineffective and effective pores. and , is represented as:

[0052] ;

[0053] ;

[0054] in, Porosity of ineffective pores; Porosity of the effective pores; Total porosity; The minimum pore throat radius of a tight reservoir; The maximum pore throat radius of the tight reservoir; The critical filling orifice throat radius; The curve shows the variation of mercury saturation with the pore throat radius.

[0055] In some specific implementation schemes, step S400 is implemented as follows:

[0056] Step S401: Combining the upper limit of the self-sealing throat radius, the curve of the throat radius changing with mercury saturation, and the critical filling throat radius, determine the porosity of ineffective pores, effective self-sealing pores, and effective unobstructed pores, expressed as:

[0057] ;

[0058] ;

[0059] ;

[0060] ;

[0061] In the formula, Porosity of ineffective pores; Porosity of ineffective pores; Total porosity; To effectively improve the porosity of the pores, % is the minimum pore throat radius of the tight reservoir; is the maximum pore throat radius of the tight reservoir. The critical filling orifice throat radius; This is the upper limit of the effective self-sealing throat radius; This is a curve showing the variation of mercury saturation with the pore throat radius.

[0062] Specifically, the orifice throat radius is located at the critical filling orifice throat radius. Upper limit of the self-sealing throat radius The pores between the cells have capillary resistance greater than the buoyancy of crude oil but less than the crude oil charging power generated by hydrocarbon generation and pressurization, making them effective self-sealing pores and the main storage space for tight oil; the pore throat radius is greater than the upper limit of the self-sealing pore throat radius. The pores are effective unobstructed pores, and the crude oil in these pores will continue to move under the action of buoyancy.

[0063] Step S402: Calculate the minimum pore throat radius of the tight reservoir. With the maximum pore throat radius of tight reservoirs Porosity of effective self-sealing pores within the interval The porosity of the effectively self-sealing pores With total porosity Calculate the ratio to obtain the oil saturation of the tight reservoir under closed conditions. ;

[0064] ;

[0065] in, Porosity of the effective pores; This represents the oil saturation level.

[0066] The technical solution of this application has at least the following advantages and beneficial effects:

[0067] This invention establishes a dynamic coupled evaluation system for hydrocarbon generation pressurization, pore throat filling, and self-sealing capability, solving the problem of large evaluation errors caused by neglecting the coupling relationship among these three factors in traditional methods. This invention obtains the filling power through hydrocarbon generation pressurization recovery technology, characterizes the pore throat filling characteristics through high-pressure mercury intrusion porosimetry, and determines the upper limit of self-sealing pore throats through the principle of mechanical equilibrium. By unifying the filling power, filling behavior, and preservation capability into the oil saturation calculation model, it achieves a dynamic reconstruction of the tight oil reservoir formation process and significantly improves the evaluation accuracy of oil saturation.

[0068] This invention achieves oil saturation calculation based on the hierarchical characteristics of pore throat radius, solving the problem that existing methods cannot distinguish the contributions of pore throats at different scales. This invention obtains continuous distribution curves of pore throat radius and mercury intrusion saturation through high-pressure mercury injection experiments, and combines the critical charging pore throat radius and the upper limit of the self-sealing pore throat radius to divide reservoir porosity into three scale intervals: ineffective pores, effective self-sealing pores, and effective unobstructed pores. The contribution of each interval to oil saturation is calculated separately, preserving key hierarchical information of the pore throat structure.

[0069] In this invention, an upper limit for the radius of a self-sealing pore throat is defined. Based on the mechanical balance principle of capillary force and buoyancy, a quantitative calculation method for the upper limit of the radius of a self-sealing pore throat is established. Taking into account geological parameters such as oil-water interfacial tension, wetting angle, formation dip angle, and fluid density, the upper limit of the radius of a self-sealing pore throat is accurately defined, providing a quantitative basis for the identification of effective reservoir space. Attached Figure Description

[0070] When considered in conjunction with the accompanying drawings, the invention can be more fully and better understood by referring to the following detailed description, and the scientific and practical nature of the invention can be better illustrated. However, the accompanying drawings, which are provided to provide a further understanding of the invention and constitute a part of this invention, are used to explain the invention and do not constitute an undue limitation of the invention.

[0071] Figure 1 This is a graph showing the trend of acoustic transit time as a function of depth.

[0072] Figure 2 Schematic diagram for evaluating the contribution of overpressure to different causes and mechanisms;

[0073] Figure 3 This is a characteristic of oil saturation as a function of capillary pressure, based on a high-pressure mercury intrusion test.

[0074] Figure 4 The curve showing the cumulative oil saturation as a function of pore throat radius;

[0075] Figure 5 Determining the upper limit of the self-sealing pore throat radius of tight reservoirs based on mechanical equilibrium;

[0076] Figure 6 To define the distribution range of different types of pores. Detailed Implementation

[0077] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0078] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0079] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0080] Example

[0081] This invention provides a method for evaluating oil saturation based on the self-sealing capability of tight reservoirs. The method is applied to a target area where the average burial depth of the target layer is 4900m, the average porosity is 5.6%, the average pore-throat ratio is about 17.7, the formation dip angle is 5°, the oil-water interfacial tension is 35mN / m, and the wetting angle is 20°.

[0082] Specifically, the implementation process is as follows:

[0083] Step S100: Based on conventional logging response data, perform hydrocarbon generation pressurization recovery in tight reservoirs to obtain the hydrocarbon generation pressurization intensity. The specific implementation process of this step is as follows:

[0084] Step S101: Using the sonic transit time data of the shallow normally compacted mudstone section from well logging, fit an exponential compaction trend line of sonic transit time as a function of depth based on the exponential compaction law (e.g., Figure 1 As shown, this is the logging data for Mahu 28.

[0085] ;

[0086] In the formula, The acoustic transit time at depth H under normal compaction conditions is expressed in μs / m. The initial acoustic transit time at the surface is μs / m; C is the mudstone compaction coefficient, m⁻¹. The burial depth is measured in meters (m).

[0087] Specifically, in this step, shallow mudstone samples with a burial depth of less than 2000m, pure lithology without cracks, and unaffected by overpressure, tectonic disturbance, or volcanic activity are selected.

[0088] Step S102: Based on the exponential compaction trend line obtained in step S101, and combined with the measured logging data of the tight reservoir section, the formation pore pressure is calculated using the Eaton method. Using formation pore pressure Subtract normal pore pressure This is the overpressure of the formation. .

[0089] Based on the principle that the degree to which the acoustic transit response of an overpressured reservoir deviates from the normal exponential compaction trend line is positively correlated with the magnitude of the overpressure, the formation pore pressure is calculated using the following formula:

[0090] ;

[0091] ;

[0092] In the formula, Formation pore pressure, MPa; The total pressure of the overlying strata is expressed in MPa. Normal pore pressure, MPa; The normal compaction acoustic transit time is μm / s; The time difference of ground acoustic waves is expressed in μm / s. This refers to the Eaton index.

[0093] Step S103: Based on the logging data, calculate the effective stress and sonic velocity, and draw the intersection diagram of effective stress and sonic velocity and the overpressure line; measure the angle between the hydrocarbon generation pressurization horizontal line and the overpressure line. Calculate the pressurization intensity caused by hydrocarbon generation; calculate the pressurization intensity caused by hydrocarbon generation as 8 MPa according to the following formula (e.g. Figure 2 (As shown):

[0094] .

[0095] Step S200: Based on the mercury intrusion porosimetry experimental data, the pore throat radius is transformed as a function of oil content to obtain the curve. The specific implementation process of this step is as follows:

[0096] Step S201: Mercury-driven capillary pressure obtained from high-pressure mercury intrusion experiments Mercury saturation The relationship between changes; combining the differences in interfacial tension and contact angle between oil-water and mercury-air, the capillary pressure of mercury displacement is considered. Converted to oil-driven capillary pressure Thus, the oil-driven capillary pressure is obtained. Mercury saturation Change relationship;

[0097] Depend on Figure 3 It can be seen that under the driving pressure of 8 MPa, the filling degree of the reservoir is 72%, which means that 28% of the pores are still occupied by bound water, which belongs to the category of ineffective pores.

[0098] The formula for converting capillary pressure under mercury-air conditions to capillary pressure under oil-water conditions can be expressed as:

[0099] ;

[0100] The orifice radius as a function of capillary pressure in oil-driven capillary tubes is obtained based on the capillary pressure formula. The relationships of change are as follows:

[0101] ;

[0102] In the formula, Let be the throat radius, in nm.

[0103] In the formula, The pressure in the oil-driven capillary is MPa. The oil-water interfacial tension is expressed in mN / m. The contact angle between oil / water and rock, in °; The mercury-air interfacial tension is expressed in mN / m. The mercury-rock contact angle is given in °. Mercury-driven capillary pressure, MPa.

[0104] Step S202: Based on the capillary pressure formula, the relationship between capillary pressure and saturation is transformed into the relationship between pore throat radius and crude oil filling degree;

[0105] like Figure 4 As shown, the orifice throat radius limit is based on a 72% filling degree. The diameter is around 9nm, which means that pores with a throat radius of less than 9nm are invalid pores. Under a driving pressure of 8MPa, these pores are difficult to be filled with oil and gas.

[0106] Step S300: Determine the critical charging pore throat radius in tight reservoirs based on hydrocarbon generation and pressurization intensity; determine the upper limit of the self-sealing pore throat radius in tight reservoirs based on the principle of mechanical equilibrium; the specific implementation process of this step is as follows:

[0107] Step S301: Determine the critical charging pore throat radius in tight reservoirs based on hydrocarbon generation and pressurization intensity;

[0108] ;

[0109] Wherein, P_hydrogenation represents the hydrocarbon generation pressure intensity; The oil-water interfacial tension is expressed in mN / m. The contact angle between oil / water and rock, in °; This indicates the critical filling orifice throat radius.

[0110] Step S302: Calculate the relationship between capillary force and pore throat radius in tight reservoirs:

[0111] ;

[0112] In the formula, The oil-water interfacial tension is expressed in mN / m. The contact angle between oil / water and rock, in °; denoted as pore radius (nm); r is the throat radius (nm).

[0113] Step S303: Calculate the buoyancy at the dip angle of the formation:

[0114] ;

[0115] In the formula, is the pore size, and is the pore throat ratio and pore throat radius. Product, nm; Density of formation water, g / cm3; Where is the density of crude oil, g / cm3; g is the acceleration due to gravity; The dip angle of the strata is °.

[0116] Step S304: Obtain the relationship between capillary force, buoyancy, and pore throat radius in tight reservoirs (e.g., Figure 5 (As shown in the figure) When the capillary pressure of the oil-driven system is greater than the hydrocarbon generation pressure, the corresponding pore throat system is difficult to fill and is an ineffective pore; otherwise, it is an effective pore. In an effective pore, when the capillary force and buoyancy reach equilibrium, the corresponding pore throat radius is the upper limit of the self-sealing pore throat radius. .

[0117] Step S400: Based on the curve of pore throat radius versus oil content, the critical filling pore throat radius, and the upper limit of the self-sealing pore throat radius, define the effective self-sealing pore throat range, determine the effective self-sealing porosity, and calculate the proportion of effective self-sealing pores within the effective self-sealing pore throat range to the total porosity, which is the oil saturation. The specific implementation process of this step is as follows:

[0118] Step S401: Based on the upper limit of the self-sealing throat radius and the critical filling hole throat radius Combined with pore distribution characteristics ( Figure 6 Determine the effective porosity Ineffective porosity Effective self-sealing porosity and effectively unblock pores The evaluation results show that 93% of the pores in the tight reservoirs in this region have self-sealing capabilities, and about 30% of the pores cannot be filled under the pressure of hydrocarbon generation from the source rocks.

[0119] ;

[0120] ;

[0121] ;

[0122] ;

[0123] ;

[0124] In the formula, The minimum pore throat radius for tight reservoirs; The maximum pore throat radius of the tight reservoir is given; other parameters are the same as above.

[0125] Step S402: Calculate the porosity within the interval based on step 401. ,Will With effective porosity The oil saturation of tight reservoirs under closed conditions can be obtained by taking the ratio. The calculation results show that the oil saturation of the tight reservoir in this region is around 63%.

[0126] .

[0127] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions of this invention based on the above description, and the scope of the invention is defined by the appended claims.

Claims

1. A method for evaluating oil saturation based on the self-sealing capacity of a compact reservoir, characterized by, The implementation process is as follows: To obtain the hydrocarbon generation pressure boosting intensity and total porosity of tight reservoirs; Substituting the hydrocarbon generation pressurization intensity into the capillary pressure formula, the critical filling orifice throat radius is calculated. ; Mercury-driven capillary pressure obtained from mercury intrusion porosimetry experiments Mercury saturation Changes in pressure; Mercury-driven capillary pressure Converted to oil-driven capillary pressure Thus, the oil-driven capillary pressure is obtained. Mercury saturation The relationship between changes; based on the capillary pressure formula, the capillary pressure in oil-driven pipelines is... Mercury saturation The relationship changes to mercury saturation. The relationship between the pore throat radius and the mercury saturation was obtained. Curve of variation with throat radius Change curve This indicates the relationship between the pore throat radius and the oil content; The pore throat radius corresponding to the equilibrium of capillary force and buoyancy in a tight reservoir is obtained, which is the upper limit of the self-sealing pore throat radius. ; Based on mercury saturation Curve of variation with throat radius The critical filling throat radius and the upper limit of the self-sealing throat radius determine the effective self-sealing porosity. To calculate oil saturation. ; ； ； in, Indicates total porosity; Indicates oil saturation; Indicates the critical filling orifice throat radius; Indicates the upper limit of the self-sealing throat radius; Indicates mercury saturation Curve showing variation with throat radius.

2. The method for evaluating oil saturation based on the self-sealing capability of tight reservoirs according to claim 1, characterized in that, Mercury-driven capillary pressure With oil-driven capillary pressure The conversion relationship between them is as follows: ； The orifice radius as a function of capillary pressure in oil-driven capillary tubes is obtained based on the capillary pressure formula. The relationship of change is as follows: ； in, For oil-driven capillary pressure; For oil-water interfacial tension; The contact angle between oil / water and rock; The interfacial tension between mercury and air; The contact angle between mercury and rock; Mercury-driven capillary pressure; Based on the pore throat radius and capillary pressure during oil displacement The relationship between the oil-driven capillary pressure and the mercury saturation is changed. The relationship changes to mercury saturation. Relationship with orifice throat radius; For each set of experimental data from the mercury porosimetry experiment Substitute the values ​​into the formula to calculate the throat radius, and obtain the point. Connecting several points yields the mercury saturation. Curve of variation with throat radius .

3. The method for evaluating oil saturation based on the self-sealing capability of tight reservoirs according to claim 1, characterized in that, Substituting the hydrocarbon generation pressurization intensity into the capillary pressure formula, the critical filling orifice throat radius is calculated. as follows: ； Wherein, P_hydrogenation represents the hydrocarbon generation pressure intensity; For oil-water interfacial tension; The contact angle between oil / water and rock; This indicates the critical filling orifice throat radius.

4. The method for evaluating oil saturation based on the self-sealing capability of tight reservoirs according to claim 1, characterized in that, The process for achieving hydrocarbon generation and pressurization intensity in tight reservoirs is as follows: Step S101: Using the sonic transit time data of the shallow normally compacted mudstone section from well logging, fit an exponential compaction trend line based on the exponential compaction law to show the change of sonic transit time with depth: ； in, This is the normal compaction acoustic time difference; C represents the initial acoustic transit time at the surface; C is the mudstone compaction coefficient. For burial depth; Step S102: Based on the above-mentioned exponential compaction trend line and combined with the logging data of the tight reservoir, the formation pore pressure is calculated using the Eaton method. In order to determine the formation overpressure ; ； ； ； ； in, Formation pore pressure; This represents the total pressure of the overlying strata. Normal pore pressure; This is the normal compaction acoustic time difference; This is the measured time difference of acoustic waves in the formation; Eaton Index; average density of the formation; The hydrostatic pressure gradient is g; g is the acceleration due to gravity. Step S103: Based on the logging data, calculate the effective stress and sonic velocity, and draw the intersection diagram of effective stress and sonic velocity and the overpressure line; measure the angle between the hydrocarbon generation pressurization horizontal line and the overpressure line. Calculate the hydrocarbon generation pressurization intensity: ； Wherein, P represents the hydrocarbon generation pressure increase intensity; This is due to formation overpressure. The angle between the hydrocarbon generation pressurization horizontal line and the overpressure line.

5. The method for evaluating oil saturation based on the self-sealing capability of tight reservoirs according to claim 1, characterized in that, The process of obtaining the pore throat radius corresponding to the balance between capillary force and buoyancy in a tight reservoir is as follows: Calculate the relationship between capillary force and pore throat radius in tight reservoirs; ； Calculate the buoyancy at different dip angles of the strata: ； In the formula, For oil-water interfacial tension, The contact angle between oil / water and rock. The radius of the throat; Pore ​​size; Density of formation water; Density of crude oil; It is the acceleration due to gravity; The dip angle of the strata; When capillary force and buoyancy reach equilibrium, the corresponding throat radius is the upper limit of the self-sealing throat radius. .

6. The method for evaluating oil saturation based on the self-sealing capability of tight reservoirs according to claim 1, characterized in that, Determine the porosity of ineffective pores, effective pores, and effectively unobstructed pores: ； ； ； In the formula, Ineffective porosity; Porosity of the effective pores; To effectively improve the porosity of the pores; Total porosity; The minimum pore throat radius of a tight reservoir; The maximum pore throat radius of the tight reservoir; The critical filling orifice throat radius; This is the upper limit of the effective self-sealing throat radius; The curve shows the variation of mercury saturation with the pore throat radius.

Images