Method for determining porosity of dolomite of grey matter leopard spot and method for predicting dessert reservoir

Abstract

The invention provides a grey matter leopard spot dolomite porosity determination method and a dessert reservoir prediction method. The porosity determination method comprises the following steps: drilling a dolomite plaque area plunger sample with a preset size; performing CT scanning on the plunger sample according to a preset rule to obtain the area of each scanned layer of pores and the area of a dolomite plaque area; utilizing the area of each layer of pores and the area of the dolomite plaque area to obtain the surface porosity of each layer of dolomite plaque area, and obtaining the total porosity of the dolomite plaque area of the plunger sample; calculating the content of dolomite minerals at the corresponding depth position under the well by using a preset first formula in combination with the obtained logging curve data of the plunger sample; and reversely calculating the porosity of the rock core by utilizing the content of the dolomite at the corresponding underground position and the total porosity of the dolomite plaque area in combination with a preset second formula. The porosity value closer to the real porosity can be obtained, and the situation that different porosity values are obtained due to different sampling positions can be avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of petroleum and natural gas geological exploration, and in particular relates to a porosity determination method for grayish leopard dolomite and a sweet spot reservoir prediction method. Background Art

[0002] Determining the core porosity of different carbonate rock types is a fundamental tool for selecting sweet spot reservoirs and plays a crucial role in predicting the distribution and scale of favorable reservoirs within a basin. Grayish leopard-spotted dolostone exhibits a macroscopically porphyritic structure, consisting of dense grayish wall rock and dolomitic leopard-spotted rock. Therefore, effectively determining the core porosity of grayish leopard-spotted dolostone constrains subsequent exploration deployment and exploration value assessment. Summary of the Invention

[0003] The inventors discovered that there are currently two main methods for determining core porosity: one is to drill 2.5 cm plunger samples and measure porosity using the empty weight method, gas permeability method, and pressure method; the other is to drill rock samples and calculate porosity using industrial CT scanning. For grayish leopard dolomite, whose porosity is only developed in the leopard patch area of ​​the dolomite, the leopard patches are formed by biological disturbance and are tubular, branched, or irregular in shape, parallel or intersecting. The leopard patches in different rock samples vary greatly in sparseness and density, and their spatial distribution is highly random. Therefore, traditional porosity testing methods for heterogeneous grayish leopard dolomite are easily affected by sampling location, resulting in different final porosity data depending on the rock plunge sampling location, making them less applicable. For example, when drilling 2.5 cm plunger samples, a high dolomite patch encounter rate results in a higher measured porosity, while a low encounter rate results in a lower measured porosity.

[0004] In view of this, it is necessary to propose a method for determining the porosity of gray leopard dolomite and a method for predicting the reservoir distribution scale. This method can overcome the problem of porosity value differences caused by different rock plunger sampling positions in traditional porosity testing methods, obtain accurate porosity values ​​of gray leopard dolomite cores, provide a basis for selecting sweet spot reservoirs, and provide a basis for predicting the distribution scale of favorable reservoirs in the basin.

[0005] Specifically, a method for determining the porosity of gray leopard dolomite includes the following steps:

[0006] Drilling the core of the gray leopard dolomite to obtain a plug sample of the dolomite patch area of ​​preset size;

[0007] The plunger sample was CT scanned according to the preset rules to obtain the area of ​​pores and dolomite patch area in each layer scanned;

[0008] The porosity of each dolomite porphyry area was obtained by using the area of ​​each layer of pores and the area of ​​the dolomite patch area, and the total porosity of the dolomite porphyry area of ​​the plug sample was obtained;

[0009] Combining the acquired logging curve data of the plunger sample, the dolomite mineral content of the plunger sample at the corresponding depth position downhole is calculated using a preset first formula;

[0010] The core porosity is reversely calculated using the dolomite content at the corresponding position of the plunger sample downhole and the total porosity of the dolomite patch area, combined with the preset second formula.

[0011] Furthermore, a plug sample of a predetermined size is drilled from the dolomite patch area, including:

[0012] Take core samples, divide the core samples into two parts, make rock thin sections from one part, and identify the dolomite patch area in the rock thin sections;

[0013] Based on the dolomite patch area identified in the rock thin section, a plug sample of preset size was drilled in the dolomite patch area of ​​another core sample.

[0014] Furthermore, making a rock thin section from one of the samples and identifying the dolomite patch area in the rock thin section includes:

[0015] The rock thin sections were stained and the dolomite patch areas were identified using a light microscope combined with the optical characteristics of dolomite.

[0016] Furthermore, a plug sample of predetermined size was drilled from the dolomite patch area of ​​another core sample, including:

[0017] Cylinders with a diameter of 5 mm and a height of 7 mm were drilled in the dolomite patch area.

[0018] Furthermore, the plunger sample was CT scanned according to preset rules to obtain the area of ​​pores and dolomite patch areas in each layer scanned, including:

[0019] Place the plunger sample in a CT scanner, set the scanning layer value according to the resolution value of the CT scanner, and then perform CT scanning layer by layer from the initial layer to the last layer.

[0020] Furthermore, the porosity of each dolomite porphyry area is obtained by using the area of ​​each layer of pores and the area of ​​the dolomite patch area, including:

[0021] The porosity of the dolomite porphyry area of ​​each layer was obtained by dividing the area of ​​the corresponding dolomite patch area.

[0022] Furthermore, the total porosity of the dolomite porphyry area of ​​the plug sample was obtained, including:

[0023] The total porosity of the dolomite porphyry area of ​​the plug sample was obtained by summing the porosity of each layer of the dolomite porphyry area and dividing it by the scan layer value.

[0024] Furthermore, the dolomite mineral content of the plunger sample at the corresponding depth position in the well is calculated using a preset first formula in combination with the obtained logging curve data of the plunger sample, including:

[0025] Obtaining well logging curve data corresponding to the downhole position of the core of the plunger sample taken, wherein the well logging curve data at least includes density data, photoelectric absorption cross-section index data, and natural gamma data;

[0026] Using the obtained well logging data, a set of equations including dolomite content, calcite content, clay mineral content, and rock porosity is established to construct a preset first formula;

[0027] The first formula is solved to obtain the dolomite content at the corresponding downhole position of the plunger sample.

[0028] Furthermore, the obtained logging curve data is used to establish a set of equations including dolomite content, calcite content, clay mineral content, and rock porosity, including:

[0029] DEN=Por*ρ por +V lime *ρ lime +V DOLO *ρ DOLO +V Sh *ρ Sh

[0030] PE=Por*PE por +V lime *PE lime +V DOLO *PE DOLO +V Sh *PE Sh

[0031] 1=Por+V lime +V DOLO +V Sh

[0032] V Sh =(GR-GR min ) / (GR max -GR min )

[0033] Among them, DEN represents the density data in the well logging curve data corresponding to the downhole position, Por represents the downhole rock porosity, ρ por Represents the fluid density in the rock pores downhole, V lime represents the calcite content in downhole rocks, ρ lime represents the density of calcite in downhole rocks, V DOLORepresents the dolomite content in the downhole rock, ρ DOLO Represents the density of dolomite in underground rocks, V Sh Represents the clay mineral content in the downhole rock, ρ Sh Represents the density of clay minerals in underground rocks;

[0034] PE represents the photoelectric absorption cross-section index in the logging curve data corresponding to the downhole position. por Represents the photoelectric absorption cross-section index of the fluid in the pores of the rock downhole, PE DOLO Represents the photoelectric absorption cross-section index of dolomite in underground rocks, PE Sh Represents the photoelectric absorption cross-section index of clay minerals in underground rocks;

[0035] GR represents the natural gamma data in the well logging curve data corresponding to the downhole position. min is the minimum value of natural gamma in the well logging curve data, GR max is the maximum value of natural gamma in the logging curve data.

[0036] Furthermore, the preset first formula is:

[0037] V DOLO =

[0038]

[0039] Furthermore, the core porosity of the gray leopard dolomite is reversely calculated by using the dolomite content at the corresponding position of the plunger sample downhole and the total porosity of the dolomite patch area in combination with the preset second formula, including:

[0040] The second preset formula is: φ3=V DOLO %×φ2

[0041] Among them, V DOLO is the dolomite content at the corresponding position of the plug sample downhole, φ2 is the total porosity of the dolomite patch area of ​​the plug sample, and φ3 is the core porosity of the gray leopard dolomite.

[0042] On the other hand, the present invention also discloses a method for predicting sweet spot reservoirs, which uses the above-mentioned method for determining the porosity of gray leopard dolomite to predict sweet spot reservoirs.

[0043] Based on the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0044] The present invention studies the gray leopard dolomite composed of dolomite patches with developed pores and dense gray surrounding rock. A plunger sample of the dolomite patch area with a preset size is drilled from the core of the gray leopard dolomite, and the plunger sample is CT scanned according to a preset rule to obtain the area of ​​each layer of pores and the area of ​​the dolomite patch area; the surface area of ​​each layer of dolomite porphyritic area is obtained by using the area of ​​each layer of pores and the area of ​​the dolomite patch area, and the total porosity of the dolomite porphyritic area of ​​the plunger sample is obtained; then, in combination with the acquired logging curve data, a preset first formula is used to calculate the dolomite mineral content of the plunger sample at a corresponding depth position underground; the dolomite content of the plunger sample at the corresponding position underground and the total porosity of the dolomite patch area are used in combination with a preset second formula to reversely calculate the core porosity of the gray leopard dolomite. This method uses well logging to interpret the mineral composition of the test plunger sample at the corresponding downhole location. Combined with CT scanning, it calculates the porosity of the dolomite patch area. The rock porosity is then reversely calculated based on the dolomite leopard spot content and the porosity measured by industrial CT scanning. This method produces a porosity value that is closer to the true porosity, thus resolving the porosity discrepancies caused by different rock plunger sampling locations in traditional porosity testing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 Schematic diagram of a process for determining the porosity of gray leopard dolomite in Example 1 of the present invention;

[0047] Figure 2 Schematic diagram of the process of step S110 in the first embodiment of the present invention;

[0048] Figure 3 The diagram shows the dolomite patches and the gray surrounding rock structure at the sampling location of the gray leopard dolomite thin section in Example 1 of the present invention;

[0049] Figure 4 The figure shows the drilling process of the plunger sample in the first embodiment of the present invention;

[0050] Figure 5 Schematic diagram of the CT image obtained by industrial CT scanning of a gray leopard dolomite plunger sample in Example 1 of the present invention;

[0051] Figure 6The figure shows a scatter plot of the porosity of a single-surface surface of a gray leopard dolomite plug sample in Example 1 of the present invention;

[0052] Figure 7 The figure illustrates the calculation of the dolomite content corresponding to the sampling position based on the mineral composition in the first embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0054] The present invention proposes a method for determining the porosity of gray dolomite, which can overcome the problem of porosity value differences caused by different rock plunger sampling positions in traditional porosity testing methods, and obtain accurate porosity values ​​of gray dolomite cores, providing a basis for optimizing sweet spot reservoirs and providing a basis for predicting the distribution scale of favorable reservoirs in basins.

[0055] The inventors have found through extensive research that the intercrystalline pores of the gray leopard dolomite are developed in the dolomite patch area, while the gray surrounding rock does not develop pores. Based on this principle, Figure 1 As shown, when the porosity determination method of the gray leopard dolomite is applied to the gray leopard dolomite of the fourth member of the Ordovician Mashantuan in the horizontal exploration well B in Basin A, the method may include steps S110 to S150:

[0056] Step S110: drilling a core of the gray leopard dolomite to obtain a dolomite patch area plug sample of a preset size.

[0057] In practical applications, combined with Figure 2 As shown, this step may include sub-steps S111-S113:

[0058] Step S111: sampling a core sample of the gray leopard dolomite, dividing the core sample into two parts, and making one part into a rock slice.

[0059] A core sample of grayish leopard-spotted dolomite from the horizontal exploration well B was cut into two sections. One section was prepared into a thin section, encompassing both the dolomite patch area and the grayish surrounding rock. The remaining section was used as a drill plug sample. The thin section preparation process can be referenced in the Petroleum and Natural Gas Industry Standard SY / T 5913-2004.

[0060] Step S112: Place the rock slice under an optical microscope to identify the dolomite patch area and the gray surrounding rock area.

[0061] The prepared rock thin sections were observed under an optical microscope to identify the petrological characteristics of the two fabrics, identifying the dark fabric areas as dolomite patches and the light gray fabric areas as grayish surrounding rock. In practical applications, the rock thin sections are preferably stained with alizarin red and, using a polarizing microscope, the optical characteristics of the rhombus-shaped dolomite can be used to confirm the corresponding fabric of the dolomite patches in the macroscopic rock sample. Figure 3 The dolomite patches and gray surrounding rock fabric at the sampling location of gray leopard dolomite thin sections are shown, among which the circled fabric is the gray mud surrounding rock.

[0062] Step S113 , comparing the dolomite patch area identified by the rock thin section, and drilling a plug sample of a preset size in the dolomite patch area of ​​another core sample.

[0063] Plug samples of preset sizes, such as cylinders with a diameter of 5 mm and a height of 7 mm, are drilled in the dark dolomite patch fabric area using a sampling device. Figure 4 The drilling of the plunger sample is shown schematically.

[0064] Step S120 , performing CT scanning on the plunger sample according to preset rules to obtain the area of ​​each layer of pores and the area of ​​the dolomite patch area.

[0065] The drilled cylinder can be placed in a nano-CT scanner, and the industrial CT scanning layer value n is set according to the resolution value of the industrial CT instrument. Then, CT scanning is carried out layer by layer from the 1st layer to the nth layer to obtain the pore area SP and the dolomite porphyry area Sd. The industrial CT scan image of the gray leopard dolomite plunger is shown in the figure below. Figure 5 In this embodiment, n=600, that is, a CT scan of 600 slices with equal distances is performed on the cylinder from bottom to top.

[0066] Step S130, using the area of ​​each layer of pores and the area of ​​the dolomite patch area to obtain the porosity of each layer of dolomite porphyry area, and obtain the total porosity of the dolomite porphyry area of ​​the plunger sample.

[0067] Using the formula: Calculate the face ratio of each dolomite porphyry area separately Figure 6 A scatter plot of the porosity of a single-surface surface of a gray leopard dolomite plug sample is shown.

[0068] The total porosity of the dolomite porphyry area of ​​the plug sample was then obtained using the average value method, and the calculation formula is:

[0069]

[0070] in: is the porosity of each dolomite porphyry area, is the total porosity of the dolomite patchy area of ​​the plug sample. In this example, the total porosity of the dolomite patchy area calculated is 4.87%.

[0071] Step S140 , combining the acquired logging curve data of the plunger sample and using a preset first formula to calculate the dolomite mineral content of the plunger sample at a corresponding depth position downhole.

[0072] Well logging data obtained by logging instruments reflect the comprehensive response of geophysical properties of the formation at a specific depth in the wellbore, including the rock skeleton, pores, and the density of oil, gas, water, or other fluids within them. Based on the interpretation of the mineral composition, the core of the plunger sample contains dolomite, calcite, and clay minerals. This allows the dolomite content at the depth corresponding to the sampling location to be calculated.

[0073] Specifically, well logging data corresponding to the downhole location of the core of the sampled plunger can be obtained. This well logging data includes at least density data, photoelectric absorption cross-section index data, and natural gamma ray data. The obtained well logging data is then used to establish a set of equations that include dolomite content, calcite content, clay mineral content, and rock porosity to construct a predetermined first formula. Finally, the first formula is solved to obtain the dolomite content at the corresponding downhole location of the plunger sample.

[0074] The obtained logging curve data is used to establish a set of equations including dolomite content, calcite content, clay mineral content, and rock porosity, including:

[0075] DEN=Por*ρ por +V lime *ρ lime +V DOLO *ρ DOLO +V Sh *ρ Sh

[0076] PE=Por*PE por +V lime *PE lime +V DOLO *PE DOLO +V Sh *PE Sh

[0077] 1=Por+V lime +V DOLO +V Sh

[0078] V Sh =(GR-GR min ) / (GR max -GR min )

[0079] Among them, DEN represents the density data in the well logging curve data corresponding to the downhole position, Por represents the downhole rock porosity, ρ por Represents the fluid density in the rock pores downhole, V lime represents the calcite content in downhole rocks, ρ lime represents the density of calcite in downhole rocks, V DOLO Represents the dolomite content in the downhole rock, ρ DOLO Represents the density of dolomite in underground rocks, V Sh Represents the clay mineral content in the downhole rock, ρ Sh Represents the density of clay minerals in underground rocks;

[0080] PE represents the photoelectric absorption cross-section index in the logging curve data corresponding to the downhole position. por Represents the photoelectric absorption cross-section index of the fluid in the pores of the rock downhole, PE DOLO Represents the photoelectric absorption cross-section index of dolomite in underground rocks, PE Sh Represents the photoelectric absorption cross-section index of clay minerals in underground rocks;

[0081] GR represents the natural gamma data in the well logging curve data corresponding to the downhole position. min is the minimum value of natural gamma in the well logging curve data, GR max is the maximum value of natural gamma in the logging curve data.

[0082] The first formula obtained using the above equations is as follows:

[0083]

[0084] By using the above formula, we can obtain the curve of calcite content, dolomite content and shale content in the well section with ash-bearing leopard dolomite in the plunger sample. Figure 7 The plunger sampling depth position shown is used to read the dolomite content corresponding to the sampling position of 3716.23m, and the value obtained is 63.9%.

[0085] Step S150, using the dolomite content of the plunger sample at the corresponding position downhole, the total porosity of the dolomite patch area, and a preset second formula to reversely calculate the porosity of the gray leopard dolomite.

[0086] The second preset formula is: φ3=V DOLO %×φ2

[0087] Among them, V DOLO is the dolomite content at the corresponding position of the plug sample downhole, φ2 is the total porosity of the dolomite patch area of ​​the plug sample, and φ3 is the core porosity.

[0088] In this embodiment, φ3=63.9%×4.87%, that is, the rock porosity of the gray leopard dolomite of the fourth member of the Ordovician Mashantuan in the sampling location of the horizontal exploration well B can be reversely calculated to be 3.11%.

[0089] The present invention studies the gray leopard dolomite composed of dolomite patches with developed pores and dense gray surrounding rock. A plunger sample of the dolomite patch area with a preset size is drilled from the core of the gray leopard dolomite, and the plunger sample is CT scanned according to a preset rule to obtain the area of ​​each layer of pores and the area of ​​the dolomite patch area; the surface area of ​​each layer of dolomite porphyritic area is obtained by using the area of ​​each layer of pores and the area of ​​the dolomite patch area, and the total porosity of the dolomite porphyritic area of ​​the plunger sample is obtained; then, in combination with the acquired logging curve data, a preset first formula is used to calculate the dolomite mineral content of the plunger sample at a corresponding depth position underground; the dolomite content of the plunger sample at the corresponding position underground and the total porosity of the dolomite patch area are used in combination with a preset second formula to reversely calculate the core porosity of the gray leopard dolomite. The present invention determines the dolomite content of the test plug sample at the corresponding position underground by interpreting the mineral components of well logging, calculates the porosity of the dolomite patch area in combination with CT scanning, and then reversely calculates the porosity of the rock through the dolomite leopard patch content and the porosity measured by the industrial CT scanning results. The present invention can obtain a porosity value that is closer to the true porosity, thereby resolving the porosity value difference caused by the different rock plug sampling positions when using traditional porosity testing methods. In practical applications, when the dolomite patch content at the location of the core is determined, the total porosity of the rock can be reversely calculated by using the porosity of the dolomite patch area measured by the present invention. The calculation result is highly accurate, and the acquisition process is simple and efficient.

[0090] The porosity determination method of the gray leopard dolomite mentioned above can also be used to classify and predict sweet spot reservoirs. The relevant methods for selecting sweet spot reservoirs according to porosity can refer to the existing technology and will not be repeated here.

[0091] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are therefore hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0092] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purposes of describing the above embodiments, but it will be appreciated by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to encompass all such changes, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including," as explained by "including," when used as a transitional word in the claims. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or."

Claims

1. A method for determining the porosity of gray leopard dolomite, characterized in that: The following steps are involved: Drilling the core of the gray leopard dolomite to obtain a plug sample of the dolomite patch area of ​​preset size; Performing CT scanning on the plunger sample according to a preset rule to obtain the area of ​​pores in each layer and the area of ​​dolomite patch areas; The porosity of the dolomite porphyry area of ​​each layer is obtained by using the area of ​​each layer of pores and the area of ​​the dolomite patch area, and the total porosity of the dolomite porphyry area of ​​the plug sample is obtained; Combining the acquired logging curve data of the plunger sample, the dolomite mineral content of the plunger sample at the corresponding depth position downhole is calculated using a preset first formula; The core porosity of the gray leopard dolomite is reversely calculated using the dolomite content of the plunger sample at the corresponding position underground and the total porosity of the dolomite patch area in combination with a preset second formula.

2. The porosity determination method of gray leopard dolomite according to claim 1, characterized in that: The method of drilling a plug sample of a dolomite patch area of ​​a preset size comprises: A core sample of gray leopard dolomite was collected and divided into two parts. One of the core samples was made into a rock thin section to identify the dolomite patch area in the rock thin section. Based on the dolomite patch area identified in the rock thin section, a plug sample of preset size was drilled in the dolomite patch area of ​​another core sample.

3. The porosity determination method of gray leopard dolomite according to claim 2, characterized in that: One of the samples is prepared as a rock thin section, and the dolomite patch area of ​​the rock thin section is identified, including: The rock thin sections were stained and the dolomite patch areas were identified using a light microscope combined with the optical characteristics of dolomite.

4. The method for determining the porosity of gray leopard dolomite according to claim 1, wherein: The plunger sample is CT scanned according to a preset rule to obtain the area of ​​pores in each scanned layer and the area of ​​dolomite patches, including: Place the plunger sample in a CT scanner, set the scanning layer value according to the resolution value of the CT scanner, and then perform CT scanning layer by layer from the initial layer to the last layer.

5. The method for determining the porosity of gray leopard dolomite according to claim 1, wherein: The method of obtaining the porosity of each dolomite porphyry area by using the area of ​​each layer of pores and the area of ​​the dolomite patch area includes: The porosity of the dolomite porphyry area of ​​each layer was obtained by dividing the area of ​​the corresponding dolomite patch area.

6. The method for determining the porosity of gray leopard dolomite according to claim 5, characterized in that: The total porosity of the dolomite porphyry area of ​​the plunger sample is obtained, including: The total porosity of the dolomite porphyry area in each layer of the plug sample is obtained by summing the porosity of the dolomite porphyry area in each layer of the plug sample and dividing it by the value of the scanned layer.

7. The method for determining the porosity of gray leopard dolomite according to claim 1, characterized in that: Combining the obtained logging curve data of the plunger sample, the dolomite mineral content of the plunger sample at the corresponding depth position in the well is calculated using a preset first formula, including: Obtaining well logging curve data corresponding to the downhole position of the core of the plunger sample taken, wherein the well logging curve data at least includes density data, photoelectric absorption cross-section index data, and natural gamma data; Using the obtained well logging data, a set of equations including dolomite content, calcite content, clay mineral content, and rock porosity is established to construct a preset first formula; The first formula is solved to obtain the dolomite content at the corresponding downhole position of the plunger sample.

8. The method for determining the porosity of gray leopard dolomite according to claim 1, characterized in that: The obtained well logging data is used to establish a set of equations including dolomite content, calcite content, clay mineral content, and rock porosity, including: DEN=Por*ρ por +V lime *r lime +V DOLO *r DOLO +V Sh *r Sh FOR=For*FOR por +V lime *INSTEAD lime +V DOLO *INSTEAD DOLO +V Sh *INSTEAD Sh 1=Por+V lime +V DOLO +V Sh IN Sh =(GR-GR min ) / (GR max -GR min ) Among them, DEN represents the density data in the well logging curve data corresponding to the downhole position, Por represents the downhole rock porosity, ρ por Represents the fluid density in the rock pores downhole, V lime represents the calcite content in downhole rocks, ρ lime represents the density of calcite in downhole rocks, V DOLO Represents the dolomite content in the downhole rock, ρ DOLO Represents the density of dolomite in underground rocks, V Sh Represents the clay mineral content in the downhole rock, ρ Sh Represents the density of clay minerals in underground rocks; PE represents the photoelectric absorption cross-section index in the logging curve data corresponding to the downhole position. por Represents the photoelectric absorption cross-section index of the fluid in the pores of the rock downhole, PE DOLO Represents the photoelectric absorption cross-section index of dolomite in underground rocks, PE Sh Represents the photoelectric absorption cross-section index of clay minerals in underground rocks; GR represents the natural gamma data in the well logging curve data corresponding to the downhole position. min is the minimum value of natural gamma in the well logging curve data, GR max is the maximum value of natural gamma in the logging curve data.

9. The method for determining the porosity of gray leopard dolomite according to claim 8, characterized in that: The preset first formula is:

10. The method for determining the porosity of gray leopard dolomite according to claim 1, characterized in that: The method of reversely calculating the core porosity of the gray leopard dolomite by using the dolomite content at the corresponding position of the plunger sample downhole and the total porosity of the dolomite patch area in combination with the preset second formula includes: The second preset formula is: φ3=V DOLO %×φ2 Among them, V DOLO is the dolomite content at the corresponding position of the plug sample downhole, φ2 is the total porosity of the dolomite patch area of ​​the plug sample, and φ3 is the core porosity of the gray leopard dolomite.

11. A method for predicting a sweet spot reservoir, characterized in that: The porosity determination method of the gray leopard dolomite as described in any one of claims 1 to 9 is used to predict sweet spot reservoirs.

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