A method for determining the lower limit of porosity in tight sandstone reservoirs

Abstract

This invention belongs to the field of determining the lower limit of physical properties of tight shale reservoirs, and in particular, it is a method for determining the lower limit of porosity of tight sandstone reservoirs. Existing methods do not consider the constraints of lithology index, cementation index, rock wettability, and hydrocarbon accumulation dynamics on the lower limit of reservoir porosity. Therefore, the determined lower limit of reservoir porosity cannot truly reflect the lower limit of oil and gas charging reservoir porosity under formation conditions, and they do not combine conventional logging parameters with reservoir physical properties, failing to fully utilize logging data, resulting in a waste of logging data resources, and even missing some favorable tight sandstone reservoir development intervals. The following solution is proposed, which includes the following steps: S1: Obtain samples through core sampling, and obtain the lithology index 'a' and cementation index 'm' through experiments. This invention achieves an organic combination of hydrocarbon accumulation dynamics and the determination of the lower limit of reservoir physical properties, providing technical support for determining the lower limit of physical properties of tight shale reservoirs.

Description

Technical Field

[0001] This invention relates to the field of determining the lower limit of reservoir physical properties in tight shale reservoirs, and in particular to a novel method for determining the lower limit of reservoir physical properties that combines well logging and geology. Background Technology

[0002] Determining the lower limit of reservoir properties is a crucial basis for identifying effective reservoirs. Currently, the most commonly used methods for determining the lower limit of reservoir properties include oil occurrence method, statistical frequency method of physical property parameters, core porosity-permeability relationship method, bound water saturation method and empirical statistical method, displacement pressure test method, oil content accumulation method, testing method, oil testing method, production capacity simulation test method, and drilling fluid invasion method (Liu et al., 2018). However, none of these methods consider the constraints of lithology index, cementation index, rock wettability, and hydrocarbon accumulation dynamics on the lower limit of reservoir porosity. The determined lower limit of reservoir porosity cannot truly reflect the lower limit of oil and gas charging reservoir porosity under formation conditions. Furthermore, they do not combine conventional logging parameters with reservoir properties, failing to fully utilize logging data, resulting in a waste of logging data resources, and may even miss some favorable tight sandstone reservoir development intervals. The matching relationship between source rock, reservoir, and hydrocarbon accumulation dynamics determines the hydrocarbon charging mode and oil saturation of the reservoir; different charging modes correspond to different lower limits of reservoir physical properties (Shi Yujiang et al., 2016). As the distance between the reservoir and the source rock increases, the hydrocarbon accumulation dynamics weaken, and oil is only hosted in large or medium-sized pores, while nanoscale pores do not contain oil. The source-reservoir distance determines the differential occurrence of oil in tight sandstone reservoirs with multi-scale porosity (Niu Xiaobing et al., 2013). This method closely integrates the determination of rock lithology index, cementation index, rock wettability, hydrocarbon accumulation dynamics, and the lower limit of reservoir porosity. The determined lower limit of tight sandstone reservoir porosity is highly consistent with the actual geological conditions, providing methodological support for the determination of the lower limit of tight sandstone reservoir porosity and efficient development. Summary of the Invention

[0003] This invention utilizes a combination of rock physics experiments, geology, and well logging to determine the lower limits of tight sandstone reservoir properties based on lithology index, cementation index, wettability, and hydrocarbon accumulation dynamics. It establishes a new method for determining the lower limit of tight sandstone reservoir porosity, solving the problems of existing methods that do not consider the constraints of lithology index, cementation index, rock wettability, and hydrocarbon accumulation dynamics on the lower limit of reservoir porosity. These methods fail to accurately reflect the lower limit of reservoir porosity under formation conditions, and do not integrate conventional well logging parameters with reservoir properties, resulting in wasted well logging data and the potential to miss some favorable tight sandstone reservoir development zones.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for determining the lower limit of porosity in tight sandstone reservoirs includes the following steps:

[0006] S1: Samples are obtained by core sampling, and the lithology index a and cementation index m are obtained through experiments;

[0007] S2: Samples are obtained by core sampling, and the wetting angle θ is obtained through experiments;

[0008] S3: Establish the lower limit of porosity Φ e The theoretical formulas for the maximum regional hydrocarbon accumulation force P1, hydrocarbon accumulation pressure P2 in the source rock development section of a single well, lithology index a, cementation index m, interfacial tension σ, and wetting angle θ are as follows:

[0009] (1)

[0010] D is the gradient coefficient of hydrocarbon accumulation pressure decreasing from P1 to P2, and the specific calculation formula is as follows:

[0011] (2);

[0012] S4: Calculate the maximum hydrocarbon accumulation dynamics P1 in the calculation area and the hydrocarbon accumulation pressure P2 in the hydrocarbon source rock development section of a single well;

[0013] S5: Calculate the lower limit of reservoir porosity using theoretical formulas (1) and (2).

[0014] Preferably, in step S1, a cylindrical sample is obtained by core sampling, and the lithology index a and cementation index m are obtained by rock electrical experiment.

[0015] Preferably, in step S1, a cylindrical sample with a diameter of 2.5 cm and a height of 3 cm is obtained by core sampling, and the lithology index a and cementation index m are obtained by rock electrical experiment.

[0016] Preferably, in step S2, a sample with a length of 2cm, a width of 1cm, and a thickness of 0.2cm is obtained by core sampling, and the wetting angle θ is obtained through experiments.

[0017] Preferably, in step S2, a sample with a length of 2cm, a width of 1cm, and a thickness of 0.2cm is obtained by core sampling, and the wetting angle θ is obtained by wettability test.

[0018] Preferably, in S3, the lower limit of porosity Φ e The unit is %, and the unit of reservoir formation pressure is MPa.

[0019] Preferably, in S3, the wetting angle θ is in degrees, and σ is the interfacial tension of mercury, 0.485 N / m.

[0020] Preferably, in step S4, the maximum hydrocarbon accumulation dynamics P1 in the region and the hydrocarbon accumulation pressure P2 in the hydrocarbon source rock development section of a single well are calculated using the sonic transit time logging curve.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] Consistent research on the lower limits of physical properties in tight sandstone reservoirs has been a challenging issue. This invention combines rock physics experiments, geology, and well logging to establish a method for calculating the lower limit of reservoir porosity using lithology index a, cementation index m, regional maximum hydrocarbon accumulation dynamics P1, single-well hydrocarbon accumulation pressure P2, and wetting angle θ. This provides a new method for determining the lower limits of physical properties in tight sandstone reservoirs and offers technical support for the development of tight sandstone reservoirs.

[0023] This invention fully considers the constraints of hydrocarbon accumulation dynamics, lithology index, cementation index, and wettability on the lower limit of reservoir porosity, establishes the relationship between lithology index, cementation index, wettability, hydrocarbon accumulation dynamics and the lower limit of tight sandstone reservoir porosity, and determines the lower limit of reservoir porosity corresponding to different hydrocarbon accumulation dynamic conditions, lithology index, cementation index, and wettability.

[0024] This invention achieves an organic combination of hydrocarbon accumulation dynamics and the determination of the lower limit of reservoir properties, fully considering the influence of hydrocarbon accumulation dynamics on the lower limit of tight shale reservoir properties, and providing technical support for the determination of the lower limit of tight shale reservoir properties. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the hydrocarbon source rock section in a well, illustrating the method for determining the lower limit of porosity in tight sandstone reservoirs proposed in this invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] Example 1

[0028] A method for determining the lower limit of porosity in tight sandstone reservoirs includes the following steps:

[0029] S1: Samples are obtained by core sampling, and the lithology index a and cementation index m are obtained through experiments;

[0030] S2: Samples are obtained by core sampling, and the wetting angle θ is obtained through experiments;

[0031] S3: Establish the lower limit of porosity Φ e The theoretical formulas for the maximum regional hydrocarbon accumulation force P1, hydrocarbon accumulation pressure P2 in the source rock development section of a single well, lithology index a, cementation index m, interfacial tension σ, and wetting angle θ are as follows:

[0032] (1)

[0033] D is the gradient coefficient of hydrocarbon accumulation pressure decreasing from P1 to P2, and the specific calculation formula is as follows:

[0034] (2);

[0035] S4: Calculate the maximum hydrocarbon accumulation dynamics P1 in the calculation area and the hydrocarbon accumulation pressure P2 in the hydrocarbon source rock development section of a single well;

[0036] S5: Calculate the lower limit of reservoir porosity using theoretical formulas (1) and (2).

[0037] In this embodiment, in step S1, a cylindrical sample is obtained by core sampling, and the lithology index a and cementation index m are obtained by rock electrical experiment.

[0038] In this embodiment, in step S1, a cylindrical sample with a diameter of 2.5 cm and a height of 3 cm is obtained by core sampling, and the lithology index a and cementation index m are obtained by rock electrical experiment.

[0039] In this embodiment, in step S2, a sample with a length of 2cm, a width of 1cm, and a thickness of 0.2cm is obtained by core sampling, and the wetting angle θ is obtained through experiments.

[0040] In this embodiment, in step S2, a sample with a length of 2cm, a width of 1cm, and a thickness of 0.2cm is obtained by core sampling, and the wetting angle θ is obtained by wettability test.

[0041] In this embodiment, in S3, the lower limit of porosity Φ e The unit is %, and the unit of reservoir formation pressure is MPa.

[0042] In this embodiment, in S3, the wetting angle θ is in degrees, and σ is the interfacial tension of mercury, 0.485 N / m.

[0043] In this embodiment, in step S4, the maximum hydrocarbon accumulation dynamics P1 and the hydrocarbon accumulation pressure P2 of the source rock development section in a single well are calculated using the sonic transit time logging curve.

[0044] Example 2

[0045] Reference Figure 1 A method for determining the lower limit of porosity in tight sandstone reservoirs includes the following steps:

[0046] S1: Obtain a cylindrical sample with a diameter of 2.5 cm and a height of 3 cm. Obtain the lithology index a and cementation index m through rock electrical experiments. Table 1 shows the tight sandstone reservoir of Chang 6 section in Baibao area. Obtain the lithology index a and cementation index m through rock electrical experiments. Calculate the average value of lithology index a and cementation index m, which are 1.058 and 2.100, respectively.

[0047] S2: Core samples were obtained by core sampling to obtain the wetting angle θ; Table 2 shows the wetting angle θ of the Chang 6 section tight sandstone reservoir in the Baibao area, obtained through wettability experiments.

[0048] S3: Calculate the hydrocarbon accumulation dynamics P2 of the source rock development section of a single well using sonic transit time logging curves. The maximum hydrocarbon accumulation dynamics P1 in the region is taken as 16 MPa.

[0049] S4: Using theoretical formulas: (1)

[0050] and (2)

[0051] Calculate the lower limit of porosity Φe;

[0052] S5: Compile a summary table of effective reservoir physical property lower limits.

[0053] Table 1 shows the lithological index (a) and cementation index (m) of the tight sandstone reservoir in the Chang 6 section of the Baibao area.

[0054]

[0055] Table 2 shows the wetting angles of the tight sandstone reservoirs in the Chang 6 section of the Baibao area.

[0056]

[0057] Table 3 is a summary table of the effective reservoir physical property lower limits.

[0058]

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the lower limit of porosity in tight sandstone reservoirs, characterized in that, Includes the following steps: S1: Samples are obtained by core sampling, and the lithology index a and cementation index m are obtained through experiments; S2: Samples are obtained by core sampling, and the wetting angle θ is obtained through experiments; S3: Establish the lower limit of porosity Φ e The theoretical formulas for the maximum regional hydrocarbon accumulation force P1, hydrocarbon accumulation pressure P2 in the source rock development section of a single well, lithology index a, cementation index m, interfacial tension σ, and wetting angle θ are as follows: （1） D is the gradient coefficient of hydrocarbon accumulation pressure decreasing from P1 to P2, and the specific calculation formula is as follows: （2）； S4: Calculate the maximum hydrocarbon accumulation dynamics P1 in the calculation area and the hydrocarbon accumulation pressure P2 in the hydrocarbon source rock development section of a single well; S5: Calculate the lower limit of reservoir porosity using theoretical formulas (1) and (2).

2. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 1, characterized in that, In S1, a cylindrical sample is obtained by core sampling, and the lithology index a and cementation index m are obtained by rock electrical experiment.

3. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 2, characterized in that, In S1, a cylindrical sample with a diameter of 2.5 cm and a height of 3 cm is obtained by core sampling. The lithology index a and cementation index m are obtained by rock electrical experiment.

4. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 1, characterized in that, In S2, a sample with a length of 2cm, a width of 1cm, and a thickness of 0.2cm is obtained by core sampling, and the wetting angle θ is obtained through experiments.

5. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 4, characterized in that, In S2, a sample with a length of 2cm, a width of 1cm, and a thickness of 0.2cm is obtained by core sampling, and the wetting angle θ is obtained by wettability test.

6. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 1, characterized in that, In S3, the lower limit of porosity Φ e The unit is %, and the unit of reservoir formation pressure is MPa.

7. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 1, characterized in that, In S3, the wetting angle θ is in degrees, and σ is the interfacial tension of mercury, 0.485 N / m.

8. The method for determining the lower limit of porosity in tight sandstone reservoirs according to claim 1, characterized in that, In S4, the maximum hydrocarbon accumulation dynamics P1 and the hydrocarbon accumulation pressure P2 of the source rock development section in a single well are calculated using the sonic transit time logging curve.

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