Method for predicting plane irreducible water saturation distribution of tight sandstone

Abstract

The invention discloses a method for predicting plane irreducible water saturation distribution of compact sandstone, which comprises the following steps of: acquiring different sedimentary microfacies compact sandstone samples of a target layer, and acquiring porosity and irreducible water saturation data of the samples by using an experiment; analyzing the change relation between the porosity and irreducible water saturation of different sedimentary microfacies tight sandstones; carrying out compact sandstone reservoir plane sedimentary microfacies, sand body distribution and physical property distribution prediction to obtain sedimentary microfacies and porosity plane distribution; and converting porosity plane distribution into irreducible water saturation plane distribution based on a porosity-irreducible water saturation relation according to different phase bands. According to the method, quantitative prediction of the irreducible water saturation of the compact sandstone on the plane can be realized, so that a basis is provided for pre-drilling compact gas well position deployment and post-drilling fracturing process design optimization, deployment risks are reduced, the reservoir fracturing gas production effect is improved, and compact gas field exploration and development benefits are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of stratum water content prediction in petroleum geological exploration and development, and in particular relates to a method for predicting the distribution of bound water saturation in a compact sandstone plane. Background Art

[0002] In 2023, the national natural gas apparent consumption will reach 3945×10 8 m 3 , output 2324×10 8 m 3 , with a foreign dependence rate of over 40%. As an effective supplement to conventional natural gas in my country, unconventional natural gas is responsible for increasing reserves and production. Among them, tight sandstone gas (referred to as tight gas) is the "leader" of unconventional natural gas production. As of 2020, the cumulative proven reserves of tight gas in China are 5.49×10 12 m 3 , the output in 2023 will exceed 600×10 8 m 3 , helping Changqing Oilfield become the largest oil and gas field in my country.

[0003] The formation water in tight sandstone reservoirs exists in the form of free water, capillary water and irreducible water. Due to the tightness of the reservoir, poor physical properties and small throat radius, the irreducible water content is relatively high. Taking the Linxing-Shenfu block of CNOOC onshore tight gas as an example, the irreducible water saturation (Swi) is between 40% and 80%. At present, the core scale irreducible water saturation analysis can be carried out indoors through core experimental methods. The mine mainly uses logging data to interpret the irreducible water saturation of a single well. There is no effective prediction method for the distribution of irreducible water saturation on the plane. Summary of the invention

[0004] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for predicting the distribution of bound water saturation in a compact sandstone plane.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for predicting the distribution of bound water saturation in a tight sandstone plane comprises the following steps:

[0007] (I) Collecting dense sandstone samples of different sedimentary microfacies in the target layer, and obtaining reservoir porosity, irreducible water saturation and other physical property parameters of dense sandstone samples of different sedimentary microfacies through experiments;

[0008] The detailed division of sedimentary microfacies of a single well is carried out based on the sedimentary characteristics of the block, logging and experimental analysis data; for each type of sedimentary microfacies, a sufficient number of core samples with different reservoir properties (porosity) of each type of sedimentary microfacies are drilled using the cores of the drilled wells, with a diameter of 25 mm and a length of 50 mm. Experimental analysis is carried out according to the national standard core analysis method (GB / T 29172-2012) to obtain the reservoir porosity of tight sandstone samples of different sedimentary microfacies. and irreducible water saturation (SWi).

[0009] (II) Analysis of the relationship between porosity and irreducible water saturation in tight sandstones of different sedimentary microfacies

[0010] According to the reservoir porosity and irreducible water saturation data of the tight sandstone samples of different sedimentary microfacies obtained in step (I), common functions such as exponential, linear, logarithmic, polynomial, and power are fitted using statistical methods to obtain the changing relationship between the porosity and irreducible water saturation of the tight sandstone reservoir, and the correlation coefficient R is selected. 2 The largest function is used as the prediction function of irreducible water saturation in tight sandstone reservoirs of different sedimentary microfacies;

[0011] (III) Carry out the prediction of the planar sedimentary microfacies, sand body distribution and physical property distribution of tight sandstone reservoirs, and obtain the planar distribution of sedimentary microfacies and porosity;

[0012] Conduct single well and well-linked sedimentary facies analysis to determine the sedimentary facies type of the target layer, use seismic facies, longitudinal and transverse wave velocity ratios and inverted sand bodies for plane constraints, and obtain the plane sedimentary microfacies distribution. The plane sedimentary microfacies and the single well sedimentary microfacies division types should be consistent; analyze the relationship between elastic parameters such as longitudinal wave impedance and porosity, use seismic phase control to conduct prestack geostatistical inversion, and obtain the plane distribution of porosity;

[0013] The pre-stack geostatistical inversion using seismic phase control in step (III) is carried out according to the literature “Qian Yugui, Ye Tairan, Zhang Shihua, et al. Application of pre-stack geostatistical inversion technology in quantitative prediction of complex reservoirs [J]. Petroleum & Natural Gas Geology, 2013, 34(6): 834-840”.

[0014] (IV) Different phase zones are divided and based on the porosity-impossible water saturation relationship obtained in step (II), the porosity plan distribution is converted into the irreducible water saturation plan distribution.

[0015] According to the porosity distribution in different sedimentary facies on the plane and the functional relationship between the porosity and irreducible water saturation of different sedimentary facies, the porosity contour lines are converted into irreducible water saturation contour lines according to the sedimentary facies zones, so as to realize the prediction of irreducible water saturation in the plane of tight sandstone reservoirs.

[0016] The beneficial effects of the present invention are:

[0017] The present invention provides a method for predicting the distribution of bound water saturation in a plane of tight sandstone by using experimental data and geophysical reservoir inversion results. The method can realize quantitative prediction of bound water saturation of tight sandstone on a plane, thereby providing a basis for tight gas well site deployment before drilling and optimization of fracturing process design after drilling, reducing deployment risks, improving reservoir fracturing gas production effects, and thus improving the exploration and development benefits of tight gas fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of the method of the present invention;

[0019] Figure 2 is the relationship between the reservoir physical properties of different sedimentary phases of tight sandstone and irreducible water saturation in Example 1 of the present invention;

[0020] Figure 3 is a planar distribution diagram of sedimentary microfacies of Example 1 of the present invention;

[0021] Figure 4 is a plane distribution diagram of porosity of Example 1 of the present invention;

[0022] Figure 5 This is a planar distribution diagram of irreducible water saturation in Example 1 of the present invention.

[0023] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0025] Example 1

[0026] Taking the tight sandstone gas reservoir of the He 8th Member of the Lower Shihezi Formation in a certain area on the eastern edge of the Ordos Basin as an example, Figure 1 As shown, the prediction method includes the following steps:

[0027] S1: The Box 8 section in the study area is a braided river delta sedimentary system. The single well sedimentary microfacies are finely divided using logging and experimental analysis data, and divided into core bars, distributary channels, natural levees, breach fans, inter-river depressions, etc. A sufficient number of core samples with different physical properties of each type of sedimentary microfacies, with a diameter of 25 mm and a length of 50 mm, are obtained by experiment to obtain the porosity of sandstone samples. Irreducible water saturation (SWi) parameter.

[0028] S2: Analyze and fit the relationship between the porosity and irreducible water saturation of tight sandstone under different sedimentary microfacies, and select the correlation coefficient R 2The larger function is used as the objective function for irreducible water saturation prediction ( Figure 2 ).

[0029] The relationship between the porosity and irreducible water saturation of the central bank microfacies (type I) is: y = 91.889e -0.1x , R 2 =0.9251;

[0030] The relationship between the porosity and irreducible water saturation of the distributary channel microfacies (type II) is: y = 114.25e -0.085x , R 2 =0.7439;

[0031] The relationship between the porosity and irreducible water saturation of natural levee and breach fan microfacies (type III) is: y = 125.57e -0.052x , R 2 =0.8188;

[0032] The microfacies of the river depression is characterized by the development of mudstone and clay-bound pores, with a bound water saturation of 100%.

[0033] S3: Carry out prediction of sedimentary microfacies, sand body distribution, and physical property change characteristics of tight sandstone reservoirs, and obtain the plane distribution of sedimentary microfacies and porosity. Mainly use the well logging and experimental analysis (lithology, grain size, etc.) data of Box 8, the results of single well and well-connected sedimentary facies division, combined with seismic attributes, seismic facies and sand body distribution prediction results, to divide the plane sedimentary microfacies of the center bar, distributary channel, natural levee, breach fan, and inter-river depression ( Figure 3 ), using seismic inversion to obtain the plane distribution of porosity of various sedimentary microfacies ( Figure 4 ).

[0034] S4: Using the "bridge" relationship between sedimentary microfacies, reservoir properties and irreducible water (using the porosity distribution on the plane, based on the relationship between porosity and irreducible water in different sedimentary microfacies), the sedimentary facies belts are divided, and the plane porosity contour map is converted into a plane distribution map of irreducible water saturation according to the fitted functional relationship between porosity and irreducible water saturation ( Figure 5 ).

[0035] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for predicting the distribution of bound water saturation in a tight sandstone plane, characterized by: The following steps are involved: (I) Collecting dense sandstone samples of different sedimentary microfacies in the target layer, and obtaining the porosity and irreducible water saturation of dense sandstone samples of different sedimentary microfacies through experiments; (II) Determine the relationship between porosity and irreducible water saturation of tight sandstone in different sedimentary microfacies; (III) Carry out the prediction of the planar sedimentary microfacies, sand body distribution and physical property distribution of tight sandstone reservoirs, and obtain the planar distribution of sedimentary microfacies and porosity; (IV) Different phase zones are divided, and based on the relationship between porosity and irreducible water saturation obtained in step (II) and the sedimentary microfacies and porosity planar distribution obtained in step (III), the porosity planar distribution is converted into the irreducible water saturation planar distribution.

2. The method for predicting the distribution of bound water saturation in a plane of tight sandstone according to claim 1, characterized in that: The sedimentary microfacies are divided according to the sedimentary characteristics of the block, well logging and experimental analysis data.

3. The method for predicting the distribution of bound water saturation in a plane of tight sandstone according to claim 1, characterized in that: The dense sandstone sample in step (I) has a diameter of 25 mm and a length of 50 mm.

4. The method for predicting the distribution of bound water saturation in a plane of tight sandstone according to claim 1, characterized in that: The relationship between porosity and irreducible water saturation in step (II) is obtained by fitting the functional relationship using statistical methods based on the reservoir porosity and irreducible water saturation data of the tight sandstone samples of different sedimentary microfacies obtained in step (I), and selecting the correlation coefficient R 2 The largest function is used as the relationship between the porosity and irreducible water saturation of tight sandstones with different sedimentary microfacies, and as the prediction function of irreducible water saturation of tight sandstone reservoirs with different sedimentary microfacies.

5. The method for predicting the plane irreducible water saturation distribution of tight sandstone according to claim 1, characterized in that: In the step (III), the planar sedimentary microfacies are divided using the single well and connected well sedimentary facies analysis results combined with seismic attributes and seismic facies analysis, and the planar sedimentary microfacies are consistent with the single well sedimentary microfacies division type of step (I).

6. The method for predicting the distribution of bound water saturation in a plane of tight sandstone according to claim 1, characterized in that: In the step (III), the planar distribution of porosity is obtained by using seismic phase-controlled inversion.

7. The method for predicting the distribution of bound water saturation in a plane of tight sandstone according to claim 1, characterized in that: The specific method of step (IV) is as follows: based on the porosity distribution in different sedimentary phases on the plane and the functional relationship between the porosity of different sedimentary phases and the irreducible water saturation, the porosity contour lines are converted into irreducible water saturation contour lines according to the sedimentary phase zones, so as to realize the prediction of the irreducible water saturation of the plane of the tight sandstone reservoir.

Images