A method for dividing shallow formation thickness under non-matching conditions of electric logging curves

Abstract

The present application provides a kind of shallow formation thickness division method under the condition of non-matching electrical curve, belongs to geological research technical field, through the method, the electrical characteristics of different lithology strata of shallow strata are counted by using coring well, well logging interpretation horizontal graph, the litho-electricity corresponding relationship of shallow strata is determined, and the electrical characteristics of corresponding sedimentary scale sand body of oil layer are analogized, and finally the shallow strata thickness division method is determined.

Description

Technical Field

[0001] This invention belongs to the field of geological research technology, and more specifically, relates to a method for dividing shallow strata thickness under conditions of mismatched electrical logging curves. Background Technology

[0002] The electrical property standard for effective thickness of oil layers in the Lasa Xing oilfield is determined based on the physical property standard. Each oilfield adopts the lower limit standard for effective thickness physical properties in accordance with Q / SY DQ0031-2005 "Operational Procedure for Core Division of Effective Thickness".

[0003] The oil layer referred to is the oil layer below 1100 meters. The curves used for thickness interpretation are: microsphere, high-resolution acoustic transit time, density, microelectrode, high-resolution deep and shallow lateral, 2.5m apparent resistivity, natural gamma, and natural potential. Thickness interpretation is divided into three categories: Class I sandstone, Class II sandstone, and effective thickness. Different curves have corresponding discrimination criteria for different thickness categories.

[0004] There are no corresponding thickness interpretation procedures for formations deeper than 1000 meters, and for shallow formations, only two electrical logging curves—the 2.5m apparent resistivity and spontaneous potential curves—are shared with the oil-bearing formations. Furthermore, since 2000, the oilfield has experienced several surface gas leaks, suspected to be gas capping incidents where gas leaks through casing leaks into the shallow formations, diffuses, and then leaks to the surface. This poses a significant challenge to the oilfield's safe production, thus necessitating reservoir characterization of shallow formations. Therefore, the first step is to interpret the thickness of the shallow formations, but the only usable electrical logging curves are the 2.5m apparent resistivity and spontaneous potential curves shared with the oil-bearing formations.

[0005] Therefore, how to classify shallow strata thickness under the condition of mismatched electrical logging curves has become a problem that needs to be solved. Summary of the Invention

[0006] 1. The technical problem that the invention aims to solve The purpose of this invention is to solve the problem of how to classify shallow strata thickness under the condition of mismatched electrical measurement curves.

[0007] 2. Technical Solution To achieve the above objectives, the technical solution provided by this invention is as follows: The present invention provides a method for dividing shallow strata thickness under conditions of mismatched electrical logging curves. The method includes the following steps: S1, determine the rock-electric relationship in shallow strata; S2, to obtain the sedimentary environment of shallow strata; S3, determine the lithological type of the framework sand body; S4, analogous to the lower limit of electrical properties of sand bodies of corresponding sedimentary scale in oil reservoirs; S5, Determine the method for classifying shallow strata thickness.

[0008] Preferably, step S1 further includes the following steps: S1.1, determine the lithology of shallow strata; S1.2, determine the electrical characteristics of different lithologies in shallow strata; S1.3, determine the correspondence between shallow strata rock and electricity; Preferably, the specific method of step S1.1 is to use the core description and gas test data of early shallow strata core wells to statistically analyze the lithological composition of the shallow strata.

[0009] Preferably, the specific method of step S1.2 is to determine the amplitude range of the 2.5m apparent resistivity and spontaneous potential curves corresponding to different lithologies, as well as the corresponding curve shape and rhythmic characteristics.

[0010] Preferably, the specific method of step S1.2 is to use shallow formation logging to interpret the transverse plot, compare the electrical correspondence between the 2.5m apparent resistivity and spontaneous potential curves and the microelectrode curve; refer to the oil layer thickness interpretation operation procedure to perform thickness interpretation of the shallow formation; respectively count the rhythm type, 2.5m apparent resistivity and spontaneous potential amplitude range corresponding to different lithologies, and summarize the electrical characteristics of different lithologies in the shallow formation.

[0011] Preferably, the rock-electric relationship in step S1 is determined and established using microelectrode curves.

[0012] 3. Beneficial effects Compared with the prior art, the technical solution provided by this invention has the following advantages: This invention provides a method for classifying shallow strata thickness under conditions of mismatched electrical logging curves. This method utilizes core wells and well logging interpretation transverse plots to statistically analyze the electrical characteristics of shallow strata of different lithologies, determine the correspondence between shallow strata lithology and electrical properties, and draws an analogy with the electrical characteristics of sand bodies of corresponding sedimentary scales in oil layers to ultimately determine the method for classifying shallow strata thickness. Attached Figure Description

[0013] Figure 1 This is a flowchart of the shallow stratum thickness division method under the condition of mismatched electrical measurement curves according to the present invention. Detailed Implementation

[0014] To facilitate understanding of the present invention, several embodiments of the invention have been provided. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the invention will be more thorough and complete.

[0015] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element; when an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element; the terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0017] Example 1 like Figure 1 As shown in this embodiment, a method for dividing shallow strata thickness under conditions of mismatched electrical logging curves is described. The method includes the following steps: S1, determine the rock-electric relationship in shallow strata; S2, to obtain the sedimentary environment of shallow strata; S3, determine the lithological type of the framework sand body; S4, analogous to the lower limit of electrical properties of sand bodies of corresponding sedimentary scale in oil reservoirs; S5, Determine the method for classifying shallow strata thickness.

[0018] Preferably, step S1 further includes the following steps: S1.1, determine the lithology of shallow strata; S1.2, determine the electrical characteristics of different lithologies in shallow strata; S1.3, determine the correspondence between shallow strata rock and electricity; The specific method of step S1.1 in this embodiment is to use the core description and gas test data of the early shallow strata core well to statistically analyze the lithological composition of the shallow strata, wherein the lithology of the shallow strata mainly includes: mudstone, silty mudstone, argillaceous siltstone, siltstone, and fine sandstone.

[0019] The specific method of step S1.2 in this embodiment is to determine the amplitude range of the 2.5m apparent resistivity and spontaneous potential curves corresponding to different lithologies, as well as the corresponding curve shapes and rhythmic characteristics. The amplitude, curve shape, and rhythmic characteristics of the 2.5m apparent resistivity and spontaneous potential curves for different lithologies are statistically analyzed: the 2.5m apparent resistivity of argillaceous siltstone is 5.5 Ω·m, and the spontaneous potential is 1.0 mV; the 2.5m apparent resistivity of siltstone is 6.0 Ω·m, and the spontaneous potential is 2.0 mV; the 2.5m apparent resistivity of fine sandstone is 8.0 Ω·m, and the spontaneous potential is 8.0 mV. The curves of siltstone and fine sandstone mostly exhibit positive rhythmic characteristics and peak-shaped composite rhythms; the curves of argillaceous siltstone mostly exhibit finger-like patterns, composite rhythms, and moderate to low amplitude values.

[0020] The specific method of step S1.3 in this embodiment is to use shallow formation logging to interpret the transverse plot, compare the electrical correspondence between the 2.5m apparent resistivity and spontaneous potential curves and the microelectrode curve; refer to the oil layer thickness interpretation operation procedure to perform thickness interpretation of the shallow formation; respectively statistically analyze the rhythm type, 2.5m apparent resistivity and spontaneous potential amplitude range corresponding to different lithologies, and summarize the electrical characteristics of different lithologies in the shallow formation: siltstone and fine sandstone formations have positive rhythm, thickness greater than 4m, and 2.5m apparent resistivity greater than 10.5Ω·m; argillaceous siltstone and siltstone formations have positive or composite rhythm, thickness between 2 and 4m, and 2.5m apparent resistivity greater than 8.5Ω·m; silty mudstone and argillaceous siltstone formations have composite or anti-rhythmic rhythm, thickness less than 2m, and 2.5m apparent resistivity greater than 12.5Ω·m.

[0021] In step S1 of this embodiment, the rock-electric relationship is determined and established using microelectrode curves, analogous to the lower limit of electrical properties of sand bodies of the same depositional scale in oil layers; the thickness is defined when the apparent resistivity of the shallow strata at 2.5m is greater than 14.0Ω·m.

[0022] The above-described embodiments are merely illustrative of certain implementations of the present invention, and are described in a relatively specific and detailed manner. However, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for dividing shallow strata thickness under conditions of mismatched electrical logging curves, characterized in that: The partitioning method includes the following steps: S1, Determine the rock-electric relationship in shallow strata, wherein the rock-electric relationship is determined and established using microelectrode curves; Step S1 further includes the following steps: S1.1 Determine the lithology of shallow strata. The specific method is to use the core description and gas test data from early shallow strata core wells to statistically analyze the lithological composition of shallow strata. S1.2, determine the electrical characteristics of different lithologies in shallow strata; The specific method of step S1.2 is to determine the amplitude range of the 2.5m apparent resistivity and spontaneous potential curves corresponding to different lithologies, as well as the corresponding curve shape and rhythmic characteristics; The specific method of step S1.2 is to use shallow formation logging to interpret the transverse plot, compare the electrical correspondence between the 2.5m apparent resistivity and spontaneous potential curves and the microelectrode curves; and refer to the oil layer thickness interpretation operation procedure to interpret the thickness of the shallow formation. The rhythm type, apparent resistivity at 2.5m, and spontaneous potential amplitude range of different lithologies were statistically analyzed to summarize the electrical characteristics of different lithologies in shallow strata. S1.3, determine the correspondence between shallow strata rock and electricity; S2, to obtain the sedimentary environment of shallow strata; S3, determine the lithological type of the framework sand body; S4, analogous to the lower limit of electrical properties of sand bodies of corresponding sedimentary scale in oil reservoirs; S5, Determine the method for classifying shallow strata thickness.

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