Evaluation method for residual hydrocarbon of post- to over-mature marine source rocks
11499957 · 2022-11-15
Assignee
Inventors
- Wenyang Wang (Beijing, CN)
- Yaping Wang (Beijing, CN)
- Xiongqi Pang (Beijing, CN)
- Zhangxing Chen (Beijing, CN)
- Wang Zhang (Beijing, CN)
- Rixiang Zhu (Beijing, CN)
Cpc classification
G01N25/20
PHYSICS
International classification
G01N25/20
PHYSICS
Abstract
An evaluation method for residual hydrocarbon of post- to over-mature marine source rocks includes the following steps: establishing a hydrocarbon generation potential evolution profile and a hydrogen index evolution profile of post- to over-mature source rocks; determining a critical condition for hydrocarbon expulsion of the source rocks, and inverting original hydrocarbon generation potential of the source rocks; inverting a critical condition for hydrocarbon generation of the source rocks; establishing a hydrocarbon generation, expulsion and retention model for the source rocks; determining a hydrocarbon generation rate, a hydrocarbon expulsion rate and a hydrocarbon retention rate of the source rocks; and calculating a hydrocarbon retention intensity and residual hydrocarbon of the source rocks. The evaluation method establishes an evaluation model for residual hydrocarbon of post- to over-mature source rocks without relying on immature to sub-mature samples.
Claims
1. An evaluation method for residual hydrocarbon of post- to over-mature marine source rocks comprising steps of: A) collecting samples of post- to over-mature marine source rocks to be evaluated from a formation; B) establishing a hydrocarbon generation potential evolution profile and a hydrogen index evolution profile of the post- to over-mature source rocks comprising steps of: obtaining a hydrocarbon generation potential index, a hydrogen index and an equivalent vitrinite reflectance through a pyrolysis experiment of the collected samples of post- to over-mature source rocks; and establishing the hydrocarbon generation potential evolution profile and the hydrogen index evolution profile of post- to over-mature post- to over-mature source rocks in marine strata lacking vitrinite based on the hydrocarbon generation potential index, the hydrogen index and the equivalent vitrinite reflectance, wherein the hydrocarbon generation potential evolution profile of the post- to over-mature source rocks is a diagram showing a relationship between the hydrocarbon generation potential index and the equivalent vitrinite reflectance; and the hydrogen index evolution profile of the post- to over-mature source rocks is a diagram showing a relationship between the hydrogen index and the equivalent vitrinite reflectance; the hydrocarbon generation potential index is
100×(S.sub.1+S.sub.2)/TOC, wherein S.sub.1, S.sub.2 are hydrocarbon yields per unit mass of source rock samples heated to 300° C. and 300-600° C. respectively, mg.Math.HC/g; TOC is total organic carbon (TOC) per unit mass of the post- to over-mature source rocks, mg/g; the hydrogen index is
100×S.sub.2/TOC; and the equivalent vitrinite reflectance is R.sub.o,
R.sub.0=0.0078T.sub.max−1.3654, wherein T.sub.max is a maximum peak pyrolysis temperature in the pyrolysis experiment of the post- to over-mature source rocks; C) determining a critical condition for hydrocarbon expulsion of the post- to over-mature source rocks, and inverting original hydrocarbon generation potential of the post- to over-mature source rocks comprising steps of: obtaining a homogenization temperature distribution map of fluid inclusions according to an inclusion experiment; determining a main peak value of a homogenization temperature for a first phase of the fluid inclusions based on the homogenization temperature distribution map of the fluid inclusions; and obtaining a corresponding minimum R.sub.min of an isotherm at the main peak value of the homogenization temperature of the first phase of the fluid inclusions according to a depositional burial history and a thermal evolution history of a typical well, wherein the corresponding minimum R.sub.min is R.sub.oe, and R.sub.oe is a critical maturity for the hydrocarbon expulsion corresponding to the critical condition for the hydrocarbon expulsion; and wherein inverting the original hydrocarbon generation potential of the post- to over-mature source rocks comprises: obtaining a hydrocarbon generation potential index envelope I.sub.g according to the hydrocarbon generation potential evolution profile of the post- to over-mature source rocks by the following equation,
I.sub.r=∫.sub.R.sub.
Q.sub.r=∫.sub.R.sub.
2. The evaluation method for residual hydrocarbon of post- to over-mature marine source rocks according to claim 1, wherein
TOC.sub.o=TOC*k; and
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Other features, objectives and advantages of the present application will become more apparent upon reading the detailed description of the non-restrictive examples with reference to the following drawings.
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DETAILED DESCRIPTION OF THE EMBODIMENTS
(9) The preferred implementations of the present disclosure are described below with reference to the drawings. Those skilled in the art should understand that the implementations herein are merely intended to explain the technical principles of the present disclosure, rather than to limit the protection scope of the present disclosure.
(10) The present disclosure provides an evaluation method for residual hydrocarbon of post- to over-mature marine source rocks. The method includes the following steps. S100: Establish a hydrocarbon generation potential evolution profile and a hydrogen index evolution profile of post- to over-mature source rocks: obtain a hydrocarbon generation potential index, a hydrogen index and an equivalent vitrinite reflectance through a pyrolysis experiment of the source rocks; and establish a hydrocarbon generation potential evolution profile and a hydrogen index evolution profile of post- to over-mature source rocks for marine strata lacking vitrinite based on the hydrocarbon generation potential index, the hydrogen index and the equivalent vitrinite reflectance, where the hydrocarbon generation potential evolution profile of the source rocks is a diagram showing a relationship between the hydrocarbon generation potential index and the equivalent vitrinite reflectance; and the hydrogen index evolution profile of the source rocks is a diagram showing a relationship between the hydrogen index and the equivalent vitrinite reflectance.
(11) S200: Determine a critical condition for hydrocarbon expulsion of the source rocks, and invert original hydrocarbon generation potential of the source rocks, where the determining a critical condition for hydrocarbon expulsion includes: obtain a homogenization temperature distribution map of fluid inclusions according to an inclusion experiment; determine a main peak value of a homogenization temperature for a first phase of the fluid inclusions based on the homogenization temperature distribution map of the fluid inclusions; and obtain a corresponding minimum R.sub.min of an isotherm at the main peak value of the homogenization temperature of the first phase of the inclusions according to a depositional burial history and a thermal evolution history of a typical well, which is R.sub.oe, meaning a critical maturity for hydrocarbon expulsion corresponding to the critical condition for hydrocarbon expulsion; the inverting original hydrocarbon generation potential of the source rocks includes: obtain a hydrocarbon generation potential index envelope I.sub.g according to the hydrocarbon generation potential evolution profile of the source rocks,
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where a, b, c and d are constants; and obtain original hydrocarbon generation potential of the source rocks based on the hydrocarbon generation potential index envelope and the critical maturity for hydrocarbon expulsion I.sub.og,
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(14) S300: Invert a critical condition for hydrocarbon generation of the source rocks: obtain a hydrogen index envelope HI based on the hydrogen index evolution profile of the source rocks; and obtain a critical condition R.sub.og for hydrocarbon generation of the source rocks based on the hydrogen index envelope and the original hydrocarbon generation potential of the source rocks, that is, an equivalent vitrinite reflectance corresponding to an intersection of the hydrogen index envelope and the original hydrocarbon generation potential of the source rocks.
(15) S400: Establish a hydrocarbon generation, expulsion and retention model for the source rocks by means of matrix laboratory (MATLAB) based on the hydrocarbon generation potential evolution profile, the hydrogen index evolution profile, the critical condition for hydrocarbon expulsion, the original hydrocarbon generation potential and the critical condition for hydrocarbon generation of the source rocks.
(16) S500: Determine a hydrocarbon generation rate, a hydrocarbon expulsion rate and a hydrocarbon retention rate of the source rocks: calculate a hydrocarbon generation rate q.sub.g, a hydrocarbon expulsion rate q.sub.e and a hydrocarbon retention rate q.sub.r of the source rocks based on the hydrocarbon generation, expulsion and retention model for the source rocks, where q.sub.g=I.sub.og−HI, q.sub.e=I.sub.og−I.sub.g, q.sub.r=q.sub.g−q.sub.e.
(17) S600: Calculate a hydrocarbon retention intensity and residual hydrocarbon of the source rocks: obtain a hydrocarbon retention intensity I.sub.r of the source rocks in different thermal evolution stages by an integral of the hydrocarbon retention rate, abundance of organic matter and a thickness and of density of the source rocks corresponding to the different thermal evolution stages; and obtain total residual hydrocarbon Q.sub.r in each geological period based on the hydrocarbon retention intensity.
I.sub.r=∫.sub.R.sub.
TOC.sub.o=TOC*k.
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Q.sub.r=∫.sub.R.sub.
(19) The present disclosure establishes an evaluation model for residual hydrocarbon of post- to over-mature source rocks without relying on immature to sub-mature samples. The present disclosure provides a scientific basis for the evaluation of shale oil and gas resources, and provides strong theoretical guidance and technical support for the selection and evaluation of shale oil and gas exploration targets.
(20) The present disclosure is described in further detail below with reference to an example of the Sichuan Basin in China.
(21) The Sichuan Basin is located in central China, with an area of about 19×10.sup.4 km.sup.2, and it is one of the major natural gas producing areas in China. The Sichuan Basin is a typical superimposed petroliferous basin. After undergoing multi-cycle tectonic movements and the superimposition and transformation of multiple types of basins, the Sichuan Basin has formed multiple sets of source-reservoir-caprock assemblages, which have the characteristics of multi-layered hydrocarbon-bearing. The Ediacaran to Lower Triassic strata in the Sichuan Basin are marine carbonate strata, and the study strata of the present disclosure are in the Upper Ediacaran Dengying Formation. According to lithology and biological characteristics, the Dengying Formation is divided into four lithological members from top to bottom, namely, Deng 4 (Z.sub.2d.sup.4), Deng 3 (Z.sub.2d.sup.3), Deng 2 (Z.sub.2d.sup.2) and Deng 1 (Z.sub.2d.sup.1). Algal dolomite, which is widely distributed in the Sichuan Basin, is an important Ediacaran source rock in the Sichuan Basin. It is mainly distributed in the Deng 4 (Z.sub.2d.sup.4) and Deng 2 (Z.sub.2d.sup.2) members. This type of source rock has a buried depth of more than 5,000 m, and has reached the post- to over-mature thermal evolution stage, with a thickness of 300-1,350 m.
(22) Referring to
(23) A hydrocarbon generation potential evolution profile and a hydrogen index evolution profile of post- to over-mature source rocks were established for marine strata lacking vitrinite, as shown in
(24) Further, R.sub.0=0.0078T.sub.max−1.3654, where T.sub.max is a peak temperature in the pyrolysis experiment of the source rocks; and R.sub.0 is in %, and T.sub.max is in ° C.
(25) S200: A critical condition for hydrocarbon expulsion from the Ediacaran algal dolomite source rocks in the Sichuan Basin was determined, and original hydrocarbon generation potential of the source rocks was inverted. Through microscopic thin section analysis and geological analysis, three phases of inclusions were found in the Dengying Formation in the Sichuan Basin. The first phase of inclusions was formed in dolomite grains. Through experimental analysis of the inclusions in the Dengying Formation, a homogenization temperature distribution map of the fluid inclusions was obtained, as shown in
(26) A hydrocarbon generation potential index envelope I.sub.g was obtained according to the hydrocarbon generation potential evolution profile of the source rocks,
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(28) An original hydrocarbon generation potential I.sub.og of the source rocks was obtained based on the hydrocarbon generation potential index envelope and the critical maturity for hydrocarbon expulsion. Specifically, a mathematical relationship between the hydrocarbon generation potential index envelope and the degree of thermal evolution was fitted. A hydrocarbon generation potential corresponding to the critical maturity for hydrocarbon expulsion on the hydrocarbon expulsion evolution profile of the source rocks was the original hydrocarbon generation potential of the source rocks. The original hydrocarbon generation potential of the Ediacaran source rocks in the Sichuan Basin was calculated as I.sub.og=756 mg.Math.HC/g TOC.
(29) Further, a critical condition for hydrocarbon generation in the Ediacaran algal dolomite source rocks in the Sichuan Basin was inverted.
(30) A hydrogen index envelope HI was obtained based on the established hydrogen index evolution profile of the Ediacaran algal dolomite source rocks in the Sichuan Basin,
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According to the obtained original hydrocarbon generation potential and hydrogen index envelope of the Ediacaran algal dolomite source rocks in the Sichuan Basin, the critical condition for hydrocarbon generation in the source rocks was obtained, that is, an equivalent vitrinite reflectance corresponding to an intersection of the hydrogen index envelope and the original hydrocarbon generation potential of the source rocks. In this example, R.sub.og=0.51%.
(32) S400: A hydrocarbon generation, expulsion and retention model for the source rocks was established by means of matrix laboratory (MATLAB) based on the hydrocarbon generation potential evolution profile, the hydrogen index evolution profile, the critical condition for hydrocarbon expulsion, the original hydrocarbon generation potential and the critical condition for hydrocarbon generation. In this example, a hydrocarbon generation, expulsion and retention model for the Ediacaran algal dolomite source rocks in the Sichuan Basin was established, as shown in
(33) S500: A hydrocarbon generation rate, a hydrocarbon expulsion rate and a hydrocarbon retention rate of the Ediacaran algal dolomite source rocks in the Sichuan Basin were determined. A hydrocarbon generation rate q.sub.g, a hydrocarbon expulsion rate q.sub.e and a hydrocarbon retention rate q.sub.r of the source rocks were calculated based on the hydrocarbon generation, expulsion and retention model for the source rocks.
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(37) S600: A hydrocarbon retention intensity and residual hydrocarbon of the Ediacaran algal dolomite source rocks in the Sichuan Basin were determined. A hydrocarbon retention intensity I.sub.r of the source rocks in different thermal evolution stages was calculated by an integral of the hydrocarbon retention rate, abundance of organic matter and a thickness and density of the source rocks corresponding to the different thermal evolution stages, and total residual hydrocarbon Q.sub.r in each geological period was calculated based on the hydrocarbon retention intensity.
I.sub.r=∫.sub.R.sub.
where H was the thickness of the source rocks; ρ was the density of the source rocks; A was a distribution area of the source rocks; and TOC.sub.O was original TOC of the source rock.
TOC.sub.o=TOC*k.
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Q.sub.r=∫.sub.R.sub.
(39) Further, refer to
(40) The above examples are merely intended to illustrate the present disclosure, and the implementation steps of the method can be changed. Any equivalent changes and improvements made on the basis of the technical solutions of the present disclosure should not be excluded from the protection scope of the present disclosure.
(41) Although the present disclosure has been described with reference to the preferred examples, various improvements can be made and components therein can be replaced with equivalents without departing from the scope of the present disclosure. In particular, as long as there is no structural conflict, the technical features in the examples can be combined in any way. The present disclosure is not limited to the specific examples disclosed herein, but shall include all technical solutions falling within the scope of the claims.
(42) In the description of the present disclosure, terms such as “central”, “upper”, “lower”, “left”, “right”, “vertical”, “horizontal”, “inner”, and “outer” indicate orientation or position relationships based on the drawings. They are merely intended to facilitate description, rather than to indicate or imply that the mentioned apparatus or components must have the specific orientation and must be constructed and operated in the specific orientation. Therefore, these terms should not be construed as a limitation to the present disclosure. Moreover, the terms such as “first”, “second”, and “third” are used only for description and are not intended to indicate or imply relative importance.
(43) It should be noted that in the description of the present disclosure, unless otherwise clearly specified, meanings of terms “install”, “connect with” and “connect to” should be understood in a broad sense. For example, the connection may be a fixed connection, a removable connection, or an integral connection; may be a mechanical connection or an electrical connection; may be a direct connection or an indirect connection via a medium; or may be an internal connection between two assemblies. Those skilled in the art should understand the specific meanings of the above terms in the present disclosure based on specific situations.
(44) In addition, terms “include”, “comprise”, or any other variations thereof are intended to cover non-exclusive inclusions, so that a process, an article, or a device/apparatus including a series of elements not only includes those elements, but also includes other elements that are not explicitly listed, or also includes inherent elements of the process, the article or the device/apparatus.
(45) The technical solutions of the present disclosure are described with reference to the preferred implementations and drawings. Those skilled in the art should easily understand that the protection scope of the present disclosure is apparently not limited to these specific implementations. Those skilled in the art can make equivalent changes or substitutions to the relevant technical features without departing from the principles of the present disclosure, and the technical solutions derived by making these changes or substitutions should fall within the protection scope of the present disclosure.