EVALUATION METHOD FOR HYDROCARBON EXPULSION OF POST- TO OVER-MATURE MARINE SOURCE ROCKS

Abstract

An evaluation method for hydrocarbon expulsion of post- to over-mature marine source rocks includes: establishing a hydrocarbon expulsion evolution profile of post- to over-mature source rocks; determining a critical condition for hydrocarbon expulsion from the source rocks, inverting original hydrocarbon generation potential of the source rocks, and establishing a hydrocarbon expulsion model for the source rocks; determining a hydrocarbon expulsion rate and cumulative hydrocarbon expulsion of the source rocks; and calculating hydrocarbon expulsion of the source rocks. The evaluation method establishes a hydrocarbon expulsion model for post- to over-mature source rocks without relying on immature to sub-mature samples. The evaluation method provides a scientific basis for the evaluation of the potential of deep oil and gas resources, and provides strong theoretical guidance and technical support for deep oil and gas exploration.

Claims

1. A method of exploring a formation using an evaluation method for hydrocarbon expulsion of post- to over-mature marine source rocks comprises steps of: A) collecting samples of post- to over-mature marine source rocks to be evaluated from a formation; B) establishing a hydrocarbon expulsion evolution profile of the post- to over-mature source rocks comprises steps of: calculating a hydrocarbon generation potential index and an equivalent vitrinite reflectance based on a pyrolysis experiment of the collected samples of post- to over-mature source rocks; and establishing the hydrocarbon expulsion evolution profile of the post- to over-mature source rocks based on the hydrocarbon generation potential index and the equivalent vitrinite reflectance, wherein the hydrocarbon generation potential index is $100\times \left({\text{S}}_1+{\text{S}}_2\right)/TOC,$ 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•HC/g; TOC is total organic carbon (TOC) per unit mass of the post- to over-mature source rocks, mg/g; and the equivalent vitrinite reflectance is R.sub.o, R.sub.o = 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 the hydrocarbon expulsion of the post- to over-mature source rocks, inverting original hydrocarbon generation potential of the post- to over-mature source rocks, and establishing a hydrocarbon expulsion model for the post- to over-mature source rocks comprises 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 inclusions according to a depositional burial history and a thermal evolution history of a typical well, wherein R.sub.min is a critical maturity R.sub.oe for hydrocarbon expulsion corresponding to the critical condition for hydrocarbon expulsion; wherein determining of inverting the original hydrocarbon generation potential of the post- to over-mature source rocks comprises: obtaining a hydrocarbon generation potential index envelope according to the hydrocarbon expulsion evolution profile of the post- to over-mature source rocks; obtaining a fitted relation Ig based on the equivalent vitrinite reflectance and the hydrocarbon generation potential index envelope by the following equation: Ig = .sub.He.sub.-:CRo-.sub.C) + d, wherein a, b, c and d are constants; and obtaining the original hydrocarbon generation potential I.sub.og of the post- to over-mature source rocks based on the fitted relation and the critical maturity for hydrocarbon expulsion by the following equation: $I_{og}=\frac{a}{1+{\text{e}}^{-\text{b}\left({\text{R}}_{\text{oe}}-\text{c}\right)}}+\text{d;}$ D) determining a hydrocarbon expulsion rate and cumulative hydrocarbon expulsion of the post- to over-mature source rocks; E) calculating the hydrocarbon expulsion of the post- to over-mature source rocks based on steps A) through D); and F) wherein when the calculated hydrocarbon expulsion of the collected sample post- to over-mature source rocks to be evaluated of the formation meets a predetermined threshold, exploring the formation.

2. The method according to claim 1, wherein establishing the hydrocarbon expulsion model for the post- to over-mature source rocks comprises: establishing the hydrocarbon expulsion model for the post- to over-mature source rocks by means of matrix laboratory (MATLAB) based on the hydrocarbon expulsion evolution profile, the critical condition for hydrocarbon expulsion and the original hydrocarbon generation potential.

3. The method according to claim 2, wherein determining the hydrocarbon expulsion rate and the cumulative hydrocarbon expulsion of the post- to over-mature source rocks comprises: obtaining the hydrocarbon expulsion rate q.sub.e and the cumulative hydrocarbon expulsion q.sub.ce of the post- to over-mature source rocks based on the hydrocarbon expulsion model for the post-to over-mature source rocks by the following equations: $q_e=I_{og}-Ig;$ $q_{ce}={\displaystyle \int q_{e}d\left(R_o\right)}$ .

4. The method according to claim 3, wherein calculating the hydrocarbon expulsion of the post- to over-mature source rocks comprises: obtaining a hydrocarbon expulsion intensity I.sub.e of the post- to over-mature source rocks in different thermal evolution stages by an integral of the hydrocarbon expulsion rate, abundance of organic matter and a thickness and density of the post- to over-mature source rocks corresponding to the different thermal evolution stages by the following equation: $I_e={\displaystyle \int \begin{array}{c}{}_{R_o}\\ {}^{R_0}\end{array}}{}_t{10}^{-3}*q_e*H*\rho *TO{C}_o*d(R_o);$ and obtaining total hydrocarbon expulsion Q.sub.e in each geological period based on the hydrocarbon expulsion intensity by the following equation: $Q_e={\displaystyle {\int }_{R_0}^{R_o}{}_t{10}^{-13}\ast q_e\ast H\ast A\ast \rho \ast TO{C}_O\ast d\left(R_o\right);}$ wherein, H is the thickness of the post- to over-mature source rocks; p is the density of the post- to over-mature source rocks; A is a distribution area of the post- to over-mature source rocks; and TOC.sub.O is original TOC of the post- to over-mature source rocks.

5. The method according to claim 4, wherein TOC.sub.o = TOC * k; and $k=\left(1-0.83\ast \frac{Ig}{1000}\right)/\left(1-0.83\ast \frac{I_{og}}{1000}\right)$ .

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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 accompanying drawings.

[0027] FIG. 1 is a flowchart of a specific example of the present disclosure;

[0028] FIG. 2A is the variation of hydrocarbon generation potential of source rocks with thermal evolution, and FIG. 2B is the hydrocarbon expulsion rate of source rocks with thermal evolution;

[0029] FIG. 3 is a hydrocarbon generation potential evolution profile of Ediacaran algal dolomite source rocks in the Sichuan Basin, China;

[0030] FIG. 4 is a homogenization temperature distribution map of Ediacaran dolomite fluid inclusions in the Sichuan Basin;

[0031] FIG. 5 is a depositional burial history and a thermal evolution history of Well Moxi 8 in the Sichuan Basin;

[0032] FIG. 6 is a hydrocarbon expulsion model for the Ediacaran algal dolomite source rocks in the Sichuan Basin; and

[0033] FIG. 7 is a hydrocarbon expulsion intensity map of the Jurassic-Ediacaran algal dolomite source rocks in the Sichuan Basin.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The preferred implementations of the present disclosure are described below with reference to the accompanying 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.

[0035] The present disclosure provides an evaluation method for hydrocarbon expulsion of post- to over-mature marine source rocks. The method includes the following steps. S 100: Establish a hydrocarbon expulsion evolution profile of post- to over-mature source rocks. Specifically, this step includes: calculate a hydrocarbon generation potential index and an equivalent vitrinite reflectance based on a pyrolysis experiment of the source rocks; and establish a hydrocarbon expulsion evolution profile of the source rocks based on the hydrocarbon generation potential index and the equivalent vitrinite reflectance, where the hydrocarbon generation potential index is 100 × (S.sub.1 + S.sub.2)/TOC , where 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•HC/g; TOC is total organic carbon (TOC) per unit mass of the source rocks, mg/g; and the equivalent vitrinite reflectance is R.sub.o, R.sub.O = 0.0078T.sub.max - 1.3654, where T.sub.max is a maximum peak pyrolysis temperature in the pyrolysis experiment of the source rocks.

[0036] S200: Determine a critical condition for hydrocarbon expulsion, invert original hydrocarbon generation potential of the source rocks, and establish a hydrocarbon expulsion model for the source rocks. Specifically, the determining a critical condition for hydrocarbon expulsion includes: obtain a homogenization temperature distribution map of fluid inclusions according to an inclusion experiment of Dengying Formation; determine a main peak value of a homogenization temperature for a first phase of the fluid inclusions in the Dengying Formation 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, where R.sub.oe is 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 according to the hydrocarbon expulsion evolution profile of the source rocks; obtain a fitted relation Ig based on the equivalent vitrinite reflectance and the hydrocarbon generation potential index envelope,

[00008]$Ig=\frac{a}{{\text{1+e}}^{-\text{b}\left({\text{R}}_{\text{o}}-\text{c}\right)}}\text{+d},$

where a, b, c and d are constants; and obtain an original hydrocarbon generation potential I.sub.og of the source rocks based on the fitted relation and the critical maturity for hydrocarbon expulsion,

[00009]$I_{og}=\frac{a}{1+{\text{e}}^{-\text{b}\left({\text{R}}_{\text{oe}}-\text{c}\right)}}+\text{d}\text{.}$

The establishing a hydrocarbon expulsion model for post- to over-mature source rocks includes: establish a hydrocarbon expulsion model for post- to over-mature source rocks by means of matrix laboratory (MATLAB) based on the hydrocarbon expulsion evolution profile, the critical condition for hydrocarbon expulsion and the original hydrocarbon generation potential.

[0037] S300: Determine a hydrocarbon expulsion rate and cumulative hydrocarbon expulsion of the source rocks. Specifically, the determining a hydrocarbon expulsion rate and cumulative hydrocarbon expulsion of the source rocks includes: obtain a hydrocarbon expulsion rate q.sub.e and cumulative hydrocarbon expulsion q.sub.ce of the source rocks based on the hydrocarbon expulsion model for the source rocks, where q.sub.e = I.sub.og - Ig, q.sub.ce = ∫ q.sub.ed(R.sub.o).

[0038] S400: Calculate hydrocarbon expulsion of the source rocks. Specifically, the calculating hydrocarbon expulsion of the source rocks includes: obtain a hydrocarbon expulsion intensity I.sub.e of the source rocks in different thermal evolution stages according to an integral of the hydrocarbon expulsion rate, abundance of organic matter and a thickness and density of the source rocks in different thermal evolution stages; and obtain total hydrocarbon expulsion Q.sub.e in each geological period based on the hydrocarbon expulsion intensity, where

[00010]$I_e={\displaystyle {\int }_{R_0{}^t}^{R_o}{10}^{-3}\ast q_e\ast H\ast \rho \ast TO{C}_O\ast d\left(R_o\right);\text{and}}$

[00011]$Q_e={\displaystyle {\int }_{R_o{}^t}^{R_o}{10}^{-13}\ast q_e\ast H\ast A\ast p\ast TO{C}_O\ast d\left(R_o\right);}$

[0039] where, H is the thickness of the source rocks; p is the density of the source rocks; A is a distribution area of the source rocks; and TOC.sub.O is original TOC of the source rock.

[0040] The present disclosure is described in further detail below with reference to FIGS. 1 to 7 and an example of the Sichuan Basin in China.

[0041] 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 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.

[0042] The present disclosure proposes an evaluation method for hydrocarbon expulsion of post- to over-mature marine source rocks. This method established a conceptual hydrocarbon expulsion model for post- to over-mature source rocks, as shown in FIGS. 2A and 2B, and was implemented by the following steps. A hydrocarbon generation potential evolution profile of the Ediacaran algal dolomite source rocks in the Sichuan Basin was established. According to parameters obtained from a pyrolysis experiment of the Ediacaran algal dolomite source rocks in the Sichuan Basin, a hydrocarbon generation potential index was calculated by 100×(S.sub.1+S.sub.2)/TOC. According to a pyrolysis parameter T.sub.max, an equivalent vitrinite reflectance R.sub.o (i.e., maturity) was calculated, and an evolution profile of 100×(S.sub.1+S.sub.2)/TOC changing with R.sub.o, that is, a hydrocarbon expulsion evolution profile of the source rocks shown in FIG. 3 was plotted.

[0043] A critical condition for hydrocarbon expulsion from the Ediacaran algal dolomite source rocks in the Sichuan Basin was determined, original hydrocarbon generation potential of the source rocks was inverted, and a hydrocarbon expulsion model for the Ediacaran algal dolomite source rocks in the Sichuan Basin was established.

[0044] 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 FIG. 4. Based on the homogenization temperature distribution map of the fluid inclusions, a main peak value of the homogenization temperature of the first phase was determined. In this example, it was determined that the peak of the homogenization temperature of the inclusions in the first phase was 120-130° C. For quantitative characterization, 125° C. was taken as the main peak value of the homogenization temperature of the inclusions in the first phase, which meant that the source rocks began to expel a large amount of hydrocarbons at this paleo-geothermic temperature. According to a depositional burial history and a thermal evolution history of the typical Well Moxi 8 in the Sichuan Basin (FIG. 5), a critical maturity R.sub.oe for hydrocarbon expulsion from the algal dolomite source rocks in the Dengying Formation was inverted. The minimum R.sub.o on the 125° C. isotherm of the Dengying Formation was the critical maturity for hydrocarbon expulsion from the algal dolomite source rocks of the Dengying Formation. R.sub.o was taken as 0.92%, which meant that the Ediacaran algal dolomite source rocks in the Sichuan Basin began to expel a large amount of hydrocarbons when R.sub.o reached 0.92%, that is, the critical maturity for hydrocarbon expulsion (R.sub.oe) was correspondingly R.sub.oe = 0.92%.

[0045] A hydrocarbon generation potential index envelope was obtained according to the hydrocarbon expulsion evolution profile of the source rocks, and a fitted relation Ig was obtained based on the equivalent vitrinite reflectance and the hydrocarbon generation potential index envelope. In this example,

[00012]$Ig=\frac{702.64}{1+{\text{e}}^{-2.17\left({\text{R}}_{\text{o}}+3.55\right)}}+\mathrm{53.48.}$

[0046] The hydrocarbon generation potential corresponding to the critical maturity for hydrocarbon expulsion (R.sub.oe) on the hydrocarbon expulsion evolution profile of the source rocks was the original hydrocarbon generation potential of the source rocks. In this example, the corresponding original hydrocarbon generation potential of the Ediacaran algal dolomite source rocks in the Sichuan Basin was 756 mg•HC/g•TOC, that is I.sub.og = 756 mg HC/g TOC.

[0047] According to the determined hydrocarbon expulsion evolution profile, critical condition for hydrocarbon expulsion and original hydrocarbon generation potential, a hydrocarbon expulsion model for the Ediacaran algal dolomite source rocks in the Sichuan Basin was established (FIG. 6). In this model, the critical condition for hydrocarbon expulsion from the source rocks corresponded to the original hydrocarbon generation potential, and the hydrocarbon generation potential index of source rocks decreased with the increase of the thermal maturity.

[0048] Further, according to the established hydrocarbon expulsion model for the Ediacaran algal dolomite source rocks in the Sichuan Basin, a hydrocarbon expulsion rate q.sub.e and cumulative hydrocarbon expulsion q.sub.ce of the algal dolomite were determined. q.sub.e was hydrocarbon expulsion per unit TOC of the source rocks at a certain degree of thermal evolution, and q.sub.ce was cumulative hydrocarbon expulsion per gram of organic carbon from the source rocks.

[0049] Further,

[00013]$q_e=702.52-\frac{702.64}{1+{\text{e}}^{-2.17\left({\text{R}}_{\text{o}}+3.55\right)}};$

[0050] where, q.sub.ce = ∫ q.sub.ed(R.sub.o).

[0051] Further, the hydrocarbon expulsion from the Ediacaran algal dolomite source rocks in the Sichuan Basin was calculated. This step took the calculation of the hydrocarbon expulsion of the Jurassic-Ediacaran algal dolomite source rocks in the Sichuan Basin as an example. First, according to the integral of the hydrocarbon expulsion rate, abundance of organic matter and a thickness and density of the Jurassic-Ediacaran algal dolomite source rocks, a hydrocarbon expulsion intensity I.sub.e of the Jurassic-Ediacaran algal dolomite source rocks was calculated. FIG. 7 shows the hydrocarbon expulsion intensity of the Jurassic-Ediacaran source rocks in the Sichuan Basin, which exceeded 1,600×10.sup.4 t/km.sup.2 at a hydrocarbon expulsion center. Through the area integration of the hydrocarbon expulsion intensity I.sub.e of the Jurassic-Ediacaran algal dolomite source rocks, the total hydrocarbon expulsion Q.sub.e of the Jurassic-Ediacaran algal dolomite source rocks was obtained.

[00014]$I_e={\displaystyle {\int }_{R_0{}^t}^{R_o}{10}^{-3}\ast q_e\ast H\ast A\ast p\ast TO{C}_O\ast d\left(R_o\right).}$

[00015]$Q_e={\displaystyle {\int }_{R_0{}^t}^{R_o}{10}^{-13}\ast q_e\ast H\ast A\ast p\ast TO{C}_O\ast d\left(R_o\right).}$

[00016]$TO{C}_o=TOC\ast k.$

[00017]$k=\left(1-0.83\ast \frac{\text{Ig}}{1000}\right)/\left(1-0.83\ast \frac{{\text{I}}_{\text{og}}}{1000}\right).$

[0052] The total hydrocarbon expulsion Q.sub.e of the Jurassic-Ediacaran algal dolomite source rocks in the Sichuan Basin was calculated to be 3958.4 × 10.sup.8 toe.

[0053] 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.

[0054] 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 accompanying 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.

[0055] 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.

[0056] 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.

[0057] 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.