Determination Method for Composition Contents of Dark Mudstone and Carbonaceous Mudstone in Oil-Type Gas

Abstract

The present invention discloses a method for determining the composition content of dark mudstone and carbonaceous mudstone in oil-type gas. The method includes: after determining that the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone, obtaining the geological ages of different gas source rock formations through the <supgt;40< / supgt;Ar / <supgt;36< / supgt;Ar ratio of the gas reservoir; obtaining the <supgt;40< / supgt;Ar / <supgt;36< / supgt>Ar end-member value of the natural gas generated by the dark mudstone in the area to be measured according to the comparison between the geological ages of different gas source rock formations and the geological age of the main gas source in the area to be measured; obtaining the composition ratios of the dark mudstone and the carbonaceous mudstone according to the end-member value, the actually measured <supgt;40< / supgt;Ar / <supgt;36< / supgt>Ar ratio of the gas reservoir, the <supgt;40< / supgt;Ar / <supgt;36< / supgt>Ar ratio of argon in the air, and the content of element K in typical dark mudstone and carbonaceous mudstone in the area to be measured. The determination method of the present invention has a simple process and accurate results, can conduct more refined gas source comparison for oil-type gas reservoirs, and provides a more accurate basis for the evaluation of natural gas resources, the prediction of favorable gas-producing areas, and the guidance of exploration of large and medium-sized gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and particularly to the technical field of a method for determining the composition contribution rates of dark mudstone and carbonaceous mudstone in oil-type gas. Background Art

[0002] In oil and gas reservoirs related to coal measure source rocks discovered in oil and gas-bearing basins, the origin of natural gas is diverse, such as coal-type gas, oil-type gas, biogas, and inorganic gas, etc., and the natural gas resources are mainly in coal measure strata. Coal measure source rocks refer to the rock layers with hydrocarbon generation ability in coal-bearing strata (or coal measures), mainly including two categories of coal and mudstone, which are rich in organic matter. The hydrocarbon generation abilities of coal measure source rocks with different lithologies in different environments vary greatly. Among them, the organic matter type of coal rock is humic type, with high organic matter abundance and relatively small overall thickness, mainly generating gas. However, with the increase of coal metamorphism degree, the organic carbon content gradually increases, but its hydrocarbon generation ability gradually decreases; mudstone mainly includes dark mudstone and carbonaceous mudstone, which are the main gas sources of oil-type gas in coal measure source rocks. The organic matter type is partial sapropelic type and can generate a certain amount of liquid hydrocarbons. Compared with carbonaceous mudstone, the organic matter type of dark mudstone is better.

[0003] In current oil and gas exploration, the research on mixed-source gas focuses on aspects such as the mixture of coal-type gas and oil-type gas, the mixture of organic origin gas and inorganic origin gas, and the mixture of natural gas generated from the same source rock at different thermal evolution stages, etc., and the contribution rates of dark mudstone and carbonaceous mudstone in oil-type gas reservoirs have not been accurately explored.

[0004] Some existing technologies have proposed a method for quantitatively calculating the age of natural gas source rocks based on the age cumulative effect of rare gas isotopes, but its calculation formula was established under the condition that the parent source rocks are all dark mudstone. However, research shows that the potassium content of the parent element of radiogenic 40 Ar in carbonaceous mudstone is much lower than that in dark mudstone, resulting in low 40 Ar formed by the normal decay of radioactive potassium in coal measure strata, and thus there will be a large error in the calculation results.

[0005] In order to solve these problems, there is an urgent need to establish a method for simply and accurately obtaining the composition contribution rates of dark mudstone and carbonaceous mudstone in oil-type gas, so as to conduct a more refined gas source comparison for oil-type gas reservoirs, and provide a more accurate basis for the evaluation of natural gas resources, the prediction of favorable gas production areas, and the guidance of exploration for large and medium-sized gas reservoirs. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and propose a method based on argon isotope calculation that can simply and accurately obtain the contribution rates of the composition contents of dark mudstone and carbonaceous mudstone in oil-type gas.

[0007] The technical solution of the present invention is as follows:

[0008] Method for determining contribution rates of dark mudstone and carbonaceous mudstone in oil-type gas, comprising:

[0009] First step: Determine whether the origin of the natural gas in the area to be measured in the oil and gas reservoir is oil-type gas, and whether the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone;

[0010] Second step: When the origin of the natural gas is oil-type gas and the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone, obtain the 40 Ar / 36 Ar ratio of the natural gas in different gas source rock formations in the oil and gas reservoir, and obtain the geological ages of different gas source rock formations based on the age accumulation effect of argon isotopes;

[0011] Third step: Compare the geological ages of different gas source rock formations with the geological age of the main gas source in the area to be measured, and use the 40 Ar / 36 Ar ratio of the gas source rock formation with the most consistent comparison result as the 40 Ar / 36 Ar end-member value of the natural gas generated by the dark mudstone in the area to be measured;

[0012] Fourth step: Obtain the contribution rates of the dark mudstone and the carbonaceous mudstone through the following calculation model:

[0013]

[0014] Wherein, ( 40 Ar / 36 Ar) gas is the 40 Ar / 36 Ar ratio actually measured in the gas reservoir; ( 40 Ar / 36 Ar) C is the 40 Ar / 36 Ar end-member value of the natural gas generated by the dark mudstone; K 1 is the percentage content of element K in the typical dark mudstone in the area to be measured; K 2 is the percentage content of element K in the typical carbonaceous mudstone in the area to be measured, x is the percentage composition of the dark mudstone in the source rock, and 1 - x is the percentage composition of the carbonaceous mudstone in the source rock; ( 40 Ar / 36 Ar) Air is the 40 Ar / 36 Ar ratio of argon in the air, which is 295.5.

[0015] According to some specific embodiments of the present invention, in the first step, the determination includes: comprehensively judging the origin of natural gas in the oil and gas reservoir by using natural gas components, stable hydrocarbon isotopes, and rare gas isotope geochemical tracer indicators, excluding the mixing of deep heterogeneous substances, determining whether the origin of natural gas in the area to be measured in the oil and gas reservoir is oil-type gas, and clarifying whether the main gas source in the area to be measured is dark mudstone and carbonaceous mudstone through investigation.

[0016] According to some specific embodiments of the present invention, the geological ages of different gas source rock formations are obtained by the following formula:

[0017] T = 530log 10 ( 40 Ar / 36 Ar) gas - 1323,

[0018] In the formula: T is the geological age of the gas source rock formation, ( 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio of the gas reservoir.

[0019] According to some specific embodiments of the present invention, the 40 Ar / 36 Ar ratio of natural gas in different gas source rock formations in the oil and gas reservoir is obtained by a rare gas isotope mass spectrometer.

[0020] According to some specific embodiments of the present invention, the geological age of the main gas source in the area to be measured is obtained through investigation.

[0021] According to some specific embodiments of the present invention, the degree of coincidence is determined by the absolute value of the difference.

[0022] The present invention can accurately obtain the contribution rates of dark mudstone and carbonaceous mudstone in oil-type gas, realize more refined gas source comparison for oil-type gas reservoirs, and provide a more accurate basis for natural gas resource evaluation, prediction of favorable gas production areas, and guidance for exploration of large and medium-sized gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a specific implementation process of the contribution rate acquisition method of the present invention.

[0024] Figure 2 For the 40 Ar / 36 Ar - 3 He / 4 He correlation diagram in the specific embodiment.

[0025] Figure 3Regarding ln(C 1 / C 2 ) - ln(C 2 / C 3 ) related diagram.

[0026] Figure 4 Regarding δ 13 C 1 - δD 1 related diagram. Specific embodiments

[0027] The present invention will be described in detail below in conjunction with embodiments. However, it should be understood that the embodiments are only used for exemplary description of the present invention and do not constitute any limitation to the protection scope of the present invention. All reasonable transformations and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0028] Referring to the attached Figure 1 , according to the technical solution of the present invention, some specific embodiments of the method for obtaining the contribution rates of dark mudstone and carbonaceous mudstone in oil-type gas include the following steps:

[0029] The first step: According to the prior art, using the Figure 2 shown 40 Ar / 36 Ar - 3 He / 4 He related diagram, the Figure 3 shown ln(C 1 / C 2 ) - ln(C 2 / C 3 ) related diagram, and the Figure 4 shown δ 13 C 1 - δD 1 related diagram, comprehensively judge the origin of natural gas in the oil and gas reservoir, exclude the mixing of deep heterogeneous substances, determine that the origin of natural gas in the area to be measured in the oil and gas reservoir is oil-type gas, and clarify through investigation that the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone.

[0030] The second step: Obtain the 40 Ar / 36 Ar ratio of natural gas in different gas source rock strata in the oil and gas reservoir through a rare gas isotope mass spectrometer. Based on the age cumulative effect of argon isotopes, use the following formula to estimate the geological age of different gas source rock strata:

[0031] T = 530log 10 ( 40 Ar / 36 Ar) gas - 1323

[0032] Where: T is the geological age of the source rock formation, Ma (million years); ( 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio of the gas reservoir.

[0033] Step 3: Compare the geological ages of different source rock formations with the geological age of the main gas source in the area to be measured, and use the 40 Ar / 36 Ar ratio of the source rock formation with the highest degree of matching as the 40 Ar / 36 Ar end-member value of the natural gas generated by the dark mudstone in the area to be measured; the degree of matching can be determined by the absolute value of the difference. Among them, the age of the main gas source in the area to be measured can be obtained through research.

[0034] Step 4: Through the K decay law, obtain the relationship of the 40 Ar content in the gas reservoir, as follows:

[0035]

[0036] Where: 40 Ar gas is the 40 Ar content in the gas reservoir; X K is the 40 K abundance in nature, which is 1.167×10 -4 ; λ K is the 40 decay constant of K decaying into 40 Ar, which is 5.54×10 -10 ; λ is the 40 total decay constant of K decaying into 40 Ar and 40 Ca, which is 5.81×10 -11 ; Ф is the porosity of the gas reservoir; K is the potassium content in the source rock; ε is the equilibrium constant; T is the source rock age, Ma; e is the natural constant.

[0037] Therefore, it can be seen that 40 Ar gas in natural gas is in a proportional linear relationship with the content of mineral K in the rock. Thus, the 40 Ar / 36 Ar values of natural gas formed by source rocks with different K contents in the same era have the following relationship:

[0038]

[0039] Where: a is the content of K in source rock A, %; b is the content of K in source rock B, %;( 40 Ar / 36 Ar) A is the 40 Ar / 36 Ar ratio of the natural gas generated by source rock A;( 40 Ar / 36 Ar) B is the 40 Ar / 36 Ar ratio of the natural gas generated by source rock B;( 40 Ar / 36 Ar) Air is the 40 Ar / 36 Ar ratio of air argon, which is 295.5.

[0040] Furthermore, the contribution rates of dark mudstone and carbonaceous mudstone are calculated using the following formula:

[0041]

[0042] Where:( 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio of natural gas;( 40 Ar / 36 Ar) C is the 40 Ar / 36 Ar end-member value of the natural gas generated by dark mudstone in the study area; K 1 is the content of K in the typical dark mudstone in the area to be measured, %, obtained by γ spectrometry; K 2 is the content of K in the typical carbonaceous mudstone in the area to be measured, %, obtained by γ spectrometry; x is the proportion of dark mudstone in the source rock, %.

[0043] Example 1

[0044] The present invention is applied to the Feixianguan Formation gas reservoir in a certain area to calculate the proportion of the contents of dark mudstone and carbonaceous mudstone components in its oil-type gas, as follows:

[0045] The 40 Ar / 36 Ar value of the natural gas in the Feixianguan Formation is measured by a noble gas isotope mass spectrometer and is distributed between 490 and 926 (Table 1). The following formula is used to calculate the age of the gas source rock:

[0046] T = 530log 10 ( 40 Ar / 36 Ar)gas -1323

[0047] Where: T is the geological age of the source rock formation, Ma; ( 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio of the gas reservoir.

[0048] The calculated age of the source rock is distributed between 104.77 and 251.59 Ma. Through investigation, it is known that the main gas source of the Feixianguan Formation gas is the Longtan Formation source rock, and its geological age is between 240 and 256 Ma. Therefore, the 40 Ar / 36 Ar ratio of Well Cheng 16 is used as the 40 Ar / 36 Ar end-member value of the natural gas generated by the dark mudstone in the area to be measured.

[0049] Then use the following formula to calculate the contribution rate of the dark mudstone and carbonaceous mudstone in the Feixianguan Formation of a certain area:

[0050]

[0051] Where: 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio of the natural gas; ( 40 Ar / 36 Ar) C is the 40 Ar / 36 Ar end-member value of the natural gas generated by the dark mudstone in the study area; K 1 is the content of K in the typical dark mudstone in the area to be measured, %, obtained by γ spectrometry; K 2 is the content of K in the typical carbonaceous mudstone in the area to be measured, %, obtained by γ spectrometry; x is the proportion of dark mudstone in the source rock, %.

[0052] The rare gas isotope data of the Feixianguan Formation natural gas in a certain area and the proportion of dark mudstone and carbonaceous mudstone can be obtained as shown in the following table:

[0053] Table 1 Rare gas isotope data of Feixianguan Formation natural gas in a certain area and the proportion of dark mudstone and carbonaceous mudstone

[0054]

[0055]

[0056] According to the calculation results, it can be seen that the proportion of dark mudstone in the natural gas source of the Feixianguan Formation in a certain area ranges from 25% to 100%, with an average of 66.2%; the proportion of carbonaceous mudstone ranges from 0 to 75%, with an average of 33.8%. This reflects that the natural gas source in this area is mainly contributed by dark mudstone, which is consistent with the lithologic distribution characteristics of the hydrocarbon source rocks in the Longtan Formation obtained from the investigation. In addition, Well A6 is located in the southern part of this area, and the contribution of carbonaceous mudstone to its gas source is relatively large, while Wells B16, C5-1, D8, and E5 are all located in the northern and central parts of this area, and the contribution of dark mudstone to their gas sources is relatively large. This distribution law is consistent with the sedimentary environment of the Longtan Formation hydrocarbon source rocks in this area gradually transitioning from continental facies to marine facies from south to north, thus proving the accuracy and reliability of the present invention.

[0057] The above embodiments are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. Method for determining the composition contribution rate of dark mudstone and carbonaceous mudstone in oil-type gas, Characterized in that, It includes: The first step: Determine whether the origin of the natural gas in the area to be measured in the oil and gas reservoir is oil-type gas, and whether the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone; Step 2: When the natural gas is oil-type gas and the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone, obtain the natural gas from different gas source rock formations in the oil and gas reservoir. 40 Ar / 36 Ar ratio, based on the age accumulation effect of argon isotopes, the geological age of different gas source rock formations is obtained; Step 3: Compare the geological ages of different source rock formations with the geological age of the main gas source in the area to be measured, and use the 40 Ar / 36 Ar ratio of the source rock formation with the highest degree of matching in the comparison results as the 40 Ar / 36 Ar end-member value for the natural gas generated by the dark mudstone in the area to be measured; The fourth step: Obtain the composition contribution rate of dark mudstone and carbonaceous mudstone through the following calculation model: Among them, ( 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio in the gas reservoir; ( 40 Ar / 36 Ar) C is the end-member value of 40 Ar / 36 Ar for the natural gas generated by the said dark mudstone; K 1 is the percentage content of K element in the typical dark mudstone in the area to be measured; K 2 is the percentage content of K element in the typical carbonaceous mudstone in the area to be measured, x is the percentage composition of dark mudstone in the source rock, and 1 - x is the percentage composition of carbonaceous mudstone in the source rock; ( 40 Ar / 36 Ar) Air is the 40 Ar / 36 Ar ratio of argon in the air, which is 295.5; Among them, the geological age of the different gas source rock strata is obtained through the following formula: T = 530 log 10 ( 40 Ar / 36 Ar) gas - 1323, where: T is the geological age of the source rock formation, ( 40 Ar / 36 Ar) gas is the measured 40 Ar / 36 Ar ratio of the gas reservoir; The geological age of the main gas source in the area to be measured is obtained through investigation.

2. The method for determining the composition contribution rate of dark mudstone and carbonaceous mudstone in oil-type gas according to claim 1, Characterized in that, In the first step, the determination includes: comprehensively judging the origin of the natural gas in the oil and gas reservoir by using natural gas components, stable carbon and hydrogen isotopes, and rare gas isotope geochemical tracer indicators, excluding the mixing of deep heterogeneous substances, determining whether the origin of the natural gas in the area to be measured in the oil and gas reservoir is oil-type gas, and clarifying whether the main gas sources in the area to be measured are dark mudstone and carbonaceous mudstone through investigation.

3. The method for determining the composition contribution rate of dark mudstone and carbonaceous mudstone in oil-type gas according to claim 1, Characterized in that, The 40 Ar / 36 Ar ratio of the natural gas in different source rock formations in the oil and gas reservoir is obtained by a noble gas isotope mass spectrometer.

4. The method for determining the composition contribution rate of dark mudstone and carbonaceous mudstone in oil-type gas according to claim 1, Characterized in that, The degree of coincidence is determined by the absolute value of the difference.

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