Selected Papers on Coal Petrology and Coal Geochemistry in Ren Deyi
Organic phase is a comprehensive embodiment of biological organic matter types and accumulation environment. The concept of organic phase originated from coal phase, but now it is independent and covers coal phase, that is, coal phase can be regarded as a special type of organic phase.
In recent years, with the development of coal-formed gas research in China, especially after Dai Jinxing (199 1) [1] put forward the concepts of natural gas accumulation zone, zone and zone and made a systematic study, it became more and more important to study the internal causality of the temporal and spatial distribution of natural gas accumulation zone, gas-generating zone and organic zone. Obviously, the key points of this study are: firstly, correctly identify and divide the organic phase of coal measures in the study area; Secondly, the representative samples of these organic phases and their source rocks are studied in gas generation performance and experiment, and the gas generation capacity of each organic phase zone is evaluated one by one, so as to divide the organic phase zones which are beneficial to maximum gas generation and provide scientific basis for finding new gas fields.
1. Division and characteristics of organic phase of coal measures in the study area.
1. Reflections on the division of organic phases in this study
(1) In great basin, Xinjiang (such as J2q of Qiketai Formation in Turpan-Hami Basin), it is sometimes difficult to strictly distinguish coal measures from non-coal measures. Therefore, considering the hydrocarbon generation performance of natural gas, we try to establish a * * * fractionation standard suitable for coal-bearing and non-coal-bearing organic phases.
(2) Give priority to the gas generation and hydrocarbon generation performance of organic phase, and give full consideration to its organic and sedimentary properties. The same organic phase has similar sedimentary environment, but it can have different sedimentary sub-environment. Dai Shifeng et al. (1998) pointed out that the maceral of different coal seams formed in the same sedimentary environment changed with the change of coal-accumulating environment when studying the relationship between maceral and sedimentary environment in Wuda mining area, Inner Mongolia [2].
(3) The main indexes for evaluating organic phase should be intuitive, convenient and operable, which are not only applicable in theory, but also convenient for quick judgment in production site. On the premise of low maturity of source rocks, the fluorescent organic component index is tried to be one of the main indexes.
(4) Coal phase is a special phase in organic phase. In the division, in addition to the fluorescence organic component index, other coal and rock parameters, such as flow index IM, tissue preservation index ITP, gelation index IG, etc. , should be used comprehensively.
Organic facies (coal-bearing facies) are divided into four mudstone sedimentary organic facies and four coal facies. See Table 1 for details.
2. Overview of characteristics of various organic phases
(1) Dry forest peat swamp facies: the content of inertinite in organic macerals is relatively high, reaching 70%, generally 50% ~ 60%, while the content of homovitrinite and structural vitrinite is relatively low, and the matrix vitrinite is mostly around 30%; Generally, chitin groups are less than or equal to 3%. The organic phase is mainly produced in the lower J2x coal seam of Xishanyao Formation in the southern margin of Junggar Basin, and the fluorescence organic component is less than 35%, the lowest is only 1 1.0%, and generally varies between 20% and 34%. The representative sample is b 1+2- 10.
(2) Peat swamp facies in periodically arid forest: matrix vitrinite and inertinite both account for a considerable amount, and matrix vitrinite is more than; Inertite formation Matrix vitrinite is 42% ~ 565438 0%; The inertinite group is mostly 30% ~ 40%. Homogeneous vitrinite and structural vitrinite account for 5% ~ 17%, which is slightly higher than peat swamp briquette with soil and water conservation forest. The crust is less than 4%, which is actually a transitional organic phase between peat swamp facies coal and dry forest peat swamp facies, but its microstructure is closer to peat swamp facies. The representative sample is B 1+2-9.
(3) Peat swamp facies of flooded forest: matrix vitrinite is dominant, generally above 55%, up to about 80%; The ratio of structural vitrinite to homogeneous vitrinite is small; Chitin content is not high, generally less than 10%, mostly around 5%; Inertite accounts for a considerable proportion, mostly between 12%-39%. The forest swamp facies coal covered by water in the lower J2x coal seam of Liudaowan coal mine in the southern margin of Junggar Basin can be taken as its representative, and a large number of matrix vitrinites in the coal indicate that water is deeply covered. At the same time, the matrix vitrinite often contains sporophyte, inertinite, clastic semivitrinite and clay minerals, showing a clastic structure, indicating that there is often running water in the peat swamp covered with water, so the flow index of this organic phase is relatively large. The content of peat swamp inertinite in J2x flooded forest in Taibei sag of Turpan-Hami basin is also high. The minerals are mainly disseminated clay, and timely and rutile can be seen. The representative sample is B 1+2-4.
(4) Peat swamp facies of heavily flooded forest: vitrinite content is high, accounting for more than 80% ~ 90%, mainly composed of homogeneous vitrinite and strongly expanded structural vitrinite, which can reach about 60%. Matrix vitrinite is generally between 20% and 40%. There are very few inerts, almost all of which are less than 1%, and the V/I ratio is greater than 7, most of which are greater than 100. However, the relative content of crustaceans is relatively high, ranging from 3% to 9%, with thin-walled horniness being the most. The total amount of inorganic elements is low. The mineral features are siderite nodules and pyrite berries formed by early diagenesis, and the crystals are developed, which can form strips and lenses several millimeters wide. Coal-forming plants are mainly ferns and gymnosperms, such as tree ferns and equisetum, and ginkgo biloba has more leaves. The swamp is flooded repeatedly, the medium is weakly reduced ~ reduced, and the water flow is calm. This organic phase is the main body of B26 coal seam in the upper part of J2x in the southern margin of Junggar Basin. The representative sample is B26-6.
(5) The organic phase of mudstone with poor fluorescent organic matter is 1: the content of fluorescent organic components is mostly less than 0.5%, and the fluorescent organic components/non-fluorescent organic components are mostly less than 0.5, which is sometimes not counted. Fluorescent organic components are mainly small keratin or shell debris. Non-fluorescent organic components are still mainly vitrinite and filamentous, and the content is also very small, generally above 1%, rarely exceeding 2%. The sedimentary environment during the formation is strong oxidation or weak oxidation-weak reduction. For example, all kinds of mudstone deposited between the branch of delta plain on water and the flood plain behind the braided river bank can be classified as this organic phase. From the microstructure point of view, the content of recycled components and inert components in vitrinite is high. The representative samples are z1-1,z 1- 19.
(6) Mudstone organic phase 2 with poor fluorescence organic matter: its formation environment is relatively humid. For example, the sedimentary environment with a certain degree of water coverage is represented by distributary channel deposits in delta underwater plain, fan delta front, braided delta front underwater distributary channel microfacies and gangue, floor, roof and false roof in coal. Although there is little difference between the maceral and the organic phase 1 deposited in the mudstone with poor fluorescence organic matter, the organic geochemical parameters are obviously different. The representative samples are Lan2- 14 and SH-8.
Table 1 Partial sedimentary organic phases of coal classification and gas generation performance evaluation
sequential
Note: the values in brackets in lM index are average values; The amount of gas observed refers to R. 0. The gas production in most areas of the working area is 69%, and the total gas production refers to R. > 0.700/0 ~ 3.260/0. Therefore, in the evaluation of gas activity, the gas production of A refers to R. < 0.70%, which approximately represents the gas production evaluation of the working area in the low maturity stage; B stands for R. 0.700/0~3.260/0, which represents the evaluation of the high mature or over-mature vitality of the workspace; D 1 1 means
(7) Moderately fluorescent organic mudstone sedimentary organic facies: This kind of organic facies is also formed in a relatively humid and reductive sedimentary environment, such as closed-flow swamp environment represented by mudstone in coal seam floor, underwater delta plain facies, braided delta plain swamp facies, delta plain intertidal swamp, braided river flood plain, shallow lake, etc. The content of fluorescent organic components is 2% ~ 8%, and the content of fluorescent organic components in some samples is less than 1, with 1
(8) Organic phases deposited by mudstone rich in fluorescent organic matter: Most of these organic phases were formed in the reducing environment covered by deep water, and the index of fluorescent organic components was greater than 8, and their contents were all greater than 8%. In the crust construction, besides a large number of sporophytes and cuticles, a considerable number of structural algae and their degradation products-mineral asphalt matrix B can be found. The combination forms are as follows: ① Pyracantha+horniness+mineral asphalt matrix: mainly found in carbonaceous mudstone containing gangue in J2x coal seam of well Xishi 2 130 in the abdomen of Junggar Basin. Coal-forming plants include algae, tree ferns, ginkgo biloba and cycads, and ostracods are also involved, which may belong to the lake environment. ② Algae+mineral asphalt matrix B+ mycelium, mainly found in J2q semi-deep lake mudstone in Turpan-Hami basin; (3) Keratin+mineral asphalt matrix B, which is mainly located in the delta underwater plain mudstone of well J2t of Pencan 2 in the abdomen of Junggar Basin. The lithology can be carbonaceous mudstone and lacustrine mudstone, and the representative sample is SH-6.
2. Evaluation of all kinds of organic phase gases in the study area.
1.Py-GC activity experiment
The purpose of this experiment is twofold: first, to understand the gas-oil ratio of source rocks with different organic matter types and abundance in different evolution stages, and to focus on their gas-producing ability and gas-producing ability; The second is to study the gas-oil ratio and gas-generating capacity of different organic phases in different evolution stages. The experimental conditions are as follows: he as carrier gas, flow rate of 50mL/min, 50m capillary column, silica gel stationary liquid; The pyrolysis program was heated to 20℃/min, and the pyrolysis products were collected with liquid ammonia and identified by FID. The heating rate of the column is 65438 00℃/min. All the samples except coal were made into kerogen. Five temperature zones were designed in the experiment, and the results are shown in Table 2.
2. Composition and main parameters of PY-GC products
Py-GC products are mainly divided into four parts: normal alkanes, normal olefins, aromatic hydrocarbons and isoprenoid hydrocarbons. In normal alkane olefins, C 1 ~ 5 is gaseous hydrocarbon, C6 ~ 14 is light liquid hydrocarbon, and C+ 15 is heavy liquid hydrocarbon. Only benzene, toluene, xylene and naphthalene can be detected in aromatic hydrocarbons. Isoprene-like hydrocarbons have been detected as palmitane, phytane, palmitene and so on. The main parameters are:
(1) C 1 ~ 5/C+6: represents the gas-oil ratio in different temperature ranges.
(2) NC6 ~ 14/NC+ 15: It reflects the relative proportion of short-chain light hydrocarbons and long-chain heavy hydrocarbons. The yield of short-chain light hydrocarbons in humic ⅲ organic matter is high.
In addition, according to the research needs, four other important parameters are put forward:
(1) gas effective carbon Cg and oil effective carbon Co: obtained by multiplying the total gas production and total oil production in each temperature range by 0.083 respectively, representing the effective carbon for generating gaseous hydrocarbons and liquid hydrocarbons in organic carbon. Cg/Co is similar to the total oil-gas ratio. In the low mature stage, the gas effective carbon Cg 1 and oil effective carbon Co 1 below 350℃ roughly characterize the hydrocarbon generation capacity (Ro≤0.70%).
(2) Cg/TOC and Co/TOC, namely "gas carbon degradation rate D 1" and "oil carbon degradation rate D2", are used to characterize the effective carbon percentage of organic carbon that can generate gas and oil.
Table 2 and Statistical Results of py-GC Experiment of Mudstone Kerogen Coal
Table 3 Evaluation system of gas source rock types in the study area (low mature stage)
Table 4 Evaluation system of gas source rock types in the study area (mature-over-mature stage)
3. Establishment of gas source rock evaluation system and gas generation evaluation.
Because most of the source rocks in the study area are in a low mature state, they are discussed in two stages: ① The temperature is.
The research results are listed in Table 3 and Table 4. According to the gas generating performance data of various organic representative source rock samples listed in Table 3 and Table 4, in terms of gas generating capacity, in the low maturity stage, the gas generating capacity is from strong to weak, in turn, ω(Cg)/ω(TOC), moderately fluorescent organic mudstone sedimentary organic phase, strongly flooded forest peat swamp organic phase, weakly fluorescent organic mudstone sedimentary organic phase is 1 2, and forest peat swamp is periodically dried. Organic phase, dry forest peat swamp phase and water-covered forest peat swamp phase are deposited in mudstone rich in fluorescent organic matter, which is consistent with the conclusion reached by Dai Shifeng et al. (2000) in studying hydrocarbon generation potential of gas source rocks with TOF-SIMS [3]; However, in the mature-high mature stage, the gas generating capacity is from strong to weak, that is, strongly flooded forest peat swamp facies, periodically dried forest peat swamp facies, organic mudstone sedimentary facies rich in fluorescent organic matter, moderately fluorescent organic mudstone sedimentary facies, flooded forest peat swamp facies, dry forest peat swamp facies, organic mudstone sedimentary facies poor in fluorescent organic matter 2, organic mudstone sedimentary facies poor in fluorescent organic matter 1. Table 1 lists the comparison of its gas generation performance with other geochemical properties.
Three. conclusion
According to the distribution of known coal-formed gas fields in Turpan-Hami basin, Shengbei gas field is located in the gas center of Taisan 2 well in Turpan-Hami basin. Hongtai gas field is located near Shanle-Xiaocaohu natural gas center; Qiu Dong Gas Field is located between Well Shen Tai 2 and Xiaocaohu Natural Gas Center. The maximum gas-generating centers of J 1b and J2x in Junggar Basin appear in Hutubi area, Jurassic coal-bearing organic facies belt in Tuha and Junggar Basin, and the gas-generating belt is closely related to the gas-accumulating belt. If the gas reservoir structure is not destroyed by the later crustal movement, the favorable gas-generating facies belt and favorable gas-accumulating belt should overlap or overlap.
Take the exam and contribute.
Dai Jinxing. Division of natural gas accumulation zone and accumulation area and its significance in natural gas exploration. Petroleum exploration and development, 199 1,18 (6):1~10.
Dai Shifeng, Ren Deyi, Peng Suping, et al. Study on the relationship between microscopic characteristics of coal and sedimentary environment in Wuda mining area, Inner Mongolia. Acta sedimentosa, 1998,16 (3):141~146.
Dai Shufeng, Ren Dayong, Jianyong Yang, et al. Study on hydrocarbon generation potential of mineral asphalt matrix. Journal of Geology, 2000,74 (1): 84 ~ 92
Organic facies and gas generation potential of Jurassic coal measures in Turpan-Hami and Junggar basins
Ye 1, Ren Deyi 2, Dai Shifeng 2,
Zhang Wei-Biao, Guo Mu-Dong 1, Li Xiao-Chi 1
(1. Xi 'an Institute of Science and Technology, Xi 'an, Shanxi 710054;
2.CUMT Department of Resource Development Engineering, Beijing 100083)
Abstract: The organic facies of Jurassic coal measures in Tuha basin and Junggar basin are divided in detail. Mudstone organic facies and coal facies can be divided into four types. According to the Py-GC experiment of gas-generating potential of samples, some important indexes reflecting the gas-generating potential of source rocks, such as Co 1, Co2, Cg 1, Cg2, D1and D22w, are put forward. According to the fluorescence maceral index (FMI), clay source rocks and coal source rocks are divided into three types, and the organic petrology-organic geochemistry evaluation system of gas source rocks is improved. According to the evaluation of the gas-generating potential of each organic phase, the current and future favorable gas-generating zones are divided. The results show that there is a corresponding relationship between favorable gas generating zones and natural gas accumulation zones.
Keywords: organic phase; Py-GC experiment; Gas source rock; Gas generation zone; Gas accumulation zone
(This article was co-authored by Yang Jianye, Dai Shifeng, Zhang Weibiao, Mou and Li Xiaochi, originally published in Journal of China University of Mining and Technology, Vol. 30,No. 1, 200 1).