Geological conditions, reservoir evolution and favorable exploration directions of marine ultra-deep oil and gas in China

Li, Jianzhong; Tao, Xiaowan; Bai, Baojun; Huang, Shipeng; Jiang, Qingchun; Zhao, Zhenyu; Chen, Yanyan; Ma, Debo; Zhang, Liping; Li, Ningxi; Wei, Song

doi:10.1016/s1876-3804(21)60005-8

“…Sichuan Basin is currently a primary target area for shale gas exploration in China, with the lower Paleozoic Silurian Longmaxi Formation marine shale as the principal target strata. − The Longmaxi Formation in southeastern Sichuan Basin, China, possesses such natural advantages for shale gas development as wide distribution area, great effective thickness, and moderate burial depth. , Unlike conventional gas reservoirs, shale gas has the characteristics of “in situ accumulation”. Typically, shale gas is distributed in nanoscale pores and adsorbed on the surfaces of organic matter and mineral particles using “free state”, “adsorbed state”, and “dissolved state”. − Among them, contents of free gas and adsorbed gas are dominant, which are major types of shale gas exploitation at this stage. , Regardless of the form of shale gas, organic matter and inorganic minerals are hosting carriers of gas, which directly controls the development of reservoir spaces and the gas content of shale. , The mineral composition of shale is complicated, typically composed of quartz, clay minerals, feldspar, and calcite with a certain amount of pyrite. Nevertheless, marked differences can be found in pore types developed by various minerals and their contributions to porosity.…”

Section: Introductionmentioning

confidence: 99%

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

He

¹

,

Li

²

,

Qin

³

et al. 2021

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Influences of the characteristics of organic matters and mineral compositions on the development of shale microscopic pores were discussed through performing low-temperature nitrogen adsorption, whole-rock "X" diffraction, and field emission scanning electron microscope on black organic-rich shale samples of Longmaxi Formation in the Dingshan area, southeastern Sichuan Basin, in combination with the characteristics of shale organic matters. The shale in the Dingshan area has complex mineral composition, which is mainly quartz and clay minerals. Both contents range from 23% to 72% and 36% to 70%, respectively. The vertical variation is obvious, and there are few feldspar and carbonate rocks; the pyrite content is more than 2%. The bottom shale has high brittleness and gradually decreases in the vertical direction. The brittleness index is between 0.481 and 0.627 and is concentrated above 0.5. It shows strong compressibility and is easy to form a complex network system in hydraulic fracturing. Quartz and feldspar mainly provide secondary dissolved pores, intercrystalline mineral pores, and nanoedge gaps in contact with organic matter. They have no obvious correlation with the specific surface area of shale but have a weak correlation with pore volume. They mainly control the development of macropores. Organic matter develops many hydrocarbon-generating pores, which strongly correlate with the specific surface area and a weak correlation with pore volume. It mainly controls the development of micromesopores. Clay minerals mainly provide a large number of interlaminar pores and interlayer fractures in the clay. The intergranular pores of clay and clay have a weak correlation with pore volume and specific surfaces. They contribute to the development of shale micropores, mesopores, and macropores. Pyrite mainly provides intercrystalline pores and mold pores. By restricting the interaction with organic matter, the development of shale pores is promoted within a certain content range. When the content exceeds this range, the development of micropores is inhibited. The conversion threshold in the Dingshan area is 5.0%.

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“…The quality of a source rock is often determined by the exploration and development of petroliferous basin. With the progress of exploration technology and the growing demand for energy, it is difficult to meet the actual needs of social development with shallow oil and gas resources, so it is necessary to shift the focus of oil and gas exploration to deep, ultra deep, and unconventional oil and gas fields. − …”

Section: Introductionmentioning

confidence: 99%

Geochemistry and Organic Petrology of Middle Permian Source Rocks in Taibei Sag, Turpan-Hami Basin, China: Implication for Organic Matter Enrichment

Miao

¹

,

Wang

²

,

Zhao

³

et al. 2021

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The Taodonggou group of Middle Permian is an important source rock in Taibei sag of Turpan-Hami basin. Due to its deep burial, drilling has only been revealed in recent years. Based on organic petrology and organic geochemistry experiments, this paper studies the organic petrology, organic geochemistry, sedimentary environment, and hydrocarbon generation potential of source rocks in Taibei sag, Turpan-Hami basin, and reveals the influence of the sedimentary environment on the organic matter abundance of source rocks. The results are as follows: (1) The organic matter of the Middle Permian source rocks in Taibei sag of Turpan-Hami basin is mainly sapropelite and exinite. The vitrinite is mainly vitrodetrinite, and the exinite is mainly lamalginiite. (2) The total organic carbon content value is 0.55–6.08 wt %, and the average value is 2.58 wt %. The PG value ranges from 0.78 mg HC/g to 30.86 mg HC/g, and the average value is 4.88 mg HC/g. Chloroform asphalt “A” is 0.046–0.8767 wt %, and the average value is 0.285 wt %. The types of organic matter are mainly III and II–III, and the R o value is 0.628–1.49 wt % (average = 0.988 wt %). The T max distribution is 329–465 °C. The average temperature is 434.7 °C, which is in the mature stage (oil window stage). The Middle Permian source rocks are mainly very good to excellent source rocks with a good hydrocarbon generation potential. (3) The source rocks are deposited in a semihumid and semiarid climate. Organic matter is input as a mixed source. The early and late stages is dominated by terrestrial higher plants. The middle stage is dominated by lower aquatic organisms, and the sedimentary environment consists of weak reduction and weak oxidation environments. (4) In the study area, the abundance of organic matter has a weak negative correlation with CPI and a positive correlation with Pr/Ph and ∑C21–/∑C22+. Under the coaction of paleoclimate, organic matter input, and redox environment, the enrichment model of organic matter with high productivity and weak oxidation environment characteristics can also form excellent source rocks. This study is of great significance and provides theoretical guidance for the exploration of deep oil and gas resources.

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“…The chemical composition and isotope of the formation water can provide insights into the geological environment and the water-rock reaction in reservoirs and is even of predictive value for the formulation of effective water avoidance measures in the course of the development of unconventional reservoirs [12][13][14]. As theory and technology advance, the exploration and development of oil and gas are developing rapidly towards deep and ultradeep [15,16]. Tarim Basin is the largest oil-bearing basin in China, and the oil and natural gas resources buried over 6000 m account for about 83% and 64% of the total hydrocarbon resources, respectively; however, the discovery rate of ultradeep oil and gas is extremely low [17].…”

Section: Introductionmentioning

confidence: 99%

Geochemistry of Formation Water and Implications for Ultradeep Tight Sandstone of DK Gas Field in Kuqa Depression

Guo

¹

,

Zhao

²

,

Han

³

et al. 2022

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Formation water is produced during gas well production, which can seriously affect gas well productivity, especially in deep and ultradeep tight sandstone gas reservoirs. In this paper, we have studied the formation water production and geochemical properties of the ultradeep tight sandstone gas reservoir in the Cretaceous Bashijiqike Formation of the DK gas field in the Kuqa Depression. The results indicate that the formation water can be classified as condensate water, gas-water transition zone water, mixed water, and isolated formation water, all of which are acidic and of CaCl2 type, with increasing salinity or chloride ion content. Sodium/chloride ratio (ρNa+/ρCl-), metamorphic coefficient (ρ(Cl--Na+)/ρ(Mg2+)), desulfurization coefficient ( 100 × ρ S O 4 2 − / ρ C l − ), and trace elements concentration parameters show that the formation water was formed in a closed and reductive environment and experienced strong water-rock interaction. The formation water may have been influenced by early seawater, but it is not significant and is more likely to have been influenced by water seepage from the overlying gypsum strata. The Sr, H, and O isotopes reveal that the different types of formation water have good homology and are not affected by atmospheric precipitation, which is propitious to the preservation of natural gas.

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Geological conditions, reservoir evolution and favorable exploration directions of marine ultra-deep oil and gas in China

Cited by 67 publications

References 14 publications

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Geochemistry and Organic Petrology of Middle Permian Source Rocks in Taibei Sag, Turpan-Hami Basin, China: Implication for Organic Matter Enrichment

Geochemistry of Formation Water and Implications for Ultradeep Tight Sandstone of DK Gas Field in Kuqa Depression

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