1. Influence of deep fluid on temperature field and pressure field in basin
Temperature and pressure field is one of the basic characteristics of the basin, which has an important influence on the generation, migration and accumulation of oil and gas. Temperature is the dominant factor in the formation of oil and gas, and oil and gas often gather in the high geothermal gradient area or high pressure zone of the basin.
Under normal circumstances, the ground temperature of the basin gradually increases at a speed of about 2.5 ~ 3.5℃/ 100 m in the longitudinal direction, with little change in the plane. This ground temperature is a steady ground temperature structure. For example, the regression equation between paleogeothermal Tmax and buried depth in Jiyang Depression is:
h = 300 19ln(Tmax)- 179625
The regression equation of Ro-H relationship in Zhanhua sag (correlation coefficient is 0.82) is:
h = 2377.33 ln(Ro)+4442. 1 1
The paleogeothermal temperature (or maturity of gas source rocks) in Jiyang Depression and Zhanhua Depression increases slowly with the increase of buried depth. However, these equations ignore the influence of magma and deep fluid on paleogeothermal. In recent years, it has been found that some areas of Jiyang Depression (such as Yangxin, Gaoqing, Pan Lin, Luojia, Binnan, Xichun and Gubei) have relatively developed magma or deep fluid, which makes the temperature and pressure fields in these areas or some well sections appear high anomalies. On the one hand, the deep fluid inherits the high temperature and high pressure from the deep, and the high temperature of the deep fluid further makes the formation generate hydrothermal pressurization and hydrocarbon generation pressurization. Therefore, the geothermal gradient and pressure gradient of deep fluid will be greatly improved. For example, the geothermal profile of some wells in YA 13- 1 gas field can be clearly divided into three sections: the upper and lower sections are normal geothermal gradient (basin background geothermal gradient, heat conduction plays a major role), and the middle section is high geothermal gradient, low geothermal gradient or even negative geothermal gradient, which is obviously lower than the normal geothermal gradient [15].
The pore fluid pressure of the single well corresponding to the above-mentioned middle section often shows abnormal high pressure, while the upper and lower parts are mostly normal pressure or the pressure coefficient is small. On the two-dimensional profile of temperature and pressure, along the active range of hot fluid, there are usually high uniform formation temperature and unusually high fluid pressure intervals. This is because the deep fluid moves along the transportation system, bringing the deep high-temperature and high-pressure fluid to the shallow layer, which not only greatly changes the temperature distribution, but also changes the ground pressure field. For example, the depth of overpressure interface in the central diapir zone of Yinggehai Basin is directly affected by thermal fluid diapir, that is, the stronger the thermal fluid diapir activity, the more strata it breaks through and the shallower the buried depth of abnormal overpressure top interface. For example, at the fluid diapir of LD 14- 1, the chaotic reflection caused by diapir activity is only 500m away from the seabed, and the high pressure top interface drilled by LD14-1is shallow (1480m).
2. Influence of deep fluid on reservoir diagenesis and porosity.
It is found that some components in the deep fluid will complicate the diagenesis of rocks in the stratum, which may lead to the development of multi-stage diagenetic products at the same depth. This is because the fluid superimposed the transverse or longitudinal thermal convection temperature field on the original heat conduction temperature field, and the shallow montmorillonite entered the dehydration zone ahead of time, and the R 1 zone of I/S mixed layer did not develop or narrow, such as the evolution of clay minerals of I/ montmorillonite mixed layer in Ying-Qiong Basin. At the same time, the shallow potential hydrocarbon rocks are baked by the heating fluid, and enter the oil generation window in advance to generate low mature oil. In addition, hot fluid enters the reservoir, which makes a large number of feldspar skeleton particles, CaCO3 foraminiferal shells and some carbonate cements dissolve and precipitate, forming a large number of "hydrothermal" secondary dissolution pores; If the hot fluid is rich in Al2O3 and SiO2, feldspar and timely secondary growth will occur. Generally, dissolution occurs at the place where hot fluid just enters the reservoir, and precipitation occurs at the top boundary of thermal convection or the upper part of the reservoir because of the temperature drop. With the continuous loss of heat of hot fluid, the whole reservoir may be precipitated. However, the secondary expansion is not unfavorable to reservoir physical properties, and the key is the compaction degree of reservoir sandstone particles when expansion occurs; The volume percentage of secondary enlarged edge is in the range of 0 ~ 6%, which is beneficial to the preservation of primary pores [19,20]. In addition, a large number of acidic solutions rich in carbon dioxide and hydrogen sulfide enter the reservoir, which can make some feldspar undergo underground weathering and form a large number of worm-like and sheet-like kaolinite; At the same time, the early chlorite was partially dissolved, and its content decreased or disappeared; The high temperature carbon dioxide and aluminosilicate undergo hydrothermal metamorphism to form flaky dawsonite minerals. In the deep burial stage, high-temperature hot fluid enters the reservoir, and hydrocarbons dissociate and accumulate, which can form a large number of strawberry pyrite, a small amount of flaky dawsonite and authigenic single crystals. In a word, the upwelling of high-temperature hot fluid can make shallow reservoirs enter the late diagenetic stage; Multi-stage thermal fluid activity makes a large number of feldspar skeleton particles, CaCO3 foraminous worm shells, some carbonate cements and aluminosilicate minerals dissolve, alter, precipitate and transform reservoir pores, forming a large number of primary+secondary mixed pores, which greatly improves reservoir properties.
It is also found that the deep fluid makes the shallow montmorillonite in Fangwang area enter the dehydration zone ahead of time, so that the R 1 zone of I/S mixed layer is missing and the corresponding secondary minerals are formed. For example, the secondary expansion edge of strong strain occurs at the buried depth1500m in Fangwang area (the shallowest depth in Dongying sag), which is 600m shallower than the shallowest depth of some wells in Shengtuo Oilfield. At the same time, the deep fluid also makes the shallow source rocks enter the mature window. Secondly, the upper reservoir of the fourth member of Shahejie Formation-reef limestone and part of carbonate cement dissolved, forming a large number of secondary dissolved pores, with porosity as high as 35% ~ 42%. According to the analysis, the content of organic acids in formation water in this area is low, so the solvents that cause reservoir dissolution are mainly H2S, SO2 and CO2 in deep fluid. A large number of acidic solutions rich in carbon dioxide enter the reservoir, which makes some feldspar change or dissolve, forming a large number of worm-like and page-like kaolinite. In addition, the shallow gas in Dongxin, Caoqiao and Yangjiaogou oilfields in Dongying Depression is a mixture of bio-thermal causes, and the shallow diagenetic minerals are abnormal, but the influence degree is less than that in Fangwang Oilfield [15].
3. Influence of deep fluid on oil and gas generation
Because the deep fluid carries a lot of heat energy, when it invades the stratum, it will inevitably increase the temperature flowing through the stratum, obviously change the geothermal structure, make the normal temperature field of the basin overlap the thermal convection temperature field, and form a local high temperature anomaly, thus promoting the thermal evolution of organic matter and hydrocarbon generation. For example, in Ying-Qiong basin, the threshold depth of hydrocarbon generation of organic matter in the zone without deep fluid influence is 3000 ~ 3 100 m, while that in the zone with deep fluid activity is only 2500 ~ 2700 m, that is, the threshold of hydrocarbon generation is reduced by 400 ~ 500 m by deep fluid. ..
Through geochemical analysis and dynamic simulation, it is found that the deep fluid obviously increases the ground temperature near T40 unconformity surface in Ying-Qiong basin, and the thermal evolution degree of organic matter is obviously enhanced, resulting in that the maturity of organic matter in the strata above the unconformity surface is obviously higher than that in the strata below it, that is, the maturity of organic matter near the unconformity surface is obviously inverted. The vitrinite reflectance (Ro) curve (semi-logarithmic coordinates) and pyrolysis peak temperature (Tmax) curve of a single well show a distorted "Z" shape. In a word, the deep fluid makes the source rocks that can't be matured under the single conduction background enter the hydrocarbon generation threshold ahead of time, which increases the horizon and volume of mature source rocks; In addition, its overpressure inhibition makes the lower limit of oil and gas cracking extend to the deep [16].
In addition, because it contains a small amount of H2 and CH4, the deep fluid can increase H2 and CH4 for the hydrocarbon generation of the source rock, and finally increase the hydrocarbon generation speed and quantity of the source rock. Furthermore, Ni, Co and other metals in deep fluid have catalytic effect on hydrocarbon generation of source rocks, which makes immature source rocks enter the hydrocarbon generation threshold under normal conditions, which not only expands the effective volume of source rocks, but also improves the hydrocarbon generation speed, and finally promotes the hydrocarbon generation evolution of source rocks.
4. Influence of deep fluid on oil and gas migration
Because the density, diffusion coefficient and viscosity of deep fluid are between gas and liquid, that is, it has strong conductivity, so it can become an important carrier of oil and gas migration. In addition, the solubility of various hydrocarbons in water increases rapidly with the increase of temperature, that is, the high temperature of deep fluid can also improve the solubility of oil and gas; Gas dissolves in water, which increases the solubility of oil. The research shows that oil and gas migrate horizontally or vertically with water-soluble phase or mixed phase as a part of deep fluid, and hydrocarbon expulsion from source rocks is not necessarily restricted by "hydrocarbon saturation", but "dissociates" or "differentiates" with the decrease of temperature and pressure conditions in pressure relief zone or relatively low potential zone, and accumulates into reservoirs when encountering good reservoirs and traps.
In addition, a large number of secondary pores are formed due to the dissolution of acidic components in deep fluid on migration channels and surrounding rocks, which provides a good space for oil and gas migration and accumulation. A large number of cracks and micro-crack networks formed by active thermal fluid diapir can become "highways" for oil and gas migration.
Deep fluid provides power for secondary migration of oil and gas. Oil and gas migration always migrates from high potential energy area to low potential energy area along the path of least resistance until it meets favorable traps to accumulate or dissipate to the surface. Active thermal fluid has high temperature and high pressure, which can form abnormal high pressure during upward migration, providing power for secondary migration of oil and gas and controlling the migration direction of oil and gas.
To sum up, the deep fluid greatly increased the paleotemperature of the basin, accelerated the hydrocarbon generation evolution of source rocks, increased the volume of effective source rocks, improved the efficiency of oil and gas migration and accumulation, and improved the reservoir properties. Therefore, deep fluid plays an important role in the whole process of oil and gas generation, migration and accumulation.
refer to
[1] Copcev-Dvornikov B C, Ya Levko Wa E б, petrova M A. Volcanic rocks and research methods. Translated by Zhou Jiqun and Huang. Beijing: Geological Publishing House, 1978.
[2] Royal Academy of Sciences, Wright J.V., Volcanic Succession: Ancient and Modern. London: Allen and Unwin, 1987.
Qiu Jiaxiang. Volcanic rocks Beijing: Geological Publishing House, 1996.
Xie Jiaying. Volcanic-intrusive lithofacies types. Volcanic Geology and Minerals, 1996, 13 (2): 23 ~ 28.
Dongdong, Yang Shenbi, Duan Zhibin. Paleogene composite volcanic facies and volcanic reservoir in Binnan Oilfield. Petroleum and natural gas geology,1988,9 (4): 212 ~ 217.
Luo Jinglan, Qu Zhihao. Relationship between weathered lithofacies, reservoir properties and oil and gas of volcanic rocks in Yunnan. Acta petrolei sinica, 1996, 17 (1): 23 ~ 27.
[7] Simple classification of volcanic rocks. Bull. Vulcan. , 1972,28 ( 2) : 172 ~ 193.
Wang Xianbin, Liu Gang, Chen Jianfa, et al. Several key problems in the study of fluid in the earth. Frontier of Earth Science,1996,3 (3-4):105 ~118.
Lu Fengxiang. Deep mantle and deep fluid. Frontier of Earth Science,1996,3 (3-4):181~186.
[10] Anderson R.N. Sedimentary basin as thermochemical reactor. 1990 and 199 1 report of lamont-Doherty Geological Observatory, 1992, 68 ~ 76.
Water in the earth's mantle: the role of nominally anhydrous minerals. Science,1992,255:1391~1397
Du Letian, Wang Ju, gas geodynamics-an important research direction. Progress in Earth Science,1993,8 (6): 66 ~ 73.
Dai Jinxing, Song Yan, Dai Chunsen, et al. Formation conditions of inorganic gas and gas reservoirs in eastern China. Beijing: Science Press, 1995.
[14], Xie, Guo Jie, et al. Analysis of generation and migration of fluids and oil and gas in the deep earth. Progress in Earth Science, 2000, 15 (3): 283 ~ 288.
[15] was splashed. Thermal fluid activity and its influence on water-rock interaction in Dongying sag. Earth Science, 2000,25 (2):133 ~136.
Xie Nong, Li Sitian, Dong Weiliang. Tracer mark of thermal fluid activity and its geological significance: taking Yinggehai basin as an example. Geoscience,1999,24 (2):183 ~188.
Tu Guangchi, Liu Yingjun, Qi Sijing, et al. Geochemistry of mineral deposits. Beijing: Geological Publishing House, 1997.
[18] Fang Hao, Sun Yongchuan, Li Sitian, et al. Promotion of active thermal fluid on organic matter evolution and hydrocarbon generation. Geoscience,1996,21(1): 68 ~ 72.
Sun Yongchuan, Chen Honghan, Li Huisheng, et al. Thermal fluid activity and organic/inorganic diagenetic response of Ying-Qiong basin cliff 13- 1 gas field. Journal of Geoscience of China Geo University,1995,20 (3): 276 ~ 282.
Gong Zaisheng, Li Sitian, Xie Taijun, et al. Analysis of continental margin basin and oil and gas accumulation in the northern South China Sea. Beijing: Science Press, 1997.