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... Abnormal pressure is a common geological phenomenon in the petroliferous basins worldwide. In recent years, consistent with the discovery of the coexistence of abnormal underpressure, normal pressure and overpressure in numerous basins in China and other countries (Belitz and Bredehoeft, 1988;Corbet and Bethke, 1992;Bachu and Underschultz, 1995;Karsten and Stefan, 2001;Liu and Xie, 2002;Dai et al., 2003;Raymond, 2005;Wang and Chen, 2007), the distribution and controlling factors of these different pressure regimes has generated interest among petroleum geologists and engineers (Luo and Vasseur, 1992;Parks and Toth, 1995;Xie et al., 2003;Jeirani and Mohebbi, 2006;Kabir and Izgec, 2009). Previous investigation has been carried out on the genetic mechanism of low pressure and high pressure systems (Powley, 1980;Law and Dickinson, 1985;Hunt, 1990;Hao et al., 1995;Warbrick and Osborne, 1998;Neuzil, 2000;Hao, 2005;Xu et al., 2009). ...
This paper focuses on the distribution and coexistence mechanism of the various pressure systems in the Malang depression of the Santanghu basin, northeast of the Xinjiang Uyghur Autonomous Region, China. According to the classification standard of formation pressure, The calculated pressure coefficient showed that the Xishanyao Formation (J2x) is underpressured, the reservoirs of the Lucaogou Formation (P1l) are both normally and overpressured, and the Upper Pennsylvanian (C2) presents the coexistence of a normally pressured system and an underpressured system. The permeability of the Xishanyao Formation (J2x) improve from the southwest to the northeast of the basin, resulting in a relatively easy fluid supply to the reservoirs, and the pressure coefficient increases gradually. Tectonic uplift had a significant influence on the decrease in the reservoir pressure. However, a difference in source-reservoir assemblages caused a difference in fluid recharge and original pressure in reservoirs during hydrocarbon accumulation. The difference in reservoir connectivity causes a difference in the fluid supply during later tectonic movement, finally leading to the formation of different pressure systems. Thus, the basic mechanism for the coexistence mechanism of the various pressure regimes in this area is the disequilibrium of the fluid supply under the restriction of oil accumulation conditions.
The Sichuan Basin contains many overpressured formations with pore pressure coefficients as high as 2.3. However, in a Nanye 1 well found in the Southeastern (SE) Sichuan Basin, low-pore pressure coefficients as low as 0.9 have been recorded at a depth between 1544.3 and 1903.6 m, indicating the presence of underpressured formations. But the knowledge of normal and underpressured formations is not well studied in the SE Sichuan Basin. In this work, the normal to underpressured formations in the SE Sichuan Basin are identified, and their origins are discussed.
We integrated the pore pressure measurement and estimation, pore pressure coefficient and pore pressure depth plot to identify the normal to underpressured formations. We also integrated basin modelling along with the faults system to determine the origins of underpressured formations. As a result, the Upper Permian Longtan and Middle Permian Maokou Formations (1906.5–2782.9 m depth) in the Nanchuan area, were identified as normal-to-underpressured gas deposits. Also, the study identified the Lower Silurian Longmaxi and Upper Ordovician Wufeng Formations (2072–2160 m depth) in the Pengshui area, SE of the Chongqing region as normal pressured gas formations. The study discovered a decrease in temperature, rock porosity rebound and gas migration out of the formations through faults as the reasons for underpressured formations in this area. The tectonic uplift and erosion resulted in a decrease in temperature and rebound of the rock porosity, which contributed to total pore pressure drop up to 46.62 MPa. The tight overlying seal rocks and underlying rocks helped to sustain the low pore pressures in these formations.
The evolution of abnormal pressure is of importance for the analysis of hydrocarbon migration and accumulation processes. However, paleo-pressure reconstruction is still a challenge with great uncertainty. In this study, the PVT simulation method and homogenization temperature-salinity method were used for abnormal pressure evolution analysis in the Huimin Depression, which is characterized by a complex distribution of abnormal pressure, including overpressure, normal pressure and underpressure. The origins of the abnormal pressure conditions were also analyzed to examine the rationality and reliability of paleo-pressure reconstruction by basin modeling and quantitative calculation. The results revealed different evolutionary processes for the paleo-pressure in the Central Deep-Sag Zone (CDSZ) and the Northern Tectonic Uplift Belt (NTUB). In the CDSZ, the abnormal paleo-pressure exhibited a rising stage during the late Oligocene owing to disequilibrium compaction. From the early to middle Miocene, the paleo-pressure decreased to hydrostatic pressure because of the elastic rebound of rocks and temperature reduction. From the late Miocene to middle Pliocene, the paleo-pressure rose again because of the deposition and hydrocarbon generation. From the late Pliocene to the present, the paleo-pressure decreased again owing to the termination of hydrocarbon generation and secondary migration of hydrocarbons. In the NTUB, the paleo-pressure remained hydrostatic without disequilibrium compaction during the late Oligocene, followed by an intense reduction process due to rock elastic rebound and temperature reduction owing to strong tectonic uplift from the early to middle Miocene. From the late Miocene to middle Pliocene, the paleo-pressure rose because of the deposition and hydrocarbon injection from the CDSZ. From the late Pliocene to the present, the termination of hydrocarbon generation, weakening of hydrocarbon injection from the CDSZ, and the gas diffusion led to the decrease of pressure again in the NTUB. This study reveals that the paleo-pressure experienced two rising and two falling stages in the CDSZ and finally is characterized from normal pressure to overpressure. The paleo-pressure in the NTUB experienced one rising and two falling stages and is currently characterized by underpressure. This study provides a new approach for assessing the paleo-pressure evolution based on multiple analytical methods and further contributes to research on hydrocarbon-accumulating dynamics and hydrocarbon-migrating processes.
Abnormal pressure is considered significant for the migration and accumulation of oil and gas. The purpose of this study is to present the lateral and vertical distribution of underpressure conditions in the Huimin Depression determined using the drill stem tests (DSTs) and the well log data. This paper also provides the origins of the underpressure both qualitatively and quantitatively, as well as the effects of the underpressure on the distribution of hydrocarbons. The results show two vertical underpressure units at depths of 1,500–2,500 m and 3,000–4,000 m with a pressure coefficient of 0.8–0.95. Laterally, the underpressure is mainly distributed in the Northern Tectonic Uplift Belt (NTUB) and Southern Slope Belt (SSB). The rock dilation and temperature reduction caused the pressure reductions of 3–4 and 1–3 MPa, respectively. The diffusion of natural gas plays a limited role on the underpressure. An analysis of the lateral seals of faults indicates that the underpressured regions developed in areas with faults with shale gouge ratio (SGR) values larger than 0.6. We propose that the widely distributed underpressure in the Huimin Depression is related to rock dilation, temperature reduction, and fault sealing. An analysis of hydrocarbon migration and reservoirs showed the pumping effect provided by the deficient pressure could make underpressured regions the primary targets for hydrocarbon accumulation, and in the Huimin Depression, underpressure might be more important than overpressure.
Three types of natural gases, including coal-derived gas, oil-derived gas and biogenic gas have been found in the Liaodong Bay. All of the natural gases in the main gas fields of the Liaodong Bay are wet gas except those in JZ31-6 which are dry biogenic gas. The natural gas mainly distributes in the northern part of the Liaodong Bay with only a small part in the southern part. In the deep, it mainly distributes in the Shahejie Formation with little in the lower Dongying Formation and the Neogene. The distribution characteristics of the natural gas is controlled by the types and thermal maturity of the organic matters, the thickness of the cap rocks and the formation mechanisms of the overpressure. The organic matter in the northern part are type II2-prone which mainly generates natural gas with a higher maturity while those in the northern part are type II1-prone which mainly generates oil with a lower maturity. The thickness of the cap rocks in the 3rd member of the Dongying Formation(E3d3) decreases from the north to the south. The overpressure which evolves in the 3rd member of the Dongying Formation(E3d3) is caused by the uncompaction, providing a good condition for the gas preservation in cooperation with the huge-thick cap rocks, while the overpressure which evolves in the 3rd member of the Shahejie Formation(E3s3) is caused by the expansion of the hydrocarbon, providing a strong power for the natural gas which migrates from the sag to the Liaoxi Salient.
A series of 18 novel 1-indolyl acetate-5-nitroimidazole 3a-3r were designed, synthesized, and evaluated for their in vitro biological activities as potential tubulin polymerization inhibitors. Among these compounds, 3p displayed strong antitumor activity with IC50 of 2.00, 1.05, 0.87 μM against A549, Hela and U251 respectively, and also showed the most potent PLK1 inhibitory activity with IC50 of 2.4 μM. Molecular docking studies within the colchicine binding site of tubulin were in good agreement with the tubulin polymerization inhibitory data and confirmed the importance of the configuration of the synthesized 1-indolyl acetate-5-nitroimidazolefor potential tubulin polymerization inhibitors.
On the basis of measuring the pressure distribution and analyzing its origin in the Carboniferous and Permian of Shenmu-Yulin
area, the evolution history of ancient pressure is restored mainly by means of the basin numerical simulation technique, in
which the paleo-pressure has been constrained by the compaction restoration and the examination of fluid inclusion temperature
and pressure. Then the development and evolution history of abnormal pressure and its effect on gas migration and accumulation
are investigated. Studies show that the pressure in southeastern and northwestern parts of studied area is near to hydrostatic
pressure, whereas in the remainder vast area the pressure is lower than the hydrostatic pressure, which is caused by difficulty
to measure pressure accurately in tight reservoir bed, the calculating error caused by in-coordinate between topography relief
and surface of water potential, pressure lessening due to formation arising and erosion. There are geological factors beneficial
to forming abnormal high pressure in the Upper Palaeozoic. On the distraction of measured pressure, paleo-pressure data from
compaction restoration and fluid inclusion temperature and pressure examining, the evolution history of ancient pressure is
restored by the basin numerical simulation technique. It is pointed out that there are at least two high peaks of overpressure
in which the highest value of excess pressure could be 5 to 25 MPa. Major gas accumulated in main producing bed of Shanxi
Fm (P1s) and lower Shihezi Fm (P2x), because of two-fold control from capillary barrier and overpressure seal in upper Shihezi Fm (P2s). In the middle and southern districts, the two periods of Later Jurassic to the middle of Early Cretaceous, and middle
of Later Cretaceous to Palaeocene are main periods of gas migration and accumulation, while they belong to readjustment period
of gas reservoirs after middle of Neocene.
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