Article

Preliminary study on contribution of rift-erosion to oil and gas accumulation

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Abstract

There are one or more erosion surfaces in oil-bearing basins. Study on the relationship of erosion surface and reservoirs could not only develop oil theory, but also could promote exploration in the eastern old oil-bearing areas of China. In this paper, a space-time relationship of oil-bearing strata and erosion surface has been established based on the statistic analysis of erosion times and quantities in oil-bearing basins and the contribution of strata rift and erosion to oil accumulation has been discussed in terms of oil accumulation mechanism by geological analysis. The statistic and geological analysis showed that the strata eroded or the strata below the erosion surface are oil-bearing beds; the time of strata rift is coincident with the time of oil accumulation; the fall of fluid temperature and the rebound of the pore during the process of strata rift and erosion will cause underpressure in the strata which pumps oil and gas in the reservoirs, especially, the rebound of the pore offers extra-space to oil and gas accumulation.

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... Widespread indications for uplift and exhumation in Cenozoic have been reported from various localities around western China, which is the fundamental process forcing hydrocarbon accumulation and migration [1][2][3][4][5]. Given that one of key processes in petroleum accumulation is largescale fluid flow, study of fluid flow is a key to understanding and predicting the distribution of oil/gas during the prospect exploration [6][7][8]. ...
... Whilst during time of 70-25 Ma, they were slowly uplifted. Furthermore, given that surface temperature is 10℃ and geothermal gradient 32.1°C/km respectively, we can calculate each sample's uplift rate and magnitude [2,16,17]. The uplift is thus more than 3400 m by multiepisodic uplift from Late Cretaceous to present in Zoige. ...
... Research into the formation and evolution history of reservoir pressure has always been a focus of petroleum geology. In recent years, with the discovery of more and more abnormally low-pressure reservoirs in China and other countries (Bachu and Underschultz, 1995; He et al, 2000; Michael and Bachu, 2001; Zeng et al, 2002; Sorenson, 2005; Dai et al, 2003; Yuan and Liu, 2005; Zhang, 2007; Zhang et al, 2009), the change in formation pressure caused by tectonic uplift-erosion and its contribution to petroleum accumulation have aroused wide concern (Luo and Vasseur, 1992; Parks and Toth, 1995; Xie et al, 2003; Jiang et al, 2004; Tian et al, 2007; Xu et al, 2009). Previous research indicates that tectonic uplift-erosion will result in an increase in porosity as the confining pressure on the rock is relaxed, causing a rebound of porosity towards the levels before the rock is compressed under higher confining pressure (Neuzil, 1993; Peterson, 1958; Jiang et al, 2007) and decrease of fluid temperature (Xia et al, 2001; Wu et al, 2006; Zhang et al, 2004), causing a decrease of formation pressure. ...
... In recent years, with the discovery of more and more abnormally low-pressure reservoirs in China and other countries (Bachu and Underschultz, 1995; He et al, 2000; Michael and Bachu, 2001; Zeng et al, 2002; Sorenson, 2005; Dai et al, 2003; Yuan and Liu, 2005; Zhang, 2007; Zhang et al, 2009), the change in formation pressure caused by tectonic uplift-erosion and its contribution to petroleum accumulation have aroused wide concern (Luo and Vasseur, 1992; Parks and Toth, 1995; Xie et al, 2003; Jiang et al, 2004; Tian et al, 2007; Xu et al, 2009). Previous research indicates that tectonic uplift-erosion will result in an increase in porosity as the confining pressure on the rock is relaxed, causing a rebound of porosity towards the levels before the rock is compressed under higher confining pressure (Neuzil, 1993; Peterson, 1958; Jiang et al, 2007) and decrease of fluid temperature (Xia et al, 2001; Wu et al, 2006; Zhang et al, 2004), causing a decrease of formation pressure. However, the ratio of formation pressure to hydrostatic pressure, namely pressure coeffi cient, is usually used to defi ne the abnormality of formation pressure. ...
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... Accordingly, most previous studies considered this stage mainly as a period of adjustment and finalization of formed hydrocarbon reservoirs, when the possibility of large-scale reservoir accumulation again was low. Although some researchers have tried to explore the accumulation of hydrocarbons during the uplift of the basin, there are few literatures reporting on large-scale accumulation of hydrocarbons in the uplift process [1][2][3][4][5] . Zhao et al. suggested that the coal-measure source rocks of the Triassic Xujiahe Formation in the Sichuan Basin experienced significant desorption and expulsion events during the uplift since the late Cretaceous, and pointed out that if gas migration and accumulation processes did exist in the uplifting environment, it must be a major progress in the understanding of gas reservoir accumulation mechanism [2] . ...
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... There are limited publications at home and abroad regarding natural gas migration and accumulation under the setting of uplift [19] . If such migration exists, it will be an important development in understanding natural gas accumulation. ...
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