Accumulation Mechanism of Complicated Deep Carbonate Reservoir in the Tazhong Area, Tarim Basin

Abstract

The Tazhong area is located in the hinterland of the Taklimakan Desert, where abundant hydrocarbon resources are contained in the deep Ordovician carbonate rocks. Great exploration results have been obtained in the Middle and Lower Ordovician Yingshan formation over recent years, and a large layered oil/gas field has been proven. The fluid properties of this reservoir are complicated, and it can be divided into condensate gas reservoir, volatile oil reservoir and oil reservoir in accordance with fluid component and PVT phase behavior. These reservoirs distribute in alternation horizontally, without apparent boundaries vertically. Based on the study and analysis on test, exploration and production data, it is believed that the diversity of fluid properties results from the multiphase uneven infusion action of oil and gas, especially the severity of gas cut at late stage: the reservoir suffered from severe gas cut became condensate gas reservoir, the one suffered from weak gas cut became volatile oil reservoir, and the one free from gas cut still keeps the original oil reservoir state. It is discovered through study that the strike-slip fault plays an important role in the occurrence of gas cut at late stage: it not only acted as the pathway of gas migration at late stage, but also had an important impact on the reformation of reservoir. The impact of reservoir nature on gas cut mainly finds expression in the difference of combination of reservoir space: the mutually connected large pore/cavity and fracture system was favorable for gas charge at late stage, where condensate gas reservoir was mostly formed; while the isolated pore/cavity where the tectoclase developed weakly was relatively sealed, was unfavorable for the sufficient infusion of natural gas at late stage, and usually keeps the original oil reservoir state or formed volatile oil reservoir. Based on the discussion to the factors that affect the severity of gas cut in the paleo-reservoir at late stage, this paper clarifies the accumulation mechanisms and controlling factors of different kinds of reservoirs, establishes the accumulation mode of 3 types of reservoirs, and this is very significant to the effective prediction of hydrocarbon distribution in the deep carbonate rocks of the Tazhong area.

Geology and Hydrocarbon Accumulation of the Large Ultra-Deep Rewapu Oilfield in Tarim Basin, China

“…China petroliferous basin's specialty and complexity underlie abundance of deep oil and gas resources (Dai et al, 2008;Zhao et al, 2009;Zhu et al, 2010;Zhou, 2013). It is revealed from drilling data about deep well of below 7000 meters ) that there are effective reserving bodies at the deep layer, and lower limit for preservation of hydrocarbon may be deeper than original data, and the potential for exploring deep petroliferous basin in Central China and West China is huge.…”

Formation and distribution characteristics of Proterozoic–Lower Paleozoic marine giant oil and gas fields worldwide

“…The Sichuan Basin sediments were marine craton carbonate with a clastic sedimentary stage in the Sinian to Middle Triassic periods (He et al 2011a). The Permian Basin has been subject to Paleozoic marine and Mesozoic-Cenozoic Compiled with data from IHS Energy , 2013), C&C Reservoirs (2005), and USGS (2007 continental sedimentary systems since the end of the Cambrian period. In the Lower Paleozoic stratigraphic sections, several unconformities exit, and most of them between shallow shelf carbonate deposits (Hills 1984;Adams and Keller 1996).…”

“…The thermal evolution extent of the hydrocarbon source rocks is highly mature to over-mature in the thirteen giant oil and gas fields, except for the LimaIndiana Trend, which has a relatively low thermal evolution extent. The type of hydrocarbon is mainly natural gas, which is mostly sourced from oil cracking (Terken and Frewin 2000;Terken et al 2001;Dakhnova et al 2011;Jin 2012;Qiu et al 2012;Zhou 2013).…”

“…Compiled with data from IHS Energy , 2013), C&C Reservoirs (2005), and USGS (2007 carbonate source rock in the Ordos Basin began to generate oil in the Middle Triassic, reached peak oil generation in the Jurassic, and over-matured to generate gas in the Early Cretaceous (Tang et al 2000). The Lower Cambrian source rock in the Sichuan Basin entered a mature stage during the Caledonian movement and stopped generating hydrocarbon as a result of the Caledonian uplifting.…”

“…The multiperiod tectonic movements resulted in the uplift and erosion of strata, forming large unconformities and providing conditions for the formation of weathering crust karst reservoirs. For example, the multiperiod tectonic movements in the PLP marine strata in the Tarim, Sichuan, East Siberian, and Permian basins produced large-scale karst reservoirs (Postnikova et al 2002;Dutton et al 2005;Kang 2008;Zhang et al 2007b;Luo et al 2008;Liu et al 2010;Zhao et al 2012b;Wang et al 2013b;Zhou 2013;Du et al 2014;Yang et al 2014). S o u t h a n d C e n t r a l O m a n S a lt B a s in E a s t e r n F l a n k Fig.…”