AAPG Middle East Region, Second EAGE/AAPG Hydrocarbon Seals of the Middle East Workshop

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Seal Capacity of Carbonate Cap Rock: Insight from Rock Mechanical Test

Abstract

Marine petroleum resource has recently been one of the focal points for oil and gas exploration in the Tethyan realm. Marine strata in China was formed at an early age and experienced several tectonic changes (Tang et al., 2001; Jia and Wei, 2002; He et al., 2005), in addition to source rocks and reservoir, the effectiveness of the cap rocks is one of the key factors in hydrocarbon accumulation, and will affect the evaluation of marine petroleum resource as well as the determination of exploration direction in China. The Tarim Basin, at the eastern Tethys, is the largest inland petroliferous basin of China, and experienced superposition of multi-period structural movements in the long evolutional process of its geological history. The quality of the oil and gas preservation is one of the important factors affecting exploration prospecting and selected-area evaluation in the Tarim Basin. In addition to regional cap rocks, the effectiveness of direct cap rocks is an important factor for oil and gas preservation. Most researches have concentrated on the traditional quality cap rocks, such as evaporite rocks (Jin et al.,2006; Gutierrez et al., 2008) and mud shale (Gasparrini et al.,2013); whereas little study has been done on the effectiveness of carbonate cap rocks. In addition to physical properties of the carbonate rock itself, micro-fractures generated by structural events are an important factor that affect the effectiveness of carbonate cap rocks. Evaluating the condition of brittle-ductile transition of carbonate rocks will contribute to understand the creation of micro-fractures. In order to define the condition of brittle-ductile transition of carbonate rocks, five groups of carbonate rock samples in north slope of Tazhong Uplift in central Tarim Basin were chosen to test rock mechanics parameters under variable confining pressures and variable temperatures. The test results were integrated with the analysis of structural movement to study effectiveness of direct cap rocks in target area, and thereby a new method for future carbonate cap rocks evaluation in marine carbonate strata is proposed.