The discovery and petroleum geological significance of Dengying Formation paleo-reservoirs in Renhuai, Guizhou

Field observation and investigation shows that the paleo-reservoir in Sinian Dengying Formation in Renhuai of Guizhou Province has the depositional environment of bank facies with doloarenite, oolitic dolomite, algal dolomite and fine-crystalline dolomite. The black solid bitumen is massive, hard, staining hands, and filled in the intercrystal pores, interparticle dissolution pores and dissolution caves of the rocks. Microscopic observation of asphalt shows the intermediate phase structure and the mosaic-like structural features, bitumen reflectance is 2.95%~3.86%, there exists double reflection and a high degree of thermal evolution, and the reservoir once experienced exposure to high temperature thermal evolution. The investigation and research on regional geology and sedimentary facies show that there probably existed platform-marginal shoal facies and shoal facies of open platform facies in Late Dengying period. The deposition pattern controlled shoal reservoir development and distribution. The formation of ancient exposures controlled the reformation of shoal dolomite in late Sinian period and Tongwan tectonic movement. Sinian Doushantuo Formation and Lower Cambrian Niutitang Formation black shales had a high organic matter abundance and good organic matter type, thus providing the ancient oil reservoir with a wealth of materials, and Lower Cambrian shale provided oil and gas with a favorable cover conditions, thus forming a good combination of reservoirs. The unconformity between Dengying Formation and Niutitang Formation controlled the channel for hydrocarbon migration, whereas the Early Caledonian movement in central Guizhou uplift created a structural and lithologic traps for oil and gas accumulation.