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Zhang J.-Y.,Hangzhou Research Institute of Petroleum Geology | Zhang J.-Y.,China National Petroleum Corporation | Zhou J.-G.,Hangzhou Research Institute of Petroleum Geology | Zhou J.-G.,China National Petroleum Corporation | And 9 more authors.
Natural Gas Geoscience | Year: 2013

The depositional environment was isolated restricted platform and a lot of depositional cycles of shallow upward oolite shoal existed at the stage from Member 1 to 2 of Feixianguan Formation of Lower Triassic in the northeast Sichuan basin, especially gypsum lagoon at the Member 2 of Feixianguan Formation in the isolated restricted platform. On the isolated restricted platform geologic setting, the main lithology of reservoir includes remnant oolitic dolomite and finely crystalline dolomite. On the shallow upward oolite shoal geologic setting, the atmospheric water eluviation results in the lithology sequence from top to bottom is tight micrite dolomite, intragranular pore or moldic pore residual oolith micritic or powder crystalline dolomite, intragranular pore residual oolith powder or finely crystalline dolomite, and intercrystalline pore dolomite. Petrology and geochemistry of reservoir show that the reservoir dolomite underwent two stages of dolomitization. The first stage is seepage-reflux dolomitization and the second is burial dolomitization. The seepage-reflux dolomitization make an important role in preservation of early pores and increase rock strength, inhibit pressure solution and cementation, but the buried dolomitization partially fill pore space. It can be recognized two types of buried dissolution. The first stage happened after seepage reflux dolomitization and before crude oil filling and it is correlated with dissolution by organic acid. The second occurred in the deep buried environment, it is correlated with acid generated by TSR. The buried dissolution can not generate reservoir porosity, but increases permeability. Based on comprehensive studies of geologic settings, reservoir petrology and geochemistry, it is concluded that the atmospheric water eluviation is prerequisite condition for reservoir porosity generation and the seepage-reflux dolomitization is necessary condition for reservoir porosity preservation.

Zhang R.,Hangzhou Research Institute of Petroleum Geology | Zhang R.,Petrochina | Yao G.,Hangzhou Research Institute of Petroleum Geology | Shou J.,Hangzhou Research Institute of Petroleum Geology | And 2 more authors.
Shiyou Kantan Yu Kaifa/Petroleum Exploration and Development | Year: 2011

Taking the Cretaceous Bashijiqike sandstones in the Kuqa foreland basin as an example and starting from the analyses of the tectonic evolution, ancient stress, sedimentary system distribution, diagenesis type and intensity of the basin, the authors studied the porosity formation mechanisms and changes of the main pay zones in the Kuqa Depression and built a porosity forecast model integrating deposition, diagenesis and structure based on a large number of experimental data (cuttings, thin core slices, mineral composition, ancient tectonic stress, particle size) and logging test data and using a multi-disciplinary knowledge of geology, mathematics and statistics. The predicting results of the model in the sandstones of the Bashijiqike Formation matches well with the logging integration porosity, providing a basis for the space evaluation and forecast of deep, effective, high-quality reservoirs of different pore types in the Kuqa Depression.

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