Study Of Forming Mechanism Of High-quality Reservoir And Favorable Target Forecasting In Cretaceous Sandstone In Kuqa Depression, Tarim Basin

Kuqa depression is one of the most important oil and gas-bearing area in Tarim basin, KL2 gas field in it is the source of West-East natural gas transmission project. The Cretaceous and Paleogene in Kuqa depression are the main reservoir stata, and the sandstone of Basijiqike Formation in Cretaceous is typically the deep-burial high-quality reservoir. This article aims at the forming mechanism and favorable target forecasting of high-quality reservoir in Cretaceous sandstone.After the study of diagenetic field and burial history of the Cretaceous in Kuqa depression, it has been discovered that lower geotemperature field is important for porosity maintaining, abnormally higher pressure field and its burial history, which is long term superficial-burial and short term deep-burial, become the vital condition of porosity maintaining and secondary modification.Through the analyses of water-rock interaction, lithology and reservoir character of Basijiqike Formation in the KL2 gas field, it has been confirmed that the formation of high-quality reservoir is due to the contribution of large quantity of secondary porosity. Selected dissolution of plagioclase is the important origin to form intragranular solution pore, casting pore and super solution pore in feldspar or detritus grain. Calcite cement, formed in the early diagenetic stage, makes the great contribution to improvement of the reservoir quality, when it was dissolved and forming secondary porosity in acidic fluid later. In the condition of same tectonic background, same or similar geotemperature field and pressure field in Kuqa depression, it has been found that the content of calcite cement in sandstone is closely correlation to the porosity.At the guide line of diagenetic field, burial history and closely correlation between calcite-porosity, combining the sedimentary facies and sandstone style, we forecast the distribution of favorable reservoirs of Basijiqike Formation in Kuqa depression,.The favorable reservoirs should distribute in the Kelasu tectonic zone and north to well Dongqiu 5-Dongqiu 8 in Qiulitage tectonic zone.