| Microbial carbonate is a new field and hot spot for petroleum exploration. The Sinian Qigebrak Formation of Tarim Basin develop a set of thick microbial dolomite, and its type, distribution rule, and reservoir genesis are still unclear. Based on the outcrop measurement and thin section observation, the sedimentary and reservoir characteristics of the microbial dolomite in Sinian Qigebrak Formation in the northwest margin of Tarim Basin were studied. Various types and scales of microbial dolomites, including stromatolite dolomite, thrombolite dolomite, spongiostromata dolomite, and microbe-related granular dolomite were found in microbial flat and microbial mound of Qigebrak Formation. There are two third-order sequences in Qigebrak Formation, in which microbial mounds develop during the TST and the early stage of HST, while microbial flats mainly develop during the mid-late stage of HST. Stromatolite dolomite is enriched in SQ1, and spongiostramata dolomite is enriched in SQ2 due to the change of environment. The microbial dolomite reservoir in the Qigebrak Formation is controlled by facies, and the mound and microbial dolomite flat on the top of the upward shallowing cycle are favorable facies zones for reservoir development. Spongiostromata dolomite could be a large-scale high-quality reservoir, which contains various types of pore space, overlays frequently in vertical and distributes stably in horizon. |
