Study Of Reservoir Sedimentation And Diagenesis Of Coal Gas In Linqing Depression

Linqing depression is one of the favorable areas of coal gas exploration in Shengli oilfield. With the foundation of detailed sedimentation studies, the paper carefully analyzes and divides the sedimentary systems and the microfacies of the Carboniferous-Permian, then builds the high-resolution sequence framework. The reservoir feature of coal gas in different sequences is analyzed and the favorable reservoir is forecasted.Firstly, there are four main depositional systems in the Carboniferous-Permian of the study area. They are tidal flat depositional system, barrier-lagoon depositional system, fluvial-dominated shallow water deltaic depositional system and fluvial-lacustrine depositional system. On the base of the sedimentary facies analyses of the single well and section, the features of sedimentary evolvement and distribution of the sandstone bodies are studied, especially the feature of the upper formation in fluvial-dominated shallow water deltaic depositional system and fluvial-lacustrine depositional system of the Carboniferous-Permian.Secondly, on the base of analyses of seismic data, well loggings and cores, combining with the features of the basin evolvement and tectonic movements, the paper recognizes and contrasts the sequence interface, and establishes the sequence stratigraphic frame of the study area. Seven sequences are marked off in the Carboniferous-Permian strata of Linqing depression. The paper analyzes sections and contrasts with nearby area of main sequence, and analyzes the distribution characters of the sandstone bodies.Thirdly, based on the recognition and division of cycles of short base level, the high-resolution sequence formation is recognized. Long base level, middle base level and short base level are divided in the systems tract of all the sequences. Moreover, the typical parasequences where reservoir exists are analyzed in the paper.Fourthly, the main reservoir of study area is sand bodies of deltaic depositional system and fluvial-lacustrine depositional system. The paper analyzes the lithology feature of sandstone, the type and evolvement of reservoir pore space, the physical characters and the diagenesis of the reservoir, the ability and its control factors of the reservoir and divides the diagenetic stages. The diagenetic event is studied and the distributing of the favorable reservoir is forecasted.