Sedimentary geological model and distribution prediction of source rocks in the Saergan Formation(Middle-Upper Ordovician) in Awati fault depression, Tarim Basin

Saergan Formation hydrocarbon source rocks of the Middle-Upper Ordovician are important marine source rocks in the Tarim Basin. Due to the large burial depth of the Middle-Upper Ordovician, a lack of drilling data for horizon calibration in Awati fault depression, and the insignificant seismic response characteristics of hydrocarbon source rocks in the Saergan Formation, it is difficult to accurately predict the distribution of the source rocks with traditional techniques. Based on the analysis of lithology types and stratigraphic configuration in the Saergan Formation together with its overlying and underlying strata on the outcrops in Kalpin area, we established a geologic model for seismic forward modeling. The combination of geological model and seismic model provides a basis for identifying and tracing seismic facies of the source rocks. Following the interpretation of 2D seismic lines one by one in the study area, we analyzed both the seismic and sedimentary facies according to the features of reflection wave groups.As to areas where source rocks occur on the outcrops but are not penetrated by wells emplaced in fault depression, we worked out methods and established the workflow for marine source rock identification, and re-recognized and predicted the spatial distribution of marine source rocks in the Middle-Upper Ordovician Saergan Formation. The results show that the Saergan Formation source rocks, developed under the control of sea level rising, belong to deposits of the deep shelf facies. The Saergan Formation source rocks are widely distributed in the study area with a predicted thickness range of about 0-120 m. It is the thickest in the southwest, thins progressively toward the northeast under the control of the Aqia and Tumuxiuke fault belts, and overlaps to the north till pinches out to the south of Well Yingmai 3; moreover, it still occurs sporadically at the western margin of Aman transitional belt to the east. © 2020, OIL & GAS GEOLOGY Editorial Board. All right reserved.