Carbonate diagenetic facies of Yijianfang Formation (Shunbei area, Tarim Basin, Southeastern China)

The Yijianfang Formation of Shunbei area in Tarim Basin (southeastern China) contains a promising hydrocarbon reservoir formation. Based on borehole logging and carbonate sedimentary analysis, the diagenetic facies of this formation have been studied. Eight diagenetic subfacies are identified, which are associated with distinctive sedimentary processes: the atmospheric-freshwater-dissolution, burial-dissolution, fracture-dissolution, penecontemporaneous-dolomitic, burial-dolomitic, seabed-cement, freshwater-cement, and burial-cement subfacies. Thus, five composite sedimentary facies are proposed: the cement- hydrothermal, fracture-dissolution, fracture-cement, fracture-hydrothermal, and dolomitic-cement facies. By combining these diagenetic facies with the sequence stratigraphic framework, it is concluded that the seabed-cement subfacies are developed in the transgressive system tract; the structural-hydrothermal, fracture-hydrothermal, and cement facies in the highstand system tract; the atmospheric-freshwater-dissolution, atmospheric-freshwater-cement, and structural-hydrothermal facies in the intraplatform shoal; the burial-dolomitic, dissolution, and cement facies in the intershoal sea; and the atmospheric-freshwater-dissolution and cement subfacies in the patch reef. Finally, under the control of tectonics, sedimentary facies, and sequence, the diagenetic facies evolution is comprehensively identified from three aspects: single well, continuous well, and root mean square (RMS) amplitude property; finally, the distribution law of diagenetic facies is confirmed.