Multi-scale evaluation of fractured carbonate reservoir and its implication to sweet-spot optimization: A case study of Tazhong oilfield, Central Tarim Basin, China

Abstract

Ordovician limestone and Cambrian dolomite are the main oil and gas producing layers in eastern Tazhong field, Tarim basin. Industrial oil flow has been obtained from drilling in this zone, proving that the Lower Paleozoic strata is important for oil and gas exploration and development. However, the main controlling factors and distribution of high-quality reservoirs remain unclear. Based on the logging constrained seismic inversion , FMI (Fullbore Formation MicroImager) log interpretation and core analysis of six wells, the main controlling factors of Paleozoic carbonate reservoirs in the study area were investigated. The results reveal that the two buried cuestas control the distribution of the Cambrian and Ordovician strata, the ratio of mudstone in north buried cuesta (NBC) is more than that in south buried cuesta (SBC), and the average porosity of ▪3xq dolomite formation is more than that of O1−2y limestone formation. FMI logging interpretation results show that fracture density of well TZ-1 is significantly higher than that of well TZ-2, combined with core observation and microscopic analysis we can believe that reconstructed dolomite reservoir has developed dissolution pores and vugs. By the means of seismic impedance reconstruction, the most favorable production areas, so-called sweet-spots, are karst residual mounds that formed independent small anticlinal high points and have been depicted. Finally, total 28 traps in the Cambrian–Ordovician​ carbonate buried hill are characterized, covering an area of 66.4 km2. 17 anticline traps with an area of 26.9 km2 in dolomite reservoirs are optimized to be the next exploration targets.