Ordovician carbonate reservoir fracture characteristics and fracture distribution forecasting in the Tazhong area of Tarim Basin, Northwest China

Abstract

Knowledge of fracture patterns is vital for Ordovician marine carbonate reservoirs in controlling the productivity of oil and gas wells. To improve the prediction of fracturing in favorable reservoirs, a range of relevant data was used, including fracture-system maps interpreted from seismic data, Ordovician top and bottom paleostructural maps, and cores obtained from 45 drill wells, to study reservoir characteristics and major controlling factors in the Tazhong area of the Tarim Basin. The effect of faulting on the development of fractures was assessed by a 3D finite element stress analysis that simulated paleostructural stress fields in the Middle Caledonian (the major fracture development period), using acoustic emission and rock mechanics data. The results show that fractures formed at a maximum effective principal compressive stress 47.9–62.4MPa (average 54.48MPa) in rock with tensile stress 4.10–8.02MPa (average 5.78MPa). Areas in potential reservoirs having the highest effective tensile stress were found to possess the most favorable fracturing pattern, distributed at the intersections of large faults in the immediate vicinity of fractured areas. This prediction matches field conditions more closely than previously reported, and provides new geological support for Ordovician fractured carbonate reservoir petroleum exploration and development in this area. The study also validates the methods of paleostructural stress field simulation for favorable area prediction.