Identification of the Ultra-deep Fault-controlled Karst-fracture-cavity Carbonate Reservoir and Its Application in Tarim Basin

Abstract

Summary A series of ultra-deep Ordovician carbonate oilfields have been discovered in the Tarim Basin. The practices demonstrate that the strike-slip fault, cutting into the Cambrian source rock, provides favourable channels for hydrocarbon migration and the karst-fracture-cavity reservoir distributing along the strike-slip fault is the main space for oil and gas accumulation. However, due to the small fault throw of the strike-slip fault and the low signal-to-noise ratio of the seismic data, it is difficult to identify strike-slip fault accurately. Moreover, the fault-controlled karst-fracture-cavity reservoir is extremely heterogeneous in space. It is difficult to identify the karst-fracture-cavity reservoir by conventional geophysical methods. In this study, the structure-oriented filtering technique is carried out to improve the signal-to-noise ratio of the seismic data and highlight the features of the fault. Then, the karst-fracture-cavity reservoir is identified by the combination of the gradient structure tensor attribute and likelihood attribute. The result is consistent with the well, indicating that the method and technique are appliable and accurate in identification of the ultra-deep fault-controlled karst-fracture-cavity reservoir. The study has guiding significance for the prediction of subsequent drilling anomalies and the economical exploitation of fault-controlled karst-fracture-cavity reservoirs.