Key Problems in Abnormal Pressure Detection during Drilling in Carbonate Formation——A Case Study of Feixianguan Formation and Changxing Formation in Northeastern Sichuan

Uncompaction theory is not suitable for carbonate formations,if this theory is used in carbonate formations,abnormal pressure detection while drilling will be wrong,bringing about threat to drilling safety.In order to solve abnormal pressure detection theory and methods,and monitoring model selection etc,based on the comparison between the vertical distribution of test pressure data in Feixianguan and Changxing Formation in Northeastern Sichuan Basin,and the distribution of formation pressure of clastic rocks in Dongying Sag,it is was pointed out formation pressure detection while drilling based on the overburden pressure gradient was not suitable for carbonate formations.It was explained that the identification marks between high pressure layer and normal pressure layer were caused by TSR reaction and tectonic compression.The pressure detection models of porous-type reservoirs and fracture-type reservoirs were different due to different evolution course of formation pressure,so this paper provided the methods to distinguish porous and fracture carbonate reservoirs,gas layers and water layers.The study above could improve the recognition of carbonate formation pressure and the level of pressure prediction and detection.