Application of Comprehensive Information at Rig Site on Discovering the Subtle Gas Bearing Reservoirs in Belketaief Gas Reservoir

Drilling engineering data,such as mud weight,formation pressure,trip gas and circulation gas chromatography,etc.,are commonly used at rig site for well control by drilling group,which are often ignored by in house study group of logging and geologic interpretation.Actually,those active hydrocarbon reservoirs may present themselves through abnormal change of engineering data at rig site soon after being drilled open and being tested.This paper introduces a successful case study of how a high productivity gas reservoir has been discovered by CNPCI at Algeria exploration blocks.Circulation gas chromatography of well killing is analyzed after the analysis on density difference between drilling mud and kill mud combined the drilling engineering data with well logging and oil test data.Good position correspondence is then discovered between the intervals with abnormal gasometry and each set of sand group in the same well through the comparison with the well log.Flow properties of single sand body are monitored one after another based on accurate pressure profile got by wireline formation test and the comparision of trip gas and circulation gas chromatography.Through comprehensive analysis and feasible operation planning,we retrieve a missing low resistivity but high productivity gas zone which are not recognized on log interpretation procedure.Thus the life of an old block being abandoned is saved.The successful application of drilling engineering data in this case provides good experience which may guide subtle gas reservoir exploration in the future.It is useful for understanding the intrinsic characteristics of the hydrocarbon reservoirs and discover the blind zone or reservoir when the chromatogram data of trip gas and circulation gas,formation pressure,fluid density and other drilling engineering data are combined with wireline data and geologic background to analyze and evaluate the potential in the exploration.