Operational Aspects of Formation Pressure Measurements W hile Drilling

摘要

The emergence of formation pressure measurements in theLogging-While-Drilling (LWD) market has highlighted thechallenge of analyzing and interpreting the pressures acquired.The dynamic condition of the borehole and the freshly builtmudcake add new variables to the problem and contribute inmaking the measurement more complex to interpret comparedwith measurements made by conventional wireline-conveyedmethods.This paper presents several formation-pressure-while-drilling case studies conducted in the North Sea. Formationpressure measurements were repeatedly performed underdifferent well conditions and at different times after the bitpenetrated the formation. The impact on the measurement ofvarious parameters is analyzed, most notably, the time afterdrilling and changes in the measurement sequence.The results obtained with the formation pressure whiledrilling tool are compared to measurements performed withconventional wireline formation testers (WFTs) conducted atthe same depths and at various times after drilling. Analysisof formation cores taken in the same intervals as the pressuretests were performed allows a better understanding of thewhile drilling-derived mobility measurements. Suggestionsare made on how to improve the quality and accuracy of themeasurements.