The Use of LWD Data for the Prediction and Determination of Formation Pore Pressure

Abstract

Abstract The ability to predict and determine formation pressure has been an important issue since the beginning of the industry. This issue has become of increasing importance in deepwater environments where the relationships between increasing pore pressures, formation fracture gradients, and ultimately wellbore stability becomes of critical importance and can determine whether or not a well can be successfully drilled to total depth (TD). Pre-drill modeling using seismic, structural, and geological data can be used to attempt to predict pore-pressure regimes. Traditional methods of monitoring pore pressure while drilling have relied on methods, such the use of drilling exponents, and other indirect methods, including the monitoring of connection gases and observations of cuttings shapes. These methods are often imprecise, and their success depends on the actual pore pressure generation mechanism. The development of new logging-while-drilling (LWD) technologies in recent years has added powerful new tools for the accurate determination of pore pressures and wellbore stability. LWD resistivity and sonic measurements can indicate overpressure in shale sequences. Measurements in hole sizes as large as 30 in. make it possible to establish compaction trends in deepwater wells from near the seabed. Direct measurements of formation pressure can now be made with LWD formation pressure tester tools, which can accurately measure formation pressures directly while drilling and, when used with pressure-while-drilling (PWD) measurements, can precisely manage effective mud weights in narrow mud weight window environments. Advanced LWD imaging technology can now be used to evaluate wellbore stress fields, which can enhance the understanding of hole stability and overpressure generation mechanisms. This paper reviews the use of LWD sensors for pore pressure analysis and uses case histories to demonstrate their application and value.