Over the past forty years, steering a horizontal well has evolved from geometric to structural to facies type and now productivity steering. This paper is aimed to summarize the evolution of wellbore steering and the impact of logging-while-drilling on well and reservoir performance.
The quest for productivity drilling began in the late 1980s with the first generation of logging-whiledrilling (LWD) technology that provided directional and formation-evaluation measurements and basic data insurance in vertical and deviated wells. The primary applications were stratigraphic and structural correlation and rudimentary formation evaluation. A shift in LWD technology in the 1990s increased the focus on exploitation of smaller, tighter, and harder-to-reach reservoirs. This second phase saw the introduction of azimuthal measurements, borehole images, instrumented steerable motors, and forwardmodeling programs for well placement through geosteering. Well architectures became more challenging as well construction evolved from geometrical designs to wells steered by geological information. In the 21st century, geosteering entered its third phase; structural steering with deep-reading LWD resistivity measurements and high-resolution imaging. This allowed operators to reposition in real-time horizontal and high-angle wellbore trajectories in anticipation of structural changes ahead of the bit.
Two recent developments since 2010 have taken geosteering to the next phase of productivity steering. The first one is reservoir mapping while drilling. It uses continuous bed boundary logs from deep azimuthal electromagnetic measurements. The second one is fluid mapping while drilling. It incorporates discrete/station measurements of reservoir rock and fluid properties from formation testing while drilling along with advanced mud gas logs. These developments have made it possible to estimate the productivity index (PI) of openhole section, in near real time, during reservoir drilling process.
The productivity index while drilling estimate can therefore be used for drilling decisions as well as completion decisions and to evaluate the effect of trajectory undulations on well productivity while drilling. Real Time Productivity Steering (RTPS) is hence no longer a myth but a reality now.