Precise Well Placement With Rotary Steerable Systems and Logging-While-Drilling Measurements

Abstract

Summary This paper demonstrates profitable geosteering of a central North Sea, U.K., horizontal well with a rotary steerable system (RSS) together with new-generation azimuthal logging-while-drilling (LWD) tools. The nature of the tertiary turbidite reservoir, with only 3 million STB, meant that to be commercial, only one horizontal well should be drilled and that the following criteria had to be met. Maximize standoff from an oil/water contact (OWC) within a sand unit with an approximately 50-ft oil column. Achieve 1,500 to 2,000 ft of good-quality reservoir. While maintaining standoff from the OWC, make a corresponding azimuth turn to follow the crestal dome structures of the reservoir trap. Avoid the risk of stuck pipe by carefully monitoring real-time drilling and well data and by using RSS technology. During well drilling, correlation software enabled comparison of offset-well and real-time LWD data and visualization of the well's position in the reservoir sequence. This modeling complemented wellsite biostratigraphic and geological correlation work and enabled changes to the trajectory to be planned, which were then achieved while constantly rotating with the RSS. Azimuthal-density measurements were used in real time and as post-well image logs for structural dip and fault interpretation. The well was geosteered into a sweet spot within 5 ft of the reservoir roof and as much as 56 ft from the OWC. The RSS completed the well in a single 3,844-ft run, with an average rate of penetration (ROP) of 68 ft/hr and no stuck-pipe problems. The target of 1,500 to 2,000 ft of pay was met with 1,980 ft of >20% porosity sand and 88% net to gross. The preplanned geometric wellpath would have missed the first 1,000 ft of the reservoir section, justifying the geosteering approach. A water saturation of 10% was much lower than prognosed, and the well has produced more oil than expected without early water breakthrough. This well demonstrates the combinability of the latest RSS and LWD technology to meet ever-demanding drilling and geological objectives successfully under circumstances of high economic risk and to ultimately maximize potential well production.