Chinese National Offshore Oil Corporation (CNOOC) planned to develop a marginal oil field in Bohai Bay, China, where a pilot study showed that the reservoirs are distributary channel sands of a shallow water deltaic depositional system. Seismic inversion indicated that the sand properties and connectivity vary dramatically across the field. A multiple-aquifer system was apparent, and the gas/oil contact (GOC) and oil/water contact (OWC) levels were unknown. Furthermore, the only well control was from three vertical exploration wells and two directional offset wells.
The plan was to drill nine horizontal wells, including one injector well, gain reservoir exposure throughout the small 9-km2, oil-bearing area of a marginal oil field. This target area was isolated by secondary faults and stratigraphic depositional borders.
Understanding the need to evaluate stratigraphic uncertainties and establish an accurate picture of the targeted reservoir, SLB provided PeriScope bed boundary mapper and EcoScope multifunction LWD service to acquire real-time measurements to guide geosteering of the horizontal wells. EcoScope service was deployed to evaluate fluid properties and identify the GOC level. PeriScope service was used to clearly delineate the channel sand body boundaries along the horizontal sections. A rotary steerable system (RSS) was included in the BHA to maximize drilling efficiency and trajectory control.
All nine horizontal wells were precisely placed in optimal positions for injection and drainage with a 100% success rate, using real-time measurements from PeriScope mapper and EcoScope service to guide geosteering. With accurate data guiding decisions and a powerful RSS for drilling, the team increased ROP and avoided unplanned exits for a 60% improvement in drilling efficiency. This improvement equated to savings of USD 3.2 million off AFE for CNOOC.
Production from these horizontal wells surpasses the set production target by 30%, with extremely low water cut. The integrated LWD, well placement, and RSS solution optimized the marginal oil field into a much more economic development oil field.
