A total of nine horizontal wells including one injector well were drilled to cover the small, 9 km2, oil-bearing area of a marginal oil field that is isolated by secondary faults and stratigraphic depositional borders in Bohai Bay, China. 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. An advance distance-to-boundary well placement technique using azimuthal deep directional electromagnetic loggingwhile-drilling (LWD) technology was applied to overcome these challenges and to enhance reservoir understanding. A multifunction LWD formation evaluation tool was deployed to evaluate fluid properties where the top gas might occur. In addition, a rotary steerable drilling system (RSS) was assembled to achieve drilling efficiency and smooth trajectory control. One injector well and eight producer horizontal wells were precisely placed in optimum position for injection and drainage with a 100% success rate; one producer horizontal well was retracted while another producer well was added based on finding definite GOC and OWC levels. Increasing the drilling penetration rate and avoiding adjustments following reservoir exits led to a 60% improvement in drilling efficiency, which is equivalent to a cost savings of USD 32 million. 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.


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