Abstract
After more than 10-years of abandonment, deepwater oilfield M was redeveloped by using four horizontal wells with 800 to 1700 m long sections. The target was the thick, porous sandstone reservoir N with the strong bottomwater drive, which had been intensively produced for 12 years with the horizontal wells placed at the middle part of the original oil column (15 to 42 m height). The local interbeds with poor properties within the reservoir were proved insufficient to block the water breakthrough. Consequently, the new horizontal sections were planned at the upper section of the clean reservoir with more than 10-m standoff to the uncertain oil/water contact (OWC) and enough distance to offset drilled boreholes. However, uncertainties from the reservoir properties, fluid characterization, and structural dip greatly complicated the effective oil trap profile and the further important well placement strategy.
Global successful cases and modeling results pushed the decision team to use an ultradeep reservoir mapping service (UDRMS) to cost-effectively optimize this redevelopment efficiency. With the depth-of-investigation (DOI) up to 30 m from the borehole, UDRMS could use the resistivity inversion to remotely and certainly detect multiple boundaries and map the properties details of this specific thick reservoir, including the reservoir top, local interbeds’ boundaries, OWC, and the intricate layering of contrasting resistivity within the reservoir. These certain and quantitative details could combine the conventional petrophysical logging data to effectively manage related uncertainties and then strategically instruct the productive drilling in the horizontal section for the expected well performance.
The successful redevelopment results validated the effective contributions from the UDRMS certain products. Along the long sections up to 1685 m, all uncertain elements were accurately ascertained. Within a corridor of approximately 100 m centered on the wellbore, up to five boundaries were mapped vertically to reveal the certain details of properties, reservoir top, and OWC. The dynamic OWC was identified as still tilted even after a long-term production shutdown and the remaining oil columns were higher than 12 m. Within the actual downdip structural framework, the smooth horizontal trajectories were placed in the upper reservoir with the quantitative distance to reservoir top and tilted OWC, while avoiding the local zones with poor properties. Even at the structural low, the special strategy was executed to guarantee the minimum 10 m standoff above OWC. The well placement efficiency satisfied the redevelopment requirements to positively affect the well performance.
As a game-changing enabler, UDRMS-derived certain products displayed their advantages for cost-effectively managing the uncertainties affecting the development of the thick reservoirs with the diverse complexities.
