In Southern Offshore China, a deepwater sandstone reservoir with the strong bottom water drive has been intensively produced for 12 years which was followed by a 10-year’s abandonment. A redevelopment campaign designs new horizontal wells at the upper section to be away from both drilled wellbores at the middle section and Oil/Water Contact (OWC). However, wellbore centre-to-centre separation factor is less than 1 in some intervals for a high well anticollision risk. Besides, current uncertain fluid distribution could cause an uncertain flooding risk in this produced reservoir. To effectively avoid above uncertain risks, it is required to accurately characterize reservoir profile to strategically place new wellbores close to reservoir top, especially within intervals with a high anticollision risk.

Global successful cases prove Ultra-Deep Azimuthal Resistivity (UDAR) technology feasible to certainly reveal reservoir-scale details of a thick reservoir. This technology could provide a resistivity inversion and related certain answer products within the Depth-Of-Detection (DOD) up to 30m from the borehole, including boundaries of reservoir and local interbed, OWC, and resistivity distribution. These reservoir mapping products can contribute to the general application for reservoir steering, but also to the new application territory for drilling engineering anticollision.

By avoiding the highlighted both engineering risks and reservoir uncertainties, actual redevelopment results validate the effectiveness and advantages of UDAR inversion derived solution and workflow for a quantitative and strategic horizontal well placement. The dynamic OWC is identified as tilted and the remaining oil columns are higher than 12m. Within the inverted structural framework, wellbores are placed in the upper reservoir with the quantitative distance to reservoir top and tilted OWC, while avoiding the local zones with poor properties. Especially, keeping wellbores close to the inverted reservoir top is guaranteed an engineering safety in intervals with a high anticollision risk.

In geological, reservoir, and drilling engineering aspects, UDAR inversion derived solution displays its effectiveness and advantages, which will push its application territory expanding broader and broader.

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