Feasibility study of the stability of openhole multilaterals, Cook Inlet, Alaska

A study of in-situ stress, rock strength, and wellbore stability was initia ted in the Hemlock sands of the McArthur River field, Cook Inlet, Alaska, t o evaluate the potential of leaving the near-wellbore portions of multilate rals uncased. A northwest/southeast direction of maximum compression and a strike-slip faulting regime were predicted from analyses of leakoff test da ta and observations of failure (break-outs) in adjacent wells. Caliper, wel l-log, and core data indicated that cementation, and hence rock strength, i s highly variable within the reservoir. Thus, it was decided to evaluate th e stability of the lateral sections (i.e., the likelihood of wellbore failu re during production) as a function of both stratigraphic position and well orientation. Laboratory rock-strength measurements were carried out on cor es selected from target intervals in adjacent wells to provide sufficient p recision to quantify the results. The results indicated that, while some re servoir intervals have high enough strengths to be left uncased when drille d in the most stable direction, these intervals are too thin to provide suf ficient support at the point where the laterals leave the parent well. This justified the decision to case back the laterals to the parent well despit e the cost.