Research on the Technical-Economic Boundaries of Complex Structure Well Development in the Late Ultra-High Water Cut Stage

Abstract

At the late stage of ultra-high water-cut development, the distribution of remaining oil is highly scattered, and the potential of well pattern infill adjustment has reached its limit. Nevertheless, relatively remaining oil-enriched zones are still present, where complex structural wells have evolved into the core technology for tapping such residual oil resources. To address the problem that the applicable conditions and techno-economic thresholds of such wells cannot be quantified, this study, based on reservoir engineering theory, seepage mechanics principles and economic evaluation methods, comprehensively adopted multiple approaches including reservoir numerical simulation, conceptual model establishment, break-even analysis and field test verification. It then defined four techno-economic thresholds for different types of complex structural wells, namely cumulative oil production, oil saturation, reservoir thickness and enrichment scale. Meanwhile, the study identified four types of potential remaining oil-enriched zones: fault margins, sand body facies transitions, perforation-avoided intervals and thick reservoir tops, as well as clarified the applicable conditions of various complex structural wells in each of these zones. The research findings resolve the critical problems of “undefined target zones and unquantified thresholds” in residual oil tapping with complex structural wells during the late ultra-high water-cut stage. The proposed techno-economic thresholds and screening methodology demonstrate universal applicability, providing robust technical support for remaining oil exploitation in the late stage of ultra-high water-cut development.