Integrated Approach to Understand Variable Water Gas Ratio Production in Naturally Fractured Carbonate Reservoir

Abstract

Abstract Innovation is pivotal for sustainability in today's dynamically changing E&P industry. Global industry downturn and the pandemic has pushed operators towards squeezing expenditures and look for cheaper, but efficient alternatives to maximize production from producing/discovered resources. Carbonate reservoirs provide a unique set of formation and productivity evaluation related challenges due to the highly variable characteristics of the natural fractures. This work elucidates how production logging data, combined with multiple wireline logs, resulted in resolving water production ambiguity in a well drilled into a Naturally Fractured Reservoir (NFR). Value of integrative data analysis to extend production logging diagnostic capability will be the focus of this paper. The well under consideration in this paper is a wildcat well located in a region which involves complex geology and intricate fracture systems. Accordingly, a two-tier methodical approach to characterize formation evaluation and assess well producibility was proposed and implemented through an integrated lens. Firstly, a combination of petrophysical and fracture image logs helped in comprehensive open-hole characterization. Next, to evaluate reservoir deliverability from the fractures, formation testing with 3D Radial probe and then extended well testing operation was performed, which confirmed hydrocarbon presence however, variable Water Gas Ratio (WGR) posed as a challenge, and it became critical to confirm the source of water for deciding future completion strategy. Finally, to solve the produced water conundrum, real-time production logging with integration of all open-hole data and mud log was performed to provide a definitive answer product. Integration of borehole image logs allowed to delineate complex producing zones based on fracture clusters with classification of variable fracture types and linkage with production log zonal contribution profile. Moreover, analyzing mud logs in the same canvas as the production log, led to establishment of linkage between surface water production and drilling fluid losses at specific depths. Ultimately, produced water anomaly at different choke sizes was resolved through real-time production logging optimization which indicated water sump build up downhole due to lack of lifting capacity from nearby perforations at higher choke sizes. Integrating all relevant well data in a single layout including production logging results helped in achieving objectives and understanding well dynamics in context of fracture flow characterization, water production, and diagnostic capabilities.