Sensitivity analysis on natural fracture properties and their effect on water intrusion and water breakthrough time in fractured reservoirs




Kemper, James Conner

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Water intrusion can drastically impact production of hydrocarbons that hold the presence of an aquifer. This study analyzed how the presence of natural fractures, within a reservoir, can impact the timing and breadth of water intrusion. Natural fracture properties were varied in order to perform a sensitivity analysis as to what properties impacted water intrusion most heavily. The natural fracture properties that were varied over the course of this study were natural fracture density (number of natural fractures in a given reservoir volume), natural fracture conductivity, natural fracture length and aquifer properties. Three models were analyzed in this study: a tight reservoir model, a conventional carbonate reservoir model, and a dry gas field study. The tight reservoir model showed matrix permeabilities on the nano-scale, so fluid propagation was primarily driven through natural and hydraulic fractures. The tight reservoir model was used as a base case to better understand natural fracture properties’ impact on water production, hydrocarbon production and producing ratio. No aquifer was present in the tight reservoir model. The conventional reservoir model had higher matrix permeabilities and porosities: however, evident through the sensitivities, natural fractures with higher conductivity still governed fluid production in the conventional reservoir model. Statistical sensitivities on producing fluid ratios, water breakthrough time and producing fluids were run for each of these models. Differing aquifer models were run and compared for this study. The aquifer models used were the Fetkovich, and Carter-Tracy model using a commercial CMG modeling software. Water breakthrough time was determined by curvature changes analysis on the water production curve and confirmed using fracture saturation visualization in the embedded discrete facture modeling. Finally, a field study was conducted using the techniques and derived in the two conceptual cases (tight reservoir and carbonate reservoir). Analysis and sensitivities concluded that natural fracture number and natural fracture length had the most effect on water rate and hydrocarbon production


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