Simple Guidelines for Screening Development Options for Oil-Rim Reservoirs

Abstract

Given various competing alternatives, the rigorous evaluation of development options for oil-rim reservoirs can be challenging and computationally intensive. For quick and robust decision-making, an efficient screening method that accounts for the relevant static and dynamic properties of the reservoir of interest is desirable. Based on controlled numerical simulation experiments, this paper proposes simple screening guidelines for oil-rim reservoirs under the mutually exclusive development scenarios of (i) sequential oil-then-gas (OTG); (ii) concurrent oil-and-gas (COG); and (iii) gas-only development (GOD). For simplicity, a two-level factorial design was used to create 17 experiments from a set of static and dynamic reservoir properties. A generic reservoir box model was then developed and used to conduct a total of 51 experiments. For each of the three development options, normalised surrogate models were developed for hydrocarbon recovery factor (RF) as a function of these static and dynamic properties. For the specific box model and the parameter space examined, it was found that the performance of the OTG option is most sensitive to oil API (viscosity), vertical anisotropy, oil relative permeability and liquid offtake rate. The COG case showed oil API, vertical anisotropy, liquid offtake rate and oil relative permeability as the heavy hitters, while the GOD option returned oil rim thickness, relative permeabilities and gas offtake rate as the key drivers of reservoir performance. Performance comparison of the three development options reveals that when reservoir properties are favourable to oil flow, OTG is the preferred oil-rim development option, while the GOD option is the most attractive when the reservoir is naturally less favourable to oil mobility. Although these guidelines provide indications of the most promising option, the final decision should be premised on further detailed studies, while considering both technical and non-technical factors that are peculiar to the specific project in question.