Integrated Completion Design for Horizontal Wells in Unconventional Reservoirs

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 147120, ’An Integrated Approach To Design Completions for Horizontal Wells in Unconventional Reservoirs,’ by R. Jain, SPE, S. Syal, SPE, T. Long, SPE, and C. Wattenbarger, SPE, ExxonMobil, and I. Kosik, SPE, Imperial Oil Resources, prepared for the 2011 SPE Annual Technical Conference and Exhibition, Denver, 30 October-2 November. The paper has not been peer reviewed. An integrated workflow was tested for designing completions for a heavy-oil-recovery process that involves injection and production through the same wellbore. To capture the effect of variations or uncertainties in reservoir and fluid-flow characteristics over time, the transient effects are particularly important while analyzing the long-term performance for these types of completions. The proposed integrated workflow involves initial screening and selection of flow-restricting completions that can meet the desired injection and production performance on the basis of a detailed wellbore-hydraulics-modeling tool. Introduction Producing heavy oil and bitumen involves technologies such as cold mining for shallower resources or in-situ viscosity reduction. The cyclic solvent-based process involves alternating cycles of injecting a viscosity-reducing solvent into the reservoir followed by production of a mixture of heavy oil and solvent, with reduced viscosity, through the same wellbore. Many cyclic-process implementations are intended for use in horizontal wells. The completion design for such a process involves ensuring good solvent distribution into the reservoir during the injection phase to mobilize the resource along the entire wellbore and maximize the well length to reduce field-development cost. The process of injecting and producing from the same wellbore entails additional constraints on the completion design. One constraint is controlled injection distribution by use of flow-restriction devices such as orifices while maintaining a minimal pressure drop across the completion during the production phase. Another challenge results from the adverse mobility ratio of the solvent mixture and bitumen during the injection process, which could result in viscous fingering. This fingering can cause wide variations in the solvent injection and may cause an undesirable pressure distribution within the reservoir, which, in turn, may affect solvent placement. Predicting such differential injection or a thief zone is difficult because of the inherent nature of instabilities associated with the fingering process.