Application of Flow-Control Devices for Water Injection in the Erha Field

Abstract

The Erha field is a deepwater subsea oil development located in OML 133 off the coast of Nigeria. Erha North is a satellite of the Erha Field and is characterized by multiple unconsolidated sand intervals separated by shale sections. Due to the potential for reservoir compaction and early water breakthrough in these multi-layered Erha North reservoirs, high rate water injection is an important element of primary production through pressure support and is considered critical to project economics and reserves capture. This paper presents a case history of a successful field application of an innovative water injector completion technique addressing the issue of long-term injection conformance. Standalone screens with flow-control devices (i.e., downhole chokes) and openhole packers were utilized on the two most challenging water injectors in the Erha field. The completion objectives were:(a) target multiple intervals to reduce well count and cost,(b) sustain target injection rates and allocations, and(c) install sand control to prevent wellbore fill. Traditional water injector completion techniques, such as frac packs or openhole standalone screens, were judged to be incapable of meeting all the completion objectives. Unfractured completions, such as openhole standalone screens, have been reported to lose injectivity over time due to plugging and require fracturing to sustain injection rates (Sharma 2000). Fracturing may result in poor injection conformance and has the potential for broaching cap shale. Application of stacked completions or intelligent well systems would have added significant cost and complexity. Detailed completion simulations and fracture modeling were conducted to design the completions to their unique geologic settings. It is expected that this completion technique will maintain the desired injection allocations to the multiple target intervals over the well life in the matrix and fracture injection regimes. Upfront planning, communication, and alignment between reservoir, subsurface, and drilling functions enabled a successful real-time completion design and resulted in an operational success with less than 5% completion non-productive time (NPT). Performance of the injectors is being monitored by downhole pressure and temperature gauges. Introduction Water injection has been a successful secondary recovery technique in the oil industry for many years. In the past 10 to 15 years, however, projects have been developed where high-rate water injection is a primary recovery method because completion reliability and economic constraints require early voidage replacement and pressure support. As water injection becomes integral to the economic justification for capital intensive (i.e., offshore, subsea) projects, considerable attention to the design and performance of the water injectors is required. Regardless of rock cementation, there are very few documented cases of long-term, high-rate water injection without some form of continual or periodic stimulation. In well cemented rock formations, successful high-rate water injection programs rely on continual formation fracturing. Highly compressible, uncemented sands such as those found in many deepwater reservoirs, including those in the Erha North Field, do not easily fracture. High-rate water injection into such sands has been very difficult for some operators even when these sands have multi-Darcy permeability. In Yemen, one operator has experienced a "check valve phenomena" when attempting to inject water into an uncemented formation. Formation water was produced at a productivity index of 400 bwpd/psi, but later attempts to reinject that same water resulted in an injectivity index of less than 10 bwpd/psi (Wilkie 1996).

Advancements in Openhole Completion Technology - Establishing and Sustaining Differentiating Sand Control Completion Performance

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Horizontal Well Completion with Multiple Artificial Bottom Holes Improves Production Performance in Bottom Water Reservoir

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