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).
SPE Members Abstract Oil companies have been forced to become more efficient and try new ideas to remain competitive in today's economic environment. This involves re-evaluating the cost effectiveness of tubing and downhole equipment designs and trying innovative ideas that have potential for significant cost savings. This paper tells how Mobil Producing Nigeria (MPN), operator of the Joint Venture between MPN and the Nigerian National Petroleum corporation (NNPC), reduced completion costs as a result of efficient tubing design. Tubing and thread design are discussed in detail and statistical tubing data is presented to show the need for thread standardization. Gravel pack and other downhole equipment designs are discussed in detail with case histories presented. Emphasis is placed on elimination of unnecessary downhole equipment and considerations for future fishing operations. This paper also discusses in detail innovative ideas that reduced workover and completion costs during the last 24 months. These include:A plugback completion design within the same reservoir that allowed the lower part of the interval to be isolated when cased hole logs were questionable.Innovative use of a joint of tubing to retrieve lost wash pipe.A gravel packed open hole completion through a milled window in an inadvertently sidetracked hole. The milled window was the original completion interval prior to the workover.Innovative use of the cementing unit to free a stuck gravel pack crossover tool. Introduction Mobil Producing Nigeria operates 17 producing offshore oil fields on behalf of producing offshore oil fields on behalf of itself (with 40 percent working interest) and its Joint venture partner the Nigerian National petroleum Corporation (60 percent working interest). The producing fields are located 12 to 25 miles (19.3 - 40.2 km) offshore of the south eastern coast of Nigeria due south of Akwa Ibom State as shown in Figure 1. These fields produce from a total of 171 oil wells drilled from 37 platforms located in 50 - 165 ft (15.2 - 50.3 m) of water - Producing reservoir depths range from 4000 Producing reservoir depths range from 4000 - 8000 ft (1219 - 2438 m) subsea. Virgin reservoir pressures for producing - reservoirs yield a normal gradient of approximately 0.45 psi/ft (10.2 Kpa/m). The sand units are poorly consolidated with porosities ranging from 20 - 40 percent. percent. P. 617
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.