Application of Intelligent-Completion Technology in a Triple-Zone Gravel-Packed Commingled Producer

Abstract

Abstract Many oil fields are comprised of stacked reservoirs, each requiring multiple individual wells for their proper and timely depletion. By commingling multiple reservoirs in a single well, the total number of wells required for full field development can be significantly reduced and the depletion life can be better managed within the design life of the attendant facilities. This can result in a significant cost savings over conventional development especially in the offshore environs. Historically one limitation of commingling has been the inability to fully optimize the recovery of the reserves from each interval. In many areas, commingling is restricted or prohibited by regulation because of this inability to optimize the depletion of the reserves. Use of intelligent completion techniques can provide the capability to properly manage the recovery of reserves from each individual zone in a commingled completion. As a follow-up to a recent discovery, Mobil Producing Nigeria Unlimited (MPN) drilled a long-reach producing well in the Usari field from an existing platform which was completed as a commingled producer in three of the seven discovered zones. Each of the three zones was completed with a gravel pack, a hydraulically operated multi-position flow control valves and downhole gauges which provide full control of each zone. This approach allows for the assessment of the characteristics of each reservoir and proper assessment of the uncertainties associated with a full development of the discovery prior to committing to new wellhead platforms. In addition, the average first-year rate for the well was approximately 11,000 BOPD whereas a single producer would have only provided about 7,000 BOPD. This paper will focus on the concept selection, interaction with regulatory agencies, the installation and the performance results-to-date. The discussion will also address the reservoir surveillance and management of the three commingled reservoirs including production back-allocation and optimization. This application is the first recorded use of hydraulically operated multi-position flow control valves (FCV) in a 9–5/8" triple-gravel packed completion. The learnings from this well are in the area of well planning, equipment installation and reservoir management. Background The Usari field is located approximately 16 miles (25 kilometers) offshore Nigeria in about 72 feet (22 meters) of water (figure 1). The field was discovered in 1964 with production streamed in 1997 after a failed attempt in the late-60's. The field development currently consists of 25 wells from two wellhead platforms which produce into a central production platform. General Geology In total, 35 reservoirs have been discovered in the Usari field. These reservoirs have been subdivided into three main categories based on fluid properties, pressure regimes and geologic setting. These categories are commonly referred to as the Shallow (18 reservoirs), Intermediate (15 reservoirs) and Deep (2 reservoirs). Currently 4 reservoirs in the Shallow, 10 reservoirs in the Intermediate and 2 reservoirs in the Deep are being produced. The main Usari structure is an annealment phase anticline on the down-thrown side of a major down-to-the-south growth fault (Fault 5) and is cut by several small faults and a large down-to-the-north antithetic fault. The Usari Intermediate and Deep reservoirs are set up by three-way dip closures on the up-thrown side of the major antithetic fault in the field. The Usari Shallow reservoirs are defined by four-way anticlinal closure with associated fault seal within the graben set up by Fault 5 to the north and the antithetic fault to the south. (Figure 2)