Intelligent Well Completion Technology Enables Selective Injection for Pressure Maintenance in Mature Field in the South China Sea

Abstract

Abstract Pressure maintenance support in mature fields where permeability heterogeneity is present requires proper distribution of injected water into the respective zones of interest. This process can be extremely challenging, if no method for allocating the proper amount of water into each zone is available. An operator in the South China Sea, who had initiated a water injection project using legacy single-string two-zone completion technology, found himself in this predicament since no selective control for pressure maintenance had been considered for the project. During the past few years, the application of intelligent completion (IC) technology has increased rapidly. This acceptance has been due primarily to its proven capabilities for reservoir monitoring and corresponding optimization of well performance without well interventions. Historically, the majority of IC applications have been in production wells; however, an increasing number of operators have started adopting IC technology for their injector wells. This paper presents a case study in which IC technology was successfully applied in an offshore field in the South China Sea to provide an efficient water-injection method for optimizing pressure support as well as sweep. The operator selected this technology, as it presented a solution for optimizing the water injection. In addition to eliminating problems experienced with the incapability of the legacy completion technology to monitor water allocation and pressure maintenance for each zone, the IC technology would allow selective well testing for each zone. By evaluating the reservoir properties and characteristics of each zone independently, an intelligent completion would provide another key benefit to the operator, since it would comply with the platform size restrictions for the pumping equipment. The paper will discuss field objectives, the conceptual design, the design obstacles, and the operational challenges experienced during the job execution. Introduction Water-flooding experiences and lessons-learned regarding this area of the South China Sea have been documented and presented (Dang, et al, 2010). The injection well discussed in this paper was in a mature field that had been producing for approximately seven years, and the production rates in other wells in this field had experienced a relatively steep production decline. Wellhead pressures varied in the injection wells in this field anywhere from 500 to 2300 psi. The variation being experienced in the wellhead injection pressures was a qualitative testament to the heterogeneity that was being observed in the reservoirs of this field. With a conventional single-string completion, the operator knew that the heterogeneity of the formation would prevent the desired distribution injection rates from entering Zones P and Q of the proposed well, since previously used legacy completion designs (see Figure 1) did not offer controlled zonal injection. The total injection rate was only 5,000 BWPD, and the operator knew that if a single string completion with uncontrolled zonal injection was used, the injection rate would probably end up with 4000 BWPD into 1 zone and only 1000 BWPD into another. This would affect pressure maintenance for the field, since they would have no injection control, and subsequently, no way to control water distribution. With this situation, it was very likely that reservoir pressure could not be sustained, much less increased. As a result, the production in the oil wells in the field for those zones would continue to decline at a higher rate than desired.