Equalization of the Water Injection Profile in a Subsea Horizontal Well: A Case History

Abstract

Abstract This paper focuses on the first global installation of a water injector well with a lower completion system that incorporates both premium sand control screens and water injection profile equalization. The equalization of the water injection profile of horizontal wells has been a key issue in many development projects worldwide and has the potential to increase the reservoirs ultimate recovery by increasing the water sweep efficiency. Inflow Control Devices integrated with premium sand control screens have a long history of application in production wells. In these cases the main objective is to create a uniform inflow profile along the horizontal section, delaying unwanted water and gas production and increasing oil recovery. The method through which Inflow Control Devices equalize the inflow of oil can also be used to equalize the outflow of water. Historically, sand control completions for water injection wells include stand-alone conventional screens and open-hole gravel packs. Stand-alone conventional screen completions do not provide equalization of the water injection profile. Open-hole gravel packs provide for an effective acid treatment of the water injector well but present operational risks, high costs, as well as expensive rig time. The installation was carried out in a subsea horizontal sea water injector well in the Campos Basin, offshore Brazil. The paper presents the overall completion plan, the lower completion installation, the acid treatment through the Inflow Control Devices, and the initial water injection results based on production logs and water injectivity tests. The main concerns during the planning phase are discussed, highlighting the procedures adopted to overcome them. The good initial results have created the expectation of many applications of this system in Campos Basin. It is believed that sharing this information will benefit many operators with horizontal water injectors in their field development plans. Marlim The Marlim field, located in the northeastern part of Campos Basin, about 110 km offshore in the state of Rio de Janeiro, was discovered in January 1985. The field covers an area of about 145 km2, in water depths ranging from 600 m (1968 ft) to 1,100 m (3609 ft). The Oligocene sandstone reservoir quality is good. Core analyses of several wells indicate mean permeability of 2,000 md, mean porosity of 30%, and highly friable sandstone. Marlim's reservoir development strategy relies heavily on water injection as a source of reservoir energy maintenance. Currently 9 Floating Production Systems (FPS) are on stream with 129 subsea wells on operation (83 producers and 46 water injectors), including 36 horizontal wells. The total production reached its peak of 650,000 bbl/d in 2002, overcoming all former production forecasts. Currently Marlim field oil production, around 450,000 bbl/d, is supported by injecting 760,000 bbl/d of sea water. The recovery factor to date is 22.9 %. The water production is 217,150 bbl/d (water cut of 33 %) and GOR is equal to the initial solubility ratio, 83 STD m3/STD m3. Water injection is into the oil leg, concentrated in the lower portions of the reservoir and production is concentrated in the upper parts, to delay water breakthrough. A thorough history of the Marlim field can found in references 1 through 6. Injection Well Strategy The water injector well under consideration for this project was to be located in the south area of the Marlim field. This injector well was planned for pressure maintenance and for sweep efficiency in the thin reservoir border of the field. The injector well, IN, and its neighboring producer wells, A, B, C, and D are shown in Figure 1.