RESERVOIR ENGINEERING

Designing of A Waterflood For Spraberry Trend

Designing of A Waterflood For Spraberry Trend

The proposed base plan has four water injectors: two into Spraberry Trend and two into Spraberry Trend. Producing wells will include three Spraberry Trend subsea wells and four Spraberry Trend TLP wells. (Slider 2009)

High injection rates are required to replace voidage and maintain reservoir pressure above bubblepoint. Initial injection rates per well (annual average) of 30,000 to 40,000 BWPD are required. Because the original operating health, safety, and environmental (HSE) case for the asset did not include the potential threat of reservoir souring after seawater injection, well-casing and -tubular materials have limited resistance to sulfide stress corrosion cracking (SSCC). (Frick 2010) This resulted in the need to recomplete the Spraberry Trend TLP direct-vertical-access (DVA) wells with qualified tubing. Spraberry Trend producers already have C100 sour-resistant casing and will not require tubing change out.

Injection Wells

The number of wells was optimized during a number of vital reviews. Sweep efficiency and return on investment were the main optimization criteria for the required total water-injection rate per day. Approximately 50% of the total project capital expenditure is related to drilling and well completion. (Slider 2009) Because economics is the dominating decision criterion for injector number, optimizing the fine details of the well bottomhole locations, well geometry, and well-completion designs retains prime importance.

Well Geometry. The 12,000-acre reservoir is to have four subsea injectors with at least 120,000 BWPD of combined annual average injection capacity. Having decided on the number of wells, ensuring the total required pore volume (PV) of water calls for optimized drilling and completion designs for those injectors. The dynamically preferred subsurface locations have been selected on the basis of careful analysis of the seismic signals, ensuring sand development and communication to producers. The wells are to intersect the reservoir in a straight vertical geometry to simplify the fracture design and maximize its chance of success. (Frick 2010)

Seawater-Injection Management

If water specifications are not met throughout the life of the waterflood, various problems can occur, including oxygen corrosion, biofouling, microbialinduced corrosion, SSCC, injectivity problems, reservoir souring, and barite scaling. The risks from souring and scaling resulted in elimination of rawseawater flooding as an option. Finding the right solutions during concept selection and detailed design required multidisciplinary teams. This ensured appropriate materials, chemical treatment, and water conditioning within the constraints imposed by project schedules and economics. (Slider 2009)

Solids, particulates, dissolved salts, and ...