Alba Field Cased-Hole Horizontal Gravel Pack: A Team Approach to Design
- Karen Alexander (Chevron U.K. Ltd.) | Suzanne Winton (Baker Hughes Inteq) | Colin Price-Smith (Dowell)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 1996
- Document Type
- Journal Paper
- 31 - 36
- 1996. Society of Petroleum Engineers
- 3.1 Artificial Lift Systems, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.5 Processing Equipment, 1.8 Formation Damage, 2.2.2 Perforating, 2.2.3 Fluid Loss Control, 2.4.5 Gravel pack design & evaluation, 3.1.2 Electric Submersible Pumps, 5.5 Reservoir Simulation, 4.3.4 Scale, 2.4.3 Sand/Solids Control, 5.4.10 Microbial Methods, 1.6 Drilling Operations, 2 Well Completion
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A 700-ft cased-hole horizontal well was gravel packed and completed in the Alba Field, central North Sea. The completion incorporated a number of new technologies adopted for a horizontal cased-hole completion, including both equipment and fluids. The zone was completed in two stages using a horizontal stack-pack approach. Perforation packing was optimized by performing a staged acid prepack with the guns in the hole using a low-density synthetic gravel substitute in a shear thinning carrier fluid. This was a world-first achievement at a cased-hole gravel pack using the stack-pack approach in a horizontal well. A solids-free fluid-loss control material was evaluated and chosen for the high-permeability Alba sands (3 darcies). Extensive lab testing was performed to ensure minimal damage from various fluids. A 30-ft physical model was used to optimize annular pack efficiency. A gravel placement computer simulation was used to design pump rate, sand concentration, and gel loading to optimize annular and perforation-pack efficiency.
The objective of the paper is to highlight the advantages of working as a team to resolve a problematic completion. This allowed use of the tools available in the industry for optimizing gravel packs to avoid damage.
The approach adopted consisted of setting up a high-efficiency team with appropriate technical knowledge and experience. The team's first task was to identify and then systematically address the concerns. The outcome of this exercise would be a procedural flowchart that fully addressed concerns by means of a solutions-based approach.
The Alba Field is located in Block 16/26 of the U.K. Continental Shelf, lying about 130 miles northeast of Aberdeen in 138 m of water. The reservoir is a long, narrow Eocene-aged sandstone deposit located at a depth of approximately 6,000 ft true vertical depth (TVD). The field was discovered in 1984, and field approval (Annex B) was granted in May 1991. First production was in January 1994.
The main challenges faced in the development of the Alba Field from a reservoir management perspective are summarized below.
1. The Alba crude is heavier and more viscous (20.6°API) than the North Sea standard (46°API)
2. The reservoir is almost totally underlain by an inactive aquifer that is forecast to cone severely, resulting in very high produced water rates in comparison to the crude oil production rates. Water cut is expected to reach 70% within 7 years, rising eventually to 95% by 2010.
3. The reservoir is unconsolidated with a permeability in the range of 3 darcies. Safe sanding threshold pressures are 200 psi for an oil-bearing sand and 0 psi for a water-bearing sand, hence sand-control techniques were required from initial production.
4. Initial reservoir pressure is 2,850 psi and artificial lift would be required as water cuts approach 55%.
In summary, the optimum development plan adopted was a horizontal well development. The function of the horizontal wells is to delay water breakthrough such that ultimate recovery of reserves can be maximized. Electrical submersible pumps (ESP's) were selected as the method of artificial lift. The standard design for an Alba horizontal well is to complete 1,500- to 2,000-ft openhole sections and install prepack screens for sand control.
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