Evolution of Frac-Pack Design and Completion Procedures for High-Permeability Gas Wells in Subsea Service

Abstract

Summary Frac-pack techniques were used in a recent subsea well-completion campaign. The sandstone layers that were targeted for completion are present generally in shallow gas reservoirs, with depths ranging from 2,000- to 4,500-ft (609.60- to 1371.60-m) true vertical depth subsea, and exhibit a varying degree of consolidation. Core data show that deeper pay intervals predominantly comprise fine-grained, poorly consolidated sandstones with good porosity development and permeabilities in the range of 100 to more than 1,000 md. These sand layers are often separated by shales and claystones. In contrast, the targeted sandstone layers in shallower intervals consist mostly of more-consolidated rock, with lower permeabilities in the range of 5 to 50 md. Up to eight sand intervals are targeted in each well. The subsea environment posed a challenge for well-completion design because of the multilayered completion strategy that was required to drain several of the pay units effectively in each well. Multizone frac-pack completions consisting of isolation packers and sand-control screens with separate pumping and production sleeves were used to provide sand control. An inner string of additional isolation seals, gauges, and intelligent control valves was run to provide zone-specific monitoring and production control. The initial well-completion work resulted in high skin values during production. A review of the post-stimulation data helped to identify the shortcomings in the designs and completion procedures. As a result, changes were made in the completion procedures, and frac-pack designs were tailored to suit the purposes. When these changes were implemented in subsequent wells, an improvement in well performance was seen, mostly in the form of reduced skin. This paper details this evolution, including favorable modification of completion procedures and the changes in pump schedule, treatment planning, and delivery methods during the frac-pack campaign. The benefit of adopting such an approach through the use of the methods and techniques implemented in this campaign can be applied to similar fields under development.