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

Abstract

Abstract Frac-Pack techniques were used in a recent subsea well completion campaign. The sandstones layers targeted for completion are generally present in shallow gas reservoirs with depths ranging from 2,000 to 4,500ft [609.60 to 1,371.60m] TVDSS and exhibit a varying degree of consolidation. Core data shows that deeper pay intervals predominately comprise of fine grained, poorly consolidated sandstones with good porosity development and permeabilities in the 100 to 1000+mD range. These sand layers are often separated by shales and claystones. In contrast to this, the target sandstone layers in shallower intervals mostly consist of more consolidated rock with lower permeabilities in the 5 to 50mD range. Up to eight sand intervals are targeted in each well. The subsea environment posed well completion design challenge because of the multi-layered completion strategy that was required to effectively drain several of the pay units in each well. Multi-zone, 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 were run to provide zone specific monitoring and production control. The initial well completion work resulted in high skin values during production. Review of post-stimulation data helped in identifying the shortcomings in designs and completion procedure. As a result of this, 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. The paper details this evolution, including favorable modification of completion procedures, as well as, the changes in pump schedule, treatment planning, and delivery methods during the frac-pack campaign. The benefit of adopting such an approach, using the methods and techniques used in this campaign, can be applied to similar fields under development.