Results From the Heidrun Field Cased-Hole Gravel Packs

Abstract

Summary During the initial phase of the Heidrun field development, five wells were precompleted with state-of-the-art cased-hole gravel-packing techniques. The wells were tested and temporarily abandoned, awaiting tieback to the Heidrun tension-leg platform (TLP). This paper describes the completion techniques applied and presents results of an evaluation of gravel-pack efficiency for the wells. Flow and buildup tests were carried out on the semisubmersible drilling rig before and after gravel packing to evaluate initial productivity. Stabilized well-test data acquired on the Heidrun TLP at full production are presented to document ultimate completion performance for each well. Innovations Perforating with tubing-conveyed perforating guns on a drillstem-test (DST) string allowed perforating, perforation cleanup and flowback, pre-gravel-pack testing, and gravel prepacking to be performed in a single run. A unique loss-control-material (LCM) formula was developed and applied to control fluid losses to the formation. Prepack modeling and alternating stages of clear brine and slurry were used to optimize gravel placement. A temporary-abandonment system was developed and installed that used a weight-actuated ball valve to abandon the well temporarily without placing any damaging fluids across the production zone. Gravel-pack screen assemblies included alternative-path gravel placement with four shunt tubes per gravel-pack screen assembly. The innovative gravel-packing techniques used at Heidrun resulted in high completion productivity and correspondingly high flow rates. A study performed to evaluate the economic impact of acceleration showed that going from a 20,000- to a 30,000-BOPD well rate added $108 million in pretax net present value to Heidrun project economics. Actual results will be greater because well rates have exceeded 43,000 BOPD. Introduction The Heidrun field lies 120 miles offshore mid-Norway in the Haltenbanken area in approximately 1,140 ft of water in the Norwegian Sea. Hydrocarbons were proven in three main reservoirs of Jurassic age: the Middle Jurassic Fangst group and the Lower Jurassic Tilje and Are formations. Fig. 1 provides a type log. The field is being developed from the world's first concrete-hull TLP. Ten wells were predrilled from the main 56-slot template along with six subsea, seawater injection wells drilled from the two four-slot satellite templates. First oil production occurred on Oct. 18, 1995. The Heidrun TLP is currently producing at plateau rate of more than 230,000 BOPD.