Deepwater DST Planning and Operations From a DP Vessel

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 90557, "Deepwater DST Planning and Operations From a DP Vessel," by Robert J. Stomp, SPE, ConocoPhillips Co.; Graham J. Fraser, The Expro Group; and Stephen C. Actis, SPE, Luke F. Eaton, SPE, and Kerry C. Freedman, ConocoPhillips Co., prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. ConocoPhillips is developing the Magnolia field with a tension-leg platform (TLP) in 4,674 ft of water in the U.S. Gulf of Mexico (GOM). The field was discovered in 1999, and appraisal wells were drilled in 2000 and 2001. The precompletion and drillstem-test (DST) operations overcame several challenges, including frac packing a thick, fine-grained interval and well testing from a dynamically positioned (DP) semisubmersible drilling rig while simultaneously transferring produced hydrocarbons to a transportation barge moored to the rig. Introduction The Magnolia asset team was formed in 2001 before drilling the last appraisal well. Front end loading leading up to field sanction in December 2001 included concept selection and field development plans. The Magnolia field would be developed from a TLP to provide direct vertical access for recompletions, future sidetrack drilling, flow assurance, and cost-effective remediation. The Magnolia development wells were predrilled (i.e., drilled from a mobile offshore drilling unit while the TLP was being built). The advantages of predrilling included minimizing capital exposure risks until shallow water-flow sands were isolated, allowing TLP well operations to be conducted with a lighter, lower-cost completion rig, which would further reduce the size and cost of the TLP hull; additional reservoir characterization before TLP installation; accelerating plateau production; and testing completion techniques in the precompleted well before “batch” completions of the remaining wells. The B-25 reservoir, the primary pay horizon at the Magnolia field, was the zone selected for a DST. Zone B-25 is characterized throughout the field by its highly laminated sequences and large gross thicknesses. Whole-core data and fluid samples were obtained from the GB783-2ST2 appraisal well. Evaluation of the appraisal-well data classified the reservoir-rock matrix as a coarse siltstone with the average mean grain-size diameter of 41 µm. Overall, the mean grain-size diameters ranged from 25 to 71 µm in Well GB783-2ST2. Test Objectives The objective of performing a precompletion DST was to obtain critical information regarding completion design and reservoir issues. This information would be needed before the planned batch-completion program scheduled to begin in the fourth quarter of 2004.