Planning and Execution of Highly Overbalanced Completions from a Floating Rig: The Ursa-Princess Waterflood Project

Abstract

The Ursa-Princess Waterflood (UPWF) targets the Lower Yellow sand, the main reservoir in the Mars-Ursa basin in Mississippi Canyon, about 60 miles south of the mouth of the Mississippi river in the Gulf of Mexico, USA. The Lower Yellow sand, a world class Upper Miocene turbidite reservoir, has been on production in the Ursa and Princess fields since 1999, and has been drawn down nearly to the bubble point. The waterflood is intended to increase and stabilize reservoir pressure, and to improve sweep efficiency. To accomplish this, four subsea injectors were designed and constructed to inject treated seawater at some 40,000 bbl/day each for a target life of 30 years.As the Lower Yellow reservoir was already highly depleted, unique risks were identified in the planned subsea completion operations, to be conducted from a Mobile Offshore Drilling Unit (MODU). Seawater, used as a completion fluid, was expected to be up to 4000 psi overbalanced to the reservoir, depending on the well location. This created the risk of either uncontrollable fluid level drop in the marine riser or extreme impairment to the sandface completion. In order to maintain well control with a fluid level at the surface and still deliver low skin completions, multiple design and procedural issues needed to be addressed, including:1. Control systems on the rig and riser system to prevent uncontrollable fluid level drop, 2.Perforating systems to minimize impairment in a high overbalance environment without adding undue risk to well control, 3.Pill designs that could both control fluid loss at the sand face and clean up effectively, 4.Downhole completion systems capable of functioning either under very high pressure differentials or against very high loss rates, 5.Development of high burst screens that could withstand pilling in the event mechanical fluid loss devices failed. As more Deepwater reservoirs approach depletion, specialized tools and procedures will be required to continue to deliver safe and effective sandface completions from floating rigs. This paper details many of these considerations, and summarizes the execution experience and results for one such reservoir.