Rig Time Was Saved in a Remote Two -Rig Operation Completing Horizontal Openhole Wells with Expandable Sand Screen Through Careful Selection and Aggressive Juggling of Multiple Reservoir Drill-In Fluids

摘要

A drilling and completion program was developed for a two-rig deepwater completion campaign in West Africa that included openhole water injectors and oil producers drilled in a highly unconsolidated sandstone reservoir with permeability that ranged from several Darcy to tens of Darcies. The limited storage onshore and discharge options mandated recycling fluids from well to well. To minimize rig time on the two semi-submersibles, a plan was developed to juggle the five required fluid systems: ? an oil-based drilling system for the uphole sections; ? a reservoir drill-in fluid; ? a screen-running fluid; ? a breaker system; ? a clear completion brine. Each system was designed and tested during the planning stage to meet project objectives. For the expanded sand screen application, the 8?-in. hole diameter could not be washed out more than 9? in. Wellbore stability required the drill-in fluid to be at least 10.8 lb/gal to control the shale and avoid hole eccentricity. Fluid rheology was critical as circulating density could not exceed 12.3 lb/gal to stay below the predicted 12.5-lb/gal fracture gradient, and good hole cleaning was essential in the horizontal sections that reached out to 1,000 m. When running the screen, particulates in the mud had to pass through the 150-μm mesh otherwise the screen would plug and ultimately collapse. To attain the required weight, the screen-running fluid utilized fine micron-grind barite to attain density while avoiding screen plugging. Once the screen was in place and expanded, a delayed breaker was spotted in the screen to eventually dissolve the carbonate filtercake left behind by the drill-in fluid. The well was then displaced to completion brine. Reducing cross contamination during these displacements was important to avoid costly disposal. The unique chemistry and properties of these systems demanded a comprehensive fluid management and quality control plan that began with product procurement, through the warehouse and mixing plant, onboard the supply vessels that stored these fluids, and final transfer and use on the rigs. Avoiding cross contamination and preservation of each of the different fluid for each successive well was crucial to minimize damage to the target sand, reduce rig time, and to reduce overall cost.