Design and Successful Field Execution of Sand Control Completions in Naturally Fractured Reservoirs

Abstract

The Clair Ridge field development is located in the UK Continental Shelf, 142 miles north of mainland Scotland. This is the second phase of the Clair Field Development involving a subsea pre-drilling campaign and programmed long term well suspensions prior to new platform arrival. Two pre-drilled horizontal wells have been successfully completed with downhole sand screens in a geologically challenging environment, and suspended with cleaned-up hydrocarbons across the reservoir until the wells can be tied back to the platform in 2016. The reservoir drilling and completion design strategy was complicated due to the reservoir section being a naturally fractured sandstone alongside high permeability and weak matrix intervals susceptible to sand production. This presented several challenges to the team: the high risk of losses whilst drilling the reservoir with the probable use of large volumes of lost circulation materials (LCM), the risk of damage to the natural fractures or high permeability zones impacting subsequent well productivity, the need for down hole sand control completions, the ability to run these across a reservoir section containing large amounts of sized calcium carbonate LCM materials and also the mitigation of screen plugging from filter cake and LCM during well start-up. The downhole completion hardware was specifically designed to allow efficient placement of chemical breaker to dissolve LCM and filter cake to reduce the risk of sand screen plugging. The importance of minimising screen plugging and formation damage was also dictated by long term suspension of the pre-drilled wells required for start-up of a new offshore platform. This paper details the reservoir sand control completion design philosophy, the drilling and completion fluid system design and assurance testing in readiness for the technical challenges to be faced and the overall operational practices used in the field execution. The well flow-back and test results exceeded expectations, indicating good flowing length, greater than predicted Productivity Index (PI) and absence of skin damage, which creates significant benefit for the Clair Ridge project.