Monitoring and continuous reservoir evaluation is very important aspect of a well-planned Waterflood program. Valuable well and reservoir information needs to be obtained during the course of waterflood operation, which helps in determining oil recovery and decide on the future strategy of the Waterflood program. Keeping this in view, KOC decided to drill some observation wells completed with cemented fiberglass casing for monitoring the flood performance in sandstone and carbonate reservoirs in two different fields. The use of fiberglass casing facilitates the application of some deep induction logging tools for measuring the changes in formation properties behind the casing. Vital information such as oil saturation change during waterflood operation, vertical sweep efficiency and arrival time of different fluid fronts can be determined from these log surveys in fiberglass casing.

Cemented fiberglass casing and liners were used over the years globally mainly for observation wells and in some cases for highly corrosive injection wells. However, the use of fiberglass tubulars as casing or liner needs careful planning for its safe deployment and longer life. The casing policy, depth, drilling mud weight and logging requirement mainly dictates the selection of a particular size and thickness of fiberglass casing. Special cementing program needs to be formulated due to its lesser strength properties (collapse, burst & axial rating) compared to normal steel casing. They can be run either as complete fiberglass casing/liner or as combination string with steel casing depending on the zone of interest and purpose of deployment.

KOC has successfully deployed 9-5/8" size fiberglass casing as combination string with steel casing in more than 20 vertical/deviated observation wells. The depth of deployment ranges from 4500 ft. in sandstone formation to around 8000 ft. in carbonate formation. Additional care was taken while preparing/ planning the cementation to prevent failure of the fiberglass casing while cementing across deeper formations.

This paper describes in detail the design and planning of the observation well completed with fiberglass casing. Different scenarios leading to selection of particular size of fiberglass casing supported by StressCheck application and cementing technique are presented. Some special consideration related to cementing and running in equipment, which needs careful attention. The paper with the deployment cases will be a quick guide to engineers.

You can access this article if you purchase or spend a download.