No abstract

Preventing and curing fluid losses in limestone formations is one of the most challenging loss situations to prevent and control. Loss zones are unpredictable, due to large vugular zones and extended and connected fracture structures. Often these limestone intervals are depleted reservoirs. Typically, calcium carbonate pills containing various size distributions are part of the lost circulation armory in reservoir sections. However, results are highly variable and not suitable for large-scale losses. This is distinguished for those situations with the most-severe lost circulation, where chemical sealants may be more applicable than treatments by plugging particles.The paper discusses about use of a cross-linking polymer fluid treatment that enables operators to cure lost circulation zones in many different applications, providing distinct operational and economic advantages over conventional reactive and temperature activated methods.The paper discusses the customization of the polymer fluid to have specific thickening or setting time so this loss circulation fluid can be pumped through the existing bottomhole assembly (bit nozzle size greater than 14/32 nd ) without losing rig time associated with tripping and mixing conventional loss circulation material treatments (LCM). The paper discusses the execution procedures and cautions to be followed to improve cross-link LCM plug placement as well as chances to arrest losses.Due to biodegradable nature of organic cross-linking polymer plugs, it was used in sensitive reservoirs with minimal effect on the formation. The cross-linked plug or pill, with time and temperature, will break back to a fluid state and may be produced back and circulated from the wellbore.The discussions in this paper will further reveal the workings and applicability of cross-link polymer fluid to lower costs for drilling fluids, cementing and casing design.

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.