The Use of Swell Packer's as a Replacement and Alternative to Cementing

Abstract

Abstract Today the cement job is the most common technique used to achieve the critical hydraulic seal between casing and formation to isolate individual zones and prevent annular flow. As such, it is often considered one of the most important operations during construction of the well. However as an isolation mechanism, it can fail, and may not provide the down hole zonal isolation needed during the life of the well. Annular packers based on the swelling of rubber in hydrocarbons are being used by different operators to replace cementing and provide the critical zonal isolation required down hole. The swell packer is able to overcome many of the shortcomings associated with conventional cement operations, and provide superior zonal isolation in both simple and complex well environments. Using swell packers also simplifies and reduces the risk of the well construction process and provides significant cost savings due to reductions in rig time and materials. This paper focuses on the application of swell packers to provide an effective hydraulic seal between the formation and the casing as an alternative to cementing and perforating. Specific case histories from Nigeria, Malaysia and the North Sea are used to illustrate the success and application of this innovative technology. Introduction The primary cement job is considered one of the most important operations in the construction of a gas, water, injector or oil well. The cement sheath provides the critical hydraulic seal between the casing and the formation, isolating individual zones and preventing annular flow. Interzonal communication can result in:Loss of productivity due to cross flow of fluids along the cement sheath, or influx of fluids from adjoining formations.Injection of fluids into unintended zones on injector wells.Incomplete stimulation of intended zones, or the escape of fluids along the annulus in either matrix or hydraulic fracturing operations.Failed Leak off or Formation Integrity tests.Sand production due to early water encroachment.Gas migration through the cement sheath, resulting in sustained casing pressure both at surface and in the intermediate strings.Expensive Remedial Operations. Whilst zonal isolation is considered one of the most important functions of cementing, designing and executing a cement job to achieve the end objective is a complex process which must take into account many variables. The different challenges down hole such as weak formations, excessive wash outs, over pressurized gas and fluid zones, deviated and horizontal well trajectories, poor casing centralization, salt formations and HPHT conditions often lead to the pumping of complex and expensive cement systems to try to achieve a hydraulic seal. This is coupled with an operation which is both equipment- and rig-time intensive. Even with extensive engineering, sophisticated cement systems and well-executed cement jobs, failures still occur during the placement of the cement slurry or during the life of the well. This is further complicated by the fact that the amount of zonal isolation required is often hard to qualify, and measuring the success of a cement job can be difficult.