The Resurgence of ECP's at Prudhoe Bay/North Slope

Abstract

Abstract This paper reviews historical and current ECP (External Casing Packer) applications by BP and ARCO in Alaska. The potential of the tool together with its reliability and effectiveness is critically evaluated. The "success rate" so far has been variable but it is believed that the reasons for this have not been properly investigated and understood up to now. Problems (related to equipment, procedures, job design, and so on) which caused various failures have been identified and analysed in detail. Case studies are presented to demonstrate why some failures occur and how they could be avoided. Procedures and proposals to combat the identified problems are recommended. Because the associated application environment and problems are better understood and the lessons learnt are better communicated, and ECP technology is being renewed at a pace not seen before, it is believed that the ECP is a viable completion tool if used properly. Introduction To obtain a better understanding of ECP's performance and to improve their effectiveness for the increasing challenges in zonal isolation in horizontal and multilateral wells, a comprehensive internal study was carried out in 1994/5 within BP world-wide and ARCO Alaska and with the cooperation of some major ECP manufacturers. This paper concentrates on part of the results relating to ECP applications in Alaska. Basics of ECP's and Setting Tool Operations It is intended here to provide some basic principles which are necessary to understand the operations and the associated problems discussed later. Principles of ECPs. ECPs or by other names such as CAPs (Casing Annulus Packer) or ACPs (Annulus Casing Packer), are made of a metal mandrel (a [pup] joint of casing) and an external elastomer tube bladder with an inflation valve system. This elastomer tube is always reinforced by typically metal ribs either continuously or only at the end sections. Both ends of the rubber tube are sealed and secured to the steel collars which have the nominal OD of the packer to protect the rubber element in the middle to a certain extent. Note conventionally the ECP is identified by the casing OD/weight/grade and the seal element length. The OD of the ECP has to be specified separately. One of the collar contains the valve system, which connects and controls the inflation fluid from inside the mandrel (the central hole) to the outside to expand and inflate the bladder and then shuts, all controlled by shear-pin-determined differential pressures. The valves are shear-pinned to predetermined pressure values to control the function of the inflation port, depending on the differential pressure between the central hole and the annulus. There are typically 2 main valves: one to open (e.g. Lock Shut Valve "LSV" or Delay Open Valve "DOV") the inflation port and the other to close it (Inflation Control Valve "ICV") once the internal pressure has reached the pre-set level. There may be some minor check valves in the system. P. 83