The Evolution, Optimization & Experience of Multistage Frac Completions in a North Sea Environment
Authors: Koløy T. R. , Brække K. , Sørheim T. , Lønning P. 
Published: October 2014

Historically, cemented plug and perf completions have been used for wells requiring multistage fracturing and stimulation in the North Sea. This is a well-known and trusted process, but also time consuming. Often the turnaround time per stage in the North Sea is 3-7 days. With high rig and frac vessel rates, this excessive operational time can negatively impact project economics and well payback times. Consequently there is a drive to develop new systems to gain efficiencies without compromising the quality of the planned stimulation treatments in these applications. This paper will review two newly developed novel completion systems that significantly reduce time spent performing multistage stimulation in environments where cost and consequence of failure are high.

North America land frac operations rely heavily on ball drop actuated frac sleeve systems now commonly available in the market, however these typically require some over displacement of the previous frac stage and typically are only available for un-cemented liners. Hence, these are not always a good fit for North Sea frac applications. In order to prevent compromising the required stimulation treatment and allow flexibility to run cemented reservoir liners with frac valves, new technologies had to be developed. Both coiled tubing and wireline manipulated sliding sleeve/valve systems and ball-drop actuated systems have been developed and deployed depending on the various completion and stimulation challenges faced. Since the first installation in 2009 these systems have been proven and refined in multiple wells for two large operators. Various well installations will be discussed, illustrating that systems are being tailored for open hole and cemented environments both for proppant and acid frac stimulation treatments. The paper will give the audience insight into the depth of options available with these systems and explain how they are tailored for different types of stimulation and zonal isolation requirements. In addition operational considerations and experience will be shared.

Testing and field data will be presented to verify the development, installation, operation and success of these systems. This data include pressure and temperature data, downhole monitoring during stimulation and sleeve manipulation. An overview of the results and efficiencies achieved in the installations will be presented and compared to conventional methodologies. These completion solutions have a broad application in areas where fracturing and stimulation is required and project cost and risks are significant, both in conventional and unconventional stimulation and fracturing operations.

The installations discussed in the paper include first ever proppant frac done offshore through these systems, and introduction of specially developed intervention tools to aid the operation of the system. It also covers the first ever successful installation of cemented frac valve reservoir liner completions in an offshore environment as well as the use of dissolvable frac balls.