Multistage Cemented Sleeves in Vertical Wells - Lesson Learned

Abstract Stacked, tight gas reservoirs in central Oman require production enhancement from hydraulic fracturing to realize economic gas rates. Typically, plug and perf techniques are utilized for this purpose. However, completion alternative technology: Multistage frac sleeves (MSF) with closeable option were considered in a three well trial to gauge effectiveness in shutting off watered out zones. Secondary advantage of MSF would be operational efficiency gains by removal of wireline interventions entirely. Cemented sleeve completions in vertical wells are not common in today's oilfields globally. To remove as much uncertainty as practical, well candidates were chosen in fields/areas with historically high fracturing success rates (proppant placement as designed). The drilling requirements and operation were generally similar to conventional completions. The fracture design was adjusted to be more conservative than standard until frac success was established. Upon completion of the frac operation, ball seats were milled to allow full-bore access in subsequent interventions and ability to reclose any sleeve The result of the MSF trials was encouraging in this first deployment. The drilling and completion processes were smooth and without issues. Cased hole operations saw the successful opening of the toe initiation valve in all cases. The proppant placement ratio was even higher as compared to offset wells. Post frac production assessment shows comparable initial results, although it still require long-term testing for full validation of the MSF as a differentiator. Operational efficiencies were not able to achieve a significantly lower stage cycle as expected despite having a similar cycle per stage as plug and perf. This was due to several challenges during execution, such as possible debris or proppant between the ball and seat which meant a leak path to below zones during the frac. A screen out was experienced, high near-wellbore friction was common and so on. These unexpected hurdles required additional interventions including coiled tubing cleanouts, added perforations, and well flowbacks.in future deployments, MSFs will be required in multiple sand bodies to ensure the better zonal coverage, this was not achieved per the radioactive tracer results. Mastering the operation and adjusting the requirement during the ball drop operation will allow reduction of operation time as well as avoiding over flush. In this paper we share the journey and lessons learned of an uncommon application of a common technology (MSF). Unlike application in horizontal wells, a vertical well with MSF provides a different point of view on the technology capability. Challenges and solutions will be discussed to enrich Middle East fracturing experience.