A Model to Minimize Risk of Cement Plug failure in HPHT Conditions

Abstract

Cement plugs play a central role in providing hydraulic isolation for oil and gas well integrity. They are routinely required for abandonment purposes, drilling sidetracks and wellbore remedial operations. Despite extensive industry experience from around the world, there are many cases in high-pressure, high-temperature (HPHT) wells where an otherwise straightforward cement plug operation has led to major non-productive time (NPT) resulting in escalation of overall well costs. There are a number of issues that increase risks especially when it involves placement of high-density cement slurries in HPHT wells. Downhole conditions present additional challenges, which make it difficult to do the job right the first time. Whenever a job goes wrong in these conditions there is often an impact apart from the immediate non-productive rig time. In addition to the increase in costs there are other associated impact, e.g. potential loss of downhole barrier with negative implications for safety and the environment. Many studies and publications have highlighted the risk of unmitigated fluids contamination during placement as one of the most common causes of cement plug failure. One service company with extensive experience operating in the North Sea has used a model that integrates design and planning combined with a structured, detail-oriented process workflow to reduce surface execution and downhole placement risks thereby increasing the chances of success. The model relies heavily on close cooperation between the service company and the operator. Following the same strategy, this model can be applied in other geographical environments with the core objective of improving quality ensuring the job is always done right the first time. Some case histories, which inspire confidence in the ability to sustain the success rate, are described in this paper.