Abstract
Abstract
One of the challenges encountered in hydraulic fracturing of unconventional resources is casing deformation. Casing deformation statistics vary across different regions of the world, but it is estimated to affect 20-30% of horizontal wells in some areas of operations. The consequences of casing failures can be varied but, in many cases, it affects the well production, wellbore accessibility and in some rare instances presents a situation of well control and its associated risks.
Incidentally, most literature on casing deformation pertains to "plug & perf" fracturing operations in cemented completions though pipe deformation is known to occur in multi-stage fracturing (MSF) sleeves type of openhole completions as well. Intuitively, the two failure mechanisms may appear similar instead they represent very diverse well conditions that lead to pipe deformation.
Tubular damage during fracturing is not caused by a single, consistent reason. Multiple mechanisms may be responsible for casing deformation; formation rock properties, wellbore configuration, cyclic loads acting on the tubulars, tubular quality, cement bond, or simply some operational aspects during drilling and completion conducive to pipe deformation. Tubing stresses analysis of the lower completion and especially of the individual components of the openhole MSF completion is seldom done. A comprehensive study was initiated by first validating the key data and parameters, multi-arm caliper data in conjunction with downhole camera imaging, and review of the physical mill-out patterns of frac plugs (in cased hole completions) and ball-seats used in MSFs to understand the damage pattern. This work was supported by detailed geo-mechanical properties profiles, diagnostic injection tests analysis, and evaluation of casing integrity under anticipated fracture loads.
One of the primary learnings from this study was that wellbore quality had a significant bearing on the post-frac wellbore integrity for both types of well completions. The study indicated that well profile, design, and tool placement in the well also had a strong influence on axial load distribution in open-hole multistage completions. The mode of failure in openhole multistage wells was different than those seen in cemented liners. These differences do not necessarily fall under the domain of formation movement experienced in geomechanically complex and tectonically active areas.
Since reservoir uncertainties are a reality, a good wellbore quality cannot always be guaranteed. It becomes necessary to manage pipe deformation with mitigating practices. This paper provides practical solutions to pipe deformation in cemented and openhole completions. The operational workflows allow upfront assessment with analytical tools to model the stress loads. By understanding the primary factors that affect well integrity, the likelihood of casing failure can be predicted and avoided ahead of time, save fracturing costs across high-risk areas, and not jeopardize production from multimillion-dollar completions. Managing well integrity is essential for development of hydrocarbon resources while preserving the environment and assuring safety of personnel.