Abstract
Abstract
The efficient placement of cement as a verified barrier above a distinct permeable zone in any oil and gas well is a constant challenge faced by the industry. Absence of isolation behind the casing represents a deficiency to the required well integrity barriers. A compromised well barrier may result in casing corrosion, leaks, and eventually sustained casing pressure which might lead the loss of the asset and/or endanger the safety or workers and/or the environment.
Ultimately, a compromised barrier implies compromised well integrity. Fluid displacement in ERD wells is different from conventional wells and the job conditions pose additional challenges. To ensure adequate cement placement in this ultra-ERD well, several challenges had to be addressed. Hence, an optimized cement placement method that focused on ECD management to prevent induced loss circulation included maintaining fluids displacement regimes, fluid density, and hydraulic friction hierarchy. Moreover, casing centralization was imperative. Limiting casing string movement once the string deployed successfully to bottom equally added to the challenge.
A system's approach was utilized to achieve the level of optimization desired. Slurry rheology and fluid loss control were adjusted. A pumping schedulethat ensured that optimum displacement efficiencies were achieved in line with the designed rheology was used. The impact of pump rates on downhole ECD regimes were equally evaluated and confirmed to be fit-for-purpose. Mud conditioning prior to the cement displacement and spacer wettability were also of paramount importance. A centralizer spacing resulting in >70% stand-off was utilized. These optimized practices represented the results of 3D modeling used to understand the fluid dynamics, and its distribution under the influence of a horizontal static pipe. This work also presented a comprehensive sensitivity analysis not only on the effects of thermal thinning on fluid rheology, but also on gravitational forces acting on the fluids in an ERD well. After execution, a combination of cement bond logs, ultrasonic measurements, and advanced interpretation techniques were used to evaluate the cement bond quality. The logs showed an improved cement bonding with minimal to no channeling, and excellent radial cement coverage.
As global hydrocarbon resources become harder to reach, ERD wells maybe required to access such subsurface targets. Adequate cementing well integrity is crucial to assuring the long-term integrity of such wells for the economic life of the assets. The practices implemented in this case history will contribute to expanding the tools and techniques available to engineers to achieving excellent barrier isolation in such wells.