Self Healing Durable Cement; Development, Lab Testing, and Field Execution

Abstract

Abstract Pressure and temperature changes during the life of the well (drilling/production) cause some Casing-Casing annulus (CCA) pressure leaks in the annulus between 13 3/8" and 9 5/8" casings, and 13 3/8" and 18 5/8" casings thereby indicating that the well barriers failed to isolate all the zones and subsequently resulting in the migration of the fluid to the surface. Such failures in wellbore isolation prevent us from taking full potential of ourhigh performance wells. Under most failure conditions, tensile strength of a cement has a greater impact on its failure as compared to the cement's compressive strength. Consequently, increasing tensile strength of a cement is higher priority than increasing its relative compressive strength. This can be achieved by using additives such as latex, polyvinyl alcohol or fibers or simply by increasing cement flexibility. The objective of this paper is to discuss the development, testing and field execution of a new type of cement, Self-Healing Durable Cement to mitigate such failures due to pressure or temperature cycling. This new cement was developed utilizing novel components that results in a cement with a reduced Young's Modulus. Lower Young's Modulus makes the cement more elastic in order to resist pressure and temperature cycling, absorb applied stresses and prevent cement cracks. The developed Self-Healing Durable Cement also provides an additional benefit of mechanical properties enhancement as the included additive exhibits swelling and sealing capacity when contacted by hydrocarbon fluids. In the event cracks form in the cement, this will be a path for the fluid to trigger the swelling and self-healing mechanism. The paper includes detailed testing data for thickening time, rheology, free water, settling at different ranges of densities. An additional test was also included to evaluate the durability of the system with time. Mechanical properties testing was performed for cement samples after 10, 20 and 30 days curing at representative targeted field conditions. Single stage triaxial tests were performed on dry cement core plugs to measure static and dynamic properties through ultrasonic and shear velocities. These properties were determined at confining pressures and included the Young's modulus, the Poisson's Ratio, and Peak Strength. Offset wells cemented with conventional formulations have shown CCA pressure with slight oil flows. The developed Self-Healing Durable Cement was applied for 13 3/8" casing covering oil bearing zones. The deployments were declared successful since negative testing and temperature and pressure cycling did not result in any CCA. Ultimately, good cementing performance is always measured by having zero psi casing/casing annulus pressure.