Robust Cement Design Ensuring Well Integrity in Cyclic Steam Stimulation Wells: A Comprehensive Approach with Case Studies

Abstract Cyclic Steam Stimulation (CSS) an Enhanced Oil Recovery (EOR) technique is a steam injection approach where multiple steam cycles are applied for recovering heavy oil by lowering its viscosity. CSS has been applied in multiple wells of western India typically having depth of 1200m, where temperature can soar up to 320°C with anticipated steam pressures at the well head reaching upto 2100 PSI. CSS wells have extreme temperature variations which creates large amount of stresses on the cement sheath. In CSS wells it is necessary to ensure quality cementation all the way up to surface to prevent steam migration into unintended zones. This is pivotal for maintaining thermal recovery effectiveness, safeguarding well integrity and addressing safety and environmental hazards. Additionally operational challenges like losses during cementation is encountered due to incompetent formations, while extreme high temperatures can lead to cracks on cement sheath and steam breakouts posing significant risks. To address aforementioned challenges, the designed cement must be lightweight, flexible, and thermally resilient in nature. Simulation studies have recommended use of 1.44 specific gravity (SG) lightweight design to mitigate losses during cementation. Meticulous laboratory testing led to developing an innovative lightweight cement design of 1.44SG, incorporating hollow glass spheres (HGS) having a density of 0.28SG. The use of HGS ensured a higher cement-to-water ratio content and improved design parameters compared to cenosphere or other lightweight based designs. The designed cement underwent multiple thermal cycling for 24 days from 75°C to 320° in a High Pressure High Temperature curing chamber simulating the actual well conditions. After rigorous testing the design met the required mechanical parameters of Young's modulus, Poisson's ratio, Compressive strength, Tensile strength and Water permeability for long term zonal isolation. Critically the young's modulus of designed cement is less than that of the formation preventing damage to the cement sheath. The role of optimized specialty additives is crucial firstly in yielding flexible cement for withstanding thermal shock absorption and secondly for preventing slurry sedimentation along with mitigating migration of lightweight HGS in cement column. In this paper detailed case studies will discuss about the innovative cement design that has been field implemented successfully for the first time in ONGC using in house expertise across 9 CSS wells in western India. The wells are presently producing after CSS application without well integrity issues. The paper will also emphasize on meticulous planning, best practices, proper dry blending and batch mixing to ensure extremely lightweight HGS remained homogeneous. The paper also highlights how the robust cement design along with holistic cementing practices like proper mud removal plan, casing centralization, mud conditioning and pipe movement are equally important for proper cementation job in CSS wells.