Development of New Nano-particle-based Well Cement Formulation for Resisting Point Loads
Designing an appropriate cement slurry formulation for cementing wells in evaporite layers is a challenging task especially in deeper formations. Under HPHT (high pressure, high temperature) conditions, these layers are prone to creep toward the borehole which may consequently result in point loads on the cement sheath. Due to low flexural strengths of the conventional set cements, point loads are likely to cause cement failure and in some cases damage and collapse of casing string. A significant example of aforementioned problem occurs routinely in Gachsaran Formation (Miocene Age) in Southern Iran. In addition to concerns about low flexural strength of the cement, application of weighting agents are reported to cause severe inhomogeneity of the slurry due to high deposition of solid contents. Field and laboratory data confirm a rather high reduction of compressive as well as tensile strength of the cement caused by deposition especially in the lower parts of the well. In this study a systematic experiment design method was employed to obtain a cement slurry formulation to reduce cementing problems in Gachsaran Formation. Nano-Silica and Ex-RIPI which is a Single Walled Carbon Nano Tube (SWCNT) were utilized in formulation to improve rheological properties as well as tensile and compressive strength of set cement.The results of the experiments confirm that the application of Nano-Silica and SWCNT combined with an appropriate change in the percentage of other additives highly benefits the rheological and mechanical properties of the cement. Deposition of the solid contents is also shown to reduce significantly. Tensile and compressive strength of samples are improved. Other advantages are also obtained with these formulations, such as lower free water, lower setting time and lower fluid loss of the slurry.
Keywords - Cement, Fluid Loss, Nano-Silica, Strength, Drilling Well, Rheology, Slurry