Design of light-Weight Cenospheres Cement Slurries Improved by a Mixture of Nano Silica, CFs and Silica Flour for Oil Wellbores

In the oil and gas industry, during drilling and cementing operations, lost circulation is a widespread common and costly problem. Lost circulation mainly occurs through the weak formations and high permeable zones. This study aimed to design and build light-weight cement slurries with high compressive strength to solve this issue. Cenospheres additive reduced the cement slurry density in order to eliminate water requirement. Then, nano-silica, due to its high pozzolanic reactions and fine particles, accelerated the cement hydrations and reduced pore areas in the cement slurry. Another vital additive was Cellulosic Fiber (CF), which improved cement properties by absorbing nano silica and Calcium Silicate Hydrate (C-S-H) gels to its surface. This fiber acted as a bridge to prevent Cenospheres from separating in the cement matrix. Silica Flour (SF) in this formulation also played a crucial role in improving compressive strength. Scanning Electron Microscopy (SEM) presented that selecting an appropriate amount of these additives in cement slurry formulations is a significant factor to obtain a condensed and packed cement structure. The results obtained in this study showed that the combined materials could reduce cement slurry density in the range of 67 to 97 lb/ft³. The best sample among them is the sample with a density of 86 lb/ft³, obtaining cement slurry with compressive strength of 2845 psi, 6 cm³ fluid lo Further density reduction which is can reduce loss circulation in depleted fields or in filed with low fracture gradients ss and zero free water. In this study, three acceptable rheological properties namely; Plastic Viscosity (PV), Yield Point (YP), Gel Strength (GS), and thickening time were also obtained in this sample.