Evaluating the Efficiency of Nigerian Local Bentonite as an Extender in Oil Well Cementation

Nigerian local Bentonite has been in use as an extender in cementing operations since 2003 but has not been widely accepted because of some of its effects and challenges on most of the cement properties. This study is on the experimental and economic evaluation of the effect of Nigerian local bentonite obtained from Awkuzu in Anambra state and the imported bentonite on fresh and salt water cement slurry. The experimental test were basically on the thickening time and the ultrasonic compressive strength. Both local and foreign bentonites proved effective in fresh water cement slurries and can be used interchangeably except in cases where higher Plastic Viscosity (PV) and Yield Point (YP) are required.The foreign bentonite proved more effective under this high rheological properties for the same concentration with the local bentonite. In the salt water cement slurries both local and foreign bentonite were not fully effective, but the local bentonite responded better in the case study design in terms of rheology and free fluid tests. For the economic evaluation, a case study of a project involving the 13 3/8 inch casing cementing operation was simulated using fresh water cement slurry. The foreign bentonite contributed 21 % to the overall cement slurry cost while local bentonite contributed 2%.leading to a total savings of $7,509.85. Therefore, local bentonite could be a more efficient and cost effective means of cement slurry extender if properly managed and evaluated