Songklanakarin J. Sci. Technol. 43 (1), 118-126, Jan. - Feb. 2021 Original Article Influence of Metakaolin and nano-clay on compressive strength and thickening time of class G oil well cement Akeem Olatunde Arinkoola 1, 2* , Kazeem Kolapo Salam 1 , Solomon Oluyemi Alagbe 1 , Ayodele Sunday Afolayan 1 , Taofeek Olalekan Salawudeen 1 , Monsurat Omolola Jimoh 1 , Ilozurike Ugochukwu Duru 3 , Olugbenga Jimoh Hammed 4 and Tunde Adamson Adeosun 5 1 Ladoke Akintola University of Technology, Ogbomoso, Nigeria 2 African University of Science and Technology, Abuja, Nigeria 3 Federal University of Technology, Owerri, Nigeria 4 African Regional Centre for Space Science and Technology Education in English, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria 5 Yaba College of Technology, Lagos, Nigeria Received: 27 August 2019; Accepted: 18 November 2019 Abstract In this research, the Compressive Strength (CS) and Thickening Time (TT) of oil well cement with different Metakaolin (MK) dosages was evaluated in the presence of Nanoclay (NC). The experiments followed a randomized Box- Behnken Design (BBD) using 5 - 15 wt. % MK by weight of cement and 5-15 wt. % NC by weight of MK. The CS and TT were assessed and optimized using Response Surface Methodology (RSM). The results show that CS increases linearly with NC and hyperbolically with MK. Cement slurries with 5–15 wt.% NC shorten TT by about 35 minutes in the presence of 5 wt.% MK. A TT reduction of 103 minutes was recorded when MK was increased to 15 wt.% in the slurry with 5wt.% NC. At the optimum conditions with 10.78 wt. % MK and 13.73 wt. % NC, CS and TT were 3029±2.65 psi and 410±1.25 minutes, respectively. Keywords: g-class cement, supplementary material, compressive strength, thickening time, Box-Behnken Design 1. Introduction Oil well cementing was introduced in the late 1920s primarily because drilling fluid alone cannot prevent the well bore from collapsing (Joshi & Lohita, 1997). Other reasons for cementing oil wells include: protecting oil producing zones against salt water, protecting the casing from collapse under pressure, protecting well casings against corrosion, reducing the risk of groundwater contamination by hydro- *Corresponding author Email address: aoarinkoola@lautech.edu.ng carbons or salt water, and zonal isolation. There are two critical conditions that a successful oil well cement should satisfy: ability to remain pumpable for a sufficient time to ensure proper placement in the well bore, and ability to build and maintain sufficient mechanical strength to provide adequate support for the casing. Ordinary Portland Cements (OPCs) have been used as oil well cements for many years. However, OPCs are reported to undergo strength loss with increased porosity and severe loss of durability at elevated temperatures, in acid rich, geothermal and deep oil well environments (Ma, Chen, & Chen, 2014; Won, Lee, Na, Lee, & Choi, 2015). Thus a special class of cements, the oil well cements (OWCs),