Instituting Retarders for Geopolymers Developed for Downhole Applications

Abstract

Geopolymers are a cementitious material that has been under study for many years. The material is noticed as a potential full replacement for traditional cementitious material both in construction and petroleum industry. The applicability of geopolymer material in the oil & gas industry, for well cementing and zonal isolation applications, is dependent on the development of chemical admixtures that can enhance performance and prepare the material for downhole conditions. Many admixtures are available in literature, however no inclusive study has been presented for their efficiency and applicability yet under a variety of temperatures from low to elevated. The results are highly dependable on the source of solid precursor, which in this case is granite-based geopolymer. In this study, chemical admixtures of different roles have been examined on granite-based geopolymer material for oil & gas applications. The solid precursor mix design was previously developed inhouse at the University of Stavanger. The study focuses on the applicability of chemical admixtures using cement testing equipment following on available standards of cement testing to create a realistic comparison with traditional cement. The study touches up on both, applicability in the field under downhole conditions and scientific analysis of chemical reactions triggered by chemical admixtures. This thesis is part of the SafeRock Project which is in collaboration between UiS and operator and service companies. Thus, the need to present efficient admixtures and focus on their behavior in downhole conditions was a necessity to progress through the project. This work is composed of a review section describing the work in this research study and published articles that dive in-depth into the scientific findings. The papers are attached in the appendix and labeled using roman numbers. The outcome of this research can be summarized by the following papers: Paper I: A variety of chemical admixtures were tested with the objective of finding a suitable retarder for granite-based geopolymer system at an operational temperature of 50oC. Rheological and short-term mechanical properties were examined for curing periods up to 7 days. Findings included the combination of different admixtures together where it was concluded that zinc and potassium species have a great impact on the setting time and that more in-depth analysis must be done specially the effect of temperature on slurry behavior and mechanical properties. Paper II: The effect of temperature and admixture concentrations was examined on workability, viscosity, fluid loss, compressive strength, sonic strength development, and crystallography. Results highlighted the effect of chemical admixture and the link between mix design and operational temperature. Paper III: Analysis of microstructure and crystallography was conducted in-depth to find the reason behind poisoning phenomenon of retarders and the properties of the outcome product. Results did not highlight any accurate visualization of the retarders’ effect, which suggests the focus must be on a reaction level. In addition, results indicated that the retarders had an active window up to 14 days, and then they were incorporated into the bulk matrix as observed in mechanical strength measurements. Paper IV: Analysis of reaction mechanism was done using computational modeling (density functional theory calculations) and Raman spectroscopy at 50oC. An in-house lab-controlled sample was developed to avoid the complexity of minerals involved in the reaction. Paper V: Investigation of possible role of calcium and sodium species as strength development agents, in addition to zinc and potassium species as retarders, was conducted at operational temperature of 60oC BHCT & 80oC BHST. Findings indicated that strength development agents can assist in countering the poisoning phenomenon imposed on mechanical properties by retarders. However, tuning of concentrations must be studied to have a mix design with superior properties. Paper VI: Development of three mix designs and tuning using solid precursors. Rheological and mechanical properties were tested to assess the applicability of these neat mix designs at a range of temperature between 5 to 60oC. It is concluded that operational temperature and composition of mix designs highly affect the kinetics of the reaction, or in other words the degree of completion of the reaction.