POROSITY–STRENGTH RELATIONSHIPS IN CLASS C, G, AND H OIL WELL CEMENTS UNDER DIFFERENT CURING CONDITIONS AND METHODS

Abstract

This thesis investigates the relationship between porosity and compressive strength of class C, G, and H oil well cements in 3 different testing series. Given the critical role cement plays in maintaining well integrity, this research aims to establish a baseline to optimize future cement formulations and recipes for oil and gas, geothermal, carbon capture and storage (CCS), and abandonment operations. There were three experimental test series conducted for this thesis: Test Series 1 comprised of standardized cubic and cylindrical samples cured at room temperature (~25ºC) over a period that ranges from 3 – 60 days, Test Series 2 consists of cylindrical samples cast in borosilicate glass vials under the same curing conditions to evaluate any effects caused by the difference in molds used, and finally Test Series #3 were cured at different temperatures (~25ºC, 50ºC, 75ºC) with both continuous curing and a 24 hours dry period curing condition for the dry samples.Porosity was measured using various techniques such as nuclear magnetic resonance (NMR) relaxometry, nitrogen gas expansion porosimetry, density methods, and sonic velocity analysis, while the strength of the cement recipes was measured using both destructive and non-destructive techniques such as standardized unconfined compressive strength (UCS) tests and ultrasonic pulse velocity (UPV), respectively. The results indicated an inverse relationship between porosity and compressive strength across all cement classes and curing conditions. Class G and H cements were observed to have similar strength evolution and both outperformed Class C due to cement compositional differences and how the chemical components react during the hydration process. Borosilicate glass molds used to cast the cement specimens yielded porosity and strength values similar to that of standardized molds, which validated their use and applicability as cost-effective single use alternatives for mass production of samples. In addition, a comparative analysis of the length-to-diameter ratio correction factors for the cylindrical samples was done to compare a new alternative model to that of existing correction models for strength prediction. This summary contributes a robust experimental foundation for predictive modeling and evaluation of cement integrity that can be used to support innovation in cement formulation and well-construction standards.