Technical Evaluation of Portland-Limestone Cement as a Replacement for Ordinary Portland Cement

Abstract

Portland -Limestone Cement (PLC) is becoming increasingly prevalent as a replacement for Ordinary Portland Cement (OPC) in many industries as a method to reduce carbon dioxide emissions associated with its manufacture. The construction industry has led this charge, and the oilwell cementing industry is catching up, especially in the Northeast United States, where one major cement manufacturer has replaced their commercially available Class A oilwell cement with a Class L cement containing ground limestone as a major component. This paper expands on the conventional lab testing from previously published case studies by comparing performance of OPC vs. PLC in tests that are less commonly seen in oilfield cement lab but are vital to understanding PLC's ability to provide long-term zonal isolation. The following four tests are performed on both OPC and PLC and their results are compared. Solubility in acid mine drainage water from a mine in Ohio, set cement expansion with various concentrations of light-burned magnesium oxide expansion agent, set cement permeability, and high temperature compressive strength testing are all performed. The high temperature compressive strength testing is performed at both 250 degrees Fahrenheit and 300 degrees Fahrenheit to compare each cement's susceptibility to strength retrogression, and the tests are also performed with the addition of silica to verify that the strength of the PLC is stabilized as it is with OPC. X-ray diffraction testing is also performed on all samples after seven days of curing to show the hydration products of both OPC and PLC, with and without silica, at elevated temperatures. The comparative results show that PLC is an adequate sealing material in many cases where OPC is currently used. Solubility of OPC and PLC are both negligible in weak acid solutions, such as acid mine drainage water. Cement matrix permeability for samples cured at 150 °F is comparable between PLC and OPC. The response of PLC to the addition of post-set expansion additives is comparable to that of OPC. The temperature stability of PLC is comparable to OPC at 200 °F and 250 °F, but at 300 °F the PLC shows compressive strength degradation which is made worse by the addition of silica.