Carbonation of Olivine Microparticles in Wellbore Cement to Mitigate Carbon dioxide Attack

Abstract:

The invasion of Portland wellbore cement-based porous matrix with subsurface geofluids of pH 2-5 stimulates leaching of calcium hydroxide (CH) and calcium silicate hydrate (CSH) increasing the porosity and precipitation of Si(Al)-anhydrous gel leading to strength loss and physical failure. Loss of strength in wellbore cement causes zonal isolation failure, compromises casing-cement bond strength, enhances lose circulation, and leakage in a depleted plugged and abandoned oil and gas well. Olivine carbonation is a well-documented process in nature that is been applied in wellbore cement to mitigate CH and CSH carbonation.

The objective of this study is to add controlled amounts of olivine to wellbore cement and investigate its inactivity in high alkaline Portland cement and initiation of self-healing in fractured Olivine enhanced wellbore cement flooded with CO₂ at the subsurface temperature of 90⁰C and 95% RH.

Neat cement was made and 5%, 15%, and 30% WOC olivine was added to cement slurry and cured for 28 days at 90⁰C and 95% RH. Scanning Electron Microscopy (SEM), Elemental Dispersive Spectroscopy (EDS), and Raman Microscopy were performed on the cleaned and dried cement plugs as well as triaxial test. Petrophysical and mechanical properties were also measured. The core plugs were fractured, CT scanned, and flooded with CO₂ brines.

From SEM and EDS analysis unreactive olivine is seen in hydrated Portland cement plugs which suggest olivine serves as a sacrificial microparticle filler within cement and will react in low pH milieus to form carbonates minimizing the carbonation of CHS and CH thus enhancing the wellbore cement. From CT scans, we expect to see carbonate formation in the fractured plugs suggesting self-healing and thus reduction in porosity and permeability. Olivine is also expected to enhance the mechanical properties of the cement. Thus, controlled amounts of Olivine can be added to cement to initiate self-healing in case fractures develop over time.