Free radical polymerisation of methacrylates with thermal initiator in clay rock

• Polymerisation method with thermal initiator developed for use in clay rock
• Porosity measurements done using C-14 PMMA autoradiography and TGA
• Zone disturbed by drilling profiled with C-14-PMMA autoradiography and SEM/EDAX
• Porosity increase in the disturbed zone result of the break-up of calcite grains

Clay rock porosity analysis with C-14-PMMA autoradiography was the focus of this work. Methodology for impregnating clay rock with C-14 labelled methacrylate, and fixing it via free radical polymerisation initiated with thermal initiator was developed towards this end. The effect of drilling was of particular interest because of their effect on the porosity and therefore they were studied in detail. Two different methacrylates were tested in this work. C-14 labelling enables measuring porosity through the autoradiography of samples impregnated with methyl methacrylate (MMA). The supporting analysis was done with thermogravimetric analysis (TGA), Scanning Electron Microscopy supplemented by energy dispersive X-ray spectrometry (SEM/EDAX) and X-ray diffraction (XRD).Procedures for impregnating clay rock and fixing C-14-labelled methacrylates in the sample were developed and optimised successfully. The two clay rock discs studied had mean porosities of (7.9 ± 0.8) % and (7.6 ± 0.8) % as measured by autoradiography. Autoradiography also shows that a disturbed zone can be seen as a region of high porosity in the drilled clay rock cores. In this case, the porosity of the disturbed zone is more or less double of the bulk porosity. TGA measurements gave bulk porosity values that varied between 4.1–15.0%. The TGA values were uncertain due difficulties associated with the sample matrix degrading at the same time as the methacrylate inside the sample. They could still be used to estimate the general range of the porosity. Pure MMA gave bulk porosity of (12.9 ± 7.5) % while mixture composed of 75% Hydroxyethyl methacrylate (HEMA) and 25% MMA gave a bulk porosity of (4.1 ± 6.0) %. SEM/EDAX results showed that calcite grains were more fractured than quartz grains in the disturbed zones. Quartz grains were mostly unaffected. This supports the conclusion that the porosity increase in the disturbed zone is intergranular and result of the break-up of calcite grains.