The effect of fluid additives on the compaction creep of sand aggregates and sandstone cylinders

Abstract

Compaction creep of reservoir rocks causes surface subsidence above producing oil and gas fields worldwide. To investigate if compaction creep could be restricted both uniaxial compaction and triaxial stress relaxation experiments are performed on sand aggregates (Beaujean) and sandstone cylinders (Bentheim and Fontainebleau) respectively. Different pore fluids were tested for their effect on compaction creep, namely distilled water, aluminium chloride solution (0.1 M and 0.01 M), sodium chloride solution (0.3 M), sodium sulfate solution (0.15 M), sodium silicate solution (silica saturated solution) and lab air (i.e. dry). The uniaxial compaction experiments were performed in constant stress mode both at room temperature and 80˚C. The stress relaxation experiments were performed at 80˚C. All samples showed creep deformation. The main compaction deformation mechanism for wet Beaujean sand and Bentheim sandstone was inferred to be fluid enhanced microcracking, which was inhibited by aluminium chloride and by sodium silicate. Creep was enhanced by sodium chloride and by sodium sulfate. The results are in line with the known effects of pH and the presence of sodium or aluminium ions on stress corrosion cracking. The stress relaxation experiments on Fontainebleau sandstone did not deliver consistent results; further research is required on this material.