Stabilization of clay-rich interburdens using silica nanoparticles

Abstract

Detachment of clay particles from clay-rich interburdens is the main source of solid production in coal seam gas wells (CSG), costing the Australian operators millions of dollars every year. Several techniques have been proposed to reduce the solid production and consequent pump failure in already constructed open hole/slotted liner wells. Amongst all remedial techniques for these existing problematic wells, chemical stabilization seems to be the most practical method. The high cost of chemical additives, their environmental issues, potential low effectiveness and technical difficulties for their placement downhole have, however, hindered their wide application. In particular, the long-term effect of current chemical additives on interburden stability and their influence on coal seam matrix gas diffusion need further investigation. In this study, the application of colloidal silica nanoparticle solution (silica SOL) as a long-term chemical stabilization method for clay-rich interburden in CSG wells was investigated. A series of comprehensive experiments were performed to investigate the effect of the silica SOL on stability of pure compacted dry smectite clays and clay-rich sandstone samples in stationary and turbulent conditions (resembling the wellbore condition during gas production) using a uniquely designed experimental setup. Additionally the effect of silica SOL on coal and its gas adsorption was analyzed. The results of this study demonstrated that the silica SOL is a suitable candidate for long-term chemical stabilization of clay minerals as a cost-efficient and environmentally friendly additive. Its non-reactivity with coal and its inert response on gas sorption is another significant benefit of the proposed chemical solution.