Mechanism of Formation Damage at Elevated Temperature

Abstract

The pore and grain surface of reservoir rocks often has clay and other fine material attached onto pore walls. It has been long recognized that brine salinity and pH are key factors affecting the attractive forces between pore surfaces and fines. If mobilized particles are assembled in sufficient quantities, they obstruct pore throats and reduce the permeability of the formation. There is anecdotal evidence of substantial fines migration during steam injection enhanced oil recovery operations. As of yet, the mechanism of fines release with temperature is unexplained. The Derjaguin, Landau, Verwey, and Overbeek theory of colloidal stability is used in conjunction with laboratory, core-scale experiments to demonstrate that high temperature, alkaline pH, and low salinity (typical characteristics of steam condensate) are sufficient to induce fines mobilization. Temperature is a key variable in calculations of fines stability. Hot-water floods are performed in Berea sandstone at temperatures ranging from 20°C to 200°C. Permeability reduction is observed with temperature increase and fines mobilization occurs repeatably at a particular temperature that varies with solution pH and ionic strength. A scanning electron microscope is used to analyze composition of the effluent samples collected during experiments. It confirms the production of fine clay material. On the practical side, this study provides design criteria for steam injection operations so as to control fines production.