State-of-the-art drilling fluid made of produced formation water for prevention of clay swelling: Experimental Investigation

Abstract

This study focuses on the feasibility of reusing formation water as inhibitive base water for water-based drilling fluids (WBDFs) to reduce the need for freshwater and commercial salts. A real produced formation water (PFB) with known composition and a synthetic produced formation brine (SPFB) were compared to commercially available clay inhibitors, i.e., KCl and NaCl salts. Experiments show that the PFB and SPFB have acceptable free swelling indexes and sedimentation rates. According to the zeta potential measurements, they similarly decrease the charge of clay surfaces and reduce swelling of Na-bentonite. Besides, the cutting dispersion test illustrates that PFB and SPFB can reduce the interaction between the Pabdeh and Gurpi shales (Iranian formations) with drilling fluid. Drilling fluids made of the PFB and SPFB have rheological properties, including apparent viscosity, plastic viscosity, yield point, and gel strength less than a typical inhibitive WBDF made of NaCl. API filtration loss of both PFB- and SPFB-based drilling fluids at high bentonite concentrations (more than 12.5wt.%) is similar to the same as the KCl-based drilling fluid, indicating their close inhibition power to the KCl solution. Finally, SEM analysis confirms that the texture/morphology of sodium bentonite exposed to the PFB and SPFB is close to that of the KCl solution and formation water inhibition power is more than NaCl and near to KCl. Eventually, formation water as a potential inhibitive water for water-based drilling fluids, is preferred to the commercial salts from both environmental and economic aspects.