An Al/Zr-Based Clay Stabilizer for High pH Applications

Abstract

Sandstone formations are exposed to a variety of high pH fluids, including: hydraulic fracturing using high pH borate gels, alkaline-based chemical enhanced oil recovery (EOR) methods, water-based drilling fluids, and cementing filtrate. High pH values can trigger fines migration, and subsequent loss of permeability and well productivity. An aluminum/zirconium-based (Al/Zr) clay stabilizer was developed to control fines migration at high pH applications. The objective of this study is to assess the effectiveness of this new stabilizer and compare its performance with commercially available stabilizers. Laboratory studies were performed using Berea sandstone (8 wt. % clays; mainly kaolinite) cores, 6 in. length and 1.5 in. diameter. Tetramethyl ammonium chloride (TMAC) and choline chloride were used for comparison as two commercial clay stabilizers. Various coreflood experiments were conducted to determine the effect of the three stabilizers on core permeability (from 64 to 100 mD) at various temperatures up to 300 °F. In these experiments, a preflush that included 2 wt. % stabilizer was injected, followed by injection of 2 wt. % NaOH solution. The latter represented high pH filtrate that can invade the formation during any treatment that includes alkaline fluids. The pressure drop across the core was measured and samples of the core effluent were collected. Inductively coupled plasma optical emission spectrometry (winlab32 software) was used to measure the concentrations of Al, Zr, Fe, Ca, and Mg. ZetaPALS (BIC software) was used to measure the surface charge on the kaolinite particles. Lab results indicated that the new clay stabilizer worked effectively up to 300 °F following 2 wt. % NaOH. No reduction in permeability was noted in any of coreflood tests using sandstone cores of various initial permeabilities. The concentrations of various cations were found to be a function of core mineralogy. TMAC and choline chloride were not effective when followed by fresh water and incompatible with the high pH fluids. The new stabilizer is environmentally friendly, and can be used in hydraulic fracturing, and alkaline-based chemical EOR methods to mitigate clay related problems.