Evaluating the Performance of Clay Stabilizers for Drilling and Fractioning Processes using Solid Surface Zeta Potential
Fracking fluids are used to increase the permeability of rocks during the hydraulic drilling process. The investigation of the interaction of these chemical additives with the subsurface rocks eases the recovery of oil and gas during drilling operations.
During hydraulic fracturing, “fracking” fluid is forced into underground rock at high pressure to open the rock and recover oil or gas. Fracking fluid is water with additives that can vary from site to site. Additives include viscosity and interfacial tension modifiers, antimicrobials, corrosion inhibitors, and proppants that wedge into the fractures and keep them “propped” open.
Another type of additive is the clay stabilizer. Depending on the rock being drilled, clays may be present that swell in the presence of fresh water, for example. If the clay swells, it can block the removal of the oil and gas and thereby limit the well’s performance. The purpose of the clay stabilizer is to prevent the clay from swelling. One strategy is to treat the clay with a polymer that adsorbs onto it and blocks the contact with water.
Currently, coreflow test is considered as a standard method to evaluate permanent clay stabilizer. In this test, water with clay stabilizer is injected into a core sample to treat the surface under the desired pressure and temperature. Afterwards, fresh water is injected. If the clay swells, a remarkable increase in the pressure drop across the core will be observed. The length of such procedure depends on the initial core permeability and the injection rate and can take up to several days.
To accelerate the clay stabilizer evaluation alternative measurement techniques are needed. In this report the interaction between the additives and the clay surface is tested using the zeta potential as an indicator for the stabilizers quality.
The clay mineral typically has a strong negative charge, so a positively charged polymer is used as the clay stabilizer to exploit favorable electrostatic interactions. If the polymer successfully coats the clay, then the measured zeta potential should become more positive thereby reflecting the change in surface chemistry. Because the underground rock can reach high temperatures, it is also important to verify that exposure to high temperatures does not degrade or break down the clay-stabilizer. Heat-aging studies thus complement the evaluation of clay stabilizers.
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