CLAY SWELLING AND NON-TARGET CONSUMPTION OF FRACTURING FLUID ADDITIVES: DIAGNOSTICS AND FIELD EXPERIENCE USING FORMATION WATER AT THE VOSTOCHNY MOLDABEK FIELD

Abstract

The effectiveness of hydraulic fracturing (HF) largely depends on how well fracture conductivity is preserved after the fracturing fluid interacts with the reservoir rock. This paper systematizes the permeability-damage mechanisms related to the water sensitivity of clay minerals interlayer smectite swelling, osmotic effects, deflocculation and fines migration and examines the non-target consumption pathways of clay stabilizers (KCl, quaternary ammonium compounds) and gel breakers (ammonium persulfate, hydrogen peroxide, enzymes) on rock minerals and co-additives. It is shown that the nominal reagent dosage, evaluated without a material balance, can simultaneously overestimate both the degree of clay stabilization and the extent of polymer network degradation. A minimum laboratory testing matrix is proposed, including oriented-sample XRD analysis, sorption isotherms, coreflood tests and retained fracture-conductivity tests. Using the Vostochny Moldabek field (Embamunaigaz JSC) as a case study, it is shown that the permeability decline observed when the reservoir is saturated with low-salinity water is caused by clay and mica swelling, whereas formation water does not cause such degradation. A formation­water-based fracturing technology is substantiated and implemented, using a polyacrylamide-based gel instead of guar gum, which is unsuitable at a water salinity above 130 g/L. Field results from eight wells show that production rates after fracturing on formation water with the synthetic polymer exceeded those of the standard technology by more than five times.