Cost-effective wells operations in tight reservoirs require the introduction of innovative approaches, including advancements in hydraulic fracturing technology. The standard hydraulic fracturing fluid (cross-linked borate gel on a guar basis) is characterized by high viscosity and low residual conductivity of the fracture. Alternative low–viscosity hydraulic fracturing fluids based on a synthetic polymer - polyacrylamide (PAA), used in low-permeable reservoirs, require studying their effect not only on the proppant pack, but also on the filtration properties of the formation.
In the laboratory of RN-BashNIPIneft LLC, tests were carried out for the regained conductivity of the proppant pack and the regained core permeability for various hydraulic fracturing fluids. Cross-linked gel, linear gel and synthetic hydraulic fracturing fluid were provided to Kondaneft Oil Company JSC by three service companies. Recommended formulations were tested, and the possibilities of increasing the cleaning degree of a proppant pack or core sample from hydraulic fracturing fluid were considered. According to tests results the least colmatating fluid was a synthetic liquid based on polyacrylamide. A cross-linked gel based is characterized by low values of residual conductivity and showed a low permeability recovery potential (32-53%). The injection of uncapsulated breaker before the cross-linked gel allowed to increase the coefficient of permeability recovery from 53 to 75%. In comparison linear gel slightly exceeds the indicators of restoring the permeability of the core sample (54-64%). For synthetic hydraulic fracturing fluid based on PAA, according to recommended formulations from service companies with high concentrations of polymer and low concentration of the breaker, a recovery of residual core permeability comparable to cross-linked and linear gels (38-59%) was obtained. With the modification of the formulation (the reduction of polymer loading and the use of a high concentration of non-encapsulated breaker) the residual permeability was improved from 59 to 86%. The conclusion was made that a decrease in the polymer concentration and an increase in the concentration of the uncapsulated breaker for standard and synthetic hydraulic fracturing fluids should contribute to a minimal impact on the permeability of the rock. In laboratory conditions low-viscosity hydraulic fracturing fluids showed a high cleaning degree of the proppant pack and rock sample compared to standard hydraulic fracturing fluid.
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