Successful Implementation of Light Weight Proppant for Stimulation of Tight Sandstones in Russia on Vinogradova Oilfield

Abstract

Abstract Hard-to-recover reserves, including low and ultra-low-permeability reservoirs, where conventional high-conductivity hydraulic fracturing approaches are not applicable, require revision of standard fracturing design approaches. The Vinogradova field in Beloyarsky district, Russia comprises thin net pay sections with relatively low permeability (~1 mD). Optimizing fracturing treatments required progressing along a long learning curve involving appropriate fracturing fluid design, proppant selection and treatment design. The primary goal of the treatments was to increase fracture half-length (Xf) while controlling frac height growth through weak barriers into water bearing zones. Initially, conventional treatments were designed to use 60 metric tons of intermediate strength proppant (ISP, SG 3.2) blended in crosslinked gel as a frac fluid. Subsequent optimization led to a design with hybrid fluid (linear and crosslinked gel), which helped to increase Xf but did not limit height growth (Ryazanov et al, 2016). The final optimized design used linear gel as the sole fluid, lightweight proppant (LWP, SG 2.6), and reduced proppant volume; this design reduced fracture height growth by 40% to 50% and increased Xf by 30% to 40%, which resulted in reduced water cut and increased cumulative hydrocarbon production. In this study we describe the process of frac fluid and proppant testing and selection, design approaches and frac geometry modeling, and explain job execution parameters. Selecting proppant is a critical step for fracture design, especially for designs using low-viscosity fluids. High-quality proppant with high roundness and sphericity and a narrow proppant particles size distribution applied within recommended stress limits minimizes fines generation and negative effect on production. Using LWP with fluids that have low proppant-carrying capacity improves vertical and horizontal proppant transport inside the fracture due to the lower weight of individual proppant grains, i.e. less settling. To evaluate the effect of LWP on well production in the Vinogradova oilfield in comparison with ISP, we studied wells with similar parameters - k*h, volume of proppant, proppant concentration, fluid type and concentration of polymer, pumping rate, and compared initial, 1-year cumulative oil production and PI. Production analysis demonstrated the benefits of using LWP over ISP in fracture treatments with low-viscosity fluid: Initial production was 30% higher and 1-year cumulative production 40% higher in wells treated with LWP. As well, wells treated with LWP showed increased PI in comparison with ISP-treated wells, where significant improvement was demonstrated during first 7 months of wells production. This confirms the benefits of LWP as a propping agent as compared with ISP in designs that use low-viscosity fluids: higher frac half-length and improved proppant transport inside fracture. LWP is widely utilized around the world mostly on conventional frac jobs with crosslinked polymer fluids. Use of ceramic LWP with low-viscosity fluid is poorly studied because most of such treatments are pumped with natural sand in shale and other unconventional formations. However, the significant difference in permeability between unconventional wells vs tight sandstones requires the use of more conductive and crush-resistant ceramics as propping agent. As the industry increasingly faces reservoirs with complex geology (including Hard-to-recover), where the conventional wide fracture design is no longer required, understanding the effect of LWP application with low-viscosity fluid in conventionals will be useful to collect experience for designing future treatments.