An Integrated Bio-Compounded Emulsion and Its Use in SRV Fracturing of Carbonate Rocks with Sand-Carrying Fracturing Fluids

Using low-molecular-weight modified bio-monomers, acrylamide monomers, hydrolysis control monomers, micro-electric-charged monomers as well as other functional additives, an integrated bio-compounded emulsion is developed through grafting polymerization to deal with the problems encountered in the stimulated-reservoir-volume (SRV) fracturing of carbonate reservoirs with sand-carrying fracturing fluids. In developing the integrated bio-compounded emulsion, focuses are placed on the fast dissolution of the drag reducers used and fast online viscosifying of the fracturing fluid. The integrated bio-compound emulsion developed has high rate of production and multiple functions. Using this integrated bio-compound emulsion, a sand-carrying fracturing fluid of high lubricating capacity high suspending capacity is developed. An optimized specific fracturing program is designed for carbonate reservoir stimulation, aimed at controlling the height of the fractures, producing complex fracture network, controlling viscosity and increasing sand content as well as stimulating the reservoir to the full. The effective concentration, degree of hydrolysis and molecular weight of the emulsion are ±30%, 40%-50% and (1,200-1,300) × 10⁴, respectively. At micro-electric-charged monomers concentration of 2.0% and low- molecular-weight modified bio-monomers concentration of 0.6%, the emulsion produced has the optimum properties; the dissolution time is less then 20 s, the 3-min viscosifying rate is more than 90%, and the CAC₁ and CAC₂ are 1.79 g/L and 3.89 g/L, respectively. Evaluation of the general performance of the fracturing fluid formulated with the emulsion showed that the percent drag reductions of the low-viscosity fracturing fluid, the medium-viscosity fracturing fluid and the high-viscosity fracturing fluid are at least 75%, 70% and 60%, respectively. The sustained drag reduction can be maintained at 96% or higher. The viscosities of the high-viscosity and the medium-viscosity fracturing fluids which are sheared 90 min at 110 ℃ and 170 s⁻¹ are 45-50 mPa·s and 20-25 mPa·s, respectively. A medium-viscosity fracturing fluid (0.4%) having Tanδ (a parameter characterizing viscoelasticity of a system) of less than 0.4 possesses good sand carrying capacity, the settling rate of the proppants in it can be as low as 0.1 cm/s. The fracturing fluid formulated with the emulsion, after gel breaking, has viscosity of less than 3 mm²/s, surface tension of less than 27 mN/m, and residue content of less than 20 mg/L. This technology has been used in fracturing the carbonate reservoirs in the Ordos Basin on 30 wells, including pilot test and large scale application of SRV fracturing with increased sand content in the fracturing fluid. The fracturing fluids used in the fracturing jobs have stable properties, with 95% of the sanding activity successfully performed and satisfied stimulation effect achieved. This new technology has provided a strong technical support to the development of tight carbonate rock reservoirs.