Abstract

The overall success of hydraulic fracturing treatments is determined by proppant placement, pay zone coverage, and conductivity sustainment. Common strategies to maximize fracturing success are to increase concentration and use high-strength proppants. Conventional low-viscosity fluid (i.e. slick water) has a poor capability to carry proppant, which usually result in early proppant settling and accumulation at the bottom of the fractures. By contrast, high-viscosity fluid (i.e. cross-linked gel) could reduce proppant-settling issues but is limited in the length and coverage of proppant placement in unconventional reservoirs due to friction losses. To overcome these limitations, an engineered low-viscosity fluid with very high proppant-carrying capacity has been developed, evaluated, and designed to improve proppant placement within developed fracture networks.

To quantify the fluid rheology and proppant-carrying capacity of the new fluid, steady shear viscosity and static column tests have been conducted at various temperatures. The newly developed fluid is characterized as non-cross-linked polymer system with low polymer loading and low viscosity, yet it is capable of suspending and transporting conventional proppants better than a high-viscosity fluid (e.g. cross-linked gel) with high polymer loading. As observed from lab data, the fluid can significantly improve proppant suspension even for relatively large particles (e.g. 30/50 sand). Moreover, it is less sensitive to higher temperature when compared to conventional high-viscosity fluid. The experimental data is integrated into a three-dimensional fracture simulator. The model is used to simulate complex fracture network growth and evaluate proppant transport efficiency under reservoir conditions.

The engineered non-cross-linked low-viscosity fluid could send proppant within both hydraulic fractures and reactivated natural fracture networks to enhance the conductive reservoir volume. Experimental tests and simulation results compare the proppant placement efficiency of the engineered low-viscosity fluid with other available fracturing fluids (including slick water and cross-linked gel). Due to unique rheology of new fluid, the pipe friction losses, and consequently, the required horsepower to pump the fluid is lower than the conventional cross-linked fluids. Additionally, the propped fracture volume could be significantly enhanced by using the engineered fluid, due to its unique proppant-carrying capacity.

This work describes both experimental and numerical procedures to evaluate and demonstrate the enhanced capabilities and performance of the engineered non-cross-linked polymer fluid. This newly invented fluid could be beneficial for significantly reducing proppant settling and improving proppant distribution and pay zone coverage in complex fracture networks. The engineered low-viscosity fluid with high proppant carrying capacity could help to enhance production by improving the proppant transport while minimizing the horsepower required for pumping.

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