Abstract
After hydraulic fracturing treatment, a reduction in permeability caused by the invasion of fracturing fluids is an inevitable problem, which is called water blocking damage. Therefore, it is important to mitigate and eliminate water blocking damage to improve the flow capacities of formation fluids and flowback rates of the fracturing fluid. However, the steady-state core flow method cannot quickly and accurately evaluate the effects of chemical agents in enhancing the fluid flow capacities in tight reservoirs. This paper introduces a time-saving and accurate method, pressure transmission test (PTT), which can quickly and quantitatively evaluate the liquid flow capacities and gas-drive flowback rates of a new nanoemulsion. Furthermore, scanning electron microscopy (SEM) was used to analyze the damage mechanism of different fluids and the adsorption of chemical agents on the rock surface. Parallel core flow experiments were used to evaluate the effects of the nanoemulsion on enhancing flowback rates in heterogeneous tight reservoirs. Experimental results show that the water blocking damage mechanisms differ in matrices and fractures. The main channels for gas channeling are fractures in cracked cores and pores in non-cracked cores. Cracked cores suffer less damage from water blocking than non-cracked cores, but have a lower potential to reduce water saturation. The PTT and SEM results show that the permeability reduction in tight sandstones caused by invasion of external fluids can be list as guar gum fracturing fluid > slickwater > brine. Parallel core flow experiments show that for low-permeability heterogenous sandstone reservoirs with a certain permeability ratio, the nanoemulsion can not only reduce reverse gas channeling degree, but also increase the flowback rate of the fracturing fluid. The nanoemulsion system provides a new solution to mitigate and eliminate water blocking damage caused by fracturing fluids in tight sandstone gas reservoirs.
Highlights
As the global demand for oil and gas increases, more and more advanced technologies are investigated to maximize production, such as horizontal well drilling and fracturing
The pressure transmission test (PTT) and scanning electron microscopy (SEM) results show that the permeability reduction in tight sandstones caused by invasion of external fluids can be list as guar gum fracturing fluid > slickwater > brine
The nanoemulsion system provides a new solution to mitigate and eliminate water blocking damage caused by fracturing fluids in tight sandstone gas reservoirs
Summary
As the global demand for oil and gas increases, more and more advanced technologies are investigated to maximize production, such as horizontal well drilling and fracturing. Completion fluid, fracturing fluid, or other external fluids are difficult to flow back after invading during the exploitation of oil and gas reservoirs, the water saturation of the reservoir increases and the oil and gas phase permeabilities decrease, which is the definition of water blocking damage (Shao et al 2010; Lei et al 2017; Meng et al 2019). Aminnaji et al (2015), Gahrooei and Ghazanfari (2017) and Liu et al (2015) used water-based fluorinated nanoemulsion to alter the wettability of carbonate and sandstone reservoirs and results showed that nanoemulsions altered the rock surfaces to be water- and oil-repellent and at the same time increased liquid mobility
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