Engineering Hydraulic Fracturing Chemical Treatment to Minimize Water Blocks: A Simulated Reservoir-on-a-Chip Approach

Abstract

Fracturing fluid trapping is one of the major sources of damage after well stimulation as the remaining fluids in the pore space reduce the effective hydrocarbon permeability. Especially in tight formations, fluid trapping can require significant time to clean up, even at a high production rate. Outcrop cores have traditionally been used to confirm the existence of damage and to quantify it. However, it is difficult to clearly discern the trapping mechanism in cores and to accurately determine the trapping location and the volume of residual fluid.In this study, a reservoir-on-a-chip approach was adapted to visualize the residual water blocking process of fracturing fluids. The major advances in using this approach are the clear visualization of the trapping process in the pore space and the control of testing parameters including formation wettability, reservoir/stimulation fluid properties, flow rate, and reservoir pore-space geometry. This study includes two sections: A fluid mechanical study to determine which reservoir conditions require chemical treatments to mitigate water blocks; and a chemical evaluation study to determine how well chemicals, such as surfactants, can alleviate severe water block conditions. Experimental results confirm that the geometry of the pore throat plays a critical role in trapping and releasing fluid. Furthermore, displacing reservoir fluid at high rates, or with a higher oil viscosity, increases cleanup efficiency. With this fundamental understanding, the reservoir conditions that require chemical treatment can be identified. Cleanup efficiency was significantly improved by using a surfactant. The designs of engineered chemical treatments to mitigate water blocks under specific conditions will be discussed in this paper. These new findings expand the industry's understanding of the fluid mechanics behind residual fluid trapping, capillary effects, and the implications for engineered fracturing fluid systems.

The Study to Improve Oil Recovery through the Clay State Change during Low Salinity Water Flooding in Sandstones

“…5 To prevent such problems, oil fields usually use bactericides, antiswelling treatments, anticorrosion treatments, and other methods to improve the quality of the sewage water. For wells with such problems, oil field companies usually use acidification 6 and fracturing 7 measures to resolve the problems. These measures might increase the economic cost of water injection.…”

The Effect of Fracturing Fluid Saturation on Natural Gas Flow Behavior in Tight Reservoirs

“…This behavior can reduce the gas flow channel, and cause aqueous phase trapping (APT), which will influence the natural gas exploitation [7,8]. Usually, through quick and effective flowback to reduce the soaking time and liquid filtration distance, the APT damage can be relieved [9], and some chemical treatments for improving the flowback rate of the aqueous phase have been widely investigated [10][11][12][13][14][15]. Some equations have been proposed to evaluate the APT damage.…”

Chip Flood (vs) Core Flood—Assessment of Flowback and Oil Productivity in Oil-Wet Hydraulic Fractured Rocks

“…In the case of gas reservoirs, evaporation of water block due to gas expansion has also been considered as another method of the removal of formation damage caused due to invasion [4] [5], but the time-scale of expansion-driven evaporation is significantly longer than that of displacement-driven flowback mechanism. The application of surfactants to reduce the capillary entrapment of invaded fluid has been a plausible solution suggested by Liang et al (2016) [11] and Kim et al (2016) [12], who demonstrated surfactant's effectiveness by conducting laboratory experiments.…”