Water Blocks in Tight Formations: The Role of Matrix/Fracture Interaction in Hydrocarbon-Permeability Reduction and Its Implications in the Use of Enhanced Oil Recovery Techniques

Abstract

Summary Hydraulic fracturing is used to obtain economical rates from tight and unconventional formations by increasing the surface area of the reservoir within the flowing distance to a high-conductivity pathway. However, a significant fraction of the fracturing fluid is never recovered, and thus may reduce the hydrocarbon permeability near the fracture. Here, we experimentally mimic the water-invasion process during fracturing, and measure the effective permeability changes in a low-permeability core. Measurements of water flowback and effective permeability as a function of interfacial tension (IFT), flow rate, and shut-in time suggest that water is being held at the fracture face because of the capillary discontinuity (i.e., when the water leaves the matrix and enters a space with minimal capillary pressure). This effect arises from the capillary interaction between the matrix and the fracture, and is akin to the capillary end effect in coreflood experiments. The results show that this effect, although only a laboratory experimental artifact for conventional reservoirs, can be a significant source of effective hydrocarbon-permeability reduction by fracturing-fluid invasion into the formation in unconventional and tight reservoirs.

Formation Damage due to Drilling and Fracturing Fluids and Its Solution for Tight Naturally Fractured Sandstone Reservoirs

“…However, gel residuals can block fractures and pores at fracture faces, thus impeding the flow of hydrocarbon [23][24][25]. Besides gel residuals, water can imbibe rock matrix and cause phase trapping, which reduces hydrocarbon permeability due to multiphase flow [26][27][28][29]. Formation damage due to drilling and fracturing fluids is likely different in the low-permeability sandstone with well-developed natural fractures.…”

An Experiment-Based Study of Formation Damage Using a Microetching Model Displacement Method

“…The image of the microscopic model of drilling fluid displacing stratum fluid after image processing (Figure 6a) clearly shows that, in the process of the damage of the model by drilling fluid, the oil from drilling fluid, stratum water, and gas are mixed with each other, forming a large number of bubbles, water droplets and oil droplets, which results in a large number of two-phase fluid or even three-phase fluid interfaces, with intense surface tension. When these interfaces move to narrow pores and throats, a very large resistance is generated, which makes fluid percolation extremely difficult, forming water and hydrocarbon lock effects [45,46]. The image of the microscopic model of drilling fluid displacing stratum fluid after image processing (Figure 6a) clearly shows that, in the process of the damage of the model by drilling fluid, the oil from drilling fluid, stratum water, and gas are mixed with each other, forming a large number of bubbles, water droplets and oil droplets, which results in a large number of two-phase fluid or even three-phase fluid interfaces, with intense surface tension.…”

The role of supercritical carbon dioxide for recovery of shale gas and sequestration in gas shale reservoirs

“…The waterblocking effect leads to a decrease in permeability. 102,114 3 CO 2 emissions and CO 2 utilization, and storage…”