The Effect of Fracture-Face Matrix Damage on Productivity of Fractures With Infinite and Finite Conductivities in Shale-Gas Reservoirs

Abstract

Summary Producing natural gas from shale-gas reservoirs presents a great challenge to petroleum engineers owing to the low-permeability nature of this type of gas reservoir. Large-scale and expensive hydraulic-fracturing operations are often required for enhancing gas well productivity. Because of the shaly characteristics of the reservoir rock, the hydraulically fractured gas wells are vulnerable to damage by fracturing fluids. However, the true significance of the formation damage in shale-gas reservoirs is still not clear. It is highly desirable to have a simple method for predicting the degree of fracture-face matrix damage and for optimizing fracturing treatments. This paper is meant to fill this gap. A new mathematical model was developed in this study to predict the effect of fracture-face matrix damage on the productivity of fractured gas wells in shale-gas reservoirs. A unique feature of the new model is that it considers reservoir/fracture crossflow in finite-conductivity fractures. Results of the model analyses were sensitized to reservoir properties and facture-face matrix-skin properties determined by the fracturing-fluid properties and treatment conditions. Large ranges of possible leakoff and spurt-loss coefficients were investigated. We concluded that, in the ranges of reservoir and fluid properties used in this study, well productivity should drop by less than 15% even if the residual matrix permeability is reduced to only 5% of the virgin reservoir permeability in the damage zone. Neglecting the resistance to flow in the fracture will overestimate the effect of matrix damage on well productivity. The well-productivity drop caused by matrix damage is most sensitive to the invasion depth and damaged permeability.

Analyses of Processes, Mechanisms, and Preventive Measures of Shale-Gas Reservoir Fluid, Completion, and Formation Damage

“…However, imbibition phenomenon can still create problems. Low-damaging fluids such as KCl solutions and leak-off controlling polymer containing fluids are preferred for hydraulic fracturing (Li et al (2012). Resin coating of the proppants can help reduce the proppant embedment and fine particle generation problems (Reiniche et al (2013).…”

“…The trends in production after hydraulic fracturing is strongly influenced by decrease of fracture conductivity and reservoir formation permeability by damage caused during fracturing and post-fracturing production impairment is influenced by various potential damage mechanisms involved in stimulation of unconventional-gas-wells (Shaoul et al 2011, Guo et al 2011, Bahrami et al 2012, and Li et al 2012. Jackson and Rai (2012) describe the sources of skin effects involved in hydraulically-fractured shale gas wells completion efficiency caused by various completion resistances.…”

“…The fluid mobility can also be reduced because of formation of emulsions, such as gas bubbles in water and water droplets in gas, during transport of a gas/water fluid system through porous media (Mikhailov and Nikolaevskii, 2000). Non-Newtonian apparent viscosity effects also may be important (Li et al, 2012). A fracturing-fluid clean-up inefficiency skin, water entrapment or blockage pseudo-skin, or multiphase pseudo-skin, s mp , results from the water-blockage due to hybrid relative permeability jail effects of the gas-water fluid system (Jackson and Rai, 2012).…”

“…Mechanical damage from the hydraulic fracturing completion damage occurs by proppantembedment layer thickness formed by proppant penetration into reservoir formation matrix as a result of increase of closure stress during production after hydraulic fracturing ( Fig. 1) depending on the proppant size distribution, concentration, and reservoir formation type and surface of hydraulically-created fracture (Guo et al 2011 andLi et al 2012). Bennion (2002) and Reiniche et al (2013) explain that the stress-induced mechanical interactions between the proppant and reservoir formation fracture surface can cause proppant embedment into the near-fracture-face formation matrix, formation grains deformation, proppant and formation grains crushing, disintegration, and fine particles generation, and subsequent pore plugging in the compacted near-fracture face formation, the near-fracture face reduced permeability region can capture the fine particles internally during production.…”

Finite Element Investigation of Flow Field Below Asymmetric Drill Bits for Reverse Circulation in Drilling Tight Oil and Gas Reservoirs

“…The low conductivity of wells is attributed not only to the natural low permeability of reservoir rocks but also the permeability damage by the water from the drilling and fracturing fluids. According to Li et al [Li, Guo, Gao et al (2012)] the productivity of wells can drop easily by 50% in hydraulically fractured wells due to water filtration, in addition to the permeability damage due to capillary pressure which is still a to pass through drill bit nozzles (nozzle is a device designed to control characteristics of a fluid flow, especially to increase velocity). While for the reverse circulation, drill cuttings need to enter the insider of drill pipe through the orifice (the size of the orifice is larger than nozzle to allow cutting getting through).…”