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Field data and lab data are presented for various fluids pumped in low perm shales, coalbed methane and tight sandstone reservoirs. Commonly used surfactants, alcohols as well as a microemulsion system (ME) are evaluated. Lab data is presented that illustrates the cleanup of injected fluids in tight gas cores. Damage mechanisms are shown to be phase trapping and high capillary pressures. The microemulsion additive results in lower pressures to displace injected fluids from low permeability core samples over conventional surfactant and methanol treatments. The observed enhanced relative permeability mechanism is the alteration of the rock-fluid interfacial tension or contact angle. It is demonstrated that this alteration effectively lowers the capillary pressure and capillary end effect associated with wellbores and fractures in low perm reservoirs by as much as 50%, thus mitigating phase trapping and therefore permitting an increased flow area to the wellbore following drilling and hydraulic fracturing. Over 300 wells were evaluated that were drilled and/or fracture treated with various fluid combinations in the Barnett, Fayetteville and Appalachian basin shales. Some 200 wells are examined in the San Juan Basin and other low perm areas such as the Pieance Basin, Uinta, Vicksburg and Cotton Valley. Drilling examples are shown for several horizontal wells. The addition of the microemulsion to fracturing treatments has resulted in more than 50 to 100% increases in load recoveries and gas production. Production analysis of horizontal wells drilled and cleaned up with the microemulsion shows a doubling of production over offsets. Pressure analysis of fractured wells shows that the damage factor is reduced by a factor of 2 with the inclusion of ME. This is a result of a combination of reduced depth of invasion, a higher relative perm in the invaded zone and/or longer effective frac lengths.

A study of completion techniques in depleted/low pressure tight permeability gas/oil reservoirs shows great promise through the use of a microemulsion (ME) additive in energized fracture stimulation treatment of new infill wells. This paper presents a comparison of four (4) wells completed according to historical stimulation practices and two (2) wells completed with microemulsion additive. See Table 1 for baseline data. The damage mechanisms from past practices were exacerbated by depleted/ low bottom-hole pressures, high water saturations, and low bubble point crude. The use of the microemulsion additive reduced the liquid load and promoted liquid recovery, enabling the base fluid gases to establish gas saturated pathways and promote the production of the natural solution gas that is the field's primary economic resource. CO2 is thought to enhance this process by promoting the reduction of the near fracture face oil saturation. The microemulsion potentially enhances this action by reducing the mobility contrast between introduced fluids and reservoir oil, water, and gas phases. Analysis of the production histories shows that the microemulsion additive significantly enhanced the reservoir conductivity and effective fracture length when compared to the historical completions when in sustained production. The two wells treated with microemulsion additive also experienced less damage as a consequence of the long shut-ins prior to sustained production, than did those with historical completions, which had much shorter shut-ins.

In this work field data and lab data are presented for various fluids pumped in the Barnett Shale. Recent fracture treatments have been light sand fracs in slick water consisting of water and friction reducer, with and without surfactants. Commonly used surfactants as well as a microemulsion system (ME) are evaluated. Lab data is presented that illustrates how the microemulsion accelerates the cleanup of injected fluids in tight gas cores. The microemulsion additive results in lower pressures to displace injected fluids from low permeability core samples and proppant packs. The relative perm to gas is increased substantially as the water saturation is decreased. The enhanced relative permeability mechanism is the alteration of the rock-fluid interfacial tension or contact angle. It is demonstrated that this alteration effectively lowers the capillary pressure and capillary end effect associated with fractures in low perm reservoirs by as much as 50%, thus mitigating phase trapping and therefore permitting an increased flow area to the fracture, hence longer effective frac lengths. Over 200 wells have been treated and analyzed in the Barnett Shale for this study. Several side by side comparisons of treatment variations are possible. The addition of the microemulsion to fracturing treatments has resulted in more than 50% increases in load recoveries and 30-40% increases in gas production. Pressure analysis of fractured wells shows that the damage factor is reduced by a factor of 2 in the Barnett shale with the inclusion of ME. This is a result of a combination of reduced depth of invasion, a higher relative perm in the invaded zone and/or longer effective frac lengths.

A new microemulsion additive has been developed that is effective in remediating damaged wells and is highly effective in fluid recovery and relative permeability enhancement when applied in drilling and stimulation treatments at dilute concentrations.The microemulsion (ME) is an optically clear, thermodynamically stable blend of biodegradable solvent, surfactant, co-solvent and water.The nanometer sized structures have extremely high contact efficiency at low concentrations (0.10-0.5%). Lab data is presented that illustrates how the Microemulsion accelerates the cleanup of injected fluids in tight gas cores. The microemulsion additive results in lower pressures to displace injected fluids from low permeability core samples and proppant packs. The relative perm to gas is increased substantially as the water saturation is decreased. The enhanced relative permeability mechanism is the alteration of the rock-fluid interfacial tension or contact angle.It is demonstrated that this alteration effectively lowers the capillary pressure and capillary end effect associated with fractures in low perm reservoirs by as much as 50%, thus mitigating phase trapping and therefore permitting an increased flow area to the fracture and longer effective frac lengths.Examples of drilling fluids with and without ME are shown in which the relative perm to gas and oil are improved with the application of the microemulsion system. Field examples are shown for fracture treatments of unconventional low permeability coals and shales, where water recovery and productivity are increased by 50% with the application of ME. A production analysis is presented for wells treated in the Barnett Shale that shows longer effective frac lengths and decreased damage surrounding the fracture.

A new microemulsion additive has been developed that is effective in remediating damaged wells and is highly effective in fluid recovery and relative permeability enhancement when applied in drilling and stimulation treatments at dilute concentrations. The microemulsion is a unique blend of biodegradable solvent, surfactant, co-solvent and water. The nanometer-sized structures are modeled after Veronoi structures which when dispersed in the base treating fluid of water or oil permit a greater ease of entry into a damaged area of the reservoir or fracture system. The structures maximize surface energy interaction by expanding to twelve times their individual surface areas to allow maximum contact efficiency at low concentrations (0.1–0.5%). Higher loadings on the order of 2% can be applied in the removal of water blocks and polymer damage. Lab data are shown for the microemulsion in speeding the cleanup of injected fluids in tight gas cores. Further tests show that the microemulsion additive results in lower pressures to displace frac fluids from propped fractures resulting in lower damage and higher production rates. This reduced pressure is also evident in pumping operations where friction is lowered by 10–15% when the microemulsion is added to fracturing fluids. Field examples are shown for remediation and fracture treating of coals, shales and sandstone reservoirs, where productivity is increased by 20–50% depending on the treatment parameters. Drilling examples are shown in horizontal drilling where wells cleanup without the aid of workover rigs where offsets typically require weeks of workover.