To evaluate fluid recovery and resulting regain of methane permeability with a range of water-and hydrocarbon-based fluids, some involving the use of CO 2 or nitrogen, specialized core-testing procedures have been developed (Figs. 1 and 2).In general, core samples representing average-or better-quality reservoir matrix are used for the testing because these are the portions of the reservoir that will experience the greatest degree of invasion and leakoff during the highly overbalanced fracturing process and are also the zones from which the majority of potential production will be sourced.There are several key points that differentiate this from common core testing with water-based fluids:• Because phase behaviour is an integral part of the cleanup mechanism, downhole pressures and temperatures must be accurately simulated. This can require pressures of 70 MPa or greater and temperatures higher than 100º`C.• A key objective is a representative comparison of hydrocarbonand water-based systems. This being the case, use of methane (or a simulated reservoir gas containing all of the light-and heavy-gas phase hydrocarbon components) rather than nitrogen is used as the reference for regained permeability to achieve meaningful results. The solubility of methane in hydrocarbons is much greater than the solubility of nitrogen, resulting in a much lower interfacial tension (IFT) at a given pressure level. This allows methane to more effectively displace hydrocarbons. Specialized equipment is required to safely pump methane at high pressures and accurately measure flow rates. AbstractThe Montney gas reservoir has become a critically important component of current western Canadian gas supply and offers exciting future potential. However, this reservoir often presents variable and unique stimulation challenges. Unlike reservoirs that display little water sensitivity, such as the U.S. Barnett Shale and possibly the Muskwa in the Northeastern British Columbia Horn River Basin, recovery of water-based fluids in the Montney can be a key consideration in achieving economic production rates.The use of water-based fracturing fluids in low-permeability reservoirs can result in loss of effective frac half-length caused by phase trapping associated with the retention of the introduced water-based fluid to the formation. This problem is increased by the water-wet nature of most tight-gas reservoirs (where no initial liquid-hydrocarbon saturation is or ever has been present) because of the strong spreading coefficient of water in such a situation.The retention of increased water saturation (Sw) in the pore system after the injection of water-based completion fluids can restrict the flow of produced gaseous hydrocarbons, such as methane. Capillary pressures of 10 MPasy-20 MPa, or much higher, can be present in low-permeability formations at low-water saturation levels. Inability to generate sufficient capillary-drawdown force using the natural reservoir-drawdown pressure can result in extended fluid-recovery times or permanent loss of eff...
The Horn River Basin covers an estimated 3 million acres in a remote and difficult to access area of northern British Columbia. A number of Operators have experimental projects in the area, using various drilling and completion techniques, in order to evaluate the shale reservoir, gas in place, and productivity; moving towards commercial projects. The Devonian age shales of the Horn River Basin have been compared to the Barnett Shale of the Fort Worth Basin, in terms of reservoir quality, productivity and recovery factors. This paper will review the following important aspects of the Horn River shale area: History of the play;General review of the Geology, reservoir properties, thickness, gas content, gas in place, permeability, etc.;Emerging drilling and completions techniques, well construction, stimulation practices, fracture diagnostics, logistical problems;Production tests, well initial productivities, and longer term production forecasts, estimated recovery factors;Production and Operations challenges;Development costs and economics;Future development hurdles, what is needed to make this play commercial?
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