Solutions for the Evaluation of Unconventional Gas Reservoirs
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Materials Characterization Solutions to Determine Unconventional Gas Reservoir Potential Until recently, tight shales were not considered an economically feasible option for hydrocarbon production. Logically, their minimal permeability and porosity made for small amounts of oil, water, and gas content that were hard to extract. However, abundance of tight shale in the earth’s crust, along with a desire to lessen import energy dependence have made the development of this non-conventional gas play very attractive. Shales are complex reservoirs and present significant challenges to...

Rock Storage Properties It is of vital importance to determine a reservoir’s capacity for adsorption of hydrocarbon gas. Often, pores smaller than 2 µm remain undetected in routine core analysis. The majority of the pore space in shales is mesoporous. Pore volume provides a measurement of the capacity of organic and non-organic components of the shale to store gas. Through the application of sub-critical nitrogen or carbon dioxide gas adsorption, the acquired analytical data will indicate capacity as well as reveal information about pore volume, area, and pore distribution. Gas adsorption...

Included Data Reduction Models SURFACE AREA PORE VOLUME PORE SIZE t-Plot (micropore volume) BJH (meso and small macropore volume) MP Dubinin-Astakhov (micropore volume) Methane Capacity of Shale at Specific Pressure and Temperature Many shale gas formations are over pressured. Super-critical gas adsorption parameters are needed to estimate total amount of gas in the system. Measuring the shale capacity for adsorption of hydrocarbon gas at pressures and temperatures that may exist at depths is important to the evaluation of a reservoir. High-pressure methane can be dosed onto shale samples...

Shale Pore Throat Size, Pore Volume, and Pore Size Distribution Mercury intrusion porosimetry is a valuable method for characterizing macro and mesopore sizes. This dynamic technique is based on the intrusion of mercury into a porous structure under precisely controlled pressures. Mercury intrusion porosimetry permits the calculation of numerous sample properties such as pore size distributions, total pore volume, total pore surface area, median pore throat diameter, and sample densities (bulk and skeletal). Capillary behavior and permeability are critical to reservoir evaluation....

Grain Density Measurement Grain density measurement of core samples is an important parameter that is used to determine the gas storage potential of rock reservoirs. Gas pycnometry is performed on intact cores or crushed samples to measure grain volume which, with the initial mass, yields grain density. Measured bulk and grain density are combined to deduce porosity. With properly crushed and cleaned sample, an absolute porosity can be determined. It is important to keep in mind that effective cleaning, drying, and crushed particle diameter will have a strong influence on the density and...

Transition Metals Measurement The use of NMR for geophysical characterization of core samples is well accepted. NMR provides information for diffusive characterization of shale samples in terms of fluid mobility, effective porosity, and to determine kerogen conversion. Core samples contain significant amounts of metallic minerals that can contaminate NMR measurements and skew results. It is prudent to measure the metallic content of the core samples to make the analyst aware of any possible contamination. The experimental approach can then be adjusted as required. • Effectively measure...

Moisture Content Moisture is a key factor in determining the potential hydrocarbon recovery in clay-rich reservoirs. The amount and distribution of water can impose a significant impact on the volume of sorbed and free gas, and relative permeability/diffusivity. Moisture content or water saturation influences the character and adsorption poten- tial of inorganic constituents in shale. • Provide critical insight into total water saturation and clay bound water saturation • Hydrophobicity may have a significant effect on gas shale fracture dynamics through the use of inappropriate hydraulic...