The Laboratory Measurement of the Gas-Storage Capacity of Organic Shales
- Richard F. Sigal (Consultant) | I. Yucel Akkutlu (Texas A&M University) | Seung Mo Kang (STX Energy) | Mery Diaz-Campos (Schlumberger Technology Corporation) | Ray Ambrose (Hilcorp Energy Company)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- June 2013
- Document Type
- Journal Paper
- 224 - 235
- 2013. Society of Petrophysicists & Well Log Analysts
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- 381 since 2007
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A significant part of the gas storage in organic shales is in nanometer-scale pores located in the organic material. These pores have gas species-specific adsorption on the surface of the pore walls and are in material that may have significant pore-volume dependence on pore pressure. In the smaller pores molecular-dynamic calculations for methane show that the storage model that consists of a single high density adsorbed gas layer and a free-gas component that obeys the equation-of-state for bulk methane is only an approximation.
The volume of the adsorption layer, which reduces the pore volume available for free gas storage, is a function of gas species, temperature and pressure. This, along with pore-volume compressibility, requires that gas storage be measured with the reservoir gas under reservoir conditions on a solid core sample. The current methods that use ground-up samples to measure adsorption with the reservoir gas but pore volume with helium do not satisfy the requirements for an accurate gas-storage determination. To address these issues, a new methodology to measure total gas storage on a core sample at reservoir conditions is described. A method to model the measured storage as an adsorbed component and free component is developed. For methane, an equation to extract an average pore radius from the modeled adsorbed-state density is developed. The methodology is illustrated on a measurement on an organic-shale sample.
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