Petrophysics of Triple-Porosity Tight Gas Reservoirs With a Link to Gas Productivity

Abstract

Petrographic work on thin sections from rock samples collected in tight gas sandstones of the western Canada sedimentary basin (WCSB) shows that the sandstones are composed of intergranular, microfracture and slot, and isolated noneffective porosities. The petrographic observations of these triple-porosity rocks have led to a petrophysical interpretation with the use of a triple-porosity model.Tight gas reservoirs are very complex heterogeneous systems that have been evaluated in the past mostly with single-porosity models. We propose that these types of reservoirs can be represented better by triple-porosity models for more rigorous quantitative petrophysical characterization. The triple-porosity model discussed in this paper fits the petrographic observations very well, leading to a more rigorous characterization of effective and noneffective porosity.The petrographic and core-calibrated triple-porosity model is then used for well-log interpretation of those wells when these data are not available. The result is a reasonable quantitative characterization of the tight gas reservoir that can be used for improving hydraulic-fracturing design, flow-units determination, reservoir engineering, and simulation studies. The data can be determined at room conditions and simulated conditions of net stress.It is concluded that honoring with a triple-porosity model the different types of porosities observed in thin sections and cores leads to more-rigorous and -useful petrophysical interpretations that can be linked to gas productivity.

Flow Units in Shale Condensate Reservoirs

“…Slots are grain-bounding openings generated during uplifting caused by cooling and unroofing. The Singh et al (2009) results were used by Devegowda et al (2012), Jin et al (2013), and Sanaei et al (2014a) to quantify the effect of pore diameter on gas-condensate properties. Slot porosity was reported in tight (Rahmanian et al 2012) as well as shale (Sonnenberg 2011) reservoirs.…”

“…This observation was used by various authors (Devegowda et al 2012;Jin et al 2013;Sanaei et al 2014a, b) to develop empirical equations for determining the shift in critical temperature and pressure as function of pore size with a view to investigate the effect of two-phase envelope shrinkage on gasand-liquid recoveries. This observation was used by various authors (Devegowda et al 2012;Jin et al 2013;Sanaei et al 2014a, b) to develop empirical equations for determining the shift in critical temperature and pressure as function of pore size with a view to investigate the effect of two-phase envelope shrinkage on gasand-liquid recoveries.…”

A Complete Petrophysical-Evaluation Method for Tight Formations From Drill Cuttings Only in the Absence of Well Logs

“…The concept has been extended to the case of gas rates by Deng et al (2011). In the case of gas-well production rates, potentials reach more than a 100 MMscf/D for macro-and megaports, more than 10 MMscf/D for mesoports, more than 1 MMscf/D for microports, and more than 0.1 MMscf/D for nanoports (shale gas and CBM are not included in this preliminary estimate).…”

“…For the case of low-permeability gas reservoirs in horizontal wells, Deng et al (2011) use the assumption that each fracturing stage is approximately equivalent, from the point of production rates, to a vertical well. In general, the same restrictions mentioned previously for oil, plus the big restriction of backpressures, apply to the preceding gas rates.…”

“…2. The graph has been developed to include conventional reservoirs, tight gas reservoirs, and shale-gas reservoirs (Aguilera 2010;Deng et al 2011). Geological size classification of pore throats (ports at r p35 ) includes megaports, macroports, mesoports, microports, nanoports, and picoports.…”