Experimental and Empirical Observations Supporting a Capillary Model Involving Gas Generation, Migration, and Seal Leakage for the Origin and Occurrence of Regional Gasifers

Secondary migration and leakage of methane from a major tight-gas system

“…Basin-centred gas accumulations go through distinct phases of pressure evolution: normal pressure during early burial, overpressure during deep burial and associated hydrocarbon generation, underpressure during early basin uplift, and return to normal pressure with further uplift12. Depressurization during uplift and erosion of overburden involves temperature reduction and pore volume dilation effects3; however, natural leakage of hydrocarbon fluids, primarily gas, is commonly thought to be the dominant factor345. In this regional study, an extensive set of natural gas composition data from petroleum wells is investigated to show that hydrocarbon fluid loss from the Montney Formation is not uniform, but is instead focused along distinct stratigraphically and structurally controlled pathways within which methane is preferentially enriched during transmission through tight-gas siltstones.…”

Spontaneous potential: Key to understanding continuous and conventional gas in Upper Cretaceous sandstones, deep eastern Greater Green River Basin, southwest Wyoming

“…Combined mean continuous-gas resources within sandstones of the Lewis Shale and Mesaverde Group in the deep eastern GGRB were estimated at just under 40 tcf gas (U.S. Geological Survey Southwestern Wyoming Province Assessment Team, 2005), which is virtually identical to the upside estimate of McPeek (1981). Burnie et al (2005Burnie et al ( , 2008 presented a fourstage model to describe the origin and evolution of basin-centered or continuous-gas accumulations, which they termed "gasifers" (in which gas, rather than water, is the continuous phase), and they used low-permeability (<0.1 md) Upper Cretaceous sandstones of the GGRB to support their model. By late stage 1 ("genesis") of their model, elevated pressure from thermogenic generation of gas has forced most mobile water from sandstone pores such that gas becomes the continuous reservoir fluid.…”

“…Finally, in stage 4 ("imbibition"), gas generation slows or ceases, while gas leakage continues and water is imbibed back into sandstone reservoirs. Within the context of this four-stage model, Burnie et al (2005Burnie et al ( , 2008 suggested that low-permeability Upper Cretaceous sandstones of the GGRB are in the stage of late genesis or early transition, because sandstone reservoirs are overpressured and gas is the continuous phase. Water, however, is described as more common in GGRB reservoirs than deepAlberta-basin sandstone reservoirs, and GGRB gas columns are reported to exceed 1500 ft (460 m) in height, with water production reportedly increasing lower in the columns.…”

Water Distribution in the Montney Tight Gas Play of the Western Canadian Sedimentary Basin: Significance for Resource Evaluation

“…Displacement of formation water during gas generation and charging is an integral component of basin-centered gas models (Gies 1984;Law and Dickinson 1985;Law 2002;Burnie et al 2008). The presence of bypassed water (Gies 1984;Burnie et al 2008) in basin-centered gas systems indicates water displacement by gas is commonly an inefficient process.…”

“…The presence of bypassed water (Gies 1984;Burnie et al 2008) in basin-centered gas systems indicates water displacement by gas is commonly an inefficient process. Meckel and Thomasson (2008) suggested gas charge can be insufficient to fully expel mobile water from tight-gas sandstone systems in which (1) source rock is volumetrically limited relative to available reservoir rock; (2) source rocks are lean; (3) source rocks are not in the main gas-generation window; or (4) reservoir rock is not in close proximity to mature source rock.…”