Methane Preservation Research Articles

Effects of lignite composition on reservoir structure, water–gas-bearing features and gas enrichment

The significant variation in production in different blocks has seriously restricted the large-scale breakthrough of China’s low-rank coalbed methane industry for a long time. This study describes in detail the effects of lignite composition on reservoir structure, gas-bearing characteristics, and methane enrichment in the Erlian Basin, thus providing a theoretical basis for accurate exploration of lignite methane. Homogenization of huminite-rich lignite results in the disappearance of cellular structure, closure of cell cavity, small pore size, and low proportion of macropore. The cell wall of inertinite-rich lignite is thin, the cell structure is well preserved, and many cellular pores are developed, providing abundant macropore space. The inertinite-rich lignite contains larger pores and throats, and the content of high coordination number pores is also more abundant. Reservoir characteristics further control the occurrence, migration, and preservation of methane. The inertinite bands provide good seepage space and channels for lignite. The inertinite-rich lignite has high permeability and a low proportion of adsorbed methane, so methane has high mobility in it. The huminite-rich lignite has an excellent “self-sealing” effect on the gas. Overall, huminite-rich lignite in the stagnant area and inertinite-rich lignite in the regional structural culmination are potential favorable positions for the enrichment of lignite methane. Moreover, the interbedded thick coal seam of huminite-rich lignite and inertinite-rich lignite can provide advantageous conditions for water infiltration and gas preservation, thus forming a complete combination of “source, reservoir, and cap rock” in the thick lignite itself.

Co-ensiling of cattle manure before biogas production: Effects of fermentation stimulants and inhibitors on biomass and methane preservation

Abstract The impact of formic acid and glucose addition on the co-ensiling of cattle manure with straw was assessed during 4 months at laboratory scale. Feedstock deprived of additives lost 67% of its methane potential for prolonged ensiling. This was mainly due to the lack of water-soluble carbohydrates and to the high methanogenic activity of cattle manure. The use of co-substrates enhanced biomass and energy conservation during ensiling. The best result was obtained for co-ensiling of cattle manure with glucose (100 g/kg of feedstock). For this condition, lactate production was extensive, which enabled biomass acidification, suppressed ammonia emissions and led to full preservation of methane potential after 4 months. Therefore, in field-scale storage, co-ensiling with a sugar-rich co-substrate appears to be the most resourceful method to optimize cattle manure preservation. Application of this promising technique will have a major impact on the methane yield of agricultural biogas plants where cattle manure has to be stored for long periods.

Geochemical Studies of Crude Oil Generation, Migration, and Destruction in Mississippi Salt Basin: ABSTRACT

ABSTRACT The main source for crude oil in the Mississippi Salt Basin is the laminated lime mudstone facies of the Lower Smackover. Crude oil generation and migration commenced at a level of thermal maturity equivalent to about 0.55% vitrinite reflectance. Short-range lateral migration of crude oil was focused to Upper Smackover and Norphlet reservoirs, but vertical migration also charged some overlying Cotton Valley, Rodessa, Lower Tuscaloosa, and Eutaw reservoirs. Following migration from the Lower Smackover, thermal maturity history of reservoir rocks controls the preservation of crude oil, gas-condensate, and methane. Slow thermal cracking of crude oil occurred in deep Upper Smackover reservoirs, resulting in formation of gas-condensate and precipitation of solid bitumen. The maximum thermal maturity for preservation of condensate is equivalent to about 1.3% vitrinite reflectance. Only methane, pyrobitumen, and nonhydrocarbon gases including hydrogen sulfide persist at higher levels of thermal maturity. Early destruction of methane in deep Upper Smackover reservoirs near the Wiggins Arch is driven by thermochemical sulfate reduction. Lesser availability of sulfate in Norphlet reservoirs in Lower Mobile Bay could account for methane preservation at higher levels of thermal maturity. One basic geochemical strategy for further exploration of the Mississippi Salt Basin is to focus exploration effort on traps with reservoirs in the thermal maturity window for hydrocarbon preservation. Another strategy is to avoid drilling traps with overmature reservoir rocks.

Environmental controls of methane production in Holocene basins in eastern Canada

Rapid rates of sedimentation from 54 to 134 cm/1000 yr are typical of the Holocene basins in St. Margaret's Bay and the Grand Manan Basin, Nova Scotia. The water column is well oxygenated but, because of the rapid rate of sedimentation, anoxic conditions developed and enhanced the preservation of organic matter and its fermentative degradation; also the concentrations of sulfide increased and soluble sulfates were rapidly depleted. A direct result of this has been the production of methane in amounts exceeding 22,000 ppm. In contrast, nearby cores with rates of sedimentation of less than 20 cm/1000 yr have only 30–40 ppm methane. High rates of sedimentation and the ensuing anaerobic conditions appear to be the principal factors for the genesis and preservation of methane. The δ 13C values and the n-alkane distribution show that there is more terrestrial organic matter in the Grand Manan Basin than in St. Margaret's Bay. This could account for the high concentrations of methane in the Grand Manan cores despite the low concentrations of organic carbon.