RESUMO
Geological bodies are important sources of greenhouse gas (GHG) emissions. Organic-rich oil shale in sedimentary basins is a good gas source rock, the GHG in which will be released into the atmosphere during crushing to affect climate change. Quantitative calculations of GHG emissions during oil shale crushing were carried out on oil shales from the Yaojie (YJ) and Fushun (FS) mining areas in China. Organic geochemistry, X-ray diffraction, and pore structure analysis experiments, as well as the relationship between storage time and GHG emissions, were analyzed to investigate the main controlling factors of GHG release in different types of oil shales. The results showed that the CH4 and CO2 released from the YJ oil shale were 0.002-0.145 mL/g and 0.011-0.054 mL/g, respectively; the CH4 and CO2 released from the FS oil shale were 0.0001-0.0008 mL/g and 0.002-0.045 mL/g, respectively. Residual CH4 release was closely related to total organic carbon (TOC) and maturity: the CH4 released from the organic-rich and mature YJ oil shale was much higher than that of the FS oil shale, which is relatively organic-lean and immature. The control factors of the released CO2 vary in different regions: CO2 released from the YJ oil shale was somewhat affected by the TOC, while that released from the FS oil shale was mainly controlled by carbonate minerals and their contributing pores. The results of pore structure and organic maceral analyses indicated that both organic and inorganic pores of the YJ oil shale are occupied by asphaltenes, forming a key gas preservation mechanism of residual CH4 and CO2 as solutes dissolved in asphaltenes. In addition, CO2 has a greater absorptive capacity than CH4 and is therefore more difficult to release during the same crushing time. As oil shale is stored for longer periods, residual CH4 will be preferentially released to the atmosphere, while residual CO2 will be released in large quantities during crushing.
RESUMO
In order to investigate the effect of tectonic compression on pore structures and methane adsorption capacity, the continental deformed shales are collected from the Rujigou section in the Ordos Basin and the Hongshawan section in the Minhe Basin as research objects. The porosity, N2 and CO2 adsorption, field emission scanning electron microscopy (FE-SEM), and methane isothermal adsorption experiments are used to investigate the pore structure and methane adsorption of continuous deformation shales. Combined with formation curvature, the quantitative correlations between tectonic compression deformation and reservoir structure parameters and methane adsorption are analyzed. The interlayer pore, intergranular pore, dissolution pore, and microfracture are developed, and the amounts of microfractures are obviously higher in anticlinal cores than that of the anticlinal wings. The porosities for the Rujigou and Hongshawan sections are 2.1-4.73% (avg 3.21%) and 1.49-9.05% (avg 4.80%), respectively. The corresponding mesopore volume, specific surface area, and average diameter for the Rujigou section are 0.022-0.038 cm3/g, 12.35-14.30 m2/g, and 8.76-11.21 nm and for the Hongshawan section are 0.0033-0.0052 cm3/g, 0.376-0.875 m2/g and 21.61-36.37 nm, respectively. The corresponding micropore specific surface area and pore volume for the Rujigou section are 11.301-16.068 m2/g and 0.0033-0.0051 cm3/g and for the Hongshawan section are 10.951-15.912 m2/g and 0.0043-0.0058 cm3/g, respectively. The methane adsorption capacities for the Rujigou and Hongshawan sections are 2.76-3.82 mg/g and 1.62-2.135 mg/g, respectively. The porosity, mesopore and micropore structure parameters, and methane adsorption capacity in synclinal core are lower than those in synclinal wings. However, the above tendency is reversed for the anticline, whose adsorption capacity in the anticlinal core is higher than that in anticlinal wings. There exist high correlations between formation curvature and pore structure, physical property, and methane adsorption, indicating that formation curvature has a significant effect on the shale reservoir. By combining theoretical maximum adsorbed gas and free gas results, it implies that the anticlinal core undergoing moderate structural compression deformation can provide more methane adsorption sites and reservoir space, which is the shale gas favorable accumulation area. This study could provide beneficial references for continental shale gas exploration and evaluation in complex structure areas.
RESUMO
Greenhouse gas (GHG) emissions from oil and gas exploration and development are major contributors to emission inventories in oil and natural gas (ONG) systems. For the developing countries, including China, studies of this aspect of the industry, being at an early stage, lack a unified method of calculation, and this leads to varied projections of national emissions. In this paper, progress is reported on direct measurement of CH4 and CO2 emissions along the oil and gas value chain, for four oil and gas fields. An improved calculation method (classification calculation method), which considers the production status of each type of oil and gas field in China, is proposed for the first time in this study. Based on in situ measurement, it is used to estimate the national CH4 and CO2 emissions from the process of petroleum exploration and development. The results showed that CH4 and CO2 emissions in 2013 were 73.29×104 and 20.32×104tonnes, respectively (in CO2 equivalent: 1559.36×104tonnes). Compared with the results (731.52×104tonnes of CH4, 1031.55×104tonnes of CO2, 16,393.48×104tonnes of CO2 equivalent) in 2013 determined by the Tier 1 method of the Intergovernmental Panel on Climate Change (IPCC), the carbon emissions from field measurement method were much lower than that of IPCC method, which indicated that carbon emissions of ONG systems in China were severely overrated by IPCC. Hence, the GHG emission results reported herein could fundamentally improve the knowledge and understanding of GHG emissions from ONG exploration and development in China.
RESUMO
Greenhouse gas (GHG) emissions from oil and gas systems are an important component of the GHG emission inventory. To assess the carbon emissions from oilfield-produced water under atmospheric conditions correctly, in situ detection and simulation experiments were developed to study the natural release of GHG into the atmosphere in the Shengli Oilfield, the second largest oilfield in China. The results showed that methane (CH4) and carbon dioxide (CO2) were the primary gases released naturally from the oilfield-produced water. The atmospheric temperature and release time played important roles in determining the CH4 and CO2 emissions under atmospheric conditions. Higher temperatures enhanced the carbon emissions. The emissions of both CH4 and CO2 from oilfield-produced water were highest at 27°C and lowest at 3°C. The bulk of CH4 and CO2 was released from the oilfield-produced water during the first release period, 0-2hr, for each temperature, with a maximum average emission rate of 0.415gCH4/(m(3)·hr) and 3.934gCO2/(m(3)·hr), respectively. Then the carbon emissions at other time periods gradually decreased with the extension of time. The higher solubility of CO2 in water than CH4 results in a higher emission rate of CH4 than CO2 over the same release duration. The simulation proved that oilfield-produced water is one of the potential emission sources that should be given great attention in oil and gas systems.
