Summary The "swelling" of coal by a penetrant refers to an increase in the volume occupied by the coal as a result of the viscoelastic relaxation of its highly crosslinked macromolecular structure. Projects relating to CO2 sequestration in coal seams suffer a serious setback in terms of injectivity loss resulting from the swelling of coal. Volumetric swelling associated with CO2 sorption on coal has a significant influence on the fracture porosity and permeability of the coal. Two coal samples differing in rank were used for volumetric strain measurements. With CO2-, the high-rank Selar Cornish coal showed a maximum volumetric strain of 1.48% corresponding to an average pore pressure of 13 MPa. A matrix swelling coefficient (Cm) of 1.77× 10-4 MPa-1 was calculated for this Selar Cornish coal. The low-rank Warndt Luisenthal coal exhibited higher strain of 1.6%, and a matrix swelling coefficient (Cm) of 8.98×10-5 MPa-1 was calculated. The rank dependence of swelling holds true in this set of experiments. Repeat volumetric strain measurement on the same Warndt Luisenthal coal core shows higher volumetric strain values for all pressure steps. A volumetric strain of 1.9% corresponding to a mean pore pressure of 14 MPa was measured. This confirms the process of sequential swelling. A unique feature of this work is that real-time permeability measurements were done under unconstrained conditions. Permeabilities were measured, reducing the pore pressure from 16 to 1 MPa at constant flow rate. Although measured permeability increased with increasing pore pressure under unconstrained swelling, in-situ permeability will actually decrease because of fracture closure in a constrained coal. To validate the permeability swelling relationship, both permeability measurements under unconstrained conditions and volumetric strain measurements were used. Introduction Maturation of coalbed methane (CBM) production operations in some basins, the emergence of injection schemes for enhanced coalbed methane (ECBM), and carbon sequestration of greenhouse gases has led to renewed focus on the behavior of coalbed reservoir properties under these conditions. Cleat permeability of coal is the most important parameter for coalbed methane production. Being normal to the bedding plane and orthogonal to each other, the face and butt cleats in coal seams are usually subvertically oriented. Thus, changes in the cleat permeability are primarily controlled by the prevailing effective horizontal stresses that act across the cleats, rather than the effective vertical stress, defined as the difference between the overburden stress and pore pressure (Harpalani and Chen 1997). Coal swelling accompanying CO2 sorption would decrease the permeability of the coal as the volume increase is compensated within the fracture porosity.
Maximizing the value of a significant gas resource base in southern Iraq for all key stakeholders is complex, driven by a number of key challenges on both the supply and demand-side of field development. The majority of the future gas supply in the south of Iraq will come from associated gas from some of the world's largest oil fields including Rumeila, West Qurna and Zubair). Successfully utilising the gas for industrial and domestic supply requires integration across upstream, midstream and downstream business segments and cooperation between multiple parties from the Government of Iraq (GoI) and the field operator contractor consortiums in Iraq. Some of the main challenges that the Iraq Oil & Gas industry faces today are lower commodity prices impacting the availability of investment capital, weak fiscal incentives for gas production, inadequate integrated gas infrastructure development, limited cross-industry gas planning and coordination & limited new exploration activity. The above issues also cary an overlay of environmental and security conditions, meaning that fully integrated development planning and decision framework modelling needs to be at the core of mapping the most attractive way forward for future investments. This paper presents an integrated workflow approach that allows modelling & assessment of the impact of technical as well as non-technical risks and uncertainties in a systematic manner along the value chain at a number of different nodes. This model follows the hydrocarbon molecules from the reservoir through to the downstream petrochemical plant enabling assessment of a potential range of scenarios across upstream, midstream and downstream. In a region where uncertainties go far beyond the technical domain, this approach allows decision makers to navigate through the potential outcomes and formulate integrated roadmaps and development strategies. It also identifies the benefits of an integrated development approach across fields developed by different contractor consortiums. The workflow facilitates; Analysis of the current gas landscape and identification of priorities, with a focus on what could be done to increase gas supply in the short to medium term;A vision for longer term gas industry development and provides guidance on nature and timing for future infrastructure required to realize this visionIdentification of key enablers to expedite gas growth in the wider southern Iraq area.
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