Hema Siriwardane

Synthesis of methane hydrate in an unconsolidated medium

Under certain conditions of low temperature and high pressure, mixtures of small gas molecules and water form crystalline, ice-like compounds called clathrate hydrates. It is believed that large quantities of natural deposits of methane hydrate are formed in unconsolidated media from natural gas and water. Development of recovery techniques for this potential natural gas resource requires comprehensive laboratory investigations of engineering properties, which in turn require a capability for reproducibly synthesizing methane hydrate in unconsolidated matrix materials. This paper presents a procedure for synthesizing methane hydrate in an unconsolidated sand matrix. Results of dissociation experiments indicate that the samples prepared according to this procedure are relatively homogeneous and suitable for use in investigations of mechanical and other properties. The methane hydrate content and porosity of the samples can be controlled in the procedure developed.

Influence of Shrinkage and Swelling of Coal on Production of Coalbed Methane and Sequestration of Carbon Dioxide

The potential for enhanced methane production and geologic sequestration of carbon dioxide in unmineable coal seams needs to be evaluated before large-scale sequestration projects are undertaken. Coal is known to competitively adsorb carbon dioxide and methane gases. Laboratory experiments indicate that coal will swell when a gas is adsorbed and shrink when a gas is desorbed. The swelling and shrinkage may change the cleat porosity and permeability of the coal. This paper deals with the influence of shrinkage and swelling of coal on the production of methane from, and injection of carbon dioxide into, a coalbed reservoir. A threedimensional swelling and shrinkage model was developed. This model is based on constitutive equations that account for coupled fluid pressuredeformation behavior of a porous medium that undergoes swelling and shrinkage. The swelling and shrinkage strains are computed on the basis of the amounts of different gases adsorbed or desorbed. The permeability of the reservoir is modified by the shrinkage or swelling. The paper presents numerical results on the reservoir performance during injection of carbon dioxide in a previous field test that has been reported in the literature. The results indicate that coal swelling and shrinkage can influence the production rates and reservoir pressure distribution in the field. Introduction Emissions of greenhouse gases such as carbon dioxide have grown progressively for many years. Anthropogenic carbon dioxide emissions can contribute to global warming, and attempts are being made to identify methods to reduce them. Geologic sequestration has been identified as one of the methods for storage of carbon dioxide. One of the promising methods of geologic sequestration is to store carbon dioxide in unmineable coal seams. It has been reported that coal seams can hold large amounts of carbon dioxide in comparison to the amounts of methane gas that they contain (Burruss, 2003). However, many technical and safety issues need to be investigated before such efforts can be undertaken. There have been several previous studies to investigate different technical issues related to carbon dioxide sequestration (Bromhal et al., 2003; Mavor et al, 2004; Gorucu et al., 2005; Reeves and Oudinot, 2005). These studies have addressed several important aspects of carbon sequestration in coal seams. One of the potential problems of injection of carbon dioxide into a coal seam is the swelling of the coal (Kelemen, et al., 2006; Mazumder, Bruining, and Wolf, 2006; Mazumder, Siemons, and Wolf, 2006; Pan and Connell, 2006). While more laboratory research work is needed to resolve the exact amount of coal swelling, it is suspected that the swelling of coal will cause a reduction of permeability, which in turn may reduce injection volumes during large scale injection operations. This paper deals with the influence of shrinkage and swelling of coal on the production of methane from, and injection of carbon dioxide into, a coalbed reservoir. As a part of the Coal-Seq project, analyses of a field study in the San Juan basin involving the injection of carbon dioxide for enhanced coalbed methane recovery recently were performed by Reeves and coworkers (Reeves et al, 2003; Reeves and Oudinot, 2005). In the work reported here, the influence of coal swelling and shrinkage on the reservoir performance of the reported field project was investigated by using a new swelling and shrinkage model. This paper contains SPE 102767 Influence of Shrinkage and Swelling of Coal on Production of Coalbed Methane and Sequestration of Carbon Dioxide H.J. Siriwardane and D.H. Smith, Natl. Energy Technology Laboratory/DOE; F. Gorucu, SPE, Advanced Resources Intl.; and T. Ertekin, SPE, Pennsylvania State U.

Water Level Detection in Silty Materials Using Ground Penetrating Radar

Detection of water level in silty soils can be complicated because of capillary action. In this study, the water level in a silty soil sample was detected using Ground Penetrating Radar (GPR) technique in the laboratory. The soil sample has dimensions of 62 cm × 48 cm × 46 cm and was kept in a clear Plexiglas container which facilitated water level measurements. Two ground‐coupled antennas with frequencies of 900 MHz and 1,500 MHz were used in this study. The soil sample was dry at the beginning of the experiment. The water level in the soil sample was raised to a pre‐determined level and radar readings were taken at different times over 24 hours. The moisture content in the soil sample above the water level increased with time due to capillary action. At the end of the experiment, the variation of moisture content with depth of the sample was experimentally determined. The GPR observations were compared with measured water depth in the soil sample. The paper presents the comparison of water level as dete...

Analysis of subsidence caused by underground mining

SummarySome aspects of subsidence caused by longwall coal mining are analysed using the finite element method. Results of the analysis are compared with a true mine panel, where measurements on subsidence were available. Rock deformations in the overburden were modelled by using an elasto-plastic constitutive model. The study indicates that the shape of the subsidence profile can be predicted reasonably well by using nonlinear finite element analysis.

Flow simulations for carbon sequestration at a coal-seam pilot site

Computer simulations of the flow and diffusion of H2 O, CH4 , and CO2 through unmineable coal seams are integral parts of the design, implementation, and interpretation of carbon sequestration field projects. Although it has seldom been discussed in the literature, coal seams may also effect-ively serve as “cap rock” for sequestration into underlying formations (brine-saturated, oil and gas reservoirs, or other coal seams). In this case, the very large sorption capacities of coal, even at low CO2 pressures; the blockage of CO2 flow through cleats when they are saturated with H2 O; and the tendency of coal to swell when it sorbs CO2 , thus reducing cleat apertures and Darcy flow, all may contribute to make coal seams effective caprock.

Laboratory Determination of Phreatic Surface During Seepage through Soils Using Ground Penetrating Radar

Ground penetrating radar (GPR) was used to detect the water level in a silty soil sample during seepage under transient conditions in the laboratory. The soil sample has dimensions of 30 cm × 25 cm × 120 cm. The soil chamber was made up of Plexiglas materials to avoid radar interference and to be able to make visual observations of the water level in the soil sample. The soil used in the experiment is silty sand and 1.5 GHz antenna was used in the study. The soil sample was dry at the beginning of the experiment. The water level at one end of the soil sample was raised to a pre‐determined level and radar readings were taken along the length of the sample at different times over 30 hours. The water level was also determined by using piezometers installed along the length of the sample. Aluminum foil was placed at the bottom of the soil chamber to get a clear reflection of radar signals. At the end of the experiment, the variation of moisture content with depth of the sample was determined at different loca...

Assessment of Gas Production Potential from Strata above Longwall Mining: ABSTRACT

Pipeline-quality gas production potential from the highly fractures methane-bearing strata above longwall coal mine panels may be many times that of the gas-in-place estimate for the minable coal bed. The permeability in these strata is increased significantly due to the fractured zone generated during longwall mining activity. This paper assesses the potential production and influence of well spacing for drainage of gas from the strata above coal mine panels. Reserves were quantified by use of the predicted extent of the failure zone, the formation gas contents, and geologic cross sections from throughout the Appalachian basin. A finite element method was used to determine the size and shape of the affected stratigraphic areas and gas contents were derived.