Abstract
Fundamental understanding of guest gas replacement in hydrate reservoirs is crucial for the enhanced recovery of natural gas and carbon dioxide (CO2) sequestration. To gain physical insight into this exchange process, this work aims at developing and validating a clathrate hydrate model for gas replacement. Most of the practical concerns associated with naturally occurring gas hydrates, including hydrate formation and dissociation in interstitial pore space between distributed sand particles in the presence of salt ions and in irregular nanometer-sized pores of those particles, irregularity in size of particles and shape of their pores, interphase dynamics during hydrate formation and decay, and effect of surface tension, are addressed. An online parameter identification technique is devised for automatic tuning of model parameters in the field. This model is employed to predict the laboratory-scale data for methane hydrate formation and decomposition. Subsequently, the model is validated with the field data of the Prudhoe Bay Unit on the Alaska North Slope during 2011 and 2012. In this Iġnik Sikumi field experiment, mixed CO2 (i.e., CO2 + N2) is used as a replacement agent for natural gas recovery. It is observed that the proposed formulation secures a promising performance with a maximum absolute average relative deviation (AARD) of about 2.83% for CH4, which is even lower, 0.84% for CO2 and 1.67% for N2.
Highlights
Potential of the proposed framework is analysed by predicting the amount of CH4 produced, and CO2 and N2 recovered in the Iġnik Sikumi field test conducted on the Alaska North Slope in 2011 and 2012
This field test starts with the injection of CO2-N2 (23–77 mol%) gas mixture into the well for 14 days, which is followed by 31.5 days of CH4 production and CO2-N2 recovery from the same bore well
Thanks to the nonlinear optimization technique, using which, we have identified the optimized parameter set online for all the production phases
Summary
Occurring hydrates form once an appropriate guest gas like methane comes in contact with the water molecules at a reasonably high pressure (i.e., more than the atmospheric pressure), and/or the low temperature[26]. Deep sea-beds and permanently frozen grounds are the favourite and habitable hosting sites for the NGH In these reservoirs, usually the hydrates are enclosed in the unconsolidated porous sand layers/sediments, and accompanied by the saline water. The salt ions, a key constituent of the saline water, interfere in the formulation of the strong hydrogen-bonded water molecules network that leads to form the hydrate cavities. Albeit they do not participate in the phase transformation, their presence usually reduces the rate of gas hydrate formation and. As mentioned and shown below, the proposed formulation has blended both the thermodynamic and kinetic aspects
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