Academic literature on the topic 'Coalbed; optimization; thermal'

In coal mining operations, coalbed methane is one of the potential hazards that must be extracted to prevent an explosion of the accumulated gas and environmental pollution. One of the mechanisms is using microwave irradiation so that the thermal stress caused by microwave heating generates fractures. In this research, we investigated the most important parameters affecting the electric and thermal fields’ distribution in coal in order to identify the effective parameters that achieve the highest temperature increase rate and to reach the highest impact and efficiency of the system with the least amount of consumed energy. In this paper, using Maxwell equations, heat transfer, mass transfer and coupling them by COMSOL, we have simulated the radiation of electromagnetic field and heat in the cavity and coal, and we have also shown the temperature dispersion inside the coal. The parameters studied included the amount of coal moisture (type of coal), operating frequency, input power and heating time, location of the waveguide, the size of the waveguide and the location of the coal, and finally the parameters were re-examined in a secondary standard cavity to separate the parameters related to the size of the environment and the cavity from the independent parameters. The results of this study show that the most effective parameter on the electric and thermal fields’ distribution within coal is the size of the resonance chamber. Additionally, the results show that the moisture of 5%, the highest input power and cutoff frequency close to the operating frequency cause the highest average temperature inside the coal, but many parameters such as operating frequency, waveguide location and coal location should be selected depending on the chamber size.

Coal seam gas (CSG), also known as coalbed methane (CBM), is an important source of gas supply to the liquefied natural gas (LNG) exporting facilities in eastern Australia and to the Australian domestic market. In late 2018, Australia became the largest exporter of LNG in the world. 29% of the country’s LNG nameplate capacity is in three east coast facilities that are supplied primarily by coal seam gas. Six geological basins including Bowen, Sydney, Gunnedah, Surat, Cooper and Gloucester host the majority of CSG resources in Australia. The Bowen and Surat basins contain an estimated 40Tcf of CSG whereas other basins contain relatively minor accumulations. In the Cooper Basin of South Australia, thick and laterally extensive Permian deep coal seams (>2 km) are currently underdeveloped resources. Since 2013, gas production exclusively from deep coal seams has been tested as a single add-on fracture stimulation in vertical well completions across the Cooper Basin. The rates and reserves achieved since 2013 demonstrate a robust statistical distribution (>130 hydraulic fracture stages), the mean of which, is economically viable. The geological characteristics including coal rank, thickness and hydrogeology as well as the present-day stress pattern create favourable conditions for CSG production. Detailed analyses of high-resolution borehole image log data reveal that there are major perturbations in maximum horizontal stress (SHmax) orientation, both spatially and with depth in Australian CSG basins, which is critical in hydraulic fracture stimulation and geomechanical modelling. Within a basin, significant variability in gas content and permeability may be observed with depth. The major reasons for such variabilities are coal rank, sealing capacity of overlying formations, measurement methods, thermal effects of magmatic intrusions, geological structures and stress regime. Field studies in Australia show permeability may enhance throughout depletion in CSG fields and the functional form of permeability versus reservoir pressure is exponential, consistent with observations in North American CSG fields.

Summary The unique properties and complex characteristics of coalbed methane (CBM)reservoirs, and their consequent operating strategies, call for an integrated approach to be used to explore for and develop coal plays and prospects economically. An integrated approach involves the use of sophisticated reservoir, wellbore, and facilities modeling combined with economics and decision-making criteria. A new CBM prospecting tool (CPT) was generated by combining single-well(multilayered) reservoir simulators with a gridded reservoir model, Monte Carlo(MC) simulation, and economic modules. The multilayered reservoir model is divided into pods, representing relatively uniform reservoir properties, and a" type well" is created for each pod. At every MC iteration, type-well forecasts are generated for the pods and are coupled with economic modules. A set of decision criteria contingent upon economic outcomes and reservoir characteristics is used to advance prospect exploration from the initial exploration well to the pilot and development stages. A novel approach has been used to determine the optimal well spacing should prospect development be contemplated. CPT model outcomes include a distribution of after-tax net present value (ATNPV), mean ATNPV (expected value), chance of economic success(Pe), distribution of type-well and pod gas and water production, reserves, peak gas volume, and capital. An example application of CPT to a hypothetical prospect is provided. An integrated approach also has been used to assist with production optimization of developed reservoirs. For example, an infill-well locating tool(ILT) has been constructed to provide a quick-look evaluation of infill locations in a developed reservoir. ILT, like CPT, is used for multiwell applications, combining the single-well simulator with a multilayered reservoir model and economics. An application of ILT to a CBM reservoir is provided, and the results are compared with the predictions of an Eclipse reservoir simulation. Introduction CBM reservoirs have a relatively short history of development compared to conventional reservoirs; therefore, few analog fields may be relied upon for extrapolation to new basins and new plays. Further, key reservoir properties such as absolute permeability vary greatly within and between existing developing basins, which complicates prediction of these parameters for new plays. The production performance of CBM reservoirs in new plays or basins, in which few reservoir data exist, is correspondingly difficult to predict. Existing conventional reservoir fields cannot be relied upon as analogs for CBM play analysis because coal-gas reservoirs differ from conventional reservoirs in their fluid-storage and -transport mechanisms. Coals act as source rocks and reservoirs to gas, and a significant amount of gas may be stored in the adsorbed state relative to the free-gas state. CBM reservoirs are often naturally fractured and may be modeled as dual-porosity, or even triple-porosity, reservoirs. Gas-transport mechanisms vary depending on the scale and location within the reservoir. For example, gas transport at the scale of the matrix between natural fractures is caused by the mechanism of diffusion, whereas Darcy flow occurs in the fracture system. Single- or two-phase (gas and water) flow can occur, and, hence, relative permeability characteristics are important. Permeability and gas content are two critical parameters that dictate the economic viability of CBM reservoirs. Unfortunately, there are many controls upon these parameters. For example, gas content is a function of the amount of organic matter within these rocks, the organic matter composition, organic matter thermal maturity, in-situ PT conditions, gas composition, and matrix and fracture gas-saturated porosity. Absolute permeability is dependent upon natural-fracture existence, frequency, orientation (with respect to in-situ stress), and degree of mineralization. Natural-fracture permeability is also stress- and/or desorption-dependent. Although the range of expected parameter values for a new unconventional play may be reduced by knowledge of basin hydrodynamic characteristics, tectonic regime, local and regional stratigraphy and sedimentology, local and regional structural geology, and existing production within the basin, the uncertainty associated with key reservoir variables is still likely to preclude a deterministic evaluation of reservoir producibility and recoverable reserves. Because of the variability in reservoir parameters that could be expected when exploring for CBM in existing or new basins, it is natural to use a statistically based (stochastic) approach in the prediction of gas in place, recoverable reserves, well performance, and economic return. A comprehensive study by Roadifer et al. demonstrated the use of MC simulation for screening key parameters affecting CBM production. Well performance is a key factor determining the economic viability of CBM reservoirs. Accurate prediction of well performance is required for development strategies such as optimized well spacing, completion gathering system, and wellsite design. The current work discusses how to integrate reservoir simulation and economics for the purpose of optimizing CBM exploration and development strategies. Central to the discussion is the use of single-well (multilayered)simulators, which were constructed in Excel* and incorporate many attributes of CBM reservoirs. These single-well (tank) models are discussed in the following section and have some utility for exploration and development applications when used on their own, but they are particularly powerful when integrated with reservoir, surface, and wellbore models, MC simulation,7 and economics. Two new tools (CPT and ILT) described in this work are examples of integrated tools for application to exploration and development, respectively.

The aim of this thesis is to investigate innovate approaches that can help to improve methane recovery and production rate from coalbed methane (CBM) reservoirs. The results of two following subjects are presented and discussed. First, thermally enhanced gas recovery from gassy coalbeds is introduced. Second, an integrated reservoir simulation-optimization framework is developed and employed to optimize infill well locations across coalbed reservoirs. When coalbed methane and geothermal activities coexist in the same field, coalbeds can be thermally treated prior to the gas production using available underground geothermal resources. Feasibility of this method is investigated both using methane sorption tests on Australian coal samples at different temperatures and also reservoir simulation. The impact of temperature elevation on methane sorption and diffusion in coal is investigated by running sorption experiments on two the Australian coal samples using a manometric adsorption apparatus. Experiments are performed to indicate that how the difference between original reservoir pressure and critical desorption pressure is decreased at elevated reservoir temperatures. Lower pressure gradient is required to extract methane from coalbed when it is thermally treated prior to gas production. Following the experimental study, the feasibility of thermally enhanced gas production from coalbeds is studied by coupling of coalbed methane and thermal simulators. The coalbed methane simulator of Computer Group Modelling (CMG) and the thermal simulator of CMG known as STARS are loosely coupled to study the effect of temperature elevation on total gas and water production. Both gas rate and ultimate gas recovery from the reservoir are increased by thermal operation. In the second part of this thesis, an integrated reservoir simulation-optimization framework is developed to intelligently obtain locations of new infill wells in a way to maximize profitability of the infill plan. This framework consists of a reservoir flow simulator (Eclipse E100), an optimization method (genetic algorithm), and an economic objective function. The objective function in this framework is to maximize discounted net cash flow of infill project. The importance of optimization is magnified when cost of water treatment is increased. When optimization approach is compared with standard five spot pattern well arrangements, the impact of water treatment cost is observed. When cost of water treatment is high, there is a large difference between the profit of the infill project calculated using the optimization approach and the standard five spot pattern. Simulation results indicate that at higher cost of water treatment, infill wells are preferably located either on the front of the water depletion zone or close to existing wells. On the other hand, when water treatment cost is low, infill wells are located in virgin sections of the coalbed where both gas content and cleat water saturation are high.
Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2013

Liquefaction is suggested to be one of the best ways to utilize coalbed methane (CBM). Different from ordinary natural gas, CBM usually contains a high proportion of nitrogen, so the liquefaction system performance, especially the heat transfer characteristics, is different from that of the ordinary natural gas liquefaction processes, and will change along with the nitrogen content of CBM feed gas. Four liquefaction processes for nitrogen/methane mixture are evaluated. For the composition with nitrogen ranging between 0 and 70% and with the methane recovery rate of 95% as the restricted index, the heat transfer characteristics for the heat exchanger systems of these four processes are investigated and compared on the basis of the optimization results given by the previous studies. This investigation provides a direction for improvement of the liquefaction system performance, and gives reference for the selection of the liquefaction process for CBM with different nitrogen content.

Abstract For the desorption of methane, thermal stimulation is an alternative to develop coalbed methane (CBM) when it is difficult to reduce the formation pressure. Microwave heating is a promising thermal method to increase the gas recovery of CBM especially for the CBM reservoir with high heterogeneity and low water content. The current study aims to establish a fully coupled numerical model to understand the enhanced gas recovery (EGR) mechanism of CBM under microwave heating. In the study, the CBM reservoir model was developed first. Then a mathematical model considering electromagnetic excitation, heat transfer, mass transfer, Langmuir adsorption, and fluid flow was built. Moreover, some important parameters were set as temperature-dependent to achieve the coupling effects among the multiphysics. Based on the above two models, a fully coupled electromagnetic-thermal-hydraulic-mechanical model was solved by the finite element, so that the distributions of electric field, reservoir temperature, methane concentration were able to be investigated. Finally, a sensitivity analysis including water content, microwave power and microwave heating mode was done based on the heating efficiency and EGR. Under microwave heating, the electric field distributes near the microwave heater with the maximum electric intensity as 1.07×103 V/m. The high electric intensity and low thermal conductivity easily enables microwaves to generate the required temperature region within CBM reservoir, so that 200 W power was applied to continuous heat the formation. Under 1 day, the maximum temperature of CBM reservoir increased to 81 °C, enabling the desorption of methane. Moreover, heating efficiency is controlled by the dielectric properties as well as electric field intensity of the CBM reservoir, although the existence of water content increases the dielectric constant within the CBM reservoir. In addition, by setting the temperature-dependent properties, microwave heating shows the ability to induce the pore volume changes by generating thermal stress, so that the porosity and permeability of CBM reservoir near the heater increase from 0.15 to 0.24 and from 0.36 mD to 1.47 mD, respectively. Based on the above positive effects of microwave heating, the CBM recovery could be significantly enhanced. Finally, in order to transfer the heat deeper into the reservoir, the feasibility of stepwise microwave heating mode has been successfully proven based on the temperature distribution within the CBM reservoir. In the study, microwave has showed great potential in enhancing the CBM recovery resulting from its high heating efficiency and pore induction effect. The results presented in this paper can provide comprehensive guidance for the optimization of microwave heating parameters.