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Abstract

The vast majority of gas production all over the world comes from conventional reservoirs that become ever-increasingly difficult to discover and exploit. However, business cycles and higher gas prices affect and change the gas production strategy of the industry. Concordantly, the significance of unconventional gas reservoirs has been increasing for recent years owing to economic viability of their development and, therefore identification of the challenges and common pitfalls regarding those have been gaining importance at the same time. In the last decades, the exploitation of unconventional gas reservoirs such as coalbed methane, shale gas, and tight gas has become an ever increasing part of world gas supply. With state of the art technology and high gas prices, these resources can be developed by achieving economical gas production. The economic viability of many unconventional gas developments hinges on effective stimulation of extremely low permeability rock by creating very complex well trajectories and fracture networks. Generally, unconventional gas reservoirs are described as having very large hydrocarbon reserves in place, a low expected ultimate recovery, and low permeability. These reservoirs cannot provide efficient amount of gas with an economical rate and they require some special stimulation treatment techniques. Mostly, horizontal wells or multilateral wells with transverse hydraulic fractures make the feasible production rates possible, and improved performance of these reservoirs should be taken into account as much accurate as possible. Evaluation of unconventional gas reservoirs is much more challenging as compared to conventional gas reservoirs due to their complex rock properties, drilling and completion techniques, and production mechanism. Each unconventional gas reservoir is unique and needs special interests to be characterized accurately. Ordinarily, it is very difficult to characterize them and choose the right recovery techniques. Accurate stimulation and determination of the unconventional gas reservoir systems plays an important role to produce natural gas commercially and optimize the recovery properly. At this point, numerical simulation approach that is the most beneficial tool to validate and predict the performance of these kinds of systems provided that adequate and reliable data are available comes into play. Although simulation of the unconventional gas reservoirs are also challenging process due to the several reasons like ultra-low permeability, desorption, complex geological characteristics, it offers remarkable potential for understanding of unconventional gas reservoirs. The main effort of this study is to investigate the well performance of coalbed methane, shale gas, and tight gas reservoirs with different well configurations and stimulation scenarios. In order to obtain the outcome of these analyses, a 3D layered geological model with a 25x25x52 grid having four different zones with different thicknesses was constructed and modified for each reservoir system with different characteristics as a means of providing some distributed properties by Petrel. On the other hand, the reason the models were created with similar areal extend is to compare the gas in place and recovery of each system. A series of reservoir simulation were performed by Eclipse as a commercial numerical simulator with two types of porosity system; dual porosity for coalbed methane and shale gas reservoirs, single porosity for tight gas reservoir. In some reservoir systems, hydraulic fractures were represented and included into the model by local grid refinement and permeability multiplier facilities of Eclipse for vertical, horizontal, and multilateral well types.

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/content/papers/10.3997/2214-4609-pdb.380.37
2013-05-15
2024-03-28
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