Abstract The importance of the role that natural gas from tight formations would play in achieving energy self-sufficiency for the United States cannot be over-emphasized. One reliable source estimates the natural gas reserves of the tight sands of the Western United States alone to be more than 5700 trillion cubic feet. However, the technology for recovering this resource remains elusive, primarily due to lack of adequate understanding of the physics of fluid flow dynamics within this type of porous media. The fluid flow in tight formations does not subscribe to that normally associated with conventional reservoirs. It is believed that tight formations frequently possess dual porosity, and the flow field in these formations may be governed by more than one mechanism. The model utilized in this study possesses proven predictive capabilities, an essential ingredient to proven predictive capabilities, an essential ingredient to production forecasting, and hence is used as a framework for the production forecasting, and hence is used as a framework for the development of optimal production strategies for the Upper Cozzette blanket sand. The model has multi-well capabilities and has options for either vertically or horizontally fractured wells and horizontal boreholes. Simulation results from a variety of production schemes are presented. The results provide some insight into production strategies involving horizontal boreholes and hydraulic fractures.
Introduction Due to diminishing natural gas reserves and the need to establish energy self-sufficiency for the United States, low-permeability natural gas reservoirs, once deemed to be noncommercial, have begun to be recognized as a possible major source of future natural gas supplies. These reserves are substantial. For example, it is estimated that natural gas reserves of the Western United States alone is more than 5700 trillion cubic feet. However, low-permeability gas reservoirs are very "tight" formations and hence produce at low rates. Techniques must be employed to enhance their productivity. These methods include hydraulic fracturing or the drilling of horizontal boreholes.
Hydraulic fracturing has been the most common method for enhancing the productivity of tight gas wells in the past, whereas the drilling of horizontal boreholes has just recently been suggested as a viable completion option. Significant reserve increases from low-permeability reservoirs also have resulted from the practice of infill drilling.
In this paper results from a number of numerical exercises, conducted to compare the recovery capabilities of various production strategies, are presented. These exercises include the production strategies, are presented. These exercises include the investigation of unstimulated vertical wells, vertically fractured wells, and horizontal boreholes for several well spacings. The Upper Cozzette blanket sand at the U.S. Department of Energy's Multiwell Experiment (MWX) is the target of the field-case study in this analysis.
Brief Description of the Numerical Model Gas transport in tight sands can be described by a multi-mechanistic approach, obtained by the superposition of two flow fields, namely a concentration gradient field and a pressure gradient field. While the first mechanism is a diffusion process, governed by Fick's law of diffusion, the latter is Darcian flow. However, the transport of water within tight formations is strictly by Darcian flow.
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