Abstract
The development of abandoned coal mine gas has multiple advantages in terms of safety, economy, environment, and society. Due to previous excavations, the gas distribution is heterogeneous, thereby hindering well location optimization. In this study, considering the Shenbei abandoned coal mine as an example, the authors developed a workflow for well location optimization through simulation. The workflow includes: (1) the setup of an initial reservoir simulation model with the preliminary well location designed by experience; (2) the optimization of the well location based on the flowline distribution, and it is preferred that the well connect a large number of flowlines; (3) the simulation based on the optimized well location, and (4) repetition of the steps until the optimized well locations are determined. Moreover, the role of fracturing is also examined through simulation scenarios. The simulation results show that the locations of the two originally designed wells (1# and 4#) should be optimized due to the relatively low gas production without fracturing. The two wells are optimized according to the flow streamlines, demonstrating performance improvement. Moreover, the simulation results also show that there is no need to optimize the well 4# location if the fracturing technology is applied. An additional well is suggested based on the flow streamline analysis and gas production performance simulation. The main conclusions drawn from this study are as follows. (1) Five optimized well locations are determined for the Shenbei abandoned coal mine, and they should be located within the “O” ring, a high permeability region nearby the previous excavation zone; (2) Fracturing is an effective method for stimulating gas production; however, the extent of fracturing varies from well to well; (3) The workflow applied in this study is effective for the well location optimization in abandoned coal mines.
Highlights
Abandoned mine gas refers to the existing methane resources in the residual coal seams, surrounding rocks, or underground spaces in the coal mines that are closed based on specific procedures due to the depletion of coal resources, failure to satisfy the safety production requirements, or other industrial technology policies (Karacan et al, 2011)
It is urgent to conduct a research on the relevant theory and technical methods of gas drainage in the abandoned coal mines, such that the potential multiple advantages offered by the abandoned mine gas are adequately exploit
Based on the simulation analysis of gas drainage in a certain mine, this study proposes a simulation workflow for the optimization of the gas production well location in the abandoned coal mines, including the following steps: 1. Establishing of a 3-D geological model and distribution of reservoir properties; 2
Summary
Abandoned mine gas refers to the existing methane resources in the residual coal seams, surrounding rocks, or underground spaces in the coal mines that are closed based on specific procedures due to the depletion of coal resources, failure to satisfy the safety production requirements, or other industrial technology policies (Karacan et al, 2011). A large-scale reservoir simulation model should be established to appropriately select the optimal well locations for the gas drainage in the abandoned coal mines in Shenbei. The basic simulation concept is to construct and assign the 3 D geological geometry model of the abandoned mine reservoir by studying the resource distribution, coal seam thickness, gas content, and working face layout, while considering the effect of land subsidence and surface water accumulation. The results illustrate that the gas production rate has been significantly enhanced by changing the well location without fracturing (Figure 7(a) and (c)) This verifies that the proposed analysis based on the flow stream effectively optimizes the well location. More gas can be extracted through well 2# and the added well 1#, after fracturing
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