Permeability Enhancement and Methane Drainage Capacity of Tree-type Boreholes to Stimulate Low-permeability Coal Seams
- PDF / 4,515,384 Bytes
- 14 Pages / 595.276 x 790.866 pts Page_size
- 84 Downloads / 178 Views
RESEARCH ARTICLE-EARTH SCIENCES
Permeability Enhancement and Methane Drainage Capacity of Tree-type Boreholes to Stimulate Low-permeability Coal Seams Liang Zhang1,2 · Zhaolong Ge1,2,3 · Yiyu Lu1,2 · Zhe Zhou1,2 · Songqiang Xiao1,2 · Shaojie Zuo1,2 Received: 24 December 2019 / Accepted: 17 September 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract Low permeability coal makes methane control in underground coal mines difficult. Drilling tree-type boreholes is a new method for improving the permeability of coal seams to stimulate cross-measure boreholes drainage. This paper presents an analysis of the permeability enhancement and methane drainage capacity of tree-type boreholes based on data from a coal mine in China. After applying the proposed method, numerical models show that a large area of enhanced permeability is created between the tree’s sub-boreholes. Compared with conventional drainage programs, tree-type boreholes increase the average rate of methane extraction by a factor of 13.9 and the effective influence radius of the borehole by a factor of 4.9. The simulated methane production rates from both types of boreholes are verified against field data from the Shoushan mine, China. This paper presents a quantitative analysis of the relationships between different tree-type borehole properties and methane drainage performance. Longer and more numerous sub-boreholes result in logarithmic drainage increases in the enhanced-permeability areas. Orienting the initial tree-type borehole angle parallel to the direction of maximum horizontal stress maximizes borehole stimulation. During drainage, the effective influence radius of tree-type boreholes expands logarithmically with sub-borehole length; cumulative methane production increases linearly with the length and number of sub-boreholes. These results can provide reliable scientific guidance for optimizing the layout of tree-type boreholes in field test. Keywords Permeability enhancement · Methane drainage · Tree-type borehole · Numerical simulation
1 Introduction Coal mine methane (CMM) is released or ejected from worked coal seams or adjacent gassy formations in coal mines [1–3]. CMM is explosive and thus potentially hazardous, but it is also a form of clean energy. Geological reserves of CMM in China amount to 1.023 × 1011 m3 , and these are the third most abundant CMM reserves in the world after those of Russia and Canada [4]. The hazards associated with CMM have led to over 2000 fatalities in more than 14,000 methane-related mining accidents in China since 1950 [5]. Underground CMM pre-drainage through
B
Zhaolong Ge [email protected]
1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
2
School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China
3
School of Resources and Safety Engineering, Chongqing University, Chongqing 400030, China
cross-measure boreholes plays a major role in mitigating CMM hazards, and CMM drainage also increases t
Data Loading...
