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The Effect of Coalbed Methane Well Hydraulic Fracturing on Coal Mining Roof Support and the Suggestions on Fracturing construction A Case Study From the Yanchuannan CBM Field, China

Abstract

In the process of coalbed methane development in china, hydraulic fracturing influences the roof stability in the subsequent coal mining. Based on the hydraulic fracturing operating data, the spatial form of the fracture geometry and the factors influencing its extension situation at the interface are summarized and the corresponding model for the study area is also established. Targeting at 18 parameter wells, combined with the geological models, the hydraulic fracturing simulation is conducted.

The primary conclusions can be obtained as follows:

1) The simulation results show that the damaged degree of coal seam roof has a strong minus relationship with the sandstone content in the 20m overlying strata. And according the damaged degree, the roof can be divided into 3 different categories: type I -high sandstone content, type II -medium sandstone content and type III -low sandstone content. While for all types of roof, it can be divided into strong damage area, medium damage area, minor damage area and non-damage area.

2) Based on the roof damaged degree and the sensitivity of induced fractures with respect to fracturing operating data, the operating scheme aiming at research area is optimized, including the discharge capacity (5.6–6.3 m3/min for type I roof, 6.9–7.6m3/min for type III roof), pad fluid volume (324–355 m3 for type I roof, 262–293 m3 for type III roof), sand carrier volume (366–401 m3 for type I roof, 296–331 m3 for type III roof), and proppant concentration (165–182 kg/m3 for type I roof, 135–151 kg/m3 for type III roof), while the counterpart data for type II proof is between that for type I and type III proof.

3) The roof failure mechanism under the effect of single well and well patterns is systematically and separately analyzed for strong damage area and medium damage area. Besides, specific suggestions that combined anchor-net shoring, bolting and shotcrete support, injection grouting and hydraulic supports are proposed in terms of roadway, cutting hole and coal face in the study area to ensure subsequent coal mining to be safe and efficient.

Key Words: Fracture characteristics, fracturing simulation, coal mining, roof support