Classification of coal/rock formation combination types and fracturing measures in Yuwu Mine

Abstract

In order to classify the types of hydraulically fractured coal and rock seam combinations, the No.3 coal seam in Yuwu wellfield of Lu’an Mining area are taken as the research object in this paper, and the lithology and mechanical characteristics of the roof was obtained by logging interpretation and mechanical testing. The coal structure of coal seam section is identified by the combination of core well and logging. The stress state was obtained according to the method of calculated stress of hydraulic fracturing stress and density logging. On this basis, types of hydraulically fractured coal and rock seam combinations were classified, and the hydraulic fracturing measures for different combination types are proposed. The results show that the types of hydraulically fractured coal and rock combinations in the study area can be classified into seven types: hard rock and hard coal, soft rock and hard coal, hard rock and soft coal, soft rock and soft coal combination of transitional type and tensile type. When hard rock and hard coal was combined, long fractures and effectively supported fractures can be created by adopting large displacement, multiple fluid volume, low or medium sand ratio and step by step sand addition. When soft rock and hard coal was combined, avoid shooting part of the coal seam to prevent fracturing fluid entering the interface between coal seams and soft rocks, which can ensure the fracturing effect. Roof hydraulic fracturing is recommended for the stretching combination of hard rock and soft coal. In the transitional hydraulic fracturing of hard rock and soft coal, the fracturing parameters are optimized according to the difference between horizontal stress and vertical stress. When soft rock and soft coal are combined, hydraulic fracturing is not recommended for reconstruction.

Keywords

• gas drainage
• hydraulic fracturing
• coal and rock combination
• ground stress
• coal body structure