Research On Gas Preserving Of Deep Sandstone Roof And Gas Control By Hydraulic Fracturing In Yongchuan Coal Mine

Aimed at the problem of abnormal gas emission at coal recovering and sandstone roof drifting in deep roof of Yongchuan coal mine. Gas geology, sedimentary petrology, core analyses and hydraulic fracturing are applied for researching gas preserving and its relation with gas emission, and gas control by fracturing. Result shows:① By analyzing the control action of geological conditions to gas preserving, in order to know gas formation, this paper concludes that, anticline structure and fault development of deep roof have gas control effect. The overlying red mudstone strata seals T3xj6 strata. Dalong coal seam in T3xj5 strata is an important gas resource to deep roof. Groundwater movement is driving power of gas migration from coal seams to deep roof where mudstone and fault become hydraulic traps. Geostress is hard to adjust and release that provides high geostess environment to gas preserving.② By discussing clastic texture and structural composition, pores characteristic, pore fluid saturation in deep sandstone roof and its relation with gas emission, in order to know disadvantage of conventional gas drainage, this paper concludes that, sandstone of deep roof is mainly made up by feldspar-quartz sandstone and lithic-quartz sandstone that both have high compositional maturity and textural maturity. Porosity and permeability of sandstone samples are low as a whole, with respectively 4.33% and 0.079×10-3μm2 with gas reserves of 7.82×108m3, and strong heterogeneity in vertical. Sandstone pores mainly contain gas with better pore throat structure type in deep, however, its connectivity is poor.③ By investigating gas emission and gas control in deep roof, conducting sandstone sensitivity test and examining permeability increasing results of hydraulic fracturing, solutions for gas control is proposed, this paper concludes that, serious gas emission from overlying strata of panel is because large scale gob provides emission space, deep roof benefits gas and oil preserving, mining and depressurization form gas flow path and emission power by gas pressure and geostress gradient. Solutions are based on method of roof pressure relief borehole, suggest add 3% KCl to fracturing water and conduct fracturing to conventional borehole to pre-drainage roof gas before extraction, then drainage gas by roof pressure relief borehole along with fracturing borehole during extraction.