In situ study of intensity of weathering-induced fractures and methane emission to the atmosphere through these fractures

The width and length of weathering-induced fractures, horizontal distances between through channels formed due to weathering, number of through channels in a very weak sandy shale surface layer, and methane emission through these fractures to the atmosphere are studied. Sampling from the studied weathered sandy shale exhibiting very low rock quality (RQD < 12%) is impossible and, for this reason, fracture characteristics of this rock were measured in situ directly in the walls of five surface vertical boreholes 1.5 m deep using an original measurement device. The radial expansion of measurement devise due to air pressure is used to press wet gypsum into the fractures in borehole surface in order to make gypsum casts of the fractures. Semi-empirical relations between methane volumetric flow rate into the atmosphere through weathering-induced fractures and dimensions, area and number of weathering-induced fractures and gas pressure difference are obtained. The comparison between the values of gas seepage through the fractures and rock matrix is performed.

► The intensity of weathered-induced fractures was studied in situ. ► The original device for measurement of fracture parameters was proposed. ► The relations between methane seepage and fracture parameters are obtained.