Shale Gas Reservoir Forming Conditions and Target Zone Optimization in Yongshun Block of Northwest Hunan

Abstract

In this paper, the reservoir forming conditions of shale gas in the Lower Silurian Longmaxi Formation in Yongshun Block of Northwest Hunan was studied based on the field outcrops, drilling and core data, and the analysis of the results of experimental tests conducted using microsection, scanning electron microscope, x- ray diffractions, magnetic resonance imaging, isothermal adsorption, etc. and taking the stratum, petrology, geochemistry and shale gas-bearing of the black shale as the priorities. And then, the target zone optimization was carried out. The researches show that in the Longmaxi Formation, the sedimentary environment of deep- water retention basin controls the development of organic-rich shale. The sedimentary thickness is within the range of 22.26~28.63m. The TOC content in the sample is mostly over 1.5%. The kerogen type is mainly I- type. The organic matter is in the early period of the overmature stage. The shale reservoir is rich in cyclopentasiloxanel and brittle mineral, which are in favor of the fracture formation and latter reservoir fracturing improvement. Many types of pores and cracks developed, forming sound shale gas reservoir space. The shale reservoir adsorption capacity is good, with the saturated adsorption capacity reaching 1.24~3.10m3/t and the average saturated adsorption capacity amounting to 2.11m3/t. It has a linearly positive correlation with the TOC content. The parameter well signifies a relatively high gas content in the shale. The burial depth is appropriate and the effective exploration area reaches 540 km2. Taking into comprehensive consideration the reservoir forming conditions, the core area of Longjiazhai syncline and Qing’anping syncline are selected as the shale gas exploration target area.