Reservoir characteristics of high clay content and microporous tight litharenites in marine-continental transitional environments

Abstract

The resource potentials for the exploration and development of tight sandstone gas, shale gas, and coalbed gas in marine-continental transitional environments are very attractive. However, previous studies have mostly focused on the geological and geochemical characteristics of marine-continental transitional shales and coals, and less attention has been paid to the associated tight sandstones. This paper takes the sandstones in the west Guizhou as an example. The Longtan marine-continental transitional tight sandstones have been investigated using various techniques (e.g., thin section, mercury injection capillary pressure, and nuclear magnetic resonance) to illustrate the reservoir characteristics. The Longtan sandstones, according to our study, are classified as litharenites, and are characterized by thin layers, high rock fragment and clay contents, abundant micropores, complex pore-throat structures, and low porosities and permeabilities. Compared with other typical tight sandstones in China, the Longtan sandstones have more lithic content and tighter pore throat structures. Therefore, tight-gas potential is interpreted to be limited in the Longtan sandstones. However, a model for the commingled production of tight-sand gas, shale gas and coalbed methane could be viable since the Longtan sandstones are interbedded with coals and shales, which provides an opportunity for unconventional gas development in marine-continental transitional environments.

Keywords

• marine-continental transitional environment
• tight litharenites
• reservoir characteristics
• unconventional gas
• longtan formation
• west guizhou area