Role of the organic matter of a shale layer in the formation of its permeability at the early catagenic stage

Abstract

The role of an important bulk component of high-carbon rocks (in particular, oil shale)—their concentrated organic matter (COM)—in the formation of epigenetic permeability is considered. Baltic kukersite shale (degree of transformation—early catagenesis) is used as an example. It is emphasized that the fluid permeability of this shale layer is manifested locally in tectonic disturbances, buried erosional valleys, and linear structural-deformation zones. The quality of shale in these zones deteriorates (the calorific value, the yield of tar, etc., decrease), and it is partially decarbonized (and decarbonated) and deformed; the shale acquires increased permeability, and its bed thickness decreases and marl varieties become more terrigenous. It is asserted that these phenomena were caused by the partial (and sometimes almost complete) loss of kukersite in the test sections of COM. The decrease of the organic matter caused the liberation of void space and then deformations, the disturbance of the integrity of layers, an increase in the permeability, and the loss of the status of fuels by the initial shale. The relationship of the degradation of the COM of shale with sulfate reduction processes in the underground hydrosphere at the early catagenic stage of the existence of a shale layer is substantiated.