Petrophysical and geomechanical effects of organic matter on shale gas production

Abstract

It has been shown that shale rocks have a multi-porosity system: organic matter (OM), inorganic matrix (IOM), and a natural fracture system. Even if many studies verified the organic matter as the source of gas, the influence of organic matter on shale gas production has not been well understood. In this article, we present the characteristics of organic matter and its effects on gas production. The definition of organic matter is presented, followed by extensive reviews on the quantity and quality of organic matter, which are important parameters for shale gas production. Since hydrocarbons are generated in organic matter, the adsorbed gas exists in organic pores. Organic pores are formed as a result of gas generation in organic matter. The hydrocarbon-wet surface of organic matter makes adsorbed gas existed on organic pore. Distinguishing organic matter from the inorganic matrix makes gas transport mechanisms become more complex: gas diffusion and desorption in organic matter and organic pores, slip flow in inorganic pores, and Darcy flow in natural fractures. During gas production, gas flows along hydraulic fractures, natural fractures, the inorganic matrix, and organic matter in order. The deformation of pores by the geomechanical properties of materials has a crucial influence on gas production. This article deals with how the presence of organic matter, which is much softer than the inorganic matrix, affects gas production in shale reservoirs. A comprehensive study of the characteristics of organic matter can improve our understanding of organic-rich shale reservoirs.