For the development of tertiary oil and gas exploitation methods, it is important to understand the interaction of the various fluid and gas phases with the hydrocarbon reservoir rocks. The wetting properties of the inner surface of the rock have a great impact on multiphase flow and saturation, as well as on productivity and recovery. The morphology of pore surfaces in clastic sedimentary reservoir rocks is formed by the modified mineral grain surfaces, and gradually altered in diagenetic processes as well as during epidiagenesis, due to changing temperature, pressure and chemical and physical conditions of the environment. Thus, very different types of surfaces can occur, ranging from very rough, fractal-like surfaces to flat, smooth crystal facets. In this paper, we analyzed sandstones from a German gas deposit by digital laser scanning microscopy, raman spectroscopy and scanning electron microscopy. The pore surface morphology shows textures of clastic grains, authigenic minerals characteristics and pore throats that have been blocked by cementation, reducing the connection between pore spaces. Authigenic minerals with needle and prism shapes, have grown in pores at the same time with and subsequently to cement accumulation. Due to the high aspect ratio, these crystals have a significant influence on fluid flow in the pore network. Although their influence on the pore volume may be small, they can dramatically decrease the permeability of the pore network, because they reduce the cross-sectional area of the pores, and they can act as pinning sites for an oil-water interface and as crystallization seeds for later, secondary cements.
