5.: Incompatibility with Clay Mineralogy

Clay minerals are a common feature in sandstone reservoirs. An understanding of their structure is key to understanding how they respond as injection water is introduced to the reservoir. They are a group of hydrous aluminum phyllosilicates, but a number of different elements can be incorporated into the structure, which invariably comprises 2D sheets. The most important clay minerals in a waterflood context are smectites (including montmorillonite), illite, kaolinite, chlorite, and mixed-layer clay minerals. The clay structures consist of both tetrahedral and octahedral sheets. The tetrahedral sheets consist of four oxygen atoms at the apex locations of a regular tetrahedron, connected to a silicon atom at the center. An interlocking array of these structures connected at three corners in the same plane by shared oxygen atoms forms a tetrahedral sheet network. Some of the tetrahedrons could have an aluminum atom at the center instead of a silicon atom, and occasionally they could have iron, or another element, instead.