Natural Forces in Fracturing Systems

Natural forces acting in a sedimentary basin can be grouped into two categories: (1) external forces and (2) internal forces.

External forces, which are created by sediment load and tectonics, are dominant during early burial.

Continuous pressure release exists, creating equilibrium with a hydrostatic pressure. With subsequent burial, both temperature and pressure increase. However, porosity and permeability decrease. Pressure release is limited because of the limitations of decreasing porosity and permeability. At that point, internal forces, which are caused by clay inter-layer reactions, mineral crystallization or petroleum generation, will dominate.

• Force of clay inter-layer reactions:
  Interaction between swelling clay and water can generate forces that cause rock volume contraction and water expulsion during both early and late diagenesis.

• Force of crystallization:
  The mineral crystallization-generated force is a consequence of precipitation from supersaturated solution and crystal growth causing a rock volume expansion .

• Force of petroleum expulsion:
  The petroleum expulsion-generated force is a consequence of kerogen maturation and petroleum generation causing rock volume expansion.

Al Duhailan, M. (2014, Fall). Petroleum-expulsion fracturing in organic-rich shales : genesis and impact on unconventional pervasive petroleum systems. Colorado School of Mines.