Changes

Fracturing and brecciation associated with folds, faults, and diapirs generally increase the reservoir quality of well-indurated rocks (see [[Evaluating fractured reservoirs]]). Fracture porosity is typically low, usually providing only about 1% porosity; however, fractures in large reservoirs may hold considerable reserves. Fracture permeability may be as high as tens of darcies and is directional in nature. Conversely, fractures filled by mineralization or with gouge may produce a permeability barrier in the direction perpendicular to the fracture. Brecciation along fracture or fault zones may occur due to shearing or dissolution and collapse. Except where mineralization has occurred in the breccia, brecciation can increase both porosity and permeability considerably. Closely spaced sealing faults can significantly compartmentalize a reservoir.

Fracturing and brecciation associated with folds, faults, and diapirs generally increase the reservoir quality of well-indurated rocks (see [[Evaluating fractured reservoirs]]). Fracture porosity is typically low, usually providing only about 1% porosity; however, fractures in large reservoirs may hold considerable reserves. Fracture permeability may be as high as tens of darcies and is directional in nature. Conversely, fractures filled by mineralization or with gouge may produce a permeability barrier in the direction perpendicular to the fracture. Brecciation along fracture or fault zones may occur due to shearing or dissolution and collapse. Except where mineralization has occurred in the breccia, brecciation can increase both porosity and permeability considerably. Closely spaced sealing faults can significantly compartmentalize a reservoir.

===[[Wettability]]===

===Wettability===

Wettability in an oil reservoir controls reservoir quality by affecting the amount of water production. When the reservoir rock is oil-wet, water is located in the central portion of the pores and will flow through the pore system with the oil. Conversely, in a water-wet reservoir, the water is restricted to the perimeter of the pores and will not flow through the pore system until much of the oil has been removed. In addition, the irreducible water saturations of oil-wet reservoirs tend to be much lower than those of water-wet reservoirs.

[[Wettability]] in an oil reservoir controls reservoir quality by affecting the amount of water production. When the reservoir rock is oil-wet, water is located in the central portion of the pores and will flow through the pore system with the oil. Conversely, in a water-wet reservoir, the water is restricted to the perimeter of the pores and will not flow through the pore system until much of the oil has been removed. In addition, the irreducible water saturations of oil-wet reservoirs tend to be much lower than those of water-wet reservoirs.

===[[Capillary pressure]]===

===[[Capillary pressure]]===