Page 115 - Hydrocarbon Exploration and Production Second Edition

102 Reservoir Geology

60°

Normal Fault

30°
Reverse Fault
"Thrust Fault" if displaced over
long distance (km range)

Wrench Fault

Figure 6.5 Types of faulting.

Faults may extend over several hundreds of kilometres or may be restricted to the
deformation of individual grains. They create vast potential traps for the accumulation
of oil and gas. However, they often dissect reservoirs and seal fluid and pressures in
numerous individual compartments. Each of these isolated blocks may require
individual dedicated wells for production and injection. Reservoir compartmentalisation
through small-scale faulting can thus severely downgrade the profitability of a field
under development. In the worst case, faulting is not detected until development is in
an advanced stage. Early 3D seismic surveys will help to obtain a realistic assessment of
fault density and possibly indicate the sealing potential of individual faults. However,
small-scale faults with a displacement (throw) of less than some 5–10m are not
detectable using seismic alone. Geostatistical techniques can then be used to predict
their frequency and direction.