Growth faults

Since faults are zones of inherent weakness they may be reactivated over geologic time. Usually, faulting occurs well after the sediments have been deposited. An exception to this is a growth feu/f (also termed a syn-sedimentary fault), shown in Figure 5.7. They are extensional structures and can frequently be observed on seismic sections through deltaic sequences. The fault plane is curved and in a three dimensional view has the shape of a spoon. This type of plane is called listric. Growth faults can be visualised as submarine landslides caused by rapid deposition of large quantities of water-saturated... 

Growth faulted deltaic areas are highly prospective since they comprise of thick sections of good quality reservoir sands. Deltas usually overlay organic rich marine clays which can source the structures on maturation. Examples are the Niger, Baram or Mississippi Deltas. Clays, deposited within deltaic sequences may restrict the water expulsion during the rapid sedimentation / compaction. This can lead to the generation of overpressures. 

Figure 5.7 Geometry of growth faulting and resulting anticline (rollover) (after Petroleum Flandbook, 1983)...

Compaction reduces porosity and permeability. As mentioned earlier during the introduction of growth faults. If the expulsion of pore water is prevented, overpressures may develop. 

Hooper, E.C.D., 1991. Fluid migration along growth faults in compacting sediments. Journal of Petroleum Geology, Vol. 14(2), pp.161-180... 

Watts, N.L., 1987. Theoretical aspects of cap-rock and fault seals for single- and two-phase hydrocarbon columns. Marine and Petroleum Geology, Vol. 4, November 1987, pp. 274-307 Weber, K.J., 1982. Influence of common sedimentary structures on fluid flow in reservoir models. Journal of Petroleum Technology, March 1982, pp. 665-672 Weber, K.J., 1987. Hydrocarbon distribution patterns in Nigerian growth fault structures controlled by structural style and stratigraphy. Journal of Petroleum Science and Engineering, 1, pp. 91-104... 

Weber, K.J. 1987. Hydrocarbon distribution patterns in Nigerian growth fault structures controlled by structural style and stratigraphy. J. Pet. Sci. Eng., 1 91-104. 

Weber, K.J., Mandl, G, Pilaar, W.F., Lehner, F. and Precious, R.G. 1978. The role of faults in hydrocarbon migration and trapping in Nigerian growth fault structures. Offshore Conf., Houston, TX, Paper OTC 3356. 

Berg, R.B. and Avery, A.H. 1995. Sealing properties of Tertiary growth faults, Texas Gulf coast. Am. Assoc. Pet. Geol. Bull., 79 ... 

Compaction curves are significantly different for sands and muds. At shallow depths, muds compact rapidly, while at greater depths compaction rates for sands exceed that of shales. Such differences may cause considerable differential compaction effects across, for instance, growth faults, which cause reactivation of such faults during burial. 

GaN, semi-sound zone < 150nm)laterai growth faulted zone (5Qnm). 

FIGURE 6 Cross sections to illustrate the different types of fault traps. (A) Reverse fault caused by compression. (B) Normal feult caused by tension. (C) Growth fault with petroleum trapped in adjacent rollover anticline. 

This demonstrates that the fault is removed repeatedly through time. Such faults are thus termed growth faults. Growth faults host petroleum traps, both where reservoir beds are truncated and sealed by the fault, and in rollover anticlines on the downthrown side. Examples are common in the Tertiary deltas of Nigeria and the Gulf Coast of the United States. 

Tabular vein-like deposits may be associated with regional fractures, shear systems and/or growth faults. Breccia fragments within these deposits are generally limited to blocks of the host rock. ... 

The growth faults may correspond to marcasite lamellae in the pyrite [395,396]. Indeed HRTEM and electron diffraction revealed them as single (101) layers of marcasite inserted between (002) layers of pyrite [397]. Dislocation loops formed during the growth of pyrite also have the a[0, 0.27, 0.5] fault vector [101]. This translation was predicted as the most probable in a coincidence-site-lattice study [398]. 

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