Fluid Migration Along Growth Faults in Compacting Sediments

Abstract

The movement of fluids up growth faults is proposed to be periodic; when faults are active they can concentrate fluid flow, but when inactive, flow is restricted. Higher flow rates are predicted to be caused by fault‐zone permeabilities and fluid potentials increasing at shear stresses close to the shear strength of the rock. In this way, significant flow is confined to the most active sections of moving faults. Since fault activity is related to sediment accumulation rates, the volume of fluid flowing up faults should be greatest when accumulation rates are high. Periodic flow explains the evidence which indicates that faults can be both barriers and avenues of fluid migration. Evidence for growth faults being avenues of fluid migration is shown by fault‐zone mineralization. lowered fluid potentials. thermal anomalies, salinity anomalies. and isotope studies. In contrast, fault‐zone porosity studies. measured flow rates, high juxtaposed fluid potential differences, differential subsidence caused by groundwater production, and hydrocarbon accumulations, all suggest that growth fault zones are of low permeability. The flow of‐oil from large pore spaces into smaller, water‐filled pore spaces requires a large potential gradient. Therefore., faults which cut water‐wet sections with variable vertical permeability are usually poor conduits for oil. In contrast, in hydrocarbon‐saturated homogeneous rocks, such as mature shales. the vertical flow of migrating hydrocarbons may be concentrated by faults. The degree of concentration will depend on the permeability of the fault zone.

Deep-seated faults and hydrocarbon leakage in the Snøhvit Gas Field, Hammerfest Basin, Southwestern Barents Sea

“…Knowing accurate time of fault reactivation phases would be an important factor for hydrocarbons spilling out of the structures which is critical for evaluation of seal risk and seal integrity (Gartrell et al, 2002;Hooper, 1991;Cartwright et al, 2007). In evidence that fluid-flow was active during the early stages of glaciation and is an ongoing process in the study area (Løseth et al, 2009).…”

Preferential petroleum migration pathways in eastern Pearl River Mouth basin, offshore South China Sea

“…A fault may act either as a conduit for vertical petroleum migration along the fault plane (transfer boundary) (Losh et al, 2002(Losh et al, , 1999Losh, 1998;Hooper, 1991), as a lateral seal for petroleum accumulation (sealing boundary) (Gibson, 1994), or as a transparent boundary where fluid migrates across the fault (Hindle, 1997;Allan, 1989). A number of faults developed in the Pearl River Mouth basin (Fig.…”

Detection of water in petroleum inclusions and its implications

“…This phase further included many subtle varieties, such as the parameter of H 2 O/(CH 3 +CH 2 ) changing largely (0.8, 2.8, 5.1 and 5.3, 1.9, 0.7), and the parameter of CH 3 /CH 2 diversifying slightly between 1.0 and 1.3, that is to say, petroleum inclusions formed within fluid in similar feature (one phase), whereas the distribution of oil and water in them shows distinct heterogeneities. We apply "episodes [28] " to describing these fluctuations sublevel to one oil charging stage as Hooper theoretically suggested.…”

“…The work in his study, as well as that by others, was mostly based on the T h data of fluid inclusions: episodes were defined by the multi-peaks shown in T h histograms [23,24] . However, Hooper [28] has addressed that fluid activated in different episodes may not show clear variation of T h and oil compositions. To the contrary, the T h data should belong to one oil filling phase.…”