GeoPressure Oilfield Cycle

Exploration: Aim is to maximise chance of finding an economically viable hydrocarbon accumulation.

Reservoir pressure analysis identifies:

• Fluid types, contacts and distribution
• Presence of reservoir compartmentalisation
• Presence of hydrodynamic flow (i.e. tilted hydrocarbon-water contacts).
• Reservoir connectivity.


Reservoir Fluids, contacts & overpressure

Reservoir Fluids, contacts & overpressure

Overpressure mapping: compartmentalisation

Overpressure mapping: compartmentalisation

Seal Capacity analysis identifies:

• Risk of seal being breached (and therefore hydrocarbon being absent).
• Seal capacity – i.e. max column height.



Inputs for determination of Seal Capacity

Inputs for determination of Seal Capacity

Aquifer Seal Capacity and Hydrocarbon Seal Capacity.

Image taken from Swarbrick, R.E., Lahann, R.W., O’Connor, S.A. and Mallon, A.J. 2010. The role of the Chalk in development of deep overpressure in the Central North Sea. In: Vining, B.A. & Pickering, S.C. (eds.) Petroleum Geology: From Mature Basins to New Frontiers, Proceedings of 7th Petroleum Geology Conference, v.1. p.493-507.

Pressure Effects on seismic response – cross-discipline application of pressure:

• Effects of pressure on AVO response.
• Pressure input into QI  modelling (in reservoirs and seal above) to understand fluid content.



AVO Classes (after Rutherford and Williams, 1989)

AVO Classes (after Rutherford and Williams, 1989)

Lateral drainage is related to fluid escape to the surface via continuous reservoirs or fault linkage, resulting in pressure regressions with increasing depth.

Naturally draining reservoirs enhance seal capacity in traps thus allowing longer-than-expected hydrocarbon columns as well as providing migration pathways, possibly into new traps

O’Connor and Swarbrick, 2008.