Capillary Pressure

Several hypotheses exist for the etiology of decubitus ulcers, with external pressures exceeding internal capillary pressures over bony prominences claimed to be the major factor. This investigation evaluated the mechanical changes that occurred in human skin as a result of its exposure to static versus cyclic normal pressures of the magnitudes earlier recorded for the heels of human subjects on various support surfaces. The skin was characterized through uniaxial tensile testing. Static pressure alone altered the tissue's mechanical properties more than dynamic pressure cycles. Tissue subjected to pressure prior to uniaxial tensile testing always was less stiff than control tissue. Damage to the initially randomly oriented tissue collagen fiber bundles in the fibrous matrix, which may occur as a result of sustained compression, may be the cause of a decrease in stiffness of tissue subjected to prior pressure loading. This is the first report of compressive-pre-load-induced stra...

The implementation of CO2 storage in sub-surface sedimentary formations can involve decision making using relevant numerical modelling. These models are often represented by 2D or 3D grids that show an abrupt boundary between the reservoir and the seal lithologies. However, in an actual geological formation, an abrupt contact does not always exist at the interface between distinct clastic lithologies such as sandstone and shale. This article presents a numerical investigation of the effect of sediment-size variation on CO2 transport processes in saline aquifers. Using the Triassic Bunter Sandstone Formation (BSF) of the Southern North Sea (SNS), this study investigates the impact a gradation change at the reservoir-seal interface on CO2 sequestration. This is of great interest due to the importance of enhanced geological detail in reservoir models used to predict CO2 plume migration and the integrity of trapping mechanisms within the storage formation. The simplified strategy was to apply the Van Genutchen formulation to establish constitutive relationships for pore geometric properties, which include capillary pressure (Pc) and relative permeability (kr), as a function of brine saturation in the porous media. The results show that the existence of sediment gradation at the reservoir-seal interface and within the reservoir has an important effect on CO2 migration and pressure diffusion in the formation. The modelling exercise shows that these features can lead to an increase in residual gas trapping in the reservoir and localised pore pressures at the caprock’s injection point.

Modeling Hysteresis is an important task when simulating water alternating gas (WAG) scheme. Since the displacement process in the reservoir changes from drainage (desaturation) to Imbibition (saturation) at different values of changing water saturation direction. Relative permeability and capillary pressure Hysteresis should reflect this process in reservoir dynamic models. Some dynamic models use only Imbibition relative permeability and capillary pressure for a given reservoir rock type. This would not allow the model to follow an "appropriate path" of saturation changes in the relative permeability and capillary pressure curves. Accounting for non wetting phase (oil) Hysteresis is more important than the wetting, since it controls oil mobility and thus recovery. This work consists of two parts: the first part consists of build a 1D model to evaluate the simulator Hysteresis model(s) by comparing the results obtained from simulator build-in Hysteresis with correlation driven "scanning" curves for relative permeability and capillary pressure. Also this model used to asses the impact of Hysteresis in a WAG case. The second part consists of constructing a 3D mechanistic model (1 Km x 1 Km) with full geological description to simulate a line-drive CO2 WAG pilot. Two WAG prediction cases were studied; one cases uses simulator build-in Hysteresis model and the other uses manual generated "scanning" curves. The pilot performance results such as oil production, recover factor, water cut, GOR and CPU time were used for comparisons. The results from both parts indicated comparable results between simulator build-in Hysteresis models and correlation models. The results from the first part indicated a significant change in recovery in the WAG case with Hysteresis in comparison with no Hysteresis case.

Two or more different fluids generally saturate chalk in oil reservoir, and therefore its behaviour can be very complicated. In this paper, a constitutive law is proposed for modelling the mechanical behaviour of a chalk saturated by two non-miscible fluids, water and oil. The effects of the capillary pressure or suction are taken into account. They are considered as an independent variable, as in the Barcelona's basic model developed for unsaturated soils. On the other hand, internal friction and pore collapse are modelled as independent mechanisms. The determination of the parameters is based on triaxial and oedometer tests. Finally, in order to validate the model, predictions are compared with experimental results of water-flooding test. Copyright © 2002 John Wiley & Sons, Ltd.

We measure primary drainage capillary pressure and the relationship between initial and residual non-wetting phase saturation for a supercritical carbon dioxide (CO2)-brine system in Berea sandstone. We use the semi-permeable disk (porous-plate) coreflood method. Brine and CO2 were equilibrated prior to injection to ensure immiscible displacement. A maximum CO2 saturation of 85% was measured for an applied capillary pressure of 296 kPa. After injection of brine the CO2 saturation dropped to 35%; this is less than the maximum trapped saturation of 48% measured in an equivalent n-decane (oil)-brine experiment. The dimensionless capillary pressure is the same to within experimental error for supercritical CO2-brine, n-decane-brine and a mercury-air system. CO2 is the non-wetting phase and significant quantities can be trapped by capillary forces. We discuss the implications for CO2 storage.