Physical properties of rocks

Aly A. Hamouda* and Omid Karoussi Department of Petroleum Engineering, University of Stavanger, 4036 Stavanger, Norway * Author to whom correspondence should be addressed; E-mail: aly.hamouda@uis.no Received: 23 April 2008; in revised form: 30 May 2008 / Accepted: 2 June 2008 / Published: 6 June 2008 Abstract: It is customary, for convenience, to use relative permeability data produced at room temperature. This paper shows that this practice underestimates oil recovery rates and ultimate recovery from chalk rocks for high temperature reservoirs. Above a certain temperature (80°C in this work) a reduction of oil recovery was observed. The reduction in oil recovery is reflected by the shift of relative permeability data towards more oil-wet at high temperature (tested here 130°C). However, both IFT and contact angle measurements indicate an increase in water wetness as temperature increases, which contradict the results obtained by relative permeability experiments. This phenomenon may be explained based on the total interaction potential, which basically consists of van der Waals attractive and short-range Born repulsive and double layer electrostatic forces. The fluid/rock interactions is shown to be dominated by the repulsive forces above 80°C, hence increase fine detachment enhancing oil trapping. In other words the indicated oil wetness by relative permeability is misleading. Keywords: Temperature, Relative Permeability, Oil Recovery, Wettability (Contact angle), Interfacial tension (IFT), Fluid/rock interaction 1. Introduction Improving oil recovery is recognized as the major target and challenge at the different stages of an oil field development. Among several methods in oil recovery, thermal recovery has been used to increase the mobility of oil specifically in heavy crude oil reservoirs. Babadagli [1-2] compared the

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Effect of Temperature, Wettability and Relative Permeability on Oil Recovery from Oil-wet Chalk

The effect of hot water injection on sandstone permeability

A thermodynamic framework is proposed to couple the effect of mechanical stress and temperature on crack opening and closure in rocks. The model is based on continuum damage mechanics, with damage defined as the second-order crack density tensor. The free energy of the damaged rock is expressed as a function of deformation, temperature, and damage. The damage criterion captures mode I crack propagation, the reduction in toughness due to heating, and the increase in energy release rate with cumulated damage. Crack closure is modeled through unilateral effects produced on rock stiffness. The model was calibrated and verified against published experimental data. Thermo-mechanical crack opening (resp. closure) was studied by simulating a triaxial compression test (resp. uniaxial extension test), including a thermal loading phase. The degradation of stiffness due to tensile stress and recovery of stiffness induced by both mechanical and thermo-mechanical unilateral effects are well captured. The thermo-mechanical energy release rate increases with thermal dilation and also decreases with ambient temperature. It was observed that there is a temperature threshold, below which the rock behaves elastically. A parametric study also showed that the model can capture hardening and softening during thermo-mechanical closure (for specific sets of parameters). These numerical observations may guide the choice of rock material used in geotechnical design, especially for nuclear waste disposals or compressed-air storage facilities.

A thermo-mechanical damage model for rock stiffness during anisotropic crack opening and closure

Temperature effects on the heavy oil/water relative permeabilities of carbonate rocks

Equipment was constructed to perform dynamic displacement experiments on small core samples under conditions of elevated temperature. Oil-water flowing fraction and pressure drop were recorded continuously for calculation of both the relative permeability ratio and the individual relative permeabilities. Imbibition relative permeabilities were measured for five samples of Boise sandstone at room temperature and at 175/sup 0/F. The fluids used were distilled water and a white mineral oil. The effect of temperature on absolute permeability was investigated for six Boise sandstone samples and two Berea sandstone samples. Results for all samples were similar. The irreducible water saturation increased significantly, while the residual oil saturation decreased significantly with temperature increase. The individual relaive permeability to oil increased for all water saturations. The individual relative permeability to water decreased with temperature increase for water saturations below the room-temperature residual oil saturation, but the relative permeability to water at flood-out increased with temperature increase. Absolute permeability decreased with temperature increase.

F.J. Casse

Papers

The Effect of Temperature on Relative and Absolute Permeability of Sandstones