Viscosity Measurement

The capillary tube viscometer is housed in the VLE experimental facility and the HPHT rig. The capillary tube is a 15.43 metre length of stainless steel tubing which has been coiled and mounted above the PVT cells within the temperature controlled bath. Two high precision 0 to 20,000 psia pressure transducers capable of measuring pressure with a resolution of 0.001 psi with a maximum full scale error of 0.006%, provide reliable data, which is essential for viscosity measurements. The viscosity is measured by flowing the high pressure gas or liquid through the capillary tube whilst measuring the flowrate and the pressure drop across it.

 Interfacial Tension (IFT) Measurement

Accurate and reliable information on interfacial tension (IFT) is of major importance in both petroleum and chemical engineering. The importance of IFT is magnified when dealing with IOR processes where the relative magnitude of interfacial (capillary), gravitational and viscous forces considerably affect the recovery of hydrocarbons. The relative permeability, which determines the flow behaviour of reservoir fluids in porous media, strongly depends on the interfacial tension at low interfacial conditions.

Pendant Drop Technique

This technique is the most commonly used method for the experimental measurement of interfacial tension (IFT) in petroleum industry. It involves suspending a droplet of liquid in equilibrium vapour and measuring the droplet dimensions. However, the size of droplet that can be generated is limited by the diameter of the tube from which it is to be suspended.

Once the dimensions of the droplet are measured, they are used along with density data of the liquid and vapour phases to calculate the IFT.

Meniscus Height Technique

The meniscus height technique has been developed in this laboratory to measure fluids with low interfacial tension values, i.e. gas condensates and near critical fluids. It was observed that during PVT analysis of reservoir fluids the dark band between liquid and vapour phases, when viewed through windows, increased in height with reducing pressure. This observation lead to the development of the meniscus height technique as a way of experimentally determining the interfacial tension of relatively low IFT systems such as gas condensate reservoir fluids. A minimum interfacial tension value of 0.001 mN / m has been measured in this laboratory.

The thickness of the dark band is related to the interfacial tension by density difference of the equilibrated liquid and vapour phases.

This technique is now used routinely to measure the interfacial tension in this laboratory.

 Fluid Characterisation

'Fluid characterisation' involves defining the C7+ fraction of reservoir fluids in terms of pseudo-components, designated as single carbon number (SCN) groups. This is the most commonly used approach by which the "plus" fraction is sub-divided into a computationally manageable number of pseudo-components, together with a residual multi-carbon number (MCN) group as the re-defined "plus" fraction.

A SCN group, 'cut' or sub-fraction of carbon number 'n' is defined by the boiling point range extending from 0.5°C above the normal boiling point of the equivalent  n-alkane of the preceding group, nC_n-1, to 0.5°C above that of the n-alkane, nC_n, with identical carbon number.

The sub-division of C7+ fractions may be achieved either through a true boiling point (TBP) distillation in a high-efficiency still or through high-temperature gas chromatography (HTGC). The former technique, producing as it does distinct 'cuts' equivalent to the SCN groups, enables physical properties to be measured directly, of which molecular weight and density are routinely measured in this laboratory, and from these data derivative properties such as Tc, Pc, Zc, and acentric factor, are obtained for the SCN groups using correlations. These derived data are then deployed in subsequent equation of state (EOS) modelling. (This also applies for the heavier 'plus' fraction obtained as the distillation residue). HTGC is the complementary method to distillation of reservoir fluids for description purposes and is applied in the analysis of the C7+ fractions, where the same SCN 'grouping' approach is used to express the composition.

 Contact Angle

The contact angle is a measure of the relative strength of adhesion of fluids to a solid. It has a major influence on the hydrocarbon distribution as well as water within reservoir rocks. The main interest in the contact angle is its contribution to the capillary pressure and multi-phase flow in reservoir rocks.

In this laboratory, the gas-liquid-solid contact angle is measured at reservoir conditions using the vapour-liquid equilibria facility. we  have observed that the contact angle is almost constant at high gas-oil interfacial tension (IFT) above a threshold value and declines at a variable rate, depending on the volatility of the mixture, approaching zero at the critical point.

 Saturation Point and Volumetric Data Measurement

The experimental facilities in the PVT and Phase Behaviour Laboratory of the Institute of Petroleum Engineering at Heriot-Watt University are routinely used to measure the phase and volumetric behaviour of reservoir fluids. Various experimental apparatus are employed to carry out conventional and unconventional PVT tests to generate reliable experimental data for improving predictive models.

The phase and volumetric behaviour of various reservoir fluids, including volatile oil and gas condensates, can be studied by performing one or a combination of following experiments:

• Constant Composition Expansion (CCE)
• Constant Volume Depletion (CVD)
• Differential Liberation
• Separator Test
• Multiple Contact 
• Forward Contact Test
• Backward Contact test
• Gas Injection
• Gas Cycling
• Condensate Accumulation Near Wellbore

In this Laboratory the volume is measured to an accuracy of ±0.01 cm³. The pressure is measured by a high pressure resonating quartz crystal transducer with a resolution of ±0.001psi.