Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
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Gas Condensate Recovery Studies - Research Programme 2002-2005

Ali Danesh of the Heriot-Watt Institute of Petroleum Engineering, discusses proposals for the latest phase of research (beginning in July 2002) on the understanding and modelling of the near-wellbore flow mechanisms that occur in gas condensate reservoirs. (Co-authors Dabir Tehrani, Graeme Henderson, M Jamiolahmadi, and R Ataei) (ali.danesh@pet.hw.ac.uk)

Hydrocarbon recovery from gas and condensate reservoirs has been studied at Heriot-Watt University since 1986. Flow visualisation using glass micromodels has been employed to investigate the flow mechanism at simulated reservoir conditions, whereas core tests have been conducted to confirm and quantify the observed results. Mathematical models and numerical simulators have been developed/implemented to generalise the results as engineering tools for optimum reservoir management. It has been concluded that the distribution of the condensate in pores, and the relatively low interfacial tension between the hydrocarbon phases, compared to gas-oil systems, are the main factors which contribute to the non-conventional flow behaviour of gas-condensate.

The current phase of the study, which is sponsored by DTI and eight major companies, will end in June 2002. It is directed mainly at the measurement and correlation of gas and condensate relative permeabilities at near well bore conditions where the positive rate effect, identified for the first time in this laboratory, as well as the negative inertial effect are significant. The developed generalised relative permeability correlations have been implemented in two of the leading commercial reservoir simulators. Figure 1 demonstrates the accelerated gas recovery due to inclusion of rate effect on relative permeability as simulated using radial local grid refinement (RLGR). Basic reservoir and well data are as follows: k = 20 mD, ??= 18%, hres = hw =150 ft, Well drainage area 5000 ft x 5000 ft, well diameter = 0.4 ft.

Figure1 - Comparison of production profiles using the Velocity Dependent Relative Permeability, once without the inertia effect (VDRP only) and once with inertia effect (VDRP+INERTIA) and the base case with no rate effect.

It is intended to employ the unique capabilities developed in this laboratory to generate information required for more efficient management of gas and condensate reservoirs in the three-year research programme beginning in July 2002. The proposed research programme investigates flow performance within the wellbore region, which controls the well deliverability.
Long term well performance is studied aiming to develop simplified relative permeability functions applicable to near wellbore conditions accounting for both positive and negative rate effects, with parameters which can be estimated using basic rock petrophysical data. Flow in perforated region is investigated to develop a skin-type general expression for use in reservoir simulators and welltest software. Core test facility capable of operating at reservoir conditions will be dedicated to conducting specific core tests required by the project sponsors for their field development and reconciling laboratory data to well test data. Well remedial studies will focus on fracturing as one of the most efficient treatment methods. It is intended to improve the technology on the design of hydraulic fracturing of gas condensate wells, which is currently based on dry gas information. Furthermore, the research is expected to produce information on describing gas-condensate flow in fractured rock, near the wellbore, by simple methods instead of using expensive very fine grid techniques in numerical reservoir simulators.

Informal closed workshops would be arranged to discuss application of recent advances related to the development of gas condensate reservoirs and in-house experience of the sponsoring companies. A workshop has been planned for 5-6 September 2002.

For further information, please contact Professor Ali Danesh, Heriot-Watt Institute of Petroleum Engineering: ali.danesh@pet.hw.ac.uk, Tel: +44 (0) 131 4513173

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