Complexities in reservoirs exit at three main levels:
- Geology, due to different depositional and tectonic processes, with reservoirs formed via deposition in fluvial environments being the most complex;
- Fluid, notably in gas condensate reservoirs below the dew point pressure and in volatile oil reservoirs below the bubble point pressure;
- Wells, particularly multilateral horizontal wells.
The combination of complex reservoirs, complex fluids, and complex wells create well test pressure behaviours that can be very difficult to interpret. Simplifying assumptions allow the derivation of analytical solutions, and these are routinely used for describing reservoir dynamic behaviours during well tests. Simplified interpretation models, however, restrict the amount of information that can be obtained from well test analysis in complex systems by not accounting for complexity. They also yield results that are often difficult to relate to reality.
The Centre of Petroleum Studies at Imperial College London has been involved in research in these areas since 1997, sponsored mainly by consortia of oil companies. Results from this work have already greatly improved the understanding of well test behaviours in gas condensate and volatile oil reservoirs; in reservoirs with commonly found geological features (such as semi-infinite channels with non-parallel boundaries; T-shaped channels; meandering channel with different well locations, channel branch widths and meander angles; and pinch-out boundaries); and in multilateral wells. They have also greatly improved the ability to interpret well tests in such reservoirs.
The objective of the present research is to expand the work performed to-date in these three area in order to develop a better understanding of well test behaviours in complex systems, and to use this understanding to develop new, practical analysis methods for calculating well and reservoir parameters, for estimating reserves, and for predicting and improving well productivity in such reservoir-fluid-well systems. Limitations and uncertainties in the analyses as a function of the data available will also be a focus of the research.
