Heavy oil contained in naturally fractured reservoirs is becoming an important resource as conventional oil reserves are depleted. However, maximizing recovery from such reservoirs is problematic due to the low flow rate of oil and the poor understanding of recovery mechanisms. One EOR method that is of particular interest is Thermally Assisted Gas-Oil Gravity Drainage (TA-GOGD). In this process, steam is injected into the reservoir. This heats the rock matrix blocks through the higher penneability fracture network and improves oil recovery principally by reducing the oil viscosity and thus increasing the rate of gravity drainage through the matrix. The work presented in this thesis aims to investigate and understand the mechanisms controlling the rate of gravity drainage during TA-GOGD and determine the key reservoir parameters that control recovery. This was achieved by studying the time scales for heating the matrix blocks by steam and gas oil gravity drainage as a function of reservoir and fluid properties using analytical formulae and detailed reservoir simulations. During the heating investigation, a simple formula for calculating the critical steam rate in the fractures is derived analytically. The formula shows that there is a critical steam injection rate for TA-GOGD in fractured reservoirs. If the injection rate is below this critical rate, the time to heat the matrix will increase and oil recovery increases with increasing injection rate. If the steam injection rate is greater than the critical rate then there is no significant increase in oil recovery with rate. The oil recovery mechanisms of TA -GOGD were also investigated numerically. The study involved the investigations of individual and collective impacts of the mechanisms of solution gas drive, C02 generation, steam distillation, connate water evaporation and gravity drainage, on the oil recovery for reservoir containing heavy oil using real field data and parameters. It was found that CO2 generation, water imbibition and oil expansion contribute more to oil recovery in the early times of oil production whereas distillation, thermal gas drive, viscosity reduction and gravity drainage mechanisms contribute more in the late times.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:555878 |
| Date | January 2009 |
| Creators | Al Raba'ani, Abdul Sallam Omar Khamis |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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