Scots look at stress on the rocks

August 18, 1995

A group of scientists at Edinburgh and Heriot-Watt universities can genuinely describe their research as ground breaking.

The Edinburgh Rock Mechanics Consortium has been investigating how rocks respond to changes in physical stress, in a project which could significantly improve the recovery of oil and gas from underground reservoirs.

When a hydrocarbon reservoir is in the late stages of production, sea water is injected into it to flush out as much oil and gas as possible. Computer simulation systems show this as a fluid flowing through a rigid skeleton of rock, but the Edinburgh work has highlighted the importance of two factors previously unaccounted for.

"When you produce oil from the ground, the ground is already under stress, and removing the oil, or injecting water to help push it out, changes the stress," said Ian Main of Edinburgh's department of geology and geophysics.

"These changes are small, but they may significantly affect the flow of fluids, and we've been doing work to measure that."

The team has also been investigating changes in the chemistry of the fluids flowing through a rock sample, since minerals may be dissolved or deposited as a result of chemical reactions between the changing fluid and the reservoir rock.

The consortium has joined forces with two commercial companies to develop a simulation system which takes account of these factors, and provides a better simulation of the flow of water and hydrocarbons through the reservoir. The researchers hope this will allow oil companies to make better decisions about what type of wells they should have, and where these should be, ultimately allowing more oil and gas to be recovered.

The system, which is being marketed by VIPS Ltd, will also help understand extreme cases in which the stress placed on the rocks round the reservoir is so great that the rocks rupture, causing small earthquakes.

This type of induced earthquake is well known in the United States, and has been reported in the North Sea this year. While it does not pose any danger to life, it could threaten production by sealing off the reservoir. Alternatively, if the rock movement compresses the reservoir, it could actually help extract more oil.

The project's Pounds 500,000 funding has come from a range of sources including three oil companies and the Government's LINK programme to bring universities and industry together. Dr Main said the successful collaboration with industry through LINK had "resulted in innovative science for the universities and the prospect of improved recovery for the oil companies".

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