Modelling helps recovery

A joint venture between researchers at Texas A&M University and the US Department of Energy has produced a new computer tool that will increase recovery of up to 218 billion barrels of by-passed oil remaining in mature US domestic oil fields. The US's current proven reserve is 21 billion barrels.

More than two-thirds of all the oil discovered in America to date remains in the ground and is economically unrecoverable with current technology. About 218 billion barrels of it, a volume approaching the proven reserves of Saudi Arabia, lies at depths of less than 5,000 feet. This by-passed oil represents a huge target for the roughly 7,000 independent producers active in the thousands of mature US fields which cumulatively account for a significant share of the country's crude oil supply.

But much by-passed oil lies in difficult-to-access pockets. And predicting the location and size of these deposits is costly because it often requires complex computing capabilities. Many independent producers aren't able to commit the personnel or buy the expensive supercomputer time required to build and operate the models needed to find these overlooked stores of oil.

Reservoir characterisation identifies regions in mature fields containing high oil or gas saturation. In this process, geoscientists first employ computer models to develop an accurate picture, or characterisation, of a productive oil reservoir. "History matching" is then used to calibrate the model by correlating its predictions of oil and gas production to a reservoir's actual production history.

The new method integrates computer simulations with history matching techniques, allowing scientists to design so-called tracer tests and interpret the data using PC-based software - a process that is much faster than conventional history matching.

A key input to the history matching process is data from these tracer tests, in which traceable gases or liquids are injected into a well to determine the paths and velocities of fluids as they move through the reservoir. This information helps reservoir engineers calculate how much oil remains in the reservoir and determine the most efficient methods to sweep the residual oil from the reservoir.

In the Texas A&M project, researchers also developed a computerised method for interpreting field tracer tests, allowing users to estimate the amounts of remaining oil in bypassed reservoir compartments.

The Texas A&M technology was developed in a project managed by the Office of Fossil Energy's National Energy Technology Laboratory which provided the research funding for the effort. Total investment was $890,000 with the government share of $630,000 and the university provided cost-sharing of $160,000 for the 3 year research project.