Quenching the world’s ever-increasing thirst for oil is a continuous struggle. The key to successfully doing so lies in locating and developing more and more petroleum reserves. And critical to doing that is being better able to “view” what is beneath the surface of the Earth. Fortunately, advancing technology continues to provide oil producers with amazing techniques.
One example is work by scientists at the University of Aberdeen. The researchers have developed an analytical technique that could help producers discover formerly uncharted oil reservoirs with mineral dating.
According to the researchers, this new method can “directly establish the timing of oil migration through a sedimentary basin by observing the minute fluid inclusions within mineral cements.” Before the technique was established, only indirect mineral dating of oil migration was possible, they say. Currently, the scientists are analyzing petroleum accumulations in deep subsea sandstone between the Shetland and Faroe Islands off Scotland.
The method
To date, geologists have relied on using indirect evidence or theoretical modeling of mineral deposits to predict the flow of oil-and in turn have relied on a not-so-small amount of guesswork. The new approach has proved able to reveal when oil entered a subsurface reservoir as well as to determine temperature, composition, and timing of past fluid flow, researchers say.
The research-led by Prof. John Parnell in the School of Geosciences at the University of Aberdeen and Dr. Simon Kelley in the Department of Earth Sciences at the Open University-offers a new way to view and study oil flow beneath the surface. The UK Natural Environment Research Council provided funding.
Parnell explains, “If the potential trap formed before oil flowed into it, there are no problems; however, if it formed after oil was moving, then this is too late, and the oil is likely to have leaked to the surface and been lost many millions of years ago.” When exploring for oil, Parnell continues, it is “extremely important to be able to predict when oil was flowing in a particular region.”
The new method, researchers explain, examines oil traces in potassium feldspar, which occurs naturally as a cement in many oil reservoirs, “filling pore spaces and coating sand grains.” The researchers say, “The presence of oil during mineral precipitation is recorded in tiny bubbles of oil trapped inside the mineral cement.”
In studying these traces, the scientists are able to measure the amount of argon produced by the radioactive decay of potassium and thus to date the occurrence of oil in the reservoir.
This new method for dating mineral cements containing “minute fluid inclusions” could ultimately help in the discovery of oil reservoirs, the scientists say. “Directly establishing the timing of oil migration through a sedimentary basin could help the discovery process, but only indirect dating of oil migration has been possible so far.”
Parnell contends, “This is a very powerful technique, which will not only help the oil industry to understand the timing of oil movement into subsurface reservoirs worldwide but will also help scientists to date fluid movement in the Earth’s crust.”
Case study
The research team’s laboratory work, by Aberdeen University graduate Darren Mark, involves high-resolution microscopy techniques in Aberdeen and measurement of argon isotopes at the Open University. Mark and his team, which includes Open University’s Sarah Sherlock, the University of Glasgow’s Martin Lee, and Advanced Geochemical Systems Ltd.’s Andy Carr, reported a successful case study late last year in the scientific journal Science.
The case study used in the research, based on the UK Atlantic Margin, constrained the date at which oil entered a deepwater reservoir 50 km west of the Shetlands. The study also determined when the oil was subsequently lost from the reservoir.
Finding new sources of oil depends upon many factors-politics, capital, and a little bit of old-fashioned luck. Still lying at the core of the search, however, are reliable and cost-efficient ways to locate hydrocarbons. Without the continuing improvement of these methods, politics, capital, and even luck are useless.✦