About 30 researchers gathered at the University of Houston Cullen College of Engineering earlier this month to discuss the latest in nuclear well logging—science of gathering and interpreting data from petroleum wells, often during drilling, through gamma radiation signals.
The group was comprised of members of the Society of Petrophysicists and Well Logging Analysts, said Richard Liu, professor of electrical and computer engineering at UH and director of the college’s Well Logging Lab.
According to Liu, there are two main forms of nuclear well logging: gamma, which relies of readings of radiation naturally emitted by rock formations, and gamma gamma, where radiation is shot at the formations and data interpretations are based on the radiation that returns to the source.
Nuclear logging, Liu noted, makes up only about 20% of the well logging field. About 70% of well logging is based on reading the electrical properties of rocks, particularly their electrical resistivity.
The changing nature of petroleum drilling and retrieval is introducing new challenges to the resistivity-based logging, Liu added. In typical rock formations, low resistivity indicates that there is little to no petroleum present. But in shale formations, which are becoming increasingly important sources of petroleum, especially in the United States, low resistivity does not indicate a lack of petroleum.
“How do we identify shale and shale layers that have oil and gas? So far this problem is not well studied,” said Liu. “We’re working with companies to find indicators of petroleum. For example, the dielectric constant, dispersion characteristics, conductivity, maybe resistivity. We think we can combine them with other measurements to identify shale layers with oil and gas.”
Another area Liu and his research team are exploring involves horizontal drilling. Given the high price of oil, petroleum companies are today retrieving resources from relatively thin layers of rock that lie roughly horizontal. These companies have equipment capable of being steered while drilling horizontally. What they lack, however, is a good way to ensure that the drill stays within its targeted layer of rock.
Traditional methods of well logging, Liu said, aren’t able to immediately locate the top and bottom of resource-rich rock layers. The Well Logging Lab, then, is developing new analytical methods that can produce this information in real time.
If history is any guide, their work in these areas should prove to be very valuable. Evidence: the Well Logging Lab receives most of its support from industry through a fee-based consortium. The consortium, also directed by Liu, provides its members with technical reports and support, addresses technical challenges and works to develop new technologies requested by its members. Its membership roster includes many of the largest companies in the petroleum industry, including BakerHughes, BP America, Chevron, China National Logging, ExxonMobil, Halliburton, Oliden Technology, Saudi Aramco, Schlumberger, and Weatherford Energy Services.