New methods cited for predicting unconventional well performance
BY KURT ABRAHAM, EXECUTIVE EDITOR
DENVER -- As operators continue to drill ever-growing numbers of unconventional wells across the U.S., at least one industry expert believes that they need to adopt additional methods for predicting the performance of those wells. Speaking to a topical breakfast audience at the SPE/AAPG/SEG Unconventional Resources Technology Conference (URTeC) in Denver Tuesday morning, Professor Hossein Kazemi said that there are four approaches to predicting such well performance. The first two are conventional approaches and include Pressure and Rate Transient Analysis, and Decline Curve Analysis. The other, more recent approaches include Reservoir Simulation and Fluid Composition Analysis and Simulation.
Kazemi is a professor of petroleum engineering at Colorado School of Mines and holds The Chesebro Chair in Petroleum Engineering. He pointed out that any reliable prediction of well performance requires contributions from many disciplines. These include petroleum geology and geophysics; petrophysics; core analysis and rock physics; well testing (flow measurement in wells); and forecasting (mathematical modeling–analytical and numerical). According to Kazemi, prevailing well testing methods from 1960 through 1990 included single-well flow testing (short- and long-duration), and multiple-well testing (all with long durations). The latter method, he said, is not very common anymore.
“On the other hand,” added Kazemi, “ever since 1990, long-duration tests have been conducted less frequently. In the last decade, however, there has been an emergence of very short-duration mini-DST tests and very long-duration rate transient tests.” With regard to the first item, the professor said a typical mini-DST tool configuration is a dual-packer module with a downhole pump that isolates a 3-ft openhole interval of the wellbore. It measures pressure, using strain and quartz crystal gauges in the lower portion of the tool. Among the well productivity drivers that need to be considered are favorable rock and fluid characteristics, and “ingenious” ways to create pore accessibility via innovative well completions techniques that improve primary production and create an opportunity for secondary production.
Therefore, compositional analysis of formation characteristics should be used, said Kazemi, because it provides valuable and otherwise unobtainable information that will help to make decisions that unlock maximum productivity. After all, he noted, shales are self-sourced, while tight sands are not. In shales, the oil window is above the gas window. By contrast, in tight sands, oil production is below gas output, as a result of a compositional gradient.