Oil Tests at Extreme Conditions Yield New Data For Reservoir Modeling

Abstract

HP/HT Research Drilling in the extremely deep waters of the US Gulf of Mexico has revealed huge oil reservoirs, and gaps in the industry’s capabilities. While much attention has gone toward creating high-performance equipment to develop and produce oil from high-pressure/high-temperature (HP/HT) formations such as the Lower Tertiary, researchers around the world have been quietly working on measuring how oil behaves under those extreme conditions. “New tools are needed to represent reservoir fluid properties at temperatures from subsea (~30°F) to the reservoir temperatures near 400°F and pressures ranges from ambient to 30,000 psi,” said Jefferson Creek, a senior research consultant at Chevron Energy Technology. “Developing numerical representations requires a solid base of appropriate measured data to benchmark performance of new equations or new procedures.” A study organized and backed by the National Energy Technology Laboratory (NETL) of the United States Department of Energy first looked to see if any laboratory had tested how oil performs at really high pressures and temperatures. “The bottom line is there are huge gaps in data in high-temperature reservoirs where they are already producing,” said Robert Enick, a research professor at the University of Pittsburgh, one of the lead researchers on the NETL project. One reason for the gap was the lack of equipment capable of making those measurements and the obstacles facing anyone who wanted to build it. It is extremely tough to prevent leaks at those pressures, and the usual measurement methods do not work because sensors cannot survive at those temperatures. The devices they created to do the job showed that the formulas commonly used at lower temperatures and pressures are a poor fit once the temperature exceeds 300°F. When commonly used models were used to extrapolate those properties under HP/HT conditions, density predictions were off by as much as 50%, and viscosity errors were as high as 75%, according to a project presentation. Based on multiple HP/HT density and viscosity tests of components that make up crude oil, equations were identified that offered a good correlation to the data. By tweaking some of the parameters in those equations it was possible to get a closer fit with the test results. Now the results are being passed on to the large oil companies working in ultradeepwater.