Deepwater Oil Production through Thick and Thin
Deepwater and ultra-deepwater oil recovery presents a set of property challenges that require greater understanding for safe optimal oil production. NETL and its research partners are helping fill knowledge gaps and unravel mysteries with project results that are leading to improvements in the way undersea oil recovery is understood and executed.
For example, reservoirs of crude oil found deep under the Gulf of Mexico are at high temperatures and pressures (as high as 500 °F and 35,000 psi). When the oil is produced, it experiences significant decreases in temperature and pressure leading to changes in the physical properties and behavior of the hydrocarbon fluids. NETL research is targeting efforts to define the properties of hydrocarbons at those conditions so that it is easier to test those properties. That testing is critical because accurate predictions of crude oil density and viscosity, for example, will enable accurate recording of oil reserves and allow operators to identify optimal conditions for production.
A kitchen experiment with molasses demonstrates how changes in viscosity, or a substance’s resistance to flow occurs. When warmed, molasses becomes ‘thinner’ – that is, its viscosity decreases. When cooled, it becomes thick again and has greater viscosity. Similar thickening – and sometimes solidification – can happen as crude oil cools during production from the reservoir.
Isaac Gamwo, Ward Burgess, Hseen Baled, and Deepak Tapriyal conduct density measurements in the High-Pressure/High-Temperature Fluid-Phase Properties lab at NETL.
“The formation of solid deposits in crude oil can clog processing lines during production and that may lead to severe equipment damage,” says Dr. Isaac Gamwo, who leads an NETL research project called “Quantifying Complex Fluid-Phase Properties at High Pressure/High Temperature.”
His research team, which, in addition to NETL experts, includes employees of URS Corporation, and researchers from the Virginia Commonwealth University, the University of Pittsburgh, and Rice University, works to better understand deepwater hydrocarbon behavior. Gamwo explained that viscosity changes are “a major issue experienced during the oil recovery process for high-temperature, high-pressure ultra-deep petroleum reservoirs such as those typically encountered beneath the deep waters of the Gulf of Mexico.”
In one recent project, Professor Mark A. McHugh, a research team member from Virginia Commonwealth and his colleagues measured liquid-solid phase transition data for some of the cyclic (ring-structured) hydrocarbons found in crude oil. Working in a range of pressures and temperatures that previously had not been tested for these hydrocarbons, the team used a high-pressure, variable-volume view cell to make measurements. They executed duplicate and triplicate measurements to ensure results. The data provided by the team represents fundamental information needed to determine the operating conditions that promote formation of solids during production.
The high-pressure density cell, made of the corrosion-resistant nickel-based alloy Inconel 625, can operate at 40,000 psi and 500 °F. The magnet beneath the cell ensures that the liquid sample in the cell is well-mixed, so that the heat generated by heating and compressing the sample is equally distributed.
Another key research area addressed the deepwater oil industry’s need for a Deepwater Viscosity Standard (DVS)—a commercially available liquid with a well-characterized viscosity that allows researchers to calibrate viscometers at the temperatures and pressures common in deepwater oil reservoirs. Calibration ensures that these devices work correctly and that measurements will be consistent.
NETL researchers Professor Robert Enick of the University of Pittsburgh, and NETL Researchers Drs. Gamwo, Bryan Morreale and Dr. Deepak Tapriyal of URS, evaluated potential candidates and proposed Dupont’s perfluoropolyether Krytox GPL 102 oil as a new DVS. Tests by the research team demonstrated that the proposed DVS has a suitable viscosity at the temperatures and pressures that occur in deepwater reservoirs.
The NETL team’s results were verified by an industry working group and oil is now being tested by research groups in several other countries using the team’s recommendation. According to Dr. Gamwo, acceptance of the oil as a DVS “may lead to NETL researchers being recognized as world leaders in the selection of promising candidates for the viscosity standard.” In addition, this NETL research will enable crude oil from beneath the Gulf of Mexico to be produced more easily and safely.
Contact: Isaac Gamwo, 412-386-6537