Abstract
Potential applications of optical fiber technologies in the well control area are to detect the presence of gas and to unfold the gas dynamics inside marine risers (gas-in-riser). These issues became even more relevant now when considering the application of managed pressure drilling (MPD) operations in deep and ultradeep waters that may allow for a controlled amount of gas inside the riser.
The application of these fiber optic technologies in the well control domain is currently being evaluated at Louisiana State University (LSU) as a part of a gas-in-riser research project granted by the Gulf Research Program (GRP). To accomplish that, an actual well was recompleted and instrumented with fiber optic sensors to continuously collect data along the wellbore and with four pressure and temperature downhole gauges to record those parameters at four discrete depths. A 2-7/8 in. tubing string with its lower end at a depth of 5026 ft and a chemical line to inject nitrogen at the bottom of the hole were also installed in the well.
This paper discusses the results of four out seven experimental runs that were performed in this full-scale apparatus using fresh water and nitrogen in order to calibrate the installed pieces of equipment, to train the crew of researchers to run the tests, to check experiments repeatability and to obtain experimental results under very controlled conditions since water and nitrogen have well defined and constant properties.
The paper also presents a mathematical model based on the unsteady-state flow of a two-phase mixture that was developed to help design the experimental runs. The results obtained in the seven runs were used to calibrate the model that was additionally modified to read the experimental parameters. The simulated results produced a remarkable agreement with the fiber optic and pressure and temperature sensors gathered data.
Finally, the paper shows and analyzes simulation results of gas-in-riser operations on an actual drilling floater unit after the mathematical model has been adapted to predict pressures and output flow rates during gas circulations out of the riser. The effects of circulation flow rate, backpressure applied at surface and amount of gas inside the riser on pressures and flow rates are displayed and analyzed.