Summary A potential application of optical fiber technologies in the well control domain is to detect the presence of gas and to unfold the gas dynamics inside marine risers (gas-in-riser). Detecting and monitoring gas-in-riser has become more relevant now when considering the application of managed pressure drilling operations in deep and ultradeep waters that may allow for a controlled amount of gas inside the riser. This application of distributed fiber-optic sensing (DFOS) is currently being evaluated at Louisiana State University (LSU) as part of a gas-in-riser research project granted by the National Academies of Sciences, the Gulf Research Program (GRP). Thus, the main objective of this paper is to present and discuss the use of DFOS and downhole pressure sensors to detect and track the gas position inside a full-scale test well during experimental runs conducted at LSU. The other objectives of this work are to show experimental findings of gas migration in the closed test well and to present the adequacy of a mathematical model experimentally validated to match the data obtained in the experimental trials. As a part of this research effort, an existing test well at the LSU Petroleum Engineering Research and Technology Transfer Laboratory (PERTT Lab) 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 2⅞-in. tubing string, with its lower end at a depth of 5,026 ft, and a chemical line to inject nitrogen at the bottom of the hole were also installed in the well. Seven experimental runs were performed in this full-scale apparatus using fresh water and nitrogen to calibrate the installed pieces of equipment, to train the crew of researchers to run the tests, to check experimental repeatability, and to obtain experimental results under very controlled conditions because water and nitrogen have well-defined and constant properties. In five runs, the injected gas was circulated out of the well, whereas in two others, the gas was left inside the closed test well to migrate without circulation. This paper presents and discusses the results of four selected runs. The experimental runs showed that fiber-optic information can be used to detect and track the gas position and consequently its velocity inside the marine riser. The fiber-optic data presented a very good agreement with those measured by the four downhole pressure gauges, particularly the gas velocity. The gas migration experiments produced very interesting results. With respect to the mathematical model based on the unsteady-state flow of a two-phase mixture, the simulated results produced a remarkable agreement with the fiber-optic, surface acquisition system and the downhole pressure sensors data gathered from the experimental runs.

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.

The main objective of this manuscript is to present and to discuss the results and significant observations gathered during 13 experimental runs conducted in a full-scale test well at Louisiana State University (LSU). The other two objectives of this manuscript are to show the use of distributed fiber optic sensing and downhole pressure sensors data to detect and to track the gas position inside the test well during the experiments; and to discuss experimental and simulated data of the gas migration phenomenon in a closed well. An existing test well at LSU research facilities was recompleted and instrumented with fiber optic sensors to continuously collect downhole data and with four pressure and temperature downhole gauges at four discrete depths within an annulus formed 9 5/8″ casing and 2-7/8″ to a depth of 5025′. A chemical line was attached to the tubing allowing the nitrogen injection at the bottom of the hole. The research facilities were also equipped with a surface data acquisition system. The experiments consisted in injecting nitrogen into the test well filled with water by two means: either injecting it down through the chemical line or down through the tubing to be subsequently bullheaded to the annulus. Afterwards, either the nitrogen was circulated out of the well with a backpressure being applied at surface to mimic an MPD operation or left to migrate to the surface with the test well closed. During the runs, the three acquisition systems (fiber optic, downhole gauges, and surface data acquisition) recorded all relevant well control parameter for a variety of gas injected volumes (2.0-15.1 bbl), circulation rates (100-300 GPM) and applied backpressures (100-300 psi). The experimental results gathered by the acquisition systems were very consistent in measuring gas velocities inside the well. The numerical model predictions matched very close the pressure behavior observed in the experimental trials. In the gas migration experiments, it was observed that the bottomhole pressure is not carried to the surface and that this pressure is a function of the volume of gas injected in the well. These facts are supported by the numerical simulation results. The manuscript shows the possibility of the use of fiber optic and downhole pressure sensors information to detect and to track the gas position inside a well or the marine riser during normal or MPD operations. Additionally, the vast amount of experimental data gathered during the experiments in which the nitrogen was left in the closed well to migrate to surface helped shed lights on the controversial issue concerning the surface pressure build-up while the gas migrates to surface in a closed well. Numerical simulations were all instrumental for supporting the findings.

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In this experimental work, the absorption and desorption of CO2 (Carbon Dioxide) in oil using a laboratory scale low-pressure experimental apparatus was conducted to study the dissolution behavior of gas in the oil. Estimating the concentration and rate of CO2 transfer from/to a non-aqueous column of static fluid is very important to understand the dissolution of natural gas in an oil-based mud within a well. Studying how natural gas dissolves in an oil-based drilling fluid is of great significance due to risks that a gas kick in an oil-based mud poses to equipment and workers’ health and safety once it is in the riser. By understanding the variables associated with this phenomena, better field practices can be developed and implemented to predict the dynamics of an influx and determine the best course of action when handling the influx. A laboratory scale experimental apparatus was designed and built to inject CO2 at the bottom of a seven-foot static column of VO. The apparatus has five test chambers that can be closed individually to isolate and measure the concentration of dissolved CO2 in oil in each of the sections. As a part of the experiment, the the backpressure applied to the column of oil was varied to observe how pressure affects the mass transfer due to absorption and desorption within the oil column. The amount of gas injected was 1.0 liter per minute of CO2 with a back pressure of the apparatus ranging from 40 to 80 psi. The results of this study will influence further experiments and testing using larger scale equipment involving the dissolution of natural gas within various oil-based drilling fluids at higher pressures. This study also allows for the development of an initial time-dependent mass transfer model which will also be used for predicting dissolution dynamics of Methane in diesel for future large-scale testing.