New Experimental Results Show the Application of Fiber Optic to Detect and to Track Gas Position in Marine Risers and Shed Light on the Gas Migration Phenomenon Inside a Closed Well
Abstract:Summary
The main objective of this paper is to present and 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 track the gas position inside the test well during the experiments, and to discuss experimental and simulated data of the gas migratio… Show more
This work complements previous efforts exploring the opportunity for safer return to operations after an influx event in deepwater drilling operations when an MPD system is installed on the floating rig. Additionally, even kicks taken during conventional drilling, with rigs equipped with adequate RGH equipment, can benefit from an alternative way to address the event. An RGH Envelope is proposed, which can be incrementally adopted in a stepwise approach. For MPD operations, influxes greater than IME circulation limits, but within RGH Envelope limits, can be introduced into the riser and then removed using the Fixed Choke, Constant Output (FCCO) method. In non-MPD operations, all influxes need to be initially addressed by shutting the well on the BOP as soon as possible. Then, for influxes within the equivalent MPD IME limits, the surface RGH system can be engaged and routed to the rig choke, and the influx is completely circulated using Driller's method through the riser system. A potential expansion of this method, for influxes exceeding the original IME limits, but within RGH Envelope limits, can be circulated into the riser and then finalized by using FCCO method. For conventional drilling operations without a rotating control device (RCD) seal installed, consideration should be given to installing the seal assembly in the RCD prior to circulating hydrocarbons to surface with an open BOP. The authors explore the RGH Envelope limits and present guidelines for a comprehensive risk assessment on RGH process, limits, and how it impacts multiple aspects of the operations.
This work complements previous efforts exploring the opportunity for safer return to operations after an influx event in deepwater drilling operations when an MPD system is installed on the floating rig. Additionally, even kicks taken during conventional drilling, with rigs equipped with adequate RGH equipment, can benefit from an alternative way to address the event. An RGH Envelope is proposed, which can be incrementally adopted in a stepwise approach. For MPD operations, influxes greater than IME circulation limits, but within RGH Envelope limits, can be introduced into the riser and then removed using the Fixed Choke, Constant Output (FCCO) method. In non-MPD operations, all influxes need to be initially addressed by shutting the well on the BOP as soon as possible. Then, for influxes within the equivalent MPD IME limits, the surface RGH system can be engaged and routed to the rig choke, and the influx is completely circulated using Driller's method through the riser system. A potential expansion of this method, for influxes exceeding the original IME limits, but within RGH Envelope limits, can be circulated into the riser and then finalized by using FCCO method. For conventional drilling operations without a rotating control device (RCD) seal installed, consideration should be given to installing the seal assembly in the RCD prior to circulating hydrocarbons to surface with an open BOP. The authors explore the RGH Envelope limits and present guidelines for a comprehensive risk assessment on RGH process, limits, and how it impacts multiple aspects of the operations.
Summary
Understanding gas dynamics in mud is essential for planning well control operations, improving the reliability of riser gas handling procedures, and optimizing drilling techniques, such as the pressurized mud cap drilling (PMCD) method. However, gas rise behavior in mud is not fully understood due to the inability to create an experimental setup that approximates gas migration at full-scale annular conditions. As a result, there is a discrepancy between the gas migration velocities observed in the field as compared to analytical estimates. This study bridges this gap by using distributed fiber-optic sensors (DFOS) for in-situ monitoring and analysis of gas dynamics in mud at the well scale.
DFOS offers a paradigm shift for monitoring applications by providing real-time measurements along the entire length of the installed fiber at high spatial and temporal resolution. Thus, it can enable in-situ monitoring of the dynamic events in the entire wellbore, which may not be fully captured using discrete gauges. This study is the first well-scale investigation of gas migration dynamics in oil-based mud with solids, using optical fiber-based distributed acoustic sensing (DAS) and distributed temperature sensing (DTS).
Four multiphase flow experiments conducted in a 5,163-ft-deep wellbore with oil-based mud and nitrogen at different gas injection rates and bottomhole pressure conditions are analyzed. The presence of solids in the mud increased the background noise in the acquired DFOS measurements, thereby necessitating the development and deployment of novel time- and frequency-domain signal processing techniques to clearly visualize the gas signature and minimize the background noise. Gas rise velocities estimated independently using DAS and DTS showed good agreement with the gas velocity estimated using downhole pressure gauges.
Summary
Accurate estimation and prediction of gas rise velocity, length of the gas influx region, and void fraction are important for optimal gas kick removal, riser gas management, and well control planning. These parameters are also essential in monitoring and characterization of multiphase flow. However, gas dynamics in non-Newtonian fluids, such as drilling mud, which is essential for gas influx control, are poorly understood due to the inability to create full-scale annular flow conditions that approximate the conditions observed in the field. This results in a lack of understanding and poor prediction of gas kick behavior in the field. To bridge this gap, we use distributed fiber-optic sensors (DFOS) for real-time estimation of gas rise velocity, void fraction, and influx length in water and oil-based mud (OBM) at the well scale.
DFOS can overcome a major limitation of downhole gauges and logging tools by enabling the in-situ monitoring of dynamic events simultaneously across the entire wellbore. This study is the first well-scale deployment of distributed acoustic sensor (DAS), distributed temperature sensor (DTS), and distributed strain sensor (DSS) for investigation of gas behavior in water and OBM. Gas void fraction, migration velocities, and gas influx lengths were analyzed across a 5,163-ft-deep wellbore for multiphase experiments conducted with nitrogen in water and nitrogen in synthetic-based mud, at similar operating conditions. An improved transient drift flux–based numerical model was developed to simulate the experimental processes and understand the gas dynamics in different wellbore fluid environments. The gas velocities, void fractions, and gas influx lengths estimated independently using DAS, DTS, and DSS showed good agreement with the simulation results, as well as the downhole gauge analysis.
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