Debris monitoring critical for Laminaria completion clean-up

Woodside Energy's Laminaria Well Construction Team embarked on a cleanup project on the field's large bore deep horizontal wellbore completions recently, and involved the Expro Group in the process. Laminaria is located off northern Australia.

The Super Green Burner is burning off production in the Laminara extended well test and cleanup project.

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The initial objectives were to clean up the wellbores in a safe and cost effective manner. The Expro Group presented five technical proposals capable of meeting the flow rate criteria.

Standard semisubmersible well testing operations worldwide are usually restricted to 10,000-15,000 b/d, due to mitigating factors such as process equipment capacity, rig deck space, radiation while flaring, environmental risk, and many other logistical and reservoir related problems incurred when dealing with extremely high flow rates. Expro Group specializes in extended well test operations.

A final proposal was modeled in Australia and involved regulatory authorities in the Northern Territories. Safety and environmental protection were engineered into the solution. Standard well testing restrictions were overcome by the complete re-engineering of the standard well test system with the addition of large bore process flowlines bypassing the well test process equipment, emergency shutdown systems, metering, burners, and integrated data acquisition and management systems.

Ultrasonic flowmeter

The innovative application of an ultrasonic flowmeter, situated upstream of the test choke manifold, allowed the single phase measure-ment of produced fluids and transformed the system capacity and operability.

Design and system management focused on the low bubble point of the oil and the extremely low gas-oil ratios that resulted in a stringent flow regime in the well test program. This dramatically reduced the costs and allowed a single phase (as opposed to a multiphase) meter to be used. The advanced agreement of these well testing parameters drove the choice of the eventual solution and ensured that all objectives were aligned.

To clean up wells at rates as high as 30,000 b/d using standard traditional well test process equipment, dual process separator trains would have been required with large bore flowlines fitted both upstream and downstream. The deck space and deck loading capacity required would have been unachievable even on a semisubmersible drilling rig, such as the Sedco 703, without extensive and expensive modifications. Neither time nor budget were available to do this.

The Expro Group had initially proposed and priced options of either multi-phase or single phase ultrasonic flow measurement devices. The costs of developing and fitting a multiphase meter for use on well testing/clean up operations remain extremely high and the results were not guaranteed due to the possibility of high sand production during the clean out of the large bore horizontal well sections.

Expro examined a variety of potential single phase products and chose a metering system from a US-based company and, through extensive onshore trials and modifications, was successful in proving the meter's accuracy with single-phase high rate flows, as well as entrained debris.

The process equipment was not made redundant because of the use of the Expro ultrasonic flow meter, as the unproven meter would require regular flow proving and a method of onsite calibration. However, it was greatly reduced in size and cost, and used for initial flows and meter-proving throughout the program. It was also required to perform surface sampling and to stabilize flow prior to switching through the large bore bypass and relying solely on the ultrasonic flow meter for gross flow rates.

Flow at 30,000 b/d

Flowing at 30,000 b/d caused concern as debris and formation sand would be greater than normal due to the large perforation intervals in the well's horizontal sections. To manage this risk on a real time basis, the Expro Group provided a non-intrusive acoustic wellhead sand detection system, which was linked directly to the on-line Expro data acquisition and management system (EDGE-X).

The system allowed for quantitative sand measurement throughout all flow periods. Expro also provided a process equipment ultrasonic wall thickness device which allowed for random wall thickness testing to ensure that erosion and abrasion risks were carefully monitored and documented.

Extreme radiation

Expro Australia deployed an array of equipment to mange debris cleanup in the Laminaria wells off Northern Australia.

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Expro Group worked closely with Sedco Forex to develop an enhanced anti-radiation deluge system and comprehensive rig temperature monitoring systems which again were tied into the EDGE-X System complete with alarms. The risks were identified and measures put in place to successfully manage them during the cleanup.

A re-design of the burner systems to accommodate five heads (two additional) and allow for not only the high flow rates, but provide a mud/emulsion burning system capability. The system proved very effective, allowing a blanket of flared diesel to pass under and through the produced hydrocarbon flare during cleanup, ensuring that debris, mud, and oil/water emulsions were burned efficiently.

This stage of the well test was considered to contain the highest potential risk to the environment and measures were put in place to manage it effectively. As another cost reduction measure, Expro utilized the perforating diesel cushion as the pilot fuel by fitting an additional diesel manifolding to the rig.

High capacity Zone II air compressors were used to increase burn efficiency. During standard flaring operations at 28,000 b/d, 4.32 MMcf/d of air per day was required for oil atomization. Expro retro-fitted large bore air flow lines specifically for this purpose and expended tremendous efforts to ensure that the environmental impact was managed effectively throughout the program.

Safety

The safety of this operation was at the forefront when planning this specialized project. Regular senior management trips to the well site, as well as close liaison at all stages of the planning and execution, ensured a visible commitment to the safety imperatives.

Unusual well parameters and high flow rates were the trigger to an insistence of nominating key focal points for engineering, contractual issues and continuity of offshore supervisory personnel throughout the project. People were recognized as one of the most powerful safety management tools on the planet and continuity enhances new learning retention. Management commitment to fund this approach fed down to the well site and ensured the buy-in at the execution phase.

As a matter of course, Expro provided project/well test specific well test planning reports on all projects. This project was given a new angle by involving Woodside and contractor team members from across a number of disciplines to review input into the planning. The safety system provided was detailed and engineered in conjunction with the Woodside and Kvaerner Sub Sea Teams.

A key difference on this project was to feed all downhole pressure and temperature data from the permanently installed down hole gauges and subseawell head pressure/temperature transducers to the Edge-X system to provide a single integrated data management system and one integrated report. Expro was able to monitor and manage all parameters from the tailpipe to the burner head thereby significantly increasing the safety of the operation in a pro-active manner.

Process safety

The well test surface safety system as proposed was designed to detect and respond to protect personnel, the environment and the process system, in a holistic approach from the tailpipe to the burners. A full and detailed system safety analysis was performed to identify and assess any and all potential hazards and operating problems. The API RP 14C safety analysis checklist (SAC), safety analysis table (SAT), and safety analysis function evaluation chart (SAFE) were performed while the process safety system and relief system were designed using API RP 14C, API 520, and API 521 as guidelines.

The safety system philosophy included process alarm and detection facilities to control the applicable process condition undesirable events: overpressure, liquid overflow, high temperature, under-pressure, low temperature, and gas blow-by.

The safety device and relief line design calculations underwent detailed technical evaluation which were used to prove that the system was capable of relieving maximum expected flow rates. Flow line sizing and nodal analysis was performed using in-house software, ensuring all flowlines, relief lines, relief valves, and process vessels were capable of handling maximum expected flow rates and pressures. A full in-house HAZOP/risk analysis was performed involving the Laminaria team members.

The critical success factors were: