New option for cost-effective, rig-less well abandonment
Oil and gas well intervention operations, particularly subsea interventions, are expensive and can take rigs away from more productive exploration and development work. Intervention suspension and abandonment operations can also impact the environment through their carbon footprint, and by the release of pollutants, such as naturally occurring radioactive material.
In response to the high-cost, waste and environmental issues surrounding suspension and abandonment, Scottish company Oilfield Innovations Ltd., is developing a cheaper, safer and more environmentally friendly wireline method, which could displace drilling rigs and pulling units from the vast majority of onshore, offshore and subsea well suspensions and abandonments. Presently, Oilfield Innovations is exploring the opportunity to conduct a joint industry project with WellTec, a Danish well technology company, as well as North Sea operators.
During rigless wireline intervention, non-intrusive and field-proven wireline tools may be used without disturbing existing wellhead barriers. Generally, the use of drilling rigs and pulling units involves significantly more risk, because existing well barriers must be removed during abandonment. This can comprise logging and plugging of wells through an existing completion.
Last year, Oilfield Innovations tested a method that involves slicing tubing longitudinally into spaghetti-like strands, Fig. 1. The tubing is severed above the shredded portion, and an inflatable packer, acting as a piston, is placed through the tubing and inflated between the severed and shredded ends within the casing. Hydraulic pressure is used to crush the tubing, so that the primary cement behind the casing can be logged prior to placing a cement plug in the unobstructed space by using the remaining uncut upper portion of the tubing.
The method may use new or proven wireline tools. For example, a conventional cutter can be used to sever the tubing, and an inflatable wireline packer—with its anchoring slip segments removed—may be used to form a crushing piston.
Oilfield Innovations has tested the method to demonstrate its viability. Tubing was placed within a horizontal casing string and crushed in a dry state. This represents the worst-case scenario, because the weight of the tubing is not transferred to its lower end, as is the case in vertical or inclined wells, where liquid also adds lubrication to reduce friction and make crushing easier.
The “dry” horizontal test arrangement demonstrated how easily tubing, that is shredded into thirds, could be crushed. The tubing was crushed to 54% of its original length, despite the friction associated with splaying, helical buckling, and the weight per linear foot of tubing acting against the crushing test piston in a horizontal arrangement.
The company also has developed simple, robust designs for a longitudinal tubing cutter that can be placed into the tubing through an intervention lubricator, and expanded to shred the tubing.
As both the casing and tubing are hollow and filled with fluid, which acts as a lubricant, a crushing piston occupying 100% of the cross-sectional area within the casing can force shredded tubing, or completion components, which usually occupy only 10% to 20% of the area, into the 80% to 90% of the liquid-filled area within the casing’s internal diameter. The strands of the shredded tubing become eccentric, and buckle helically within the casing, easily collapsing under the tens to hundreds of tons of crushing force applied hydraulically by the piston area.
Currently, the company is talking with service providers about furthering this technology on a commercial scale. “There are a number of common denominators between Oilfield Innovations’ approach to solving challenges in the industry and our own,” said Brian Sidle, V.P. of marketing at Welltec. “This development adds another tool for further enabling e-line, well abandonment techniques.”
As shown in Fig. 2, modern subsea intervention lubricators can be used to access subsea wells and deploy tools to carry out Oilfield Innovations’ suspension and abandonment method.
Subsea intervention operations involve the use of a boat to suspend a subsea lubricator in the water and latch it onto a subsea tree. Like the surface version, the subsea lubricator latches a blowout preventer and riser section, containing wireline tools, onto the production subsea tree. The subsea tree is then opened via a control umbilical to deploy wireline tools suspended from a winch on the boat. Two circulation hoses can communicate between the well tubing and annulus via the boat’s pumps. The wireline tools shred and cut the tubing to place the piston, while the circulation hoses are used to pressure the piston to crush the tubing and place new cement.
Logging of existing cement behind the casing is performed between the crushing of tubing and the placement of new cement downhole. If logging shows that a drilling rig is required, plugs can be set to lower rig-based costs. Alternatively, if a rig is not required, the tubing and any associated natural radioactive materials can be left downhole.
Light wireline intervention is possible in subsea wells, but only drilling rigs, with total spread costs up to $1 million per day, can be used for abandoning subsea wells. Wireline is usually regarded as the lowest-cost and safest means of intervening in a live well.
Presently, well plugging operations continue to use higher-cost and higher-risk well abandonment alternatives. Oilfield Innovations has successfully tested a wireline method, which can use existing field-proven technology to provide rig-equivalent well abandonment that is safer and more environmentally friendly at a fraction of the cost.
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