ABERDEEN, Scotland—An innovative method of completing rigless well abandonment that isolates a well’s production using a resin-based sealant rather than traditional methods was carried out by Oceaneering in the Gulf of Mexico (GoM).
Oceaneering was contracted in 2016 to assess options with a client, plan and execute the plug and abandonment (P&A) of a challenging well in the GoM. The main concern was the well’s integrity, and this posed significant challenges. An increase in sand production prompted the P&A, but significant soil erosion around the wellhead complicated the project plan and its execution.
An innovative yet operationally efficient solution was needed.
The subsea well was located in about 500 m (1,640 ft) of water in the GoM and had been drilled directionally to 6,222 m (20,413 ft). It had been completed with eight strings of casing and production tubing, worked over in 2009 and then produced until September 2013 when it was shut in due to high sand production. In 2015 the operator decided to make plans to permanently abandon the well. During the planning stage with the operator, the main concern was the significant soil erosion around the wellhead. This created structural integrity concerns, and the operator was unsure whether the wellhead could withstand the additional load from the BOP.
The absence of a BOP coupled with cumulative reservoir pressure meant that an isolation fluid needed to be pumped down the production tubing into the formation. Further complicating matters was the presence of an obstruction in the flow path that limited the injection rate.
The challenge posed by the well meant that detailed planning with the project teams, supply chain and regulatory bodies was needed if this P&A was to be granted approval and risk properly assessed and mitigated to ensure an effective solution.
Selecting An Isolation Fluid
Selection of the isolation fluid was one of the critical factors in enabling a successful abandonment of the producing zone.
“To overcome the challenges posed by the well, the isolation fluid could not be susceptible to contamination associated with pumping it along with completion brines,” Leigh Martin, regional manager for service, technology and rentals at Oceaneering International Services. explained during Subsea Expo. “In addition, the fluid needed to be pumped around the obstruction in the well and squeezed into the formation without particles separating from the fluid and packing off the flow path.”
Oceaneering worked with the client to assess the isolation fluid options based on the performance criteria, which were minimal risk of contamination with calcium chloride or calcium bromide, the ability to squeeze through small clearances without bridging and of course, sufficient mechanical properties that exceed requirement to act as a permanent barrier.
“When the client was evaluating the isolation fluids against these requirements, the resin offered the superior performance,” Martin added. The next step was to collaborate with Oceaneering and the client’s resin provider to develop a single vessel-based intervention solution using Oceaneering’s well stimulation tool.
Project Planning, Regulatory Approval
The project required significant planning and testing by the operator, resin manufacturer and the project team to gain approval from the U.S. Bureau of Safety and Environmental Enforcement (BSEE). At the time, cement was the only isolation barrier recognized by the regulators. The client and manufacturer completed months of lab testing to ensure that there were no compatibility issues and to confirm hardening times over various temperature extremes. They needed to make sure that the resin would not harden in the topside equipment, well simulation tool or tree hardware.
Based on the data provided, exemption was granted by BSEE to proceed with the first deepwater resin only permanent abandonment.
The project started on Jan. 26, 2016. The multiservice vessel was 95 m (312 ft) long, had 950 sq m (10,225 sq ft) of deck space, two work class ROVs and a 150 t heave compensated crane. The project required modifications to the topside pumping, mixing and blending equipment to account for the dry chemical resin that was in two parts and needed fluid to complete the mix.
“Because the execution of the well kill was performed during the winter months there was an additional concern regarding severe sea state weather that could have postponed or interrupted the operation,” Martin said. “The team needed a 24-hour weather window to start and finish pumping operations. A partial resin pump would have been detrimental to the success of the job, leaving no alternative way of adding more resin.”
In the absence of a BOP stack, the well stimulation tool was mounted on top of the tree and the subsea controls had to be configured for an alternative interface with the tree, while at the same time keeping excessive loads to a minimum and also meeting BSEE well control requirements.
Plugging The Wellhead
Thirty-five barrels of resin were pumped down the production tubing, through and around the obstruction into the formations. To keep the resin at static conditions after placement, Oceaneering displaced the well with brine and checked the pressure at the surface. After the resin hardened, positive and negative pressure tests confirmed isolation.
“Due to the timely execution of operations, the lower abandonment project was completed under the customer’s budget and ahead of schedule with zero equipment downtime during operations,” Martin said. “Real time monitoring of the tree, well and well stimulation tool was supplied to the onshore project team to ensure the safe execution of the project activities and mitigated the majority of the risk. The use of resin resulted in 100%proven reservoir isolation allowing for the upper abandonment to be completed using a light intervention vessel.”
Given the system’s smaller, lighter and more cost-effective footprint against traditional plug and abandonments, the results suggest this method can be used on a host of other structures and applications.
As for cost, on the face of it the resin costs about 10 times as much as the cement for this kind of volume. But in this case the special circumstances, such as the obstruction and soil erosion, this option provided a very cost-effective option. “The client estimated that this operation typically costs around $30 million and this project was completed for just under half of that,” Martin said.
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