Permanent P&A performed on coiled tubing, setting rock-to-rock barriers and protecting potable water sources

MICHAEL RONSON, Weatherford  

Permanent plug and abandonment (P&A) operations are a necessary step when an oil or gas well reaches the end of its economic life. To abandon and secure a well, several operational phases must take place: effectively and permanently: 

• Phase 0–1: Reservoir abandonment is completed when the permanent primary and secondary barriers secure and fully isolate the main reservoir. 
• Phase 2: Intermediate abandonment occurs when all potential flow from oil-bearing zones has been identified and isolated through the setting of full lateral barriers. 
• Phase 3: Wellhead and conductor removals require the removal of surface or seabed structures—any contaminants are recovered from the wellhead annuli and an environmental barrier set ahead of the cutting of the wellhead.  

Permanent barriers must extend across the full cross-section on the well and seal both vertically and horizontally, forming a rock-to-rock barrier and mimicking the natural properties of the caprock, effectively restoring the caprock to a state equal to the predrilled state. These permanent barriers prevent the uncontrolled flow of reservoir fluids, protecting aquifers and the surface environment. Traditionally, to conduct the full scope of these operations (pending well classification), a drilling rig or heavy-duty workover unit (HDWU) would have been used to conduct Phase 2 operations. Additionally, the production tubing must be pulled to provide access to the casing adjacent to the caprock depth where the permanent plug is to be placed.  

Weatherford has worked closely with several operators over the last several years to find new ways to advance P&A operations and eliminate the need for a rig or HDWU, as well as the required removal of production tubing. This drastically reduces costs by eliminating potentially risky fishing operations (due to pipe corrosion) and the handling, shipping and disposal of contaminated tubulars. The project objective called for a rig-less solution (where possible) that facilitated leaving the production tubing in place and setting rock-to-rock barriers from the tubing bore, while still creating full lateral isolation of the wellbore and reservoir fluids. By using rig-less P&A methods, higher horsepower rigs can focus on drilling and provide returns to shareholders, while coiled tubing packages focus on P&A operations—this eliminates days of rig time from nonproductive operations, such as fishing.  

To this end, Weatherford has developed the Reclaim system, which offers the potential to P&A a well from Phase 0 to 3, using a coiled tubing or workover unit. As part of its larger portfolio, Weatherford can deploy multi-string isolation logging (MSIL) and multi-barrier corrosion logging (MBCL) tools and draw on the expertise of an advanced team of interpretation, evaluation and systems (IES) engineers, whose focus is on evaluating the well conditions ahead of P&A operations. MSIL and MBCL tools allow for a unique understanding of the cement bond and corrosion condition across both annuli—these are critical factors to understand ahead of any thru-tubing P&A operations, including the Reclaim system.  

Fig. 1. An overview of the charge performance, showing the path created from the ‘A’ annulus to the ‘B’ annulus.

The Weatherford Reclaim solution comes in two forms and has been developed to combat various ‘A’ annulus conditions. The primary offering focuses on a largely free annulus. In this situation, before any P&A operation is started, the well is displaced ahead of the completion run, and the IES team validates that very little mud solids and contaminates (such as barite and calcium carbonate) are present in the annulus.  

In this instance, the Weatherford patented straddle system was run to the target depth (as agreed between the Weatherford team and the operator and based on legislative practices) and was set and triggered to allow the cementing of the ‘A’ annulus. The straddle system facilitated the ability to trigger perforating guns positioned between the packing system at several locations and then bridge the newly made perforation, facilitating injectivity and circulation testing to the ‘A’ annulus.  

The straddle and gun system is designed to deliver a 360° shot coverage (6 SPF–12 SPF and 60–60/120 phasing) with an entry hole diameter (EHD) that ensures pressure between the cups is built at the time of pumping, providing an even coverage of cement and fluid flow. Furthermore, the gun systems have been designed, so that only the selected annulus is perforated. This is critical to ensuring that the annulus receives even coverage when both washing and cementing and to prevent uncontrolled flow when the fluid takes the path of least resistance. With cement in place, the disconnect is activated and the straddle left in situ, forming a base for the subsequent ‘B’ annulus cement plug.  

With the ‘A’ annulus remediated, a log can be initiated to help establish an element acceptance criterion for future wells in the same field and of the same architecture. After the barrier is established, selective annulus charges are run to create a path through the newly cemented ‘A’ annulus to the ‘B’ annulus, Fig. 1.  

Fig. 2. Cross-sections following the rigging down of coiled tubing and the removal of casing.

The shots extend across the full length of the plug zone, stopping short of the top of cement (TOC). Stopping short of the TOC and creating defined annulus levels helps establish a clear transition when logging both annuli, as shown in the images from Aberdeen field trials, Fig. 2. 

The charges used not only guarantee selective perforating across the remediated annulus—they create 360° coverage with carefully controlled EHD developed through the use of complex computational fluid dynamics (CFD) models. This ensures a perf, wash and seal (PWS) method of cementing that can be deployed effectively.  

The PWS method uses a dynamic cementing method interfaced with an interference fit cup-type tool, more commonly known as the acid wash tool. The acid wash tool has two modes. First, with an open ID, fluid can flow to the bottom of the assembly and return in a conventional flow path via the tool bypass, Fig. 3.  

Fig. 3. The flow path of fluid in the acid wash tool and bypass.

In the second mode, the ID is blocked via a ball landed on the bypass ball seat, multiples of which can be included in the bottomhole assembly (BHA). With the ball on the seat, fluid is diverted between the cups, allowing fluid to flow from the ID of the tool to the exterior of the tool via nozzles, or slots, positioned between the cups. The sealing nature of these cups creates a chamber where positive pressure builds as fluid exits, ensuring an even flow of fluid to the ‘B’ annulus via the previously created perforations. In this mode, the ‘B’ annulus will be flushed and cemented.  

To perform the washing cycle, the coiled tubing is moved downward through the wellbore, and the annulus is flushed with wash fluid. The wash fluid is comprised of a solvent-surfactant blend, more commonly known as MaxClean Plus. The purpose of the fluid is to clean the ‘B’ annulus and leave it water-wet, ensuring a good bond at the time of cementing. Throughout the wash cycle, pressures are monitored until a linear trend is observed and found suitable to facilitate the modeled cementing operations. 

With the well flushed and in suitable condition for cementing, the AWT is positioned at the lowermost perforation. The cement slurry—designed specifically for the well needs and pumping requirements—is then spotted at the AWT before pumping and pulling at a pre-calculated rate to spot the cement, both in the main bore and ‘B’ annulus. As the AWT reaches the uppermost perforation, pressure will build on the standpipe manifold as the flow area reduces; the cups will eventually blank off in the casing and leave no area for the fluid to exit and return.  

At this time, the pressure is built in the ID of the AWT, and a bypass ball seat shifts to allow fluid to flow conventionally to the bottom of the BHA, returning via the coiled tubing annulus. The string is picked up further, spotting a cement plug to a predetermined depth before a bottoms-up is conducted ahead of pulling out of the hole, leaving a permanent well barrier that extends both laterally and horizontally across the wellbore. 

A variation of the Reclaim system is used when the ‘A’ annulus is expected to hold solids or is an unknown in terms of its condition. In this instance, two PWS operations are conducted. The first remediates the ‘A’ annulus while the second remediates the ‘B’ annulus. It should be noted that while the benefits to washing out solids are manifold, the cost and time do increase, due to the quantity of charges required and the additional time to drill out the bore. Nevertheless, this version of the system has been employed successfully.  

Fig. 4. The Phase 2 plug location and architecture.

Reclaim dual annulus operations. A U.S. tier-one operator undertaking an abandonment campaign engaged Weatherford to determine a coiled tubing-deployed solution—so the drilling rigs could maintain their drilling schedule—to efficiently and permanently abandon wells on coil. The barriers to be set were the Phase 1, 2 and 3 barriers, with particular focus on the Phase 2 barrier, where there was concern regarding the potential of a failed plug leading to the contamination of an aquifer used as a potable water source.  

The challenge of setting these plugs was enhanced by the architecture of the well at the required setting depth. The plugs were to be set from the bore of the 5 ½-in. production casing and extend across the 7 ⅝-in. intermediate casing, 10 ¾-in. surface casing and large 17 ½-in. rat hole. The plug extending from below the 10 ¾-in. shoe into the 17 ½-in. rat hole was 277 ft in vertical length, Fig. 4. 

In addition, the plugs were required to form a rock-to-rock barrier and meet the legislative requirements of the Texas Railroad Commission—which discussed the project with both Weatherford and the operator present—before being approved for deployment. To meet the requirements, Weatherford recommended the Reclaim system (Fig. 5) as part of a comprehensive P&A program that covered the scope of the plug deployment and cementing operations, inclusive of the cement recipe and pumping schedule.  

Fig. 5. Reclaim system deployment, October 2024.

The program was successfully executed in October 2024. A total of 4 ½ days were needed to: 

• Rig up coiled tubing  
• Set the cast iron bridge plug at 12,580 ft 
• Set a 15.9-ppg cement plug from 12,580 ft. to 12,280 ft 
• Set a 15.9-ppg cement plug from 9,570 ft to 9,270 ft 
• Set 277 ft of a 15.9-ppg cement plug, using the Reclaim system from a depth of 1,060 ft to 783 ft (full lateral and vertical rock-to-rock plug) 
• Set 50 ft of a 15.9-ppg environmental plug from a depth of 50 ft to the surface, using an AWT to create a rock-to-rock barrier 
• Rig down coiled tubing. 

It is worth noting that the ‘A’ and ‘B’ annuli were washed with MaxClean Plus as part of the Reclaim plug deployment, removing the 13.7 ppg and 10.2 ppg oil-based mud (OBM) that was left in the annuli when the casing was locked down during well construction. The use of the MaxClean Plus meant the annuli were left water-wet ahead of cementing. 

On completion of each stage of the plugging operations, the TOC were found as programmed, and all subsequent pressure tests were successful. The well has since had the wellhead and conductor removed, and the land restored back to its original state.  

Due to the success of operations, Weatherford is now planning subsequent wells for the operator. 

MICHAEL RONSON is a Global Project manager for Weatherford, situated in the Well Construction group. He joined Weatherford in February 2011 and has 22 years of experience in the upstream oil and gas industry. He has served in numerous roles, working across a host of disciplines covering drilling, completion, workover, and drilling and completion fluids, as well as working with both rig and rig-less operations.