Longer, deeper and hotter wells are upping the stakes for well integrity, driving an evolution in zonal isolation methods that give operators the assurance their completions endure for the life of the well. Research and development efforts for mechanical, fluid-activated and chemical solutions are ongoing to meet the rising challenges of these harsher downhole conditions that impact everything from elastomers to packers to cement. At the same time, the use of diagnostic tools to detect problems before they become problematic is growing.
Cement coverage is especially challenging in wells with low-pressure conditions or a high degree of large, natural fractures that can lead to unexpected losses. “Low pressure means we’re going to have problems lifting or placing the cement, which is heavier than drilling mud, and achieving good cement coverage in the well,” explained Greg Dean, Business Development Manager, Global Cementing for Baker Hughes, a GE company (BHGE).
Poor isolation results in the need for remedial measures, such as cement squeezes, which add rig time and cost for operators. “We’ve estimated that about one-third of the spend in cementing and drilling products are related to loss situations,” added Antonio Bottiglieri, BHGE Global Cementing Support Manager.
In terms of cement slurry and spacer design, high-pressure, high-temperature (HPHT) conditions are especially challenging for ensuring integrity during well construction and for the life of the well, Mr Dean noted. “Much of our research efforts are related to cement slurry chemistry, but we also focus on mud removal prior to cementing. Without proper mud removal, or hole-cleaning, before the cement job, we won’t achieve good wellbore isolation, regardless of the quality or performance of a cement slurry.”
In April, BHGE introduced SealBond Ultra, the latest addition to the company’s portfolio of cement spacer systems, to address extreme lost-circulation issues while cementing, including formations where gaps in naturally fractured formations are too large for conventional lost-circulation material (LCM) technologies. The system, which can plug fractures with a sealing capability up to 4 mm, versus the conventional 1 mm, is based on a hydrophobically modified polysaccharide that concentrates micelles and fill in the pores when they come in contact with a permeable formation.
“Post-job analyses of successful cementing jobs where equivalent circulating density has exceeded the estimated fracture gradient by as much as 1 lb/gal indicate the effectiveness of the new seal bond spacer system,” Mr Dean added.
The system enables the use of high-density slurries, which are more cost-effective than lower-density materials, and provides an alternative to more sophisticated cementing methods, such as lightweight extended slurries or two-stage cementing jobs.
The new cement spacer system is suited for any environment experiencing LCM issues or challenges related to cementing and zonal isolation. A Colombian producer successfully deployed the technology in a field where high-permeability sand zones were causing losses prior to cementing. The operator achieved effective isolation across all the high-permeability zones, as evidenced by a cement evaluation log, with no safety incidents. The technology has since been implemented in all production liner jobs in the field.
A Holistic Approach
Halliburton takes a holistic approach to well integrity, working with drilling engineers in the well construction and planning phase to identify trouble zones and then with the completion team, explained Ben Wellhoefer, Global Product Champion and Technical, Open-hole Isolation. “By balancing both sides of the equation, we can offer a complete isolation package, identify environmental challenges and comply with changing regulations to ensure effective zonal isolation, safety and regulatory compliance.
“Knowing where and how to place packers in key zones, especially in exploratory wells, is a primary well integrity challenge,” he continued. “It is critical to isolate those zones to minimize sustained casing pressure and isolate water or trouble zones while drilling.” Often, open-hole isolation systems are deployed during the well construction process to back up cement, traditionally the primary zonal isolation method. Additionally, isolation systems must withstand optimized drilling fluids, both on the run-in-hole side and the production side.
Halliburton’s Swellpacker isolation systems, with self-healing elastomers that swell when contacting oil or water in cased and open holes, are being enhanced to provide swelling capabilities in high-salinity brines and drilling mud systems, eliminating the need to swap fluids to swell the packers, Mr Wellhoefer said.
Continued research and innovation center on the issue of elastomers becoming more pliable in hotter, more pressurized environments. The K2 high-pressure end rings help eliminate extrusion, prevent rubber from flowing and allow packers to hold higher pressures. Halliburton also is enhancing the SwellSim software with real-time capability and has enhanced its delay systems – elastomer coatings that enable accurate control of packer swell rates.
During a development drilling campaign offshore Latin America, an operator ran 5-in. isolation systems with expandable liners to increase reservoir contact and reduce well completion time and risk in a highly depressurized zone requiring reduced hole sizes. The isolation systems were run 1,214 ft (370 m) into the well, with no dragging or restrictions. The operator saved 10 days of completion time and $3 million.
ZoneGuard, the latest iteration of Halliburton’s legacy open-hole packer systems, is being updated with a new anchor system to facilitate a full suite of zonal isolation options. The family includes three designs, including the ZoneGuard FP (frac packer), a short, economical packer for the US land market. The FP was recently deployed in the MidContinent Basin, where more than 40 individual packers were run in a single wellbore. For wellbore compartmentalization when using inflow control devices or screens, offshore applications and as a bottom packer for cementing, ZoneGuard standard range or ZoneGuard high expansion packers are often utilized.
Ball-in-Place Cuts Water Usage
Innovation is also increasing the reliability and efficiency of mechanical isolation methods in unconventional plays. In a move to mitigate the limitations of traditional plug-and-perforation operations, GEODynamics has introduced a composite plug system designed to ensure zonal isolation throughout plug-and-perf operations.
The system reduces time and water usage while eliminating the risks associated with previous strategies used to gain these efficiencies, explained Raymond Shaffer, Vice President, Completion Tools. “The biggest challenge with multizone plug-and-perforation operations with ball-on-seat – running perforating guns to depth, setting the plugs, firing the perforating guns, coming out of the hole and then initiating the fracturing operation – is if the guns don’t fire, an intervention utilizing a coiled-tubing unit is required to convey the perforating guns.”
The company’s EVOLV with FracTrap technology provides operators the ability to confidently run the ball in place, eliminating the need to pump a ball from surface after the plug is set. “Another key benefit of running the ball in place is the ability to test the zone as soon as the plug has been set to ensure the plug is holding the differential pressure before the fracturing operation begins,” Mr Shaffer added.
Launched in April, the system uses less water to seat the ball, resulting in significant water savings on every stage, and reduces pump time. “On a typical Permian Basin well with 40 to 60 stages, we can save about 15 minutes per stage and anywhere from $50,000 to $80,000 in costs, including water reduction, by not pumping the ball down,” he said.
In the event a perforating gun fails to fire, a fishing tool inside the setting kit allows the operator to flow back to catch the ball, come out of the hole and pump down another gun string to continue operations. The plug, constructed of molded composite material and rated up to 10,000 psi, is capable of milling rapidly and yields small particles of debris. Several versions are available for various wellbore environments. The full composite version is preferred by most operators because it is easy to drill out, while other operators are more comfortable with a composite plug that utilizes cast iron slips, Mr Shaffer noted.
Since undergoing field trials for 18 months in the Permian Basin and the Eagle Ford, the system has seen more than 8,000 US runs, including in the DJ Basin and the Rocky Mountain region. “We’ve had the opportunity to flow back and catch more than 60 balls, mitigating the need for CT intervention,” he said.
Diagnostics Behind the Barriers
Alongside those efforts, companies are increasingly recognizing the value of using diagnostic systems to detect issues that compromise well barriers. “Because most well integrity problems occur in the outer periphery of the well, behind barriers such as tubulars and cement, a process for sensing and locating leaks, or flow paths along the annulus, is crucial,” said Ken Feather, Chief Marketing Officer, TGT Oilfield Services. The company provides “through-barrier” diagnostics using thermal, electromagnetic (EM) and acoustic energy.
“Barriers, such as tubulars, cement, elastomers, packers and valves must be in good condition and must have good sealing performance,” he noted. “A barrier may look to be in good condition but not sealing. The mechanical properties of cement, for example, may be robust and provide coverage around the annulus, but it may not be sealing properly because of invisible micro-annuli or cracks that cause unwanted flow paths.” Additionally, cement, tubulars and other zonal isolation components experience degradation over time.
EmPulse multi-tube imaging, in its fourth generation, combines electromagnetic sensors with proprietary measurement and modeling techniques to measure the wall thickness of metal tubulars in well systems. “Wall thickness is an indicator of barrier condition and is used to quantify corrosion, which is progressive over time. Severe corrosion can lead to seal failures, leaks and unwanted flow paths, so routine surveillance is important,” Mr Feather said. In the Middle East, known for highly corrosive aquifers, the system has quantitatively recorded the individual tubular thickness of up to four concentric barriers.
The acoustic-based spectral cement channel detection system records and analyzes the sound spectrum in the wellbore to detect the presence of fluid flow in otherwise undetectable micro-cracks or channels within annular cement that can result in leaks along the annulus after the well is put on production.
“From a production standpoint, this capability is important, particularly where one reservoir is communicating with another in a producing well,” he noted. “In water injection wells, the technique can confirm if the injected water is reaching the target reservoir or being diverted elsewhere.” Integrity failures resulting in sustained annulus pressure are often visible at the surface before problems escalate, so operators are embracing diagnostics as a proactive method for preventing zonal isolation issues, particularly in the Middle East, he said. “Historically, the industry has been reactive, but we believe there are significant benefits in conducting surveillance regularly and routinely to monitor the tube integrity and seal integrity of wells barriers.”
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