Drilling technology: Drilling the deepest relief well in history

SHAUN RENSHAW, Halliburton   

OVERVIEW 

An operator in Asia experienced a kick (an unexpected influx of formation fluids into the wellbore) while conducting a wireline-fishing operation in a natural gas well. The operator could not control the kick from the surface, and the well flowed uncontrolled.   

Loss of well control occurred at a depth of more than 21,000 ft (6,500 m), with pressures of more than 20,000 psi, temperatures of 150ºC (302ºF), and in thick salt formations of up to 700 ft (~ 216 m). Each of these items presented challenges to overcome before regaining control of the well.   

With the use of Halliburton’s magnetic ranging solutions, the operator navigated these challenges and drilled and intercepted the deepest blowout well in history. This achievement highlights the critical role of innovation, precision and technical excellence necessary to overcome complex well control challenges. 

OVERCOMING WELL INTEGRITY CHALLENGES 

Relief well drilling is one of the biggest challenges in well control operations, with formation integrity being a major concern. When high pressure and the potential for early hydraulic communication between the target and relief well are present, that challenge increases. To manage the pressure during the well-kill process, the relief well must intercept the target well within a precise window.  

To locate and intercept target wells, Halliburton developed WellSpot^®—an active magnetic ranging system. This system injects current into the formation from a relief well through electrically isolated wireline bridles. It travels through the formation and generates a unique magnetic field at the target well. The magnetic field is then measured by a wireline tool from the relief well to determine and calculate the location of the well.  

WellSpot active magnetic ranging has been used to locate and intercept target wells since the 1980s in various applications. These applications include relief well drilling, steam-assisted gravity drainage, carbon capture, utilization and storage (CCUS), coalbed methane and well abandonment.    

The design plan for a relief well must be flexible to react to challenges in drilling performance and ranging results for the location of the well. It must also consider the relief well’s construction—the interception depth, target well surveys and directional drilling constraints.    

LOCATE, FOLLOW, INTERCEPT  

The ranging well plan consists of three phases: locate, follow and intercept. The locate phase has the highest positional uncertainty. This uncertainty is at its peak before the target well is detected by a ranging run. Once a ranging determination is made, the ellipse of uncertainty (EOU) reduces to the ranging call box.   

Ranging experts first determine the ranging depth at the point where the EOUs of the relief and target wells intersect, which corresponds to a separation factor of SF = 1. For most relief well operations, this depth falls within the detection range of the WellSpot system. However, in some cases, the combined EOU for both wells at SF = 1 lies outside the detection range. To proceed with drilling, an anti-collision ranging run is conducted to avoid accidental intersection during the next drilling interval. The next drilling interval is designed to keep the wells no closer than half the modeled detection range. This process repeats until the target well is detected.  

The large detection range and WellSpot modeling accuracy mitigate anti-collision concerns without numerous ranging determinations. The follow phase bridges the locate and intercept phases, aiming to keep the target well within detection range and maximize the length of drilling intervals. The intercept phase begins when the relief well approaches the target well and continues to reduce positional uncertainty until the relief well intercepts the target well.  

A STRATEGIC APPROACH   

The interception of the target well required careful planning because of high temperatures, pressures and multiple salt zones, along with its deep depth of more than 21,000 ft (~ 6,500 m).  

WellSpot Active Magnetic Ranging System

With a total depth of more than 21,000 ft (~ 6,500 m), the target well required intercepting a fish that was stuck deep in open hole. Due to its depth, the well had a relatively large EOU. At the intercept depth, the ellipses’ semi-major axis was approximately 82 ft (~ 25 m). Ranging operations on the target well began at about 17,880 ft (~ 5,450 m) with the location of the target well.   

At this phase, a pass-by was used to triangulate the location of the target well and reduce the uncertainty between the target and relief well. The WellSpot model refined this with the use of signal intensity and rapid changes in the high side to target.   

The ranging plan then entered the follow phase. For the target well, this phase spanned from 18,300 ft to 19,600 ft (~ 5,675 m to 5,975 m). This kept the relief well between 16 ft and 32 ft (~ 5 m to 10 m) away from the target well. Once the relief well reached an acceptable depth, it transitioned to the intercept phase and began the approach to the target well. In this phase, another pass-by was conducted to triangulate the target well's location. 

Throughout the well, the formation contained hundreds of thin layers and multiple larger sections of salt, some as large as 700 ft (≈ 215 m). One of the factors that can impact the detection range of the WellSpot tool is formation resistance.  

Salt can be resistive and prevents the current from reaching the target well. To mitigate the impact of high-resistance formations, the process requires careful planning and procedures. If the salt zone is thin, there is the possibility that the formation will reduce but not impact the WellSpot current from traveling to the target well.  

The loss of current is a challenge. A relief well plan requires a design to close the separation between the target well and relief well before the formation starts. Larger salt zones prevent the collection of currents on the target well but have no impact on the signal when the excitation current is already on the target well.   

With proper preparation, the ranging assembly keeps the excitation source in the ranging assembly above the salt layer. To re-establish detection below the salt layer, the WellSpot system shortens the distance between the excitation source and the WellSpot tool sensors to allow the current to travel below the salt layer.  

In collaboration with on-site geologists, the ranging engineers designed a ranging assembly on a per-run basis to mitigate any negative effects of the salt. This allowed for a ranging determination on every active magnetic ranging run.    

In the end, the relief well achieved hydraulic communication and killed the blowout well at a depth of about 20,760 ft (≈ 6,330 m), the deepest relief well in history.  

This achievement was made possible by the team’s expertise and their collaboration with local service providers. They planned each run to avoid any impact from salt layers, monitored tool temperatures to prevent equipment damage from the well's heat, and ensured the relief well’s position was far from the target well to avoid premature hydraulic communication. This was accomplished on the first attempt—with a single wellbore—without the need for any sidetracks to complete the interception.  

COLLABORATING WITH TECHNICAL EXPERTISE AND TECHNOLOGY  

In the face of extreme operational challenges, the success of this relief well project demonstrates the importance of the use of technology and technical expertise. The collaboration between the operator and Halliburton exemplifies how careful planning, precise execution and innovative solutions can achieve successful outcomes with difficult conditions.  

As the energy sector evolves, this historic success serves as a reminder of the resilience and ingenuity required to navigate to a recovery after a loss of well control. It is a testament to Halliburton’s innovation and technical excellence, which shapes the future of energy exploration and production.  

SHAUN RENSHAW is a senior ranging specialist at Halliburton with more than 20 years of experience in the oil and gas industry. This includes over 10 years of ranging operations in SAGD, well abandonment, and relief well drilling. He earned a BS degree in mechanical engineering from the University of Alberta in 2003.