Preventing cascade failures requires well control experience and innovative technologies
Through pad drilling, an operator can drill multiple wells from a single, compact piece of land. Doing so saves time and money by reducing drilling operations and production infrastructure for those wells. Unfortunately, pad drilling creates additional well containment risks.
The primary well control risk related to pad drilling is cascade failure. A cascade failure occurs when a single well blows out and catches fire, resulting in subsequent sealing element failures on nearby pad wells, which cause those wells to blow out and catch fire. With the recent increase in pad drilling, well control companies have reported a rise in emergency response to more pad well blowouts than in previous years.
Pad well blowouts and fires are exponentially more expensive and time consuming to mitigate than single-well blowouts. Radiant heat or even direct flow from offset wells can impede well control options, damaging well control equipment or injuring personnel. Destroyed offset well production equipment must be carefully removed to allow access to the blowout well’s surface equipment. Typically, offset wells under risk of cascade failure also must be killed and secured before remedial operations can begin.
PREVENTING CASCADE FAILURES
Every production pad is different. Profitability requirements, risk/cost analysis, and even pad size may limit which different preventative measures can be deployed to prevent well pad cascade failures. The following methods give a glimpse into some of the leading high-tech options available to operators.
When it comes to well control, prevention continues to be paramount for cost-effective, proactive steps that operators can take when prepping a site for the worst-case scenario. To prevent cascade failures, a wellhead audit should be executed by a qualified engineer who can perform a complete inspection of the wellhead and all of its associated equipment.
A rating point is assigned based on the condition. Ratings are used to plan an intervention that ensures the system functions at the optimal level. Some components of the audit can include pressure monitoring and pressure management. If the audit determines that potentially dangerous pressure is present and posing a risk to wellhead components, well control specialists can perform an intervention method, such as cryogenic freeze, to correct the issue before it becomes a serious problem.
Radiant heat modeling produces state-of-the-art, virtual data that determine the amount of heat that offset wells can successfully resist during a close well blowout and fire, Fig. 1. Modeling results can be used for more precise risk/cost analysis to determine if additional cascade failure mitigations are necessary, such as increasing well pad spacing. If pad space permits, permanent concrete barriers can be staged between pad wells. These concrete barriers offer protection to offset wells from radiant or direct heat in the event of a nearby well blowout.
For many years, the use of heat-reflective corrugated tin by well control personnel has protected equipment and crews during critical, close-in work on well fires. To prevent against cascade failures, crews use this resilient material to protect offset wells from radiant heat during pad fire responses. Well control technology has led to the development of specialized corrugated tin well caps specifically designed and fabricated for rapid deployment to protect offset wells from radiant heat during a blowout and fire.
On wellsites, it’s common to see well flowlines and valves on production trees oriented toward one another. However, this practice creates an even greater risk for cascade failures if a nearby well blows and ignites. Direct fire can cause a well’s surface containment to fail. Depending on the intensity, this failure can occur in a matter of minutes. While not always possible because of pipeline, production or drilling infrastructure requirements, wells will experience improved longevity when staggered or oriented in an arrangement that prevents direct flames on offset wells.
Simultaneous operations plan. Well control industry experts report numerous blowouts during hydraulic fracturing and flowback operations. Creating and following a simultaneous operations plan (SIMOPS) is an excellent way to prevent well pad cascade failures. SIMOPS plans contain requirements and thresholds for shutting in nearby producing wells, with regards to well fracing or flowback operations. SIMOPS allows operators to actively monitor surface pressures on offset wells during frac operations. The SIMOPS data identify communication with offset wells during operations, allowing operators to mitigate any further damage or failure.
Subsurface safety valves (SSSVs) persist as one of the most common prevention options that work to protect multi-well production pads from the costly, destructive forces of cascade failures. SSSVs comprise devices installed in a well’s production tubing to provide emergency closure in the event of a blowout, as well as other emergencies. SSSVs employ a wide variety of technologies to power the closing mechanisms. Some SSSVs use external hydraulic control lines—run along the outside of production tubing—designed to be fail-safe-closed during any loss of hydraulic pressure in the control line. Other SSSVs are designed to close when reaching a specific pressure differential.
RESPONDING TO CASCADE FAILURES
Response to well pad blowouts requires a wide variety of specialized techniques and technologies, coupled with a great deal of experience. In case of a well pad blowout or fire, well control crews shut in and bullhead dead all nearby offset wells. This prevents those wells from failing at surface from excessive heat or damage sustained during the blowout surface intervention process. In essence, the first step in the response is a prevention measure. Containment is key, keeping a singular incident from becoming a multiplied disaster.
If multiple wells are on fire, Venturi tubes can be employed to shift the fire up and away from equipment and personnel, Fig. 2. This allows equipment and personnel to operate in a cooler environment below the fire. After a well’s surface components are removed through use of a jet cutter to orient the blowout and fire straight up, Venturi tubes are installed with an Athey Wagon. Multiple blowout wells on a pad may require Venturi tubes installed before well control remediation ever begins.
If a well cannot be fixed at surface due to damaged casing, excavation is often necessary. Excavating uncovers undamaged casing that can then be cut with a jet cutter to redirect the blowout and fire to a vertical orientation. Special care is taken when excavating to remove adjacent well flowlines and pressurized vessels necessary for further well control operations. Adjacent well components not removed need to be identified, confirming zero pressure in each location. Removal of existing production infrastructure is careful and deliberate, as some infrastructure may be buried or hidden by other burned, damaged equipment.
Corrugated tin covers, installed by well control personnel, protect undamaged wells that survive excavation. Corrugated tin acts as an excellent heat reflector and is commonly used to protect equipment and personnel when working close-in on a well fire. Additionally, water spray keeps nearby pad and well infrastructure cool and intact. Channels and large pits are required to collect the great amounts of water necessary to handle blowouts and fires. Quite often, well pads offer limited space for operations, so proper water management as a means to keep equipment cool, or even use thereof, may be impossible.
TYPICAL RESPONSE
The following scenario provides a summary of different well pad blowout experiences recently encountered by Cudd Well Control, highlighting the assessment and forward planning that occur soon after arrival on site. We also will review common steps taken to remove debris around a well to allow access to the wellhead, along with ways to protect and mitigate damage to offset wells located on the same pad. The summary concludes with a look at the difference methods available to secure the blowout, which include capping, diverting, bullheading, and/or dynanmic kill of the well.
In the event of a well control incident, time is of the essence. Immediately after Cudd Well Control receives an emergency call, data gathering begins. Such information includes current status, presence of fire, wellbore and surface equipment schematics for the blowout and offset wells, previously known pressures for all wells, formation, and much more.
After arriving on location, Cudd begins working with the client representatives to source and order the appropriate third-party equipment needed to perform the blowout assessment and initial critical well control intervention operations. An initial in-person blowout assessment must be carried out. Unfortunately, sometimes access to the pad is dangerous or not immediately available. In those situations, it is necessary to rig up a deluge system to provide water spray to reduce lower explosive limit (LEL) levels and keep personnel safe as they approach the blowout or fire. The blowout assessment includes:
- Status of containment walls and well cellars
- State of nearby production wells
- Presence of damaged production equipment or other wellsite debris
- Condition of well valves on the blowout offset wells
- Fluid type and levels of any liquids collecting on location and any potential hazards caused by the terrain layout
- Check for bubbling gas of additional craters on location
- Availability of water supply
- LEL readings
After the blowout assessment, a forward action plan will be developed in consultation with the customer. A general forward action plan on a pad well blowout might look like this (not always in this exact order):
- Remove debris and gain wellhead access
- Offset well wellhead repairs and hydrostatic securement
- Cellar excavations and dirt work
- Removal of damaged well components through unflanging or use of jet cutter
- Installation of Venturi tubes
- Capping and diverting blowout well
- Hydrostatic securement of blowout well
After the forward action plan is developed, the typical first course of action involves debris removal to gain access to the wellhead. Production lines should be confirmed as bled off, and all equipment needs to be carefully and meticulously removed. Poor implementation of equipment removal techniques can lead to well damage or injuries to personnel.
Offset wells are sometimes damaged or are not hydraulically contained. Damage to other wells on the pad during well control remediation operations could lead to adjacent well blowouts, further exacerbating the difficulty of the project. To prevent this, other pad wells are repaired, killed, and shut in securely, as soon as possible. A corrugated tin well cap is placed on secured offset wells to protect them if the blowout well is on fire or has the potential to catch fire.
When offset wells are secure, excavation and dirt work can begin. Wells in cellars require paths that allow for heavy equipment access. Water runoff collection channels are sometimes necessary to handle the large amounts of excess water that may be produced when responding to a blowout. In the scenario of very large multi-well fires with extreme radiant heat, personnel and equipment cannot safely make an approach. In those cases, large amounts of sprayed water and an associated water collection channel system are required to keep personnel cool, lower LEL levels, and handle the excess runoff.
After offset wells are secured and cellar excavations and dirt work are complete, work must be performed to orient the blowout and fire straight up and make the well ready for capping. Orienting the blowout or fire straight up is generally accomplished by unflanging and removing well components or through the use of a jet cutter, Fig. 3. Jet cutters use water and abrasive sand under high pressure and rates to cut damaged casing or well components and reveal clean cut casing, ready for capping.
If an offset well is so damaged that securement is not possible, a Venturi tube can be placed on those wells to move the fire up and away from personnel and equipment working on other wells. These can be placed by Athey Wagon or crane and can be permanent installations or moved in place, only when equipment and personnel need to approach the well pad for close-in work.
Capping a well involves placing either a stack of valves on an existing flange and flanging them up or placing the stack on freshly jet-cut casing and energizing a wellhead. Sometimes, blowouts are so prolific that they cannot be shut in immediately on a nonpressure-tested capping stack. In these cases, a diverter system is set up to divert the well flow from the well to a burn pit, Fig. 4. The diverter system is a series of large ID pipage with block or targeted bends, chokes, and ignition system.
Once a well is capped and shut in, it can then be bullheaded dead and secured. If the well has to be placed on a diverter system and cannot be shut in on a nonpressure-tested containment system, coiled tubing can be run to the bottom of the well and used to kill the diverted well dynamically.
In instances where surface intervention is not possible, it may be necessary to drill a relief well to secure a blowout well. Well control specialists use relief wells, fitted with special sensors, to identify ferrous materials located in blowout wells. However, relief wells used to mitigate multi-well pad blowouts may be of limited viability. If a well is blowing out on a multi-well pad, other wells may interfere with the relief well’s ferrous material sensors.
ELIMINATING CASCADE FAILURES
Pads containing multiple wells present unique hurdles during drilling, workover, or production operations. The challenge becomes exponentially greater when a blowout is present. Even when only one other well sits adjacent to a blowout on a well pad site, it is imperative that a well control response team takes the necessary steps to protect the other wells on a pad, containing the presence of any excessive radiant heat or direct flow that poses a threat to all adjacent well infrastructure by eliminating the risk of a cascade failure. Performing these critical prevention measures results in significant equipment and production savings, as well as the protection of human life and the environment.
Proper time-tested techniques, combined with high-tech processes and well control experience, lead to the safe resolution of well pad blowouts, preventing a cascade failure, if one has not already occurred. Proactive planning and emergency response solutions mitigate damage with the three most important words in well control: prevention, prevention, prevention.
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