CODY BEYER and JESSICA STUMP, NOV
Fig. 1. NOV Cellar Tech’s below-grade cellar enables SIMOPS, eliminating the need to shut in producing wells during return-to-pad drilling operations.
Simultaneous operations (SIMOPS) are essential for efficient pad development in shale plays, but they introduce logistical and safety challenges. In return-to-pad drilling campaigns, operators often shut in nearby producing wells for extended periods, due to surface congestion and equipment interference. These interruptions result in deferred production, increased downtime, and lost revenue.
Above-grade wellheads require wide spacing to ensure safety, maintenance access, and proper rig alignment. Vertical production trees further obstruct pad access and equipment mobility, limiting SIMOPS. Bringing the shut-in wells back online can be difficult, costly, and time-consuming, frequently requiring workovers that reduce their net present value.
Just as an underground parking garage increases surface space while keeping cars secure, NOV has developed a below-grade containment well cellar that reclaims pad space without sacrificing protection. By positioning the wellheads and production equipment below the surface, the cellar creates an unobstructed, fully contained workspace that enables SIMOPS, improves pad optimization, and enhances safety, Fig. 1.
TRADITIONAL WELL CELLARS
Conventional cellars often rely on corrugated metal pipe, known as “tin horns,” to isolate the wellhead and production tree from surrounding soil. While these components are widely available, they were originally engineered for stormwater drainage rather than the structural and containment demands of an oil and gas well cellar.
Even with the addition of a poured concrete base, tin horn systems typically do not create a continuous seal at the excavation floor. Over time, concrete cracks, allowing fluids to escape into the surrounding soil. Multiple operators have reported regulatory compliance issues, with some penalties exceeding six figures, following spills near the wellhead.
From a structural standpoint, tin horns are not rated to support rig surcharge loads or withstand the mechanical stress imposed by heavy equipment during drilling and completion operations. Failures, such as deformation and collapse, have been documented at the pad level and at locations where openings were cut into the pipe wall for access or flowlines.
Fig. 2. The fully seam-welded steel construction effectively contains any fluids that enter the cellar throughout the well life cycle.
Operational access and maintenance present further challenges. Without an integrated platform, fiberglass grating or pea gravel is often used to create a working surface near the wellhead. These materials can create uneven footing and contribute to accelerated corrosion of exposed components. During active drilling operations, the cellar floors are frequently accessed, using temporary ladders placed directly in the mud, which increases the risk of slips, trips and falls.
Given these limitations, operators are increasingly evaluating alternative cellar designs that improve structural integrity, enhance personnel safety, and support regulatory compliance over the life of the multi-well pad.
BELOW-GRADE INFRASTRUCTURE
NOV Cellar Tech’s below-grade containment well cellars were first deployed in Alaska, where sub-zero temperatures and sensitive terrain demanded a safer, more reliable alternative to open pit-style cellars. The cellar isolates fluids and shields equipment from extreme weather, providing a controlled, engineered workspace that enhances safety, reduces surface disruption, and streamlines wellsite operations.
Each cellar is a fully welded, sealed structure designed to capture and isolate liquids that may enter throughout the well life cycle, Fig. 2. Water, brine, drilling mud, cuttings and hydrocarbons remain within the structure and can be vacuumed out and disposed of properly.
Constructed from hot-dip-galvanized steel, the cellar is designed to resist corrosion and material breakdown for a minimum of 25 years. The walls are engineered to withstand side-loading from rigs and soils and are verified, using finite element analysis (FEA) to confirm structural integrity under dynamic load conditions.
Fig. 3. Structural cover plates are designed to support the weight of the catwalk or ancillary equipment, such as pumps or tanks, directly over the wellhead.
Internal stairways, handrails, and davit-arm retrieval points enable secure, routine access without triggering confined-space entry under OSHA standards. Designed for continuous occupancy, the structure provides a stable workspace for daily inspections and wellhead or blowout preventer (BOP) operations.
Excavation is straightforward and does not require specialized equipment. In typical soil conditions, the minimal over-dig design allows excavation to be completed in a few hours. The cellars are lowered over existing casing and welded in place.
If the conductor or mousehole is to be drilled after the cellar installation, drill-through adapters are used. Once the cellars are set and leveled, they are backfilled, using a flowable fill slurry to secure the structure and stabilize the surrounding soil.
Structural cover plates and bar grating protect both the surface area above the cellar and the equipment inside, Fig. 3. Rated for heavy equipment, trucks, and rig substructures, these components enable safe load-bearing operations directly over the wellhead. By placing wellhead and production infrastructure below grade, the system reduces the risk of impact hazards, and limits exposure to traffic and weather, thus supporting continuous, uninterrupted operations.
SIMULTANEOUS OPERATIONS
Traditional wellhead protection relies on above-ground cages that limit pad access and increase surface congestion. During rig returns for drilling or workover operations, producing wells are typically shut in, resulting in deferred production losses for operators that can total millions of dollars. Restarting those wells adds time and operational complexity.
Fig. 4. The fully below-grade configuration houses all artificial lift, wellhead, and production equipment within each cellar, increasing well density and improving pad efficiency.
NOV’s below-grade containment well cellar changes that dynamic. By housing wellheads, production trees, flowlines, and associated equipment fully below grade, the system clears the surface for SIMOPS—drilling, completions, production, and workover—while maintaining safety, containment, and accessibility, Fig. 4.
During drilling, the below-grade configuration eliminates the need for surface cages traditionally used to protect the wellhead during rig moves. Each cellar is a fully enclosed steel structure that provides structural support for the casing while shielding the wellhead from impact and related hazards. The cover plate, rated to 2,000 lb/ft2, enables rigs, trucks, cranes, and other heavy equipment to travel directly over the well location without compromising wellhead integrity.
Access ports and hatches provide direct entry to key wellhead components, such as valves and BOP connections. This design typically reduces nipple-up and nipple-down time by approximately 2 to 3 hrs/well, due to improved accessibility and reduced obstruction around the well center.
During the completions phase, pad activity and surface congestion reach their peak. High-pressure fracturing equipment, water and sand delivery systems, and wireline units all compete for space around the wellheads.
Relocating the wellhead and production tree below grade removes these obstructions and provides a flat working surface across the pad. This unobstructed pad access allows completion engineers to design more efficient and flexible fracturing layouts.
Equipment, such as frac manifolds, zipper manifolds, sand storage units, and water transfer lines, can be positioned closer to the well centers, shortening hose and iron runs. Reduced iron length improves pressure control and simplifies pressure testing, while the open surface enhances traffic flow for sand and water deliveries.
The below-grade cellar includes engineered access hatches positioned directly above critical components, such as the lubricator port, choke, and master valves. These hatches provide customized access to the frac stack, enabling crews to safely install, operate and remove the high-pressure valve assembly without removing the cover plate or disrupting containment. The configuration enables fracturing, wireline, and coiled tubing operations to occur at the same time.
Because the wellhead remains enclosed, any fluids released during fracturing or flowback are fully contained within the steel structure and can be removed and disposed of safely. The sealed design minimizes environmental exposure and reduces cleanup requirements between stages.
Once the well begins production, the fully seam-welded steel construction contains any fluids that enter the cellar. Accumulated liquids can be vacuumed out and disposed of through approved waste handling processes.
The sealed design also protects the wellhead and valves from environmental exposure, reducing corrosion and mechanical wear. During rig returns or workover operations, producing wells located in adjacent cellars can remain online safely. This capability allows operators to conduct SIMOPS without shutting in active wells, reducing deferred production.
PAD OPTIMIZATION
Surface space is a major constraint in shale operations. Above-grade wellheads require wide spacing for safety, maintenance access, and rig alignment. By eliminating these vertical obstructions, below-grade containment systems enable tighter well spacing and higher pad densities.
Smaller pads also require fewer access roads, shorter flowline runs, and less surface grading, all of which lower construction and reclamation costs.
For operations in environmentally sensitive areas, this approach also helps limit surface disturbance and visual impact. By concentrating activity within a smaller, contained footprint, operators can drill more wells to meet production targets.
CASE STUDIES
To maintain production continuity during return-to-pad drilling campaigns, operators in West Virginia and New Mexico deployed NOV’s containment well cellars. In the Appalachian basin, the below-grade cellars were installed across 20 well pads, enabling the operator to avoid the deferral of approximately 25 Bcfe of natural gas and condensate.
In the Permian basin, deployment on a five-well pad enabled continuous production during drilling, resulting in 504,000 additional barrels of oil and more than $30 million in annual incremental revenue.
Both deployments reduced nonproductive time, avoided unnecessary interventions, and supported more efficient pad-level logistics and operations, improving capital efficiency.
CONCLUSION
NOV Cellar Tech’s below-grade containment well cellar is redefining how operators approach multi-pad development. By enabling safe, simultaneous drilling and production operations, Cellar Tech solutions help reduce costly downtime, improve pad efficiency, and support greater asset utilization. The modular design streamlines installation, allowing scalability and adaptability across a wide range of wellsite layouts and terrains.
As operators continue to balance productivity and safety in increasingly complex environments, the ability to perform true SIMOPS—without compromising well integrity or operational control—represents a significant step forward. The fully welded, sealed design ensures long-term containment integrity, protecting the wellhead and production equipment throughout the life of the well.
From Alaska to the shale plays of North America, and soon at a major carbon capture, utilization, and storage project in Australia, NOV is helping advance the industry through engineering innovation that supports safer, more efficient field operations.
CODY BEYER is the Business Development manager for NOV Cellar Tech. He has more than 14 years of experience with multiple product lines at NOV. Mr. Beyer has a bachelor’s degree and master’s degree from Texas A&M University.
JESSICA STUMP is a senior writer at NOV. She has written about the energy industry for more than 14 years. Ms. Stump has a bachelor’s degree in journalism from Texas Tech University.
