Fracking Operations and Site Engineering Notes

Water Storage and Initial Fluid Transfer

• The process begins at the water source, which involves the use of Above-ground Storage Tanks (AST).
• The capacity for these AST units varies, often being a $10,000$ barrel AST (roughly $10,000$ feet across), but sometimes appearing as $20,000$ or $6,000$ barrel units.
• Water is moved from these sources via several different pumps.
• From the initial storage, the water is pushed to the blender.
• This transfer to the blender is considered the "low pressure side" of the operation.
• Because there is a large volume of water moving at very low pressure, there is generally no "red tape" or major safety perimeters (red zones) restricted around this specific equipment.

The Blending Process and Chemical Additives

• Once the water reaches the blender, the actual stimulation process begins as various components are combined.
• The low pressure side of the blender allows for the mixing of sand and specific chemicals before the mixture is sent to the high-pressure pumps.
• Biocide: Added to the water to kill bacteria and organic material. If bacteria were to go down-hole, it could react negatively with the formation and cause significant production issues.
• Scale Inhibitor: Used to prevent the build-up of scale. This is similar to hard water build-up seen in household appliances. In a well, scale can plug up perforations and micro-fractures, ruining the expensive completion process.
• Friction Reducer (FR): This chemical creates what is known as "slick water."
  • When pumping abrasive fluid (water with up to $2.5$ pounds of sand per gallon) through small pipes at high rates, there is a massive spike in pressure due to turbulent flow.
  • The FR acts as a "slipper" material to reduce that friction, allowing for lower operating pressures.
  • It is not an infinite benefit; engineers must find the right mixture of FR relative to rate and pressure to avoid wasting money on unneeded chemicals.
• Acid: Historically, two white tanks on the site map designate acid storage.
  • Acid is pumped at the very first part of a stage.
  • It helps clean up the perforations where the guns rubblized the steel casing and rock.
  • By cleaning the pathway, the acid helps drop the pressure and allows the stimulation fluid to start "breaking" the rock to initiate the stage.

Sand (Proppant) Specifications and Handling

• Sand is managed at the off-wood facility where belly dump trucks deliver the material.
• Sand Sizes: Operations typically pump $100$ mesh sand or $40/70$ mesh sand. The process usually starts with the smaller $40/70$ mesh.
• Material Properties: The sand is described as being super clean, super hard, and pressure resistant. Much of it is sourced from Missouri.
• Strength Rating: The proppant is rated to withstand approximately $13,000\,psi$ (pounds per perimeter/square inch).
• Concentrations: Sand concentration typically starts at a quarter pound ($0.25\,lb$) per gallon and increases to $2.5\,lb$ per gallon by the end of the stage. As the stage progresses, the density of the sand-to-water ratio increases.

High-Pressure Pumping and High-Risk Zones

• There are approximately $20$ to $22$ pumps on site ($10$ or $11$ on each side).
• These pumps take the low-pressure fluid from the blender and boost the pressure from roughly $100\,psi$ to as high as $13,500\,psi$.
• This high-pressure section is known as the "hairy" part of the operation, necessitating "red zones" where personnel are restricted to avoid accidents.
• The equipment is subject to extreme wear and tear; things break and wear out very fast due to the abrasive nature of the fluid and the extreme pressures.
• A new frac pump is valued at approximately $3,000,000$ dollars.

Stage Isolation and the "Plug" Mechanism

• Stage isolation is required to ensure only the desired section of the reservoir is stimulated.
• A Plug is set right above the last set of perforations to isolate the previous stage.
• Mechanism: The plug operates on a concept similar to a "Chinese finger trap." A setting tool strikes down with several hundred pounds of impact, forcing "slips" to expand and lock into the casing. It cannot move either up or down once set.
• Durability: The plug can withstand $12,000$ pounds of pressure for hours and will not give up.
• Deployment: The plug is pumped down the hole at speeds of $800$ to $1,000\,ft/min$ using fluid moving at $20\,BPM$ (barrels per minute).
• Drill Out: After the fracturing is complete, a separate process called "drill out" is performed to remove the plugs (upwards of $110$ plugs in a single well).

Perforation and Wireline Operations

• Perforating is the process of creating holes in the steel casing to access the formation.
• Wireline Truck: This unit drops a tool string into the well on an "e-line," which provides communication for setting the plug and firing the guns from inside the truck.
• Perforation Guns: A typical setup might include $7$ guns. Each cluster might have $4$ shots (bullets).
• Penetration: Charges are designed to penetrate the formation between $8.6$ to $10\,inches$, though some specialized charges can penetrate up to $42\,inches$.
• Rate per Hole: The rule of thumb is to aim for $2$ to $3\,BPM$ per perforation hole. If a well is being pumped at $90\,BPM$, the number of holes must accommodate that flow.

Zipper Fracturing and Operational Efficiency

• Zipper Fracturing: This involves two people (crews) on location at the same time to enable continuous operation. While one well is being fracked, a wireline crew is working on the adjacent well.
• Timing: Wireline runs take approximately $50\,minutes$ to $1\,hour$. A frac stage lasts just shy of $2\,hours$.
• Switching: The goal is to keep the frac pumps running as much as possible. When a stage ends on one well, the crew swaps to the next well in roughly $60\,seconds$.
• This involves flipping over $20$ valve handles on the accumulator. This must be done with perfect communication between the blender, the consultant, and the wellhead tech to avoid over-pressuring or cutting the wireline.

Dual-Fuel Technology and Energy Consumption

• Operations are extremely fuel-intensive. A typical site burns between $1,500$ and $1,700$ gallons of diesel per hour, operating nearly $24$ hours a day.
• Dual-Fuel Substitution: Modern pumps use natural gas to substitute diesel to save costs.
• Efficiency Ratio: One MCF (thousand cubic feet) of natural gas (costing about $2.00$, $3.00$, or $4.00$ dollars) can replace $6$ gallons of diesel (worth about $24.00$ dollars at $4.00$ per gallon).
• Load Range: Pumps burn natural gas most efficiently when at a $60\%$ to $80\%$ load. As they approach $100\%$ load, they must feather back toward diesel.
• Infrastructure: A company called Nacelle manages the gas transition from the pipeline (at $500$ to $600\,psi$) to the pumps (at roughly $100\,psi$).
• Risk: Any liquid or water fallout from the gas line reaching the pumps would ruin the $3,000,000$ dollar equipment.

The Data Van and Monitoring Systems

• All operations are visualized and controlled from the data van.
• Parameters Monitored: Pressures, rates, volumes, and chemical concentrations are tracked in real-time. This can be monitored remotely via smartphones.
• Pressure Thresholds: The maximum allowable pressure is generally $13,000\,psi$, but crews usually aim for a treating pressure of $12,500\,psi$.
• Casing Pressure: Operators monitor the pressure between casing strings. It should ideally be at zero or negative. A fluctuation here indicates a potential failure of the main production casing.
• Complex Fracture Networks: The goal is to create a complex network in the shale, which has porosity but low permeability. High rates are essential; "rate is your friend."
• Screen Outs: A