Operator Workflow

A Frac Job From the Inside: Stages, Proppant and the Pressure Curve

A frac job is how many modern wells are made to produce. Fluid is pumped down the well at high pressure, and that pressure opens fractures in the rock around the wellbore. Proppant, usually sand, rides into those fractures in the fluid. When the pumps stop, the fractures try to close, and the sand holds them open. That network of open cracks is the path the oil or gas follows to the well. It looks simple from the road: trucks, tanks, and pipe. Inside, it is a careful sequence of stages, pressures, and records. This article explains that sequence the way a crew sees it.

Why a horizontal well is fractured in stages

A horizontal well crosses a long stretch of producing rock, but it is not treated all at once. The well is completed in sections, one stage at a time. Crews isolate one section, pump a treatment into it, and then move on to the next. Treating in stages means each part of the rock gets its own fracture network.

Isolation between stages is usually done with plugs. A plug is set in the wellbore below the section to be treated, and it seals off the work from the rest of the well. The crew then opens the casing at the new stage so the fluid can reach the rock. That opening is made with perforations, holes punched through the casing and the cement, or with ports in the casing that open when the stage is pumped. Perforate and plug is the common method on modern horizontal wells. When the stages are done, the plugs are drilled out or dissolve, and the well can produce.

Each stage takes a large volume of water, and a well can run many stages. Getting that water to the location is a field operation of its own, covered on the page about frac water sourcing and transfer.

On location during a stage

The center of the location is the pumping spread: a row of high-pressure pump trucks at the wellhead. Beside them sit the blender, which mixes the fluid, and the sand handling equipment, which feeds proppant into the blender. Water comes from tanks or pits, chemicals from totes in small amounts. A control van holds the data system and the people who run the job.

A stage does not start with sand in the water. The crew first pumps clean fluid, called the pad, to start the fracture growing. Sand is then added to the water in steps. The concentration starts low and climbs on a set schedule. The blender meters the sand and the pumps hold the rate. If the rock takes fluid faster or slower than planned, the crew adjusts the schedule on the fly.

Through all of it the crew watches treating pressure. Treating pressure is the pump pressure at the wellhead, the force pushing fluid into the formation. It is watched second by second, because it is the fastest honest signal of what the rock is doing downhole.

What the pressure curve tells the crew

On the data screen the stage shows up as curves: treating pressure, pump rate, and sand concentration. The pressure curve is the real-time story of the job. Read with the rate and the sand, it tells the crew whether the fracture is growing as planned or going sideways.

As fluid is pumped and the fracture grows, treating pressure generally rises. A steady climb at a steady rate usually means the fracture is taking fluid and growing as planned. Sudden changes are what get attention. A sharp drop can mean the fluid found an easier path, such as a natural fracture that opens up and takes the fluid. The crew also watches for a screenout, when the sand bridges off and stops moving forward in the fracture. A screenout often shows on the curve before it takes hold, giving the crew time to cut the sand or flush the wellbore before sand sets in it.

The curve also tells the crew when a stage is done. When the planned sand is in and the stage is flushed, the pumps shut down and pressure falls off. That ending, and the shape of the whole curve, stays in the well record. The curve is exact, and it stays with the well file.

Water, chemicals, and the public record

Frac fluid is mostly water and sand. Water carries the sand and delivers the pressure, and sand holds the fractures open. Chemicals are added in small amounts to do specific work: thin the fluid, carry more sand, kill bacteria, or reduce friction.

That documentation is public, not just internal. Operators report frac fluid information to FracFocus, the national chemical disclosure registry. FracFocus records are searchable by well and list the chemicals and amounts for each treatment. The registry gives landowners, regulators, and the public a way to see what went into a well.

State agencies oversee the work. In Texas, the Railroad Commission regulates oil and gas operations, from drilling permits to well reporting. Rules differ from state to state, and operators follow the rules where the well sits. After the treatment, much of the water comes back up, and handling it is its own job, covered on the page about flowback operations.

The paper trail a job leaves

A frac job leaves paperwork. Before the job, the pump schedule lays out the plan for every stage: rates, sand concentrations, and the order of materials. During the job, the ticket records what was pumped, how much sand went in, which chemicals were used, and when each stage started and ended. Afterward, the chemical list ties the loads back to the FracFocus report.

The frac job ticket and the service crew timesheets are the kind of field paperwork tracked in OpsFlo, ticket, dispatch, timesheet, approvals and document software built for field crews. The ticket is also what the billing is built from, so a straight ticket means a straight invoice.

None of this is busywork. When a well underproduces, the pump schedule and the ticket are the first records anyone pulls. When a regulator asks what was pumped, the chemical list answers. The crews who run fracs do not just move water and sand. They keep an account of every stage, and it stays with the well.

Sources and further reading

• FracFocus: Chemical disclosure registry
• Texas Railroad Commission: Oil and gas
• EPA: Hydraulic fracturing study