What is flowback?

A flowback is a process in which fracture fluid is recovered from the well to the surface.  The process may also include the return of any energized gases that have been injected into the well during the fracturing process such as nitrogen or carbon dioxide.  The purpose of the flow back is to safely recover these substances from the well and transition the marketable hydrocarbons of the well stream to a sales pipe line or storage tank.  To safely conduct a flowback operation, it is important to understand what is occurring beneath the surface.  Below is a description of the occurrence.

What is Perforation and Fracturing?

After drilling the well, steel pipe is run all the way to the bottom of the hole and cemented in place. This stops oil, gas, and salt water from coming into the hole from formations above or below the intended production zone.

A device called a "perforating gun" (A) is lowered into the hole at the depth where the oil or gas formation is found.  After the gun is lined up properly, powerful explosive charges are fired (B) from the control panel in the truck...up at ground level.  These explosives blast a hole in the steel casing and cement, up to several feet out into the rock.  Finally, the oil and gas fluids are able to flow into the holes and up the well to the surface (C).

Upon perforating the well, it is sometimes necessary to perform a process called fracturing.  Fracturing increases the flow of fluids by connecting many pre-existing fractures and flow pathways in the reservoir rock with a larger fracture. This larger, man-made fracture starts at the well and extends out into the reservoir rock for as much as several hundred feet. The man-made or hydraulic fracture is formed when a fluid is pumped down the well at high pressures for short periods of time (hours). The high pressure fluid (usually water with some specialty high viscosity fluid additives) exceeds the rock strength and opens a fracture in the rock. A propping agent, usually sand carried by the high viscosity fluid, is pumped into the fractures to keep them from closing when the pumping pressure is released. The high viscosity fluid becomes a lower viscosity fluid after a short period of time. Both the injected water and the now low viscosity fluids travel, energized by bottom-hole pressure, back through the man-made fracture to the well and up to the surface.  The recovery of these fluids is called flowback.