Oil and Gas Well Stimulation Technology
The oil and gas industry has long used well service fracturing pumps units “frac pumps” in a process of well production stimulation where pressurized fluid is pumped down the well bore and forced out into the producing zone to break up or washout the formation and provide additional flow path for hydrocarbons to be flow.
This method of stimulation is known as “fracking” and is performed after a well bore has been made through vertical or horizontal drilling. The frac pumps that were initially used early on when the technology was originally developed, were not very powerful or efficient and in some cases not even powerful enough to cut through the rock formations. Often, a proppant such as sand or ceramic media was mixed with water to create a slurry to be pumped into the newly fractured openings to support the formation “Prop-Up” and prevent collapse under the immense pressures and gravity.
In order to meet the needs of modern-day horizontal drilling stimulation methods such as “slick-water fracs”, newer frac pumps feature higher horsepower, digital control and enhanced lubrication systems making them capable of operating at higher pressures for longer periods of time.
As a result of the enhanced development and growth of the fracking technology in the US, there is a high demand for frac pumps capable of efficiently pumping fracking fluid slurries (consisting of water, silica sand, and chemicals) into the deep wellbores.
What are Frac Pumps?
Frac pumps are engineered, special purpose pieces of equipment mounted on a trailer or truck chassis. They consist of a high horsepower prime mover such as a diesel engine or electric motor to drive a reciprocating plunger pump via a multi-speed powershift transmission. Additional components include large hydraulic driven forced air-cooled radiators and operator control & monitoring system.
How Does a Frac Pump Work?
Frac pumps consist of a diesel engine or electric motor driving a reciprocating, positive displacement, plunger pump. These pumps are equipped with a mechanically driven power end and are attached to a high-pressure plunger pump fluid end. These pumps are designed to withstand the demanding conditions of hydraulic fracturing, including the high pressures up to 15,000 PSI and harsh fluids involved in the process.
These pumps are connected together with others via a high-pressure manifold system with special valving and well head protection. Additionally, a digital pressure & flow monitoring system is utilized to manage the safety of the process. This manifold and monitoring system plays a crucial role in preventing the fracking fluid from flowing back up the well and potentially harming equipment and personnel. This same fluid is responsible for creating cracks in the shale rock formations that extend beyond the well bore between 200 and 400 feet, as required to release the oil and natural gas trapped within.
Common Types of Frac Pumps
Triplex (3-plungers)
Triplex pumps are reciprocating positive displacement pumps that are rated for input power up to 2,250 & 3,000 break horse power (BHP). They are capable of pumping a wide variety of fluids, including corrosive substances, abrasive fluids, and slurries with large particulates. These pumps utilize three pistons or plungers that operate within cylinders using a single power source. The reciprocating motion of the plungers causes high flow rates with pulsations that effectively pump both low and highly viscous liquids into a well. Similar to an internal combustion engine, triplex pumps convert the rotation of the motor shaft to the reciprocating motion of pistons and plungers contained within the solid carbon or stainless steel fluid end.
Quintuplex (5-plungers)
Quintuplex pumps are similar to the triplex version but are capable of higher break horse power (BHP) ratings up to 5,000 BHP. These pumps with additional plungers are designed to improve efficiency with increased flow rates during pressurised pumping, while also reducing the number of trucks needed in the fleet to perform the required well treatment design. These pumps enable lower operational speeds, resulting in longer life of the engine or electric motor & transmission and reduced fatigue cycles. Additionally, they offer better serviceability in the field, leading to reduced downtime. Quintuplex pumps also significantly reduce noise pollution, which for some locations can be very important especially when working long hours near residential neighborhoods. Compared to triplex pumps, quintuplex pumps with 8 & 9 speed transmissions offer a narrower flow rate variation, ranging from 94% to 102% of the average flow rate.
Frac Pump: Other Well Stimulation Applications
Coiled Tubing
Steel Tubing is inserted down the shaft of the well bore using a hydraulically driven mechanical injector head. This down-hole tubing carries different fluids that aid in the stimulation of extracted of oil and gas. When shafts are drilled to longer vertical and horizontal lengths, longer tubing runs are required. As a result, greater pump capability is needed to generate the necessary pressure to complete the job. The pumps can be mounted on a skid, truck, or trailer.
Acidizing
Optimal production of oil and gas from the well is vital, and acidizing is one of the most widely used techniques to do so. Pumping acid down the shaft during the initial stimulation and fracturing process provides a clean bore, enhances fractures, and dissolves any materials that may block the pathway.
In heavy-duty acidizing treatments (acid frac, matrix acidizing, acid stimulation), the success of the treatment depends on the pressure and flow rate of the servicing pump.
