Stimulation execution

Stimulation execution

A good understanding of job execution is necessary for making decisions on the applicability
and risk of various treatments. As with any well work, basic safety procedures must be
developed and followed to prevent catastrophic failure of the treatment, which could result
in damage to or loss of the well, personnel and equipment. Specific standards and
operating procedures have been developed for stimulation treatments, which if followed
can lead to a safe, smooth and predictable operation.
Matrix stimulation
Matrix stimulation, mainly acidizing, is the original and simplest stimulation treatment.
More than 40,000 acid treatments are pumped each year in oil and gas wells. These
treatments (Fig. 1) typically involve small crews and minimal equipment. The
equipment usually consists of one low-horsepower, single-action reciprocating pump, a
supply centrifugal and storage tanks for the acid and flush fluids.
Blending equipment is used when solids are added to the treatment.
The most common process is for the fluids to be preblended at the service company facility
and then transported to the location. This allows blending small volumes accurately,
controlling environmental hazards. The fluids are then pumped with little effort
or quality risk.
Hydraulic fracturing
Unlike matrix stimulation, fracturing can be one of the more complex procedures performed
on a well (Fig. 2). This is due in part to the high rates and

Figure 1 Matrix stimulation treatment using a coiled tubing unit, pump truck and
fluid transport.

Figure 2 This large fracturing treatment used 25,000 hydraulic horsepower and 1.54 million gal of fracturing fluid to place 6.3 million lbm of propping agent. The job
11 hours.


pressures, large volume of materials injected, continuous blending of materials and large
amount of unknown variables for sound engineering design. The fracturing pressure is
generated by singleaction reciprocating pumping units that have between 700 and 2000
hydraulic horsepower (Fig. 3). These units are powered by diesel, turbine or
electric engines. The pumps are purpose-built and have not only horsepower limits but job
specification limits. These limits are normally known (e.g., smaller plungers provide a higher
working pressure and lower rates). Because of the erosive nature of the materials (i.e.,
proppant) high pump efficiency must be maintained or pump failure may occur. The limits
are typically met when using high fluid velocities and high proppant concentrations (+18
ppg). There may be numerous pumps on a job, depending on the design. Mixing equipment
blends the fracturing fluid system, adds the proppant and supplies this mixture to the high-
pressure pumps. The slurry can be continuously mixed by the equipment (Fig. 4) or batch
mixed in the fluid storage tanks. The batch-mixed fluid is then blended with proppant in a
continuous stream and fed to the pumps.