A proppant transport technology, which is a proppant and fluid system in one, was designed to make completions simpler by reducing pumping time and water consumption in addition to eliminating extraneous chemicals. The Propel SSP hydrogel polymer wrapped around a proppant rapidly swells and suspends the proppant by just adding to water. The hydrated polymer reduces a proppant’s effective specific gravity (SG), enabling uniform proppant distribution throughout a thin frack fluid. Once in the fracture, the polymer is cleanly broken with a traditional breaker. This more efficient hydraulic fracturing system expands the reservoir drainage radius from a longer effective fracture half-length.

This new technology simplifies downhole chemistry, eliminating compromises faced by the industry for decades. Because traditional proppant falls out of the frack fluid before reaching the fracture tip, engineers have increased frack fluid viscosity and/or pumping rates. Frack fluid additives that increase viscosity can be costly, and the chemistry can damage the formation and proppant pack. Engineers have chosen finer-mesh, lower-conductivity proppant to achieve enhanced transport.

The required mesh size can be pumped, and proppant is evenly transported throughout the fracture length and height. Engineers can plan pumping designs without certain frack fluid additives, including guar, crosslinkers and friction-reducers. The Propel SSP technology maximizes the reservoir contact area.

Technology design, fluid systems
The hydrogel polymer is wrapped around a proppant substrate of frack sand or ceramic. The substrate’s characteristics are not altered. When mixed with water, the hydrogel polymer expands, reducing the substrate’s effective SG to resist settling and enabling the proppant to stack higher in fractures.

The hydrogel, which remains wrapped around the proppant during fluid transport, reduces friction while pumping and imparts minimal viscosity of approximately 5 centipoise (cp) to 7 cp per parts per gallon (ppg) of proppant. This low-viscosity fluid remains in the pay zone. Proppant travels farther into the formation and throughout the fracture half-length. Slick water, one of the most common fracturing fluids, reduces the friction generated as fluid is pumped down the wellbore. Although perceived to be low-cost, slick water offers poor proppant transport, requires a high pumping rate and excessive water, damages formation permeability, and results in reduced effective fracture half-lengths.

Linear gel reduces treating pressure, allows lower pump rates and increases the frack fluid’s proppantcarrying capacity. Crosslinked gel generates higher viscosity in the range of 200 cp to 1,000 cp, further improving proppant-carrying capacity and increasing the fracture width and height compared with linear gel and slick water. Despite the improved proppant transport and fracture geometry, linear gel and crosslinked gel can place fluid and proppant out of zone while leaving behind damaging residue. A comparison of the technology against slick water and crosslinked gel systems is shown in the table.

Surface handling
Prior to pumping, the technology must not stick together in the high heat and humidity of a South Texas summer. This is the benchmark climate condition for moisture resistance to ensure product integrity using traditional shipping methods from proppant terminal to well. Fairmount Santrol R&D developed and refined this important attribute based on close monitoring of initial field trials.

Even in cold weather, the technology swells without using a hydration unit. Unlike conventional gel-based fluids, this robust technology achieves 190% expansion within 30 seconds of pumping when stored at subzero temperature and added to 4.4-C (40-F) water. Additional water heating is unnecessary when pumping in cold climates.

Oilfield services companies are pumping the system without modifying surface equipment or changing equipment controls, regardless of climate conditions.

Pressure pumping
As the technology rapidly hydrates in water, maintaining shear stability is important. Shear stability is the polymer-coating capacity to remain attached to the proppant from the frack blender through the pumps, perforations and fracture network. Shear stability ensures the coated proppant uniformly distributes and stacks throughout the fracture. If the polymer were to detach, there could be two negative effects. First, the fluid viscosity would increase, potentially resulting in fracking out of zone. Second, the technology’s unique stacking effect that increases propped fracture height would be absent.

The swollen, shear-stable polymer coating lowers the proppant substrate’s effective SG. When pumping proppant at a concentration of less than 3 ppg, lower SG enables efficient proppant transport. This transport is accomplished by reducing the fluid velocity needed to keep proppant flowing. As proppant concentration increases above 3 ppg, SG plays a less important role with this technology. Typically, at or above this concentration, the technology consumes all free water in a fluid column, resulting in uniform suspension in the frack fluid and ideal proppant transport.

Polymer breaking
The technology is pumped with traditional oxidizing breakers. The breaker is absorbed within the hydrogel and carried downhole as the technology hydrates. Once at bottomhole conditions, the breaker causes the hydrogel to unwrap from the proppant and break down to a low molecular-weight fluid that can flow back easily. After fluid flowback, there is no residue left in the fractures or around the proppant pack as with traditional fluid systems.

Breaker testing was conducted with commercially available breakers, including ammonium persulfate and magnesium peroxide. More than 10 oilfield services companies have used their proprietary chemistry to do the same. Test conditions comprised various technology concentrations, temperature, breaker loading rates and time.

Prior to pumping, polymer breaking should be verified by testing the fluid viscosity and proppant pack attributes. The polymer will flow back when the viscosity reduces to near that of water. The proppant pack should appear identical to an uncoated substrate, feel gritty and visually fill the same volumetric space as a sand sample of equal mass.

More detailed analytical and performance tests also confirm a clean break. Analytical tests, including loss on ignition and spectra analysis, have validated no residue remains on the proppant’s surface. Long-term regain proppant pack conductivity and retained core permeability performance tests also validate exceptional polymer cleanup compared with slickwater and gelled frack fluids that can reduce hydrocarbon flow by more than 50%.

Compelling production
Thirteen E&P companies have pumped the technology in more than 40 wells throughout the U.S. and Canada plays. When compared with the offset wells completed with different fluid systems and the same pump schedule, the technology typically has increased hydrocarbon production by more than 30% within six months. In several cases, operators have achieved greater than 50% production gains within two months simply by achieving a higher proppant concentration. In addition to enhanced production with higher proppant concentrations, the technology has enabled operators to reduce water, chemical and energy consumption.