Tech Watch: Highly conductive nanostructured proppants boost recovery

Unconventional reservoirs are growing rapidly in importance both domestically and internationally. To unlock tight formations, use of technologies such as hydraulic fracturing and propping agents, which induce and maintain reservoir permeability, has grown commensurately.

Conventional proppants trade strength for weight. Ceramic proppants are strong, but heavy, and as a result transport poorly in low-viscosity fluids. Operators are typically forced to employ heavy proppant, which poses additional issues. They can achieve well-propped fractures while damaging their formations with expensive permeability-destroying gelled fluids or achieve poorly propped fractures (and possibly also unwanted fracture height growth) with large quantities of inexpensive, low-viscosity/low damage “slickwater.” In both instances, production rates and ultimate recovery are impaired, often substantially.

Given the poor strength of commercially available lightweight proppants, operators typically are forced to employ heavy proppant, which poses additional issues. They can achieve well-propped fractures while damaging formations with expensive permeability-destroying gelled fluids or achieve poorly propped fractures (and possibly unwanted fracture height growth) with large quantities of inexpensive, low-viscosity/low damage “slickwater.” In both instances, production rates and ultimate recovery are impaired, often substantially.

Proppants that exhibit both high strength and low weight are required to maximize recovery in unconventional reservoirs.
Simply, the more fracture length is propped with highly conductive proppant, the more rock is producing in the reservoir, improving both production rate and total recovery.

OxFrac is Oxane’s lightest proppant (2.0 SG, 40/70 mesh size; 2.2 SG, 20/40 mesh size) and is focused on wells of moderate depth. Conductivity testing suggests that OxFrac affords Darcy conductivity better than sand through 6,500 psi (40/70 mesh) and 8,500 psi (20/40 mesh). (Images courtesy of Oxane Materials, Inc.)

Technology answers industry need
Oxane Materials Inc. is introducing two new nanostructured proppant technologies, OxFrac and OxBall, which couple conductivity with reduced weight/improved proppant transport.

Depending on job design, reservoir type, and Oxane proppant type, initial proppant transport modeling conducted by Oxane scientist Rob Skala and Duke University Professor and Oxane co-founder Mark Wiesner suggests that Oxane’s proppants could transport 30% to more than 50% deeper in slickwater relative to conventional proppants of comparable size and conductivity.

The proppants are expected to be employed as an additive in the portion of the fracture where they can afford maximum value (i.e., beyond the conventional proppant pack or in the conductivity-limited near-wellbore region or both). It is expected that Oxane’s proppants will comprise 20% to 30% of the total proppant pumped and conventional proppants will comprise the balance.

Oxane’s proppants afford operators new degrees of freedom in hydraulic fracturing job design (proppant density, proppant size, fluid selection, and pumping rate) which improve the probability that frac jobs will be successful while reducing operating cost and environmental impact. A lighter proppant requires less horsepower to place, reducing the propensity of fractures to grow out of zone (particularly in slickwater) and the total amount of horsepower required, thus reducing cost, CO2 emissions, and noise/surface disturbance. The cost associated with placing frac materials out of zone (waste prop, chemicals, and fluid) also should be reduced.

Increased degrees of freedom per job design extend to chemical and water use. Lower density proppants require less fluid viscosity to transport, enabling the use of simpler, less chemically loaded (gels, breakers, etc.) completion fluids again reducing cost, environmental impact, and reservoir damage.

Freshwater requirements could be reduced, possibly substantially, as fewer pounds of proppant are pumped per volume of propped fracture area created. Simply, fewer pounds of proppant may be required per job. This effect is augmented should fracture height growth be contained due to reduced placement of water out of zone.

Finally, it is possible that more pounds of lightweight proppant could be loaded per gallon of completion fluid pumped due to the improved transportability of lightweight proppant, further reducing water requirements.

Depending on formation type, 40% to 90% of load water pumped is lost to the formation and effectively removed from the water cycle. Lightweight, high-strength proppant should improve load water recovery as it provides an extended highly conductive pathway for load water to flow successfully to the well bore. Improvements in load water recovery not only benefit the environment, but also reduce reservoir damage as less water remains to blockade formation porosity and/or imbibe into formation porosity.

Conductivity testing suggests that OxBall affords Darcy conductivity comparable to traditional intermediate strength ceramic proppant through 10,000 psi (40/70 mesh) or 12,000 psi (20/40 mesh).

The new proppants should afford several benefits to pressure pumpers. First, reduced pumping rates should improve the longevity of equipment and reduce pump maintenance expense and amount of “safety horsepower” required per job, which will cut down on capital investment in pumps. Second, lightweight, round, highly spherical proppants should erode pumps at a less aggressive rate than jagged, angular sand or traditional ceramics, further improving pump longevity while reducing maintenance expense. Third, should lightweight proppant enable operators to execute smaller frac jobs successfully, pressure pumpers will be able to turn pump fleets at faster rates.

OxFrac is the company’s lightest proppant (2.0 specific gravity (SG), 40/70 mesh size; 2.2 SG, 20/40 mesh size) and is focused on wells of moderate depth. Conductivity testing suggests that OxFrac affords Darcy conductivity better than sand through 6,500 psi (40/70 mesh) and 8,500 psi (20/40 mesh).

Focused on deeper wells, OxBall is heavier and considerably stronger. Conductivity testing suggests that OxBall affords Darcy conductivity comparable to traditional intermediate strength ceramic proppant through 10,000 psi (40/70 mesh) or 12,000 psi (20/40 mesh).

Initially available in 40/70 and 20/40 mesh ranges, OxFrac and OxBall exhibit extremely tight size distributions (typically five to 10 mesh wide vs. 30+ mesh wide for conventional ceramics) and superior sphericity/roundness relative to conventional ceramic proppants, improving Darcy conductivity and reducing deleterious non-Darcy flow effects.

When exposed to hydrochloric acid and water, OxFrac and OxBall exhibit corrosion resistance comparable to that of traditional ceramics. Extended exposure to hot brine (300?F (149?C) for 10 days) in an acid digestion bomb suggests that Oxane’s proppants exhibit low solubility. Further, crush-fine levels for the solubilized proppant are largely unchanged. As with other conventional non-bauxite proppants, the use of OxFrac and OxBall in conjunction with hydrofluoric acid is not recommended.

Oxane plans to introduce its products in staged fashion. The initial product produced will be 25/35 mesh OxBall 2.75 SG, which is expected to find strong application in the Anadarko Basin, South Texas, and East Texas. Other product offerings are expected to be introduced rapidly thereafter.

Oxane presently is forming field test partnerships with both operators and service companies.