Novel waterfrac proppant increases flow capacity and production

Hexion's Oilfield Technology Group (OTG) has introduced its Prime Plus partially cured, resin-coated proppant for waterfrac treatments of low-permeability reservoirs. Unlike conventional proppants, Prime Plus promises no proppant flowback and a significant decrease in fines generation, allowing users to enjoy higher fracture-flow capacity and increased production.

The success of any waterfrac treatment requires the proppant to be transported into the natural or created fractures and then to maintain the fractures' flow capacity throughout the lifetime of the well. Conventional proppants such as uncoated sands, ceramics, or tempered resin-coated sands are susceptible to crushing that occurs when the fracture closing stress exceeds the material strength of the proppant.

This leads to a generation of fines and flowback of the proppant. Even relatively small amounts of fines generation can have a major impact on flow capacity. In SPE paper 3298 by Coulter and Wells, the authors calculate that 5% fines generation can result in a 60% decrease in fracture-flow capacity. In addition to lower fracture-flow capacity and diminished well-production rates, proppant flowback may damage surface facilities and downhole tubulars.

Prime Plus reportedly circumvents many of these problems due to its composition and mode of manufacture. Hexion states that it is the only partially cured 40/70 mesh proppant available in the waterfrac market. This resin coating reduces proppant crushing by providing strength to the underlying grains and by generating uniform stress distribution throughout the pack. The coating also encapsulates any loose fines, thus preventing fines migration.

The partially cured proppant resists flowback by incorporating Hexion's Stress Bond technology, which causes individual proppant particles to bond together inside a fracture experiencing closure stress and temperature. This provides increased fracture-flow capacity.

Laboratory tests simulate downhole conditions

To more accurately simulate downhole conditions and put Prime Plus through its paces, Hexion developed the Wet, Hot Crush Test and Cyclic Stress Test.

The Wet, Hot Crush Test is a variation on the standard API RP-56 crush test, which is run on dry proppant samples at ambient temperatures. The Hexion test is run at elevated temperatures [200° F] and in a wet environment [a 2% aqueous potassium chloride (KCl) solution], which is closer to real-world conditions.

Prior to testing, the proppant is exposed to the 2% KCl solution environment at elevated temperature for 24 hours under 1,000-psi closure stress. It then undergoes a crushing step, after which the materials are dried in a convection oven and any generated fines are measured. In a comparison with other conventional proppants, the Prime Plus demonstrated significantly lower fines generation, as the chart below shows.

Throughout a well's life cycle, a proppant pack is typically subjected to numerous stress cycles due to well interventions or shut-ins. As a result, the proppant pack may shift and experience heightened stress levels that bring about the generation of additional fines. Hexion's Cyclic Stress Test was designed to simulate these real-world changes in closure stress and the tendency for fines generation.

As in the Wet, Hot Crush Test, the Cyclic Stress Test exposes the proppant to a 2% KCl solution at a constant 200° F for 24 hours prior to testing. The proppant pack is then subjected to pressures cycling from 3,000 to 8,000 psi for a total of three cycles at a constant temperature of 200° F in the 2% KCl solution. After the crushing cycle, the tested material is dried in a convection oven and any generated fines are measured.

In a direct comparison with an economy lightweight ceramic proppant, the Prime Plus proppant generated only 0.8% fines, while the ceramic generated 9.1% fines, which is equivalent to a 65% decrease in fracture conductivity.

Hexion states that its proppant technology is ideally suited for waterfrac treatments in reservoirs with closure stresses between 6,000 and 10,000 psi and bottomhole static temperatures up to 450° F. The proppant is introduced downhole with the injection water using conventional pumping and injection equipment.

In a series of east Texas field trials, the proppant technology has reportedly produced significant and sustainable production increases. One operator treated two similar Lower Cotton Valley offset wells with Prime Plus, injecting a total of 260,000 lbm of proppant in one well and 199,000 lbm in the other, each at a rate of 65 bbl/min. The operator reported a 143% increase in initial production after the treatment and a 90-day production level that was 300% higher than preproduction levels.

Hexion states that Prime Plus has been pumped in hundreds of jobs throughout North America, and operators have reported the elimination of flowback problems, a reduction in wellbore cleanouts, increased on-site safety, and ultimately, an increase in well production. To learn more about Hexion's Prime Plus proppant technology, please visit www.hexion.com.

Ted Moon is the Technology Editor of JPT Online. He brings information on emerging technologies, R&D successes, new field applications, updates from SPE papers about recent innovations, and more. If you have a question or suggestion for future article topics, email Ted at teched@spe.org.