Hexion
Winter 2008
 
fracline
 
Proppant Crushing and
Fines Generation in Waterfracs

Loose Fines Encapsulation

Design engineers must consider numerous criteria when selecting waterfrac proppants. The most critical of these is long-term fracture flow capacity, which is directly influenced by the amount of fines present in the proppant pack.

The most predominant problem that occurs due to improper proppant selection is proppant crushing. Proppant crushing occurs when the fracture closure stress exceeds the strength of the proppant that is placed in the fracture. This leads to the creation of fines which can migrate and plug a proppant pack, causing diminished well production.

5% fines generation = 60% decrease in fracture flow capacity*
*Fracture flow capacity reduction calculated using the Coulter & Wells Method (SPE Paper 3298).

Prime Plus™ reduces proppant crushing and fines migration in several distinct ways. The resin coating provides additional strength to individual grains, generates uniform stress distribution throughout the pack, and mitigates fines migration by encapsulating loose fines within the resin coating.

“Real-World” Fracture Flow Capacity

A variety of variables influence fracture flow capacity, which directly relates to well production. The table below clearly shows how Prime Plus compares to other proppants used in the waterfrac market.

Factors Affecting
Fracture Flow Capacity
Prime Plus Northern White Frac Sand Tempered
Resin Coated Sand
Economy Lightweight
Ceramics
Baseline Proppant Conductivity Excellent Poor Excellent Excellent
Proppant Flowback Control Excellent None None None
Reduced Fines Generation
and Migration
Excellent None Fair None
Proppant Pack Cyclic
Stress Resistance
Excellent None Poor None

Comparing Proppant Performance with Laboratory Conductivity Data

Effects of Fines Generation on Fracture Flow Capacity
Baseline long-term conductivity at 250°F (121°C) between Ohio sandstone core (0.1 millidarcy, 129 cm2) with 2% KCl. Reduced effective conductivity based on Coulter & Wells findings of effects of fines.

The graph represents fines impact on fracture flow capacity. The conductivity reduction was calculated using the Coulter & Wells Method (SPE Paper 3298). A typical baseline conductivity test is run at a flowrate of .0051 CFD, therefore fines do not migrate. Typical waterfrac flowrates are 1-10 MMCFD, which causes migration of fines and a decrease in conductivity. Compared to the lab testing, a “real-world” flowrate is a billion times greater or more.

 

Fines Generation Comparison of Waterfrac Proppants

Effects of Fines Generation on Fracture Flow Capacity
Modified API RP-56 crush resistance test procedure ran to more realistically represent downhole conditions. Prior to testing, samples are exposed to 2% KCl fluid at 200°F (93°C) for 24 hours under 1,000 psi closure stress.

The chart shows that Prime Plus offers the lowest fines generation of any waterfrac proppant. Hexion’s Wet, Hot Crush Test was used to compare Prime Plus to Northern White Frac Sand, Economy Lightweight Ceramic, and Tempered Resin Coated Sand. The fines generated by other waterfrac proppants greatly decrease well production. The photos below demonstrate what each proppant looks like under 8,000 psi and 10,000 psi closure stress.

 

Cyclic Stress Resistance – Comparison of Prime Plus to
Economy Lightweight Ceramic

Cyclic Stress Chart
The proppant pack is subjected to numerous
stress cycles throughout the life of the well

Throughout the life of a well, a proppant pack is subjected to numerous stress cycles caused by well interventions and shut-ins. These changes in stress can cause the proppant pack to shift, fatigue, and generate fines - leading to decreased conductivity

Cyclic Stress Testing Procedure:

  • Cycled from 3,000 psi to 8,000 psi for a total of 3 cycles
  • Temperature held at 200° F
  • Exposed to 2% KCl solution

Results:

  • Economy Lightweight Ceramic 40/70 generated 9.1% fines - equivalent to a 65% decrease in conductivity
  • Prime Plus generated only 0.75% fines - minimal decrease in conductivity

 

 

 

 
 
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