Special Edition 2010

Haynesville Case History Compares Prime Plus 40/70 vs. LWC 40/80

Haynesville MapThe Haynesville Shale is one of the largest producing shale plays in the US. The play is located primarily in northwest Louisiana and runs into east Texas and southern Arkansas. The Haynesville formation has typical measured depths of 14,000 to 18,000 ft. True vertical well depths (TVD) in the Haynesville Shale typically range from 10,000 to 13,000 ft with 4,000 ft laterals or longer. Closure stress ranges from 9,000 to 12,000 psi and bottom-hole temperatures reach 325°F or more. This makes the Haynesville one of the deepest shale plays in North America with HPHT (high pressure, high temperature) well conditions. 

Fracture Treatment Production Results Comparison of Prime Plus vs. LWC

Haynesville ProductionThe Haynesville Shale study reviewed the production results of sixteen wells. All the fracture treatments were completed on wells in DeSoto Parish, Louisiana. The wells had similar characteristics, completion techniques, frac stages, and proppant volumes. The proppants used were Prime Plus™ 40/70 which is a curable resin coated sand (CRCS) and a 40/80 mesh lightweight ceramic (LWC). The differences in well production seen in the study were due to proppant pack cyclic stress, proppant embedment, and downhole proppant scaling. 

As you can see in the chart (click on chart to enlarge), the results showed that the average seven month cumulative gas production for the Prime Plus wells was 1,525 MMcf, while the LWC production was only 1,211 MMcf.  The wells that utilized Prime Plus proppant provided 26% higher production than the LWC wells. 

Proppant Pack Cyclic Stress Resistance

Wet Hot Crush TestThe amount of proppant fines generated after cyclic stress was measured for Prime Plus, LWC, and uncoated frac sand (UFS). The results of these tests showed that Prime Plus had the least amount of fines, while the percentage of fines for LWC and UFS was many times higher (as shown in the chart). A sieve analysis was conducted on these fines to determine the particle size distribution. The percentage of fines smaller than 100 mesh are as follows: 

  • Prime Plus fines < 100 mesh = 0% 
  • UFS fines < 100 mesh = 56.2% 
  • LWC fines < 100 mesh = 71.3% 

Proppant fines smaller than 100 mesh are more likely to migrate through the proppant pack, reducing pack permeability compared to larger particles.       

Proppant Embedment

Proppant EmbedmentEmbedment is another major concern, especially in soft shale formations.  Proppant embedment leads to reduced frac width and the creation of formation fines. The photo of Haynesville Shale core shows major embedment of LWC 40/80 proppant.

The results of our testing showed that LWC 40/80 proppant embeds 202 microns into Haynesville core. The published mean diameter of a 40/80 LWC is 308 microns. The published propped width of LWC 40/80 at 1 lbm/ft² is 3,151 microns. The reduced frac width from LWC 40/80 embedment is 2,747 microns which is a 13% reduction. 

Haynesville EmbedmentAs shown in the chart, LWC 40/80 has almost twice the embedment depth into Haynesville shale core as Prime Plus 40/70. The amount of formation fines generated from embedment was also determined by using the mean particle diameter and embedment depth for each proppant tested. The amount of formation fines from embedment is 75% more for LWC 40/80 compared to Prime Plus 40/70. 

SpallingAnother detrimental aspect associated with proppant embedment is spalling. Spalling is the creation of formation fines that are formed as proppants embed into the fracture face. The circled area in the photo shows formation fines spalling up around uncoated proppants embedded in a shale core. This issue can cause loss of proppant pack permeability, which results in decreased well productivity.

Proppant Scaling

Proppant scaling is a geochemical reaction that occurs between an uncoated ceramic proppant pack and the formation in a wet, hot environment. The result of downhole proppant scaling is a severe loss of proppant pack porosity and permeability as fines and debris are created in the proppant pack.

Scaling forms from the combination of: 

  • Aluminum from lightweight ceramics
  • Silica from shale
  • HPHT conditions
  • Formation water 

Proppant ScalingLaboratory tests were run at 300°F (149°C) under 3,000 psi closure pressure using a Haynesville shale core and simulated Haynesville water to model downhole conditions. The Prime Plus, LWC, and shale core samples were left in these conditions for 15 days. During this time, scale formed on the LWC proppants, while Prime Plus did not form any scale. The photo shows the amount of scale that can form in just a short amount of time and how it can plug proppant pack porosity.

The effect of scaling is extremely detrimental to well production.  Uncoated ceramics can lose up to 90% pack permeability in only a few days (Weaver et al., SPE 118174, 2008). Resin coated proppants inhibit the formation of scale, resulting in improved fracture flow capacity.

The circled area of the scaling photo also shows a small hole in the LWC which is potential pitting. Further investigation is warranted to determine the actual cause of this issue.

The laboratory tests and field studies conducted clearly demonstrate that Haynesville Shale wells fractured with curable resin coated proppants have higher productivity. Production results combined with laboratory research verified that proppant fines, proppant embedment, and proppant scaling were the primary reasons for lower production on the LWC wells. 


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