The numbers game: are more perforation clusters better?

December 15, 2020

You know what they say; more is better. But is it always?

For many years now, the most common method for horizontal multistage fracturing in tight rock formations has been Plug-and-Perf (PnP), utilizing several perforation clusters along the lateral section of the well in an attempt to create multiple fractures in any single stage. The basic assumption initially was that all clusters receive equal stimulation. However, irregularities in production performance and post-frac evaluations have led to the conclusion that the placement of these perforation clusters is critical. The number of perforation clusters has a significant impact on how effectively fractures can be created in the formation.

Formation heterogeneity can cause variations in the local stress field and variable frac gradients. This causes stimulation treatments to induce dominant fractures at perforation clusters with the lowest gradients rather than achieving equal distribution. To optimize the number and spacing of perforation clusters, understanding the stress distribution and fracture mechanics is essential. Sounds simple, right?

There are numerous data acquisition technologies available to examine post-stimulation results in horizontal wells with low permeability. Distributed acoustic and temperature sensing (DAS/DTS) and microseismic analysis are commonly utilized, and studies have found that, in some cases, 30% of perforation clusters do not contribute to production. Downhole cameras and downhole sonic tools are among the diagnostic technologies recently employed to evaluate the impact of erosion on the perforations and determine the cluster efficiency. Other studies have used radioactive tracers to demonstrate that not all the clusters are being stimulated in limited entry completions.

In a technical paper (SPE 168633), one operator in West Texas estimated that as much as 40% of the reservoir was not being stimulated due to variable fracture gradients. A microseismic survey in the field identified fractures extending far beyond the model calculations and communicating with an existing wellbore more than 3,000 feet away.

Recent trends indicate that operators favor longer wellbore lateral lengths, higher pump rates, and increased total proppant per stage. Undoubtedly, operators are emphasizing the need to collect and analyze as many data points during fracturing operations as possible. Having more data helps inform decisions on critical parameters such as the ideal number of clusters to achieve optimal control of the stimulation treatment and to ensure the maximum production performance of the well. However, technical and financial challenges arise when utilizing the most common fracture diagnostic tools.

So, maybe not as simple as it sounds. Thankfully, we’re getting closer than ever to a cost-effective, real-time solution. With technologies like sealed wellbore pressure monitoring (SWPM), it is now possible for completions engineers to monitor Volume to First Response (VFR) and conduct a more thorough evaluation of the actual cluster efficiency. This will significantly help E&Ps determine the right number of perforation clusters to maximize production performance.

To learn more about how much closer you are to the holy grail of well completions optimization, reach out to our Professional Services team via email or give us a call at (720) 662-7771. Let us know what we can do to help you!

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