Avoiding Screenouts in Fracturing: Optimize Operations

Guest post by Leon Massaras

Abstract

Screenout (SO) refers to a condition where proppant pumped into a fracture accumulates at the near- wellbore area or in the wellbore itself, blocking or “screening out” the flow path and preventing further proppant from entering the fracture. This article presents and elaborates upon three simple and straightforward methodologies for detecting and avoiding screenouts: Enhanced Fracture Entry Friction Analysis, Median Ratio Methodology, and Inverse Slope Methodology. Each methodology offers high predictive accuracy and allows for corrective measures to be taken prior to starting – and even during – the mainfrac.

Types of Screenout

There are two primary types of screenout: Gradual and abrupt (or wellbore). Gradual SO arises from the slow accumulation of proppant in the near-wellbore area, causing a gradual increase in surface pressure, as shown in Figures 4 and 5. Abrupt SO (also called wellbore SO) results from proppant gradually blocking the entire perforated interval, ultimately creating a complete obstruction that causes an abrupt, vertical rise in surface pressure, as illustrated in Figure 1. Massaras and Massaras (2012), and Massaras (2024)

Causes of Screenout

Screenouts can occur due to various causes, divided into primary and secondary. There is only one primary cause, namely: Near-wellbore friction, which is widely regarded as the most frequent reason for SO, responsible for 90–95% of screenouts. Cleary et al. (1993); Massaras et al. (2011). 

Secondary causes include:

• High differential (Deviatoric) stress
• Non-compliant geologic formations
• Multiple fractures
• Segmented en-echelon fractures
• Backstress due to reservoir depletion, and
• Fracture tip dilatancy.

Tip Screenout in Conventional and Unconventional Reservoirs

Contrary to common belief, Tip Screenout (TSO) does not occur during fracturing of conventional and unconventional reservoirs. Despite numerous publications on the subject—876 results from a search on OnePetro with “TSO” as of November 14, 2024—TSO is only relevant in hydraulic fracturing of high-permeability, unconsolidated formations (Frac-Pack), where screenout is the objective rather than a challenge. For a comprehensive explanation, see Barree (1991, 2022) and Barree and Conway (2001).

Screenouts are Costly and Time Consuming

Screenouts are very costly and very time consuming issues in hydraulic fracturing. In some regions, approximately 25-30% of propped hydraulic fracturing treatments experience screenouts and numerous methodologies have been developed over the past 70 years to address these issues. The most widely implemented approach is the Net-pressure Plot (a.k.a. Nolte Plot), Nolte and Smith (1981), which is a key tool in most commercially available fracture propagation simulators. Many recent methodologies, driven by Artificial Intelligence (AI) and Machine Learning (ML), promise to improve predictions but are not yet widely adopted due to the lack of large training datasets – for each specific field – and specialized personnel.

Screenout Detection and Avoidance Methodologies

Three simple and straightforward methodologies for detecting and avoiding screenouts are presented. They are categorized into two groups: Post-Minifrac and Real-Time. 

The Post-Minifrac group includes:

• Enhanced Fracture Entry Friction Analysis

• Median Ratio Methodology

The Real-Time group includes:

• Inverse Slope Methodology

A. Post Minifrac 

Enhanced Fracture Entry Friction Analysis

The original Fracture Entry Friction (FEF) Analysis methodology, as introduced by Cleary et al. (1993), lacked predictive accuracy due to limitations in its implementation. The enhanced version of FEF, presented by Massaras et al. (2007), addresses these limitations, offering more reliable results.

FEF analysis uses data from a Rate Step-down Test (RST), which involves four equal rate reductions to zero. The key advantage is the ability to analyze the rapid pressure drop and its associated patterns, as progressively smaller pressure reductions are considered ideal. By examining deviations from ideal pressure reduction patterns, the methodology helps identify the dominant friction components. Fracture Entry Friction loss can be split into two components: Perforation friction and near-wellbore friction, as illustrated in Figure 2. Cleary et al. (1994); Massaras et al. (2007).

The two types of Fracture Entry Friction exhibit distinct flow behaviors, and thus plotting behaviors: 

• Perforation friction — because of flow in a circular conduit — follows a flow rate squared pattern, f(Q²), and plots concave upwards, as shown in Figure 2a. This plotting behavior indicates that perforation friction dominates (is larger than near-wellbore friction).
• Near-wellbore friction — because of flow between two plates — follows a square root of flowrate behavior, f(√Q) or f(Q¹/²),  and plots concave sideways, as shown in Figure 2b. This plotting behavior indicates that near-wellbore friction dominates (is larger than perforation friction). Cleary et al. (1994); Massaras et al. (2007).

The deviation from ideal pressure reduction pattern and the difference in plotting behavior allow for accurate identification and quantification of each friction component by simultaneous solution of the two equations, as presented by Massaras et al. (2007) and as shown in Figure 3.

A deeper understanding of Bernoulli’s principle and the Venturi effect is essential to fully grasp the FEF analysis. The analysis yields values for perforation friction and near-wellbore friction, which can guide decision-making as outlined by Massaras et al. (2007) and as shown in Table 1.

Median Ratio Methodology

The Median Ratio (MR) is defined as:  MR = ∆P4÷∆P1                                                     

Where, ΔP4 and ΔP1 represent the pressure changes at specific rate reduction ΔQ4 and ΔQ1, as illustrated in Figure 2, and as outlined by Massaras et al. (2011) and Massaras (2024).

For the MR to be valid, the rate reductions (ΔQ) must be approximately equal, as shown in Figure 2. A low MR (between 0.2 and 0.5) indicates a low likelihood of screenout, while a higher MR (between 0.5 to 1.0) correlates with a greater risk of screenout. In extreme cases (MR values above 1.0), screenouts can occur even with small proppant sizes (e.g., 100 mesh). The relevant ranges for MR and their associated risks were originally presented by Massaras (2024), and are summarized in Table 2.

B. Real-time

Inverse Slope Methodology

The Inverse Slope methodology – developed empirically by Massaras and Massaras (2012) – uses surface pressure data to provide early warning signs of impending screenouts during hydraulic fracturing. It allows for real-time monitoring and decision-making, enabling operators to extend or terminate treatments as needed. 

When proppant-laden slurry is pumped into the wellbore the hydrostatic pressure gradually increases, while surface pressure decreases, following a Negative Surface Pressure slope. Once the wellbore is fully loaded with slurry at maximum proppant concentration, i.e., hydrostatic pressure is maximum as the proppant concentration is at a plateau, the surface pressure flattens and may remain constant for a time. 

As slurry containing higher proppant concentration and larger proppant mesh sizes moves through the near-wellbore region, friction increases, causing the surface pressure to rise and this is reflected as an Inverse Slope on the pressure plot, as illustrated in Figures 4, 5 and 6. The rate of the Inverse Slope incline depends largely on the proppant concentration and mesh size in the near-wellbore area. The inclination is usually of equal magnitude but opposite (inverse) of the Negative Surface Pressure trend.

As long as the Surface Pressure remains aligned with the Inverse Slope, the treatment can proceed as planned. The treatment can even be extended as illustrated in Figure 6, provided that there are enough materials on location available, loaded, and ready to place. The methodology is applicable to both Conventional and Unconventional reservoirs as illustrated in Figures 4 and 5 respectively.

If the Surface Pressure deviates from the expected Inverse Slope trend and follows a Deviated Slope, as illustrated in Figures 4 and 5, it signals the onset of a screenout. At this point, operators must immediately begin the displacement (flush) operation to avoid a screenout and the associated complications, delays, and cost overruns.

When considering extending the treatment, it is crucial that the surface pressure does not exceed the Pressure Stabilization level as illustrated in Figure 6. This precaution allows enough room for Hydrostatic Clearance, and prevents reaching the pressure limitation of the equipment (wellhead, casing, tubing, and isolation tools). If the pressure limitation is reached, the automatic shut-down system will be activated, it will shut-down of the pumps, and the treatment will be terminated.

Conclusion

The methodologies outlined provide simple yet effective tools for detecting and avoiding screenouts during hydraulic fracturing. By leveraging techniques such as Enhanced Fracture Entry Friction Analysis, Median Ratio methodology, and the Inverse Slope methodology, operators can make pre-frac modifications to both the completion and mainfrac treatment, and monitor and adjust the mainfrac treatment in real-time, improving efficiency and safety while reducing the risk of costly failures.

Literature Cited

1. Barree, R. D. “A New Look at Fractures Tip Screenout Behavior.” J Pet Technology 43 (1991): 138–143. doi: https://doi.org/10.2118/18955-PA
2. Barree, R. D., and M. W. Conway. “Proppant Holdup, Bridging, and Screenout Behavior in Naturally Fractured Reservoirs.” Paper presented at the SPE Production and Operations Symposium, Oklahoma City, Oklahoma, March 2001. doi: https://doi.org/10.2118/67298-MS
3. Barree, Robert. “Processes of Screenout Development and Avoidance.” Paper presented at the SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, USA, February 2022. doi: https://doi.org/10.2118/209125-MS
4. Cleary, M. P., Johnson, D. E., Kogsbøll, H-H. , Owens, K. A., Perry, K. F., de Pater, C. J., Stachel, Alfred, Schmidt, Holger, and Mauro Tambini. “Field Implementation of Proppant Slugs to Avoid Premature Screen-Out of Hydraulic Fractures with Adequate Proppant Concentration.” Paper presented at the Low Permeability Reservoirs Symposium, Denver, Colorado, April 1993. doi: https://doi.org/10.2118/25892-MS
5. Cleary, M. P., Doyle, R. S., Teng, E. Y., Cipolla, C. L., Meehan, D. N., Massaras, L. V., and T. B. Wright. “Major  New Developments in Hydraulic Fracturing, with Documented Reductions in Job Costs and Increases in Normalized Production.” Paper presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, September 1994. doi: https://doi.org/10.2118/28565-MS
6. Massaras, Leon V., Dragomir, Alexanndru, and Daniel Chiriac. “Enhanced Fracture Entry Friction Analysis of the Rate Step-Down Test.” Paper presented at the SPE Hydraulic Fracturing Technology Conference, College Station, Texas, U.S.A., January 2007. doi: https://doi.org/10.2118/106058-MS
7. Massaras, Leon V., Massaras, Dimitri V., and Salim Al-Subhi. “The Median Ratio and Near Wellbore Friction: Useful Proppant Admittance Criteria for Design and Placement of Safe and Effective Propped Hydraulic Fracture Treatments.” Paper presented at the SPE/DGS Saudi Arabia Section Technical Symposium and Exhibition, Al-Khobar, Saudi Arabia, May 2011. doi: https://doi.org/10.2118/149092-MS
8. Massaras, Leon V., and Dimitri V. Massaras. “Real-Time Advanced Warning of Screenouts With the Inverse Slope Method.” Paper presented at the SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, February 2012. doi: https://doi.org/10.2118/150263-MS
9. Massaras, Leon, V. 2024. ‘Screenout Detection and Avoidance’. Contemporary Developments in Hydraulic Fracturing. IntechOpen. doi:10.5772/intechopen.112450
10. Nolte, Kenneth G., and Michael B. Smith. “Interpretation of Fracturing Pressures.” J Pet Technol 33 (1981): 1767–1775. doi: https://doi.org/10.2118/8297-PA

About the Author:

Leon Massaras is a highly experienced hydraulic fracturing consultant and educator, with more than 25 years of expertise in conventional and unconventional reservoirs. He holds a BS in Civil Engineering from the University of Massachusetts at Amherst and has worked in over 30 countries across five continents for Halliburton, Resources Engineering Systems (RES), and as an Independent Consultant. Leon has authored numerous papers and a book chapter, and has presented an SPE Webinar. He currently offers consulting and training services globally via FracMentor.com.

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