Approach Investigates Need for Extreme-Limited-Entry Applications
Authors: Carpenter Chris 
Published: May 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204185, “Practical Design Considerations for Stage Length, Perforation Clusters, and Limited-Entry Pressure Intensities,” by Paul Huckabee, SPE, Chris Ledet, SPE, and Gustavo Ugueto, SPE, Shell, et al. The paper has not been peer reviewed.

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This paper presents design considerations for determining practical dimensions and limits for interdependencies associated with stage length, perforation clusters, and limited-entry pressures. Aggressive limited entry has been an enabler for successful extended-stage-length applications. The authors challenge the need for extreme limited entry in resource development across multiple North American basins. This synopsis does not focus on field trial applications, which are provided in the complete paper.

Managing Threats to Stimulation Distribution Effectiveness (SDE) in New Completions
Before any discussion of recommendations and trial results for stage length, perforation clusters, and limited-entry pressure intensities, it is important to consider the threats and risks to effective stimulation distribution. The authors detail the following risks in the complete paper:
- Effective design and execution of limited-entry practices
- Proppant transport in horizontal wellbores
- Plug or ball leakage
- Cement channeling
- Casing erosion
- Equipment reliability (pumps and injection lines or manifold leaks)

How Much Limited-Entry Pressure Is Needed for Improved SDE?
Effective limited-entry design and application must consider the differentials of the following interdependent geomechanical variables with the risks mentioned previously:
- Fracture initiation pressure
- Minimum in-situ stress
- Fracture extension net pressure (process-zone stress)
- Near-wellbore complexity pressure drop and changes with slurry erosion
- Stress shadow effects (interstage, intrastage, and interwell)
A diagnostic that the authors have used to enable quantification of some of these critical variabilities is coiled-tubing-actuated cemented-sleeve-stimulation systems. In these systems, sleeves are actuated by setting the bridge plug and shifting the sleeve to the treatment, or open, position. The bridge plug isolates treatment pressures in the wellbore of the active treatment sleeve from other downhole sleeves. The treatment proppant slurry is pumped down the coiled tubing by casing annulus. Pressure communication exists to the coiled tubing, which enables pseudomeasurements of bottomhole-treatment pressures and trends through a dead-leg pressure measurement at surface. Operational practices include pumping a very low rate down the coiled tubing to ensure that solids are not allowed to enter the coiled tubing side of the bottomhole assembly, so the authors recognize that these are pseudo-dead-leg measurements. The frictional pressure drop in the coiled tubing is assumed to be negligible for their calculations.
If the downhole sleeves are left in the open position, an assessment of treatment isolation can be made. For sequential sleeve treatments, where good isolation exists between successive sleeves, some of the critical pressure differentials for different length dimensions in the lateral can be assessed. These length dimensions are limited to increments of the sleeve-spacing dimensions.