Summary

Limited-entry (LE) perforating is a well-established and cost-effective technique to stimulate unconventional oil and gas wells. Recent field tests integrating Fiber Optic (FO) technology demonstrate that fracture initiation and propagation is observed in most perforation clusters (PCs) throughout the clean fluid (pad) portion of the stimulation. However, LE treatment effectiveness during proppant slurry placement is highly impacted by several key parameters that may change significantly during stimulation. This paper shows how the combined results of FO Distributed Acoustic Sensing (DAS) data; treatment injection rates (Qi) & pressures (PTR); and LE calculations can be integrated to provide deeper insights into key variables that impact LE treatment efficiency.

Perforation diameter (D) and perforation discharge coefficient (Cd) are observed to increase significantly during the proppant slurry placement due to erosional effects. Qi may vary as a result of equipment reliability issues, design objectives, and stimulation practices. The data and diagnostics presented in this paper very conclusively show that failure to maintain desired perforation friction (Ppf) throughout slurry placement results in some portion of the PCs being under-stimulated.

This paper will demonstrate why it is important to understand the drop in Ppf due to perforation erosion should be accounted for in LE design and why the recommended practice of increasing rate throughout the hydraulic fracture treatment to maintain desired Ppf is the cornerstone of effective slurry distribution. Lastly, estimates of post-treatment D are presented, based on these observations, to estimate the change in perforation diameter due to proppant slurry erosion.

Introduction to LE Design Principles

Limited entry perforating was first pioneered by Murphy and Juch [1] as a cost-effective technique to stimulate multiple pay zones in vertical wells with varying in-situ stresses. Conventional completion techniques would involve blanket perforating the entire interval with 4 shots per foot. The technique was revolutionary in that it recommended "limiting" the number of perforations to distribute fracture stimulation fluids into multiple intervals with "variable physical characteristics".

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