This paper presents design considerations and field trial applications for determining practical dimensions and limits for interdependencies associated with stage length, perforation clusters and limited entry pressures. Recent applications by multiple authors and companies have begun to reverse the decade-long trend of reducing stage length and perforation spacing, in favor of extending stage lengths, to capture free cash flow value for unconventional resource development. Aggressive limited entry has been an enabler for successful extended stage length applications. Multiple authors have advocated "eXtreme Limited Entry" (XLE) applications. We present diagnostics data and applications that challenges the need for XLE and better constrains the necessary amount of limited entry pressures for effective stimulation distribution for resource development across multiple North American Basins.Data is presented from integrated application of field trials, stimulation distribution diagnostics, and well performance analysis. Field trials and well performance analysis are from the Permian Delaware Basin Wolfcamp. The field trials include both: greater perforation cluster intensities for base design stage lengths; and extended stage lengths of 50% greater than the base designs. Diagnostics are from multiple North American Basins and include discrete treatment pressure diagnostics and optic fiber distributed sensing. Data is presented to quantify the magnitude and variability for components necessary for maintaining active fracture extension for multiple perforation clusters. Components include: fracture breakdown pressures; in-situ stress, net fracture extension pressure, and near wellbore complexity pressure drop.Data and examples are presented from multiple wells, and resource development areas, to show the variability in measured treatment pressures for different length scale dimensions. This variability is used to determine the amount of limited entry pressure required to maintain fracture extension, dependent on the stage length dimension. Although Aggressive Limited Entry (ALE) is generally required to enable effective stimulation distribution and extended stage lengths in multiple cluster stages, examples are presented that demonstrate XLE is generally not required. We also discuss some of the considerations and observations that limit perforation cluster spacing intensities. Well performance data from the field trials is presented to validate the applications.This work demonstrates the value of integrated application of field trials, stimulation distribution diagnostics, and well performance analysis to capture free cash flow value from improved completions and stimulation designs. The discussion will include an assessment of future opportunities for further extension of stage length dimensions.
Comprehensive and integrated diagnostics associated with the NETL-GTI Hydraulic Fracture Test Site 2 (HFTS2) in the Permian Delaware Basin enabled a unique opportunity to evaluate stimulation distribution effectiveness (SDE) in the wellbore, near-well and far-field regions (WBR, NWR, FFR) for upper Wolfcamp completions. This paper will summarize the experimental design, execution and analysis for HFTS2 well completions. Results and observations are translated into applications and opportunities for Wolfcamp completions and resource development optimization. A Completions Sub-Committee was created to allow for broad industry input to design the scope of trials to be considered for execution in the HFTS2 wells. Primary objectives were to evaluate Stimulation Distribution Effectiveness (SDE) and test eXtended Stage Lengths (XLS) for stimulation value opportunities. Trials included: 1) HFTS2 operator base-plan completions; 2) more Aggressive Limited Entry (ALE) practices; 3) tapered number of perforations per cluster; and 4) XLS up to ∼ 330’ stage lengths, with ALE practices. Diagnostics included multiple wells with Optic Fiber and Step-Down Tests to evaluate stimulation domain characteristics in the WBR, NWR and FFR regions. The combination of multiple wells with permanent optic fiber installed, and controlled sequencing the stimulation treatment placement operations, enabled good understanding of the frac domains created in the WBR, NWR and FFR. Evaluation of the base-design completions demonstrated good SDE for most applications, from the optic fiber distributed sensing. EXtreme-Limited-Entry (XLE) applications were determined to not be necessary for SDE in the Permian Wolfcamp. Tapered perforation designs were not necessary for good SDE. Risks to SDE were clearly observed with injectivity loss due to mechanical problems with the pumping operations. Risks to SDE were also observed when stage isolation was not effective. Extended Stage Lengths (XLS), up to ∼ 330’ stage lengths with 10 perforation clusters, were generally effective with ALE practices. Acquiring and maintaining injection rate was critical for the higher cluster count stages. The FFR stimulation domain dimensions were generally consistent with the WBR dimension distributions. Significant non-uniformity was observed in the FFR at a cluster dimension resolution. There was good correlation with domain dimensions in the FFR when there was lack of stage isolation the treatment well. Staggered landing depths of the wells, and an instrumented vertical monitor well, enabled assessment of vertical fracture geometry characteristics. Application of integrated diagnostics for completion and stimulation design evaluation enabled assessment of multiple designs in just a few wells. Optic Fiber Distributed Acoustic, Temperature and Cross-Well Strain Sensing (DAS, DTS & DSS), in combination with selective Step-Down Tests, enabled evaluation of stimulation domain characteristics in the WBR, NWR and FFR regions. The results and observations enabled greater confidence for timely completions, stimulations and resource development applications for the Permian Delaware Basin.
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