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Perforation erosion and consequential changes to perforation friction pressure have a significant practical influence on limited entry hydraulic fracturing treatments and have been comprehensively documented (
The latest generation of borehole video cameras efficiently capture high definition images of erosion to individual perforations after hydraulic fracture treatment. Qualitative and quantitative evaluation of these images allow confirmation of proppant placement and fracture initiation depths that are resolved to the location of individual perforations. The methods described updates the previous work of Roberts,
In their goal for optimal recovery Stimulation Engineers, Geoscientists and Reservoir Engineers evaluating treatment success have a fundamental question to answer - where exactly did the frac go? This apparently simple question has hitherto proven difficult, and costly, to answer. We demonstrate that evaluating perforation erosion provides straightforward and intuitive data to precisely confirm proppant placement, define the origin of individual fractures and help quantify treatment distribution.
We present results illustrating the effectiveness of the method including examples of acquired perforation images. New methods are introduced demonstrating evaluation techniques used to confirm proppant transport through specific perforations, fracture initiation and treatment consistency. Initial work to demonstrate in-situ correlation between erosion and pumped proppant volume / weight is presented.
We conclude that the method can be successfully applied to evaluate changes to stimulation treatment design parameters such as stage length, cluster number and spacing, proppant and fluid properties, pumping criteria and many aspects of perforation design including perforation charge type, count per stage and cluster and shot orientation.
Existing hydraulic fracture diagnostic methods are limited in number, scope and sometimes accuracy. Analysis of in-situ perforation erosion using visual analytics provides an additional and complementary data source to evaluate the success of engineered treatment programs. The method provides measurements at a depth resolution that is not otherwise possible, allowing specific entry holes and fracture initiation points to now be evaluated.
Recent step changes in downhole video technology and image analysis have coincided with a growing understanding of how perforation erosion can be used to measure the effectiveness of limited entry hydraulic fracturing. This has led to rapid growth in video-based perforation imaging and produced a substantial database of measured and statistically analysed perforations. A review of recurring patterns and common trends identified in the database provides useful insights on proppant placement and distribution.
An analysis was undertaken on a dataset that includes detailed individual perforation dimensions from more than 6,000 clusters and 600 stages. With a focus on understanding the uniformity of proppant distribution, the initial phase was to identify significant recurring patterns in cluster level proppant placement derived from perforation erosion measurements. Multiple treatment design parameters were then analysed to understand their influence on proppant distribution. Among those considered were stage length, number and spacing of clusters per stage, the number of perforations shot per cluster, perforation charge type and phasing.
While every well produces a unique set of results, several recurring trends were identified across the database. These often indicated sub-optimal proppant placement with undesirable consequences for production and ultimate recovery. Results demonstrate that Proppant placement is often significantly non-uniform across a stage A strong tendency for greater heel-side perforation erosion is typically observed for ‘geometric’ stage and cluster designs A similar strong preference for proppant to be placed in perforations located towards the low-side of the wellbore is also apparent More uniform proppant distribution can be obtained using an engineered design approach Although they are often inter-related several treatment parameters can be engineered with relative ease to produce more uniform proppant placement
Proppant placement is often significantly non-uniform across a stage
A strong tendency for greater heel-side perforation erosion is typically observed for ‘geometric’ stage and cluster designs
A similar strong preference for proppant to be placed in perforations located towards the low-side of the wellbore is also apparent
More uniform proppant distribution can be obtained using an engineered design approach
Although they are often inter-related several treatment parameters can be engineered with relative ease to produce more uniform proppant placement
Analysis methods, results, treatment parameter considerations, primary conclusions and other relevant findings will be discussed in detail.
The majority of research on treatment design parameters that influence proppant placement has mainly used CFD-DEM models. The approach presented in this paper, however has used empirical, in-situ data. The size of the dataset and the frequency at which certain tendencies are observed provide some confidence that the approach and results are valid and can help improve treatment design. It is hoped that the results of the study will provide hydraulic fracture specialists with further evidence-based guidelines that ultimately help increase production and enhance ultimate recovery.
Abstract Fracture treatments and stage designs for new wells have evolved considerably over the past decade contributingto significant production growth. For example, in the acreage discussed hererecently used higher intensity fracturing methods provided an ~80% increase in recovery rates compared with legacy wells. Older wells completed originally with less efficient techniques can also benefit from these more up-to-date designs and treatments using re-fracturing methods. These offer the prospect of economically boosting production in appropriately selected wells. While adding in-fill wells has often been favored by Operators as a lowerrisk option the number of wells being re-fractured has grown every year for the last decade. In this case study two adjacent Eagle Ford wells, comprising a newly completed and a re-fractured well, allow both methods to be considered and compared. Completion design and fracture treatment effectiveness are evaluated using the uniformity of proppant distribution at cluster and stage level as the primary measure. Perforation erosion measurements from downhole video footage is used as the main diagnostic. Novel data acquisition methods combined with successful well preparation provided comprehensive and high-quality datasets. The subsequent proppant distribution analysis for the two wells provides the highest confidence results presented to date. Clear, repeatable trends in distribution are observed and these are compared across multiple stage designs for both the newly completed and re-fractured well. Variations in design parameters and how these effects distribution and ultimately recovery are discussed. These include changes to perforation count per cluster, cluster spacing, cluster count per stage, stage length, perforation charge size and treatment rates and volumes. As a final consideration production records for the evaluated wells are also discussed. Historical industry data shows that the number of wells being re-fractured increases relative to the number of newly drilled wells being completed during periods of low oil and gas prices. With the industry again facing harsh economic realities an increasing number of decisions will be made on whether new or refractured wells, or a combination of both, provide the best solution to replace otherwise inevitable production decline. This paper attempts to provide a detailed understanding of how proppant distribution, as a significant factor in production for hydraulically fractured wells, can be evaluated and considered in these decisions.
Abstract Perforation-imaging studies have indicated highly variable results on effectively treating all perforation clusters within a given fracturing stage in horizontal well plug-and-perf applications, even when limited entry designs were used. A field test was executed to trial differing perforating designs and levels of perforation friction for identifying a preferred technique for evenly distributing treatment volume along the lateral. The test was implemented in a horizontal well in the Eagle Ford formation of south Texas. After treatment and plug drill-out operations were completed, a downhole camera was run to visualize perforation entry holes along the entire lateral section. Shaped perforating charges described as equal entry hole charges were used in all stages. The resulting images were analyzed to determine entry hole dimensions and erosion characteristics to determine if alternate perforating strategies provided improved results, as compared to the standard design of multi-phase perforating with 1200 psi of perforation friction. Test results indicate that orienting perforations in a straight line (zero-phase) along the high side of the wellbore significantly improved treatment distribution among perforation clusters. Oriented perforating achieved this benefit without needing to increase initial perforation friction beyond the area standard of 1200 psi. Another result from this project was development of a statistical process for evaluating perforation entry hole erosion data. Entry hole erosion datasets are complex and difficult to analyze. The statistical process presented in this paper demonstrates a clear way to compare the effectiveness of different perforation designs. This paper also covers the operational difficulties encountered during the project which added complexity to analyzing the results. Lastly, this paper offers suggestions for future modifications for oriented perforation designs to further improve limited entry effectiveness.
Abstract This paper presents the continuing evolution of our Bakken advanced completion design with the added enhancement of Extreme Limited Entry (XLE) perforating. With this cost-effective XLE strategy, we are consistently stimulating more than eleven perforation clusters per stage. Confirmation of this high number of active clusters, or fracture initiation points, has been directly measured with radioactive tracers and fiber optic diagnostics, and more importantly, is validated through improved production relative to offset completions. The goal of this strategy is to consistently and confidently drive a high number of clusters per stage, ultimately increasing capital efficiency by right sizing the cluster and stage count per well. Practically, the number of stages for a 9,500-ft. lateral is limited to 40 or 50 stages in the Bakken due to operational and cost limits. We believe the published trends on stage count are fundamentally linked to the number of active clusters per stage or fracture initiation points, and by driving significantly more active clusters per stage with XLE perforating in combination with previously presented High Density Perforating (HDP), we now have proven the ability to reduce stage count without sacrificing performance. Liberty now incorporates XLE as a key design technique to successfully stimulate 15 clusters per stage. Production performance is encouraging and post frac fiber optic diagnostics support prior radioactive proppant tracer data in showing that over 11 of the 15 clusters shot can be stimulated with slickwater at 80 bpm. XLE operational considerations for frac plug ratings, oriented perforating, even-hole perforating charges, variable pipe friction and a review of existing papers on limited entry are included as well. Limited entry perforating has been around for over 50 years; however, its effectiveness has been limited in the horizontal revolution due to insufficient perforation friction relative to the variability in stress and near-wellbore tortuosity found within a stage. This paper presents the improved results for specifically designing perforations and stimulation injection rates to achieve diversion to almost all 15 perforation clusters per stage. For this paper, we define XLE as completion designs with perforation friction exceeding 2,000 psi. Since the beginning of 2015 we have reduced our standard stage count from 50 down to 27, for a 9,500-ft lateral, while continuing to significantly outperform offset operators. When it comes to value creation, the cost per barrel of oil produced is a critical metric to assess development opportunities and achieving the same or increased oil production with less capital has led to significant gains in capital efficiency.