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 (Cramer 1987), (Crump, Conway 1988), Long (2015) and others. Both effects are widely acknowledged but undesirable phenomena that stimulation specialists encounter and must mitigate during every treatment. The emergence of the alternative fracture diagnostic method described in this paper means however that perforation erosion can also have beneficial consequences for those trying to diagnose and optimize fracturing performance. 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, Lilly and Tymons (2018) to now directly quantify perforation erosion. This improves the identification of clusters that have been successfully stimulated against those that are under or over-stimulated. Measurement and comparison of perforation erosion, area, diameter and azimuth permit a statistical evaluation of the consistency of fracture distribution across clusters and stages. 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 thatProppant placement is often significantly non-uniform across a stageA strong tendency for greater heel-side perforation erosion is typically observed for ‘geometric’ stage and cluster designsA similar strong preference for proppant to be placed in perforations located towards the low-side of the wellbore is also apparentMore uniform proppant distribution can be obtained using an engineered design approachAlthough 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.

Technology to interrogate perforations to quantify cluster efficiency in limited entry, plug and perf completions has improved in operational efficiency, image quality and quantity. The entire pipe wall of the lateral is now visually imaged, and the discovery of significant casing erosion damage caused by leaking frac plugs during stimulations is easily observable, often multiple times in the same well. The effect of a breached casing with significant erosion between stages could potentially divert proppant from the intended perforation targets leading to reduced cluster efficiency and uncertainty of proppant distribution results. Video images have been used for several years to evaluate proppant distribution. The recent introduction of array side-view camera technology now provides highly detailed images of the full 360 circumference of the wellbore over extended intervals. Image logging methods for unconventional wells have changed from capturing a limited number of images of individual perforations through a small ‘spy hole’ to a complete panoramic view of the entire wellbore. Perforations, connections and everything in between can be efficiently imaged and analysed. Enhanced processing methods have additionally improved visualization of results and allowed quantification of areas of interest with image-based dimensioning. Greatly enhanced borehole image coverage has allowed the discovery of unintended interactions that can be very detrimental to fracture treatments. Evidence of these unwanted effects that were previously difficult to diagnose are now uncovered during routine fracture diagnostics. Evidence includes Erosion at plug setting depths has been observed in a relatively high proportion of wells Multiple casing breaches have also been observed in some wells with as many as 35% of plug setting depths subject to this issue The areal extent of erosion at plugs has been measured in the range of 10% of the casing circumference up to 100% full parting While the exact effects on the fracture treatment of potentially large volumes of fluid and proppant being diverted away from their intended target has not yet been quantified the catastrophic effect on well integrity is very clear. Examples, analysis methods, results, primary conclusions, and other relevant findings are discussed in detail. The technology we discuss is undoubtedly helping raise awareness in the industry of the potential extent of this previously under-diagnosed issue. Increased awareness and improved understanding of the issue will lead operators to better equipment selection, enhanced procedures and ultimately more productive and profitable wells. Hydraulic fracture performance will improve while cases of compromised well integrity will decline.

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