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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.
Summary The primary objectives of perforating a lengthy cased‐and‐cemented wellbore section for fracture stimulation are to enable extensive communication with the reservoir and control the allocation of fluid and proppant into multiple intervals as efficiently as possible during fracturing treatments. Simultaneously treating multiple intervals reduces the number of fracture stages required, thus reducing treatment cost. One way to control the allocation is to use limited‐entry perforating. Execution and optimization of limited‐entry perforating requires awareness of the factors that can affect performance. This paper presents a case study of plug‐and‐perforate horizontal‐well treatments in an unconventional shale play in which various diagnostic methods were used to better understand these factors. Within the case study, three types of perforation‐evaluation diagnostics were implemented: injection step‐down tests and pressure analysis of the fracturing treatments, video‐based perforation imaging, and distributed acoustic sensing (DAS). Injection step‐down tests indicated that all perforations were initially accepting fluid. Surface‐pressure analysis of the main fracturing treatments indicated that in certain cases, several perforations were not accepting fluid and proppant (slurry) by the end of the job. Video‐based imaging indicated that a large majority of perforations showed unambiguous evidence of significant proppant entry. Evaluation of the erosion patterns on the perforations showed a positional bias where for a given fracture stage, perforations in clusters nearest the heel of the well were more eroded than perforations in clusters nearest the toe of the well. DAS analysis showed a positional bias, allocating more slurry volume to clusters nearest the heel of the well. However, DAS analysis also showed that changing the number of perforations in a cluster had a larger effect than the positional bias. The results of the case study indicated that a staggered perforation design using more gradual changes among clusters would lead to a more balanced treatment. This scenario was evaluated along with a job design featuring high excess perforation friction and an equal number of perforations in each cluster. Fracture‐simulation runs indicated that both tactics are likely to improve slurry allocation.
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.
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.
Abstract The primary objectives of perforating a lengthy cased-and-cemented wellbore section for fracture stimulation are to 1.) enable extensive communication with the reservoir and 2.) control the allocation of fluid and proppant into multiple intervals as efficiently as possible during fracturing treatments. Simultaneously treating multiple intervals reduces the number of fracturing stages required, thus reducing treatment cost. One way to control the allocation is to use limited entry perforating. Limited entry is the process of either limiting the number of perforations or reducing the size of the perforation entry-hole to achieve significant perforation friction pressure during a hydraulic fracturing treatment. Perforation friction establishes a backpressure in the wellbore that helps to allocate flow among multiple, simultaneously-treated perforation intervals/clusters that have differing fracture propagation pressures. Execution and optimization of limited entry perforating requires awareness of the factors that can affect performance. This paper presents a case study of plug-and-perf horizontal well treatments in an unconventional shale play in which various diagnostic methods were used to better understand and quantify these factors. Within the case study, three types of perforation evaluation diagnostics were implemented: 1.) injection step-down tests and pressure analysis of the fracturing treatments, 2.) video-based perforation imaging and 3.) distributed acoustic sensing (DAS). Injection step-down tests indicated that all perforations were initially accepting fluid. However, history-matched solutions of step-down tests are non-unique due to multiple variables involved in the calculations and uncertainty regarding the exact initial-perforation conditions. Surface pressure analysis of the main fracturing treatments indicated that in certain cases, several perforations were not accepting fluid and proppant (slurry) by the end of the job. The number of inactive perforations was typically equivalent to the amount contained in two clusters. Video-based imaging highlighted several trends and concepts for perforating. Zero-phase perforating toward the high side of the well was advantageous for obtaining quality images and relatively consistent perforation dimensions. A large majority of perforations showed unambiguous qualitative evidence of significant proppant entry. Even though images captured were post-stimulation, it was apparent that initial perforation dimensions were significantly smaller and gun phasing had a more significant effect than originally predicted. Evaluation of the erosion patterns on the perforations showed a positional bias where for a given frac stage, perforations in clusters nearest the heel of the well were more eroded than perforations in clusters nearest the toe of the well. Distributed acoustic sensing (DAS) analysis confirmed the conclusions of the surface pressure analysis. In the example provided, the data showed all clusters accepting fluid during the step-down test. Later in the stage, the DAS data showed two clusters not accepting fluid at different times of the stage. DAS analysis was able to confirm the timing and position of the two clusters. The DAS data also showed a positional bias, allocating more slurry volume to clusters nearest the heel of the well. However, DAS analysis also showed that changing the number of perforations in a cluster had a larger effect than the positional bias. The staggered perforation design featuring two fewer perforations in the cluster closest to the heel effectively counteracted the positional bias but resulted in diverting too much slurry volume from that cluster. The results also highlight the importance of perforator quality control in terms of perforation hole size. Treating pressure and DAS analysis indicated a particular cluster stopped taking slurry relatively early in the treatment and post-frac imaging dimensioned the hole sizes and revealed they were extremely undersized from the expected hole size. Based on the results of the case study, it was recommended to use a staggered perforation design with more gradual changes. This was verified with modeling using updated parameters which showed that the resulting changes are likely to improve slurry allocation.