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Shammam, F. O. (Missouri University of Science and Technology) | Alkinani, H. H. (Missouri University of Science and Technology) | Al-Hameedi, A. T. (Missouri University of Science and Technology / American University of Ras Al Khaimah) | Dunn-Norman, S. (Missouri University of Science and Technology) | Al-Alwani, M. A. (Missouri University of Science and Technology)
Abstract Over the past decade, the oil industry witnessed an expansion in the refracturing activates instead of drilling and fracturing new wells. This work aims to test the efficiency of the refracturing treatments by analyzing the post refracturing production trend of wells in the most active shale plays in the United States (Bakken, Niobrara, Marcellus, Permian, Eagle Ford, Barnett, and Haynesville). FracFocus was used to collect data of more than 130,000 wells in the United States completed between 2012 and 2019. In this study, 39 refractured wells (Barnett wells were vertical, Niobrara wells were deviated, and the other shale plays were horizontal) in the created database were further processed by adding their production data to analyze the production data of the refractured wells and test the efficiency of refracturing as a stimulation technique to increase production. In terms of production gain, the results showed that the selected wells in the Eagle Ford shale play yielded the highest production gain from refracturing with a 174% increase of production post refracturing followed by Bakken (160%), Marcellus (133%), Barnett (46%), Niobrara (43%), Haynesville (34%), and Permian (32%), respectively. Overall, the highest production gain from refracturing is achieved during the second month after refracturing and the decrease of production gain starts during the third month after refracturing. On the other hand, the results showed that there are more factors than formation type and perforation length that need to be considered to predict the production response of refracturing as some wells showed a high gain during the first three months after refracturing, while other wells showed a lower production gain during the first three months after refracturing. Moreover, the refracturing operations have shown a production increase in vertical, deviated, and horizontal wells. Introduction Since the oil price drop in 2011, refracturing old wells and producing from shale reserves have become a new trend in the oil industry in the United States. Refracturing operations aim to maximize production through refracturing old fractured wells (Jacobs, 2015). The technology itself is not new and it has been known and active in the United States since the 1970s. However, the process of refracturing horizontally drilled multi-staged wells is a new technology that started to appear in the industry back in 2011 (Dutta, 2017). Since the oil price drop in 2011, refracturing shale reserves started to emerge in the industry due to the size of the unconventional reserves and the economic viability of producing through refracturing (King, 2014). To highlight the economic efficiency of refracturing, when comparing the cost of refracturing an existent well and fracturing a new well in the Eagle Ford, it was found that the cost of producing through a refracture is 1 to 1.5 million dollars, while the profit of producing through a new fracture is estimated to be 2 to 4 million dollars (Fu et al., 2017). Refracturing operations have some drawdowns associated with the availability of data on the surface and their rate of success is determined by many factors (Yanfang & Salehi, 2014). Therefore, it is important to consider all the associated factors of success of a refracturing operation and include a refrac plan in the initial stage of the well development phase to get a high return of investment in a short period (Dutta, 2017). One of the main factors of the refracturing operation success is the formation of the refrac. The refracture formation depends on the pressure distribution around the pre-existent fracture and the cluster spacing between the fracture stages. In some cases, a new fracture would be initiated and reaching more of the un-depleted spots in the reservoir, which dramatically increases the production of the well. However, in other cases, the refracture would be initiated through reopening the initial fracture (Fu et al., 2017). All these factors contributing to the refracture formation can lead to a high level of uncertainty that requires an intensive analysis of data before starting a refracturing operation.
Travers, Patrick (Dolan Integration Group) | Burke, Ben (HighPoint Resources) | Rowe, Aryn (HighPoint Resources) | Hodgetts, Stephen (Dolan Integration Group) | Dolan, Michael (Dolan Integration Group)
Abstract Scope: The management, treatment and disposal of hydraulic fracturing flowback fluids and produced water presents a major challenge to operators. Though the volumes of water are tracked closely during operations, the sources of that water are not well understood. The objective of this study is to apply a cost effective and proven technique, stable isotope analysis, along with an extensive sampling program (n>1,500 samples) to describe the contributions of variable water sources through completions, flowback and the production lifecycle of multiple horizontal, hydraulically fractured wells in the Denver Basin, Colorado. Methods: The water stable isotopes of hydrogen (H and H) and oxygen (O and O) are conservative tracers and particularly advantageous because they occur naturally in these systems and rely on well-established scientific and analytical techniques. Sample collection is simple and does not require specialized equipment or operational downtime. 80 horizontal, hydraulically fractured wells completed in the Cretaceous Niobrara or Codell Formations were selected for this study. More than 1,500 samples were collected and analyzed in total, including: baseline samples of the source water used to stimulate the well, time series samples collected at daily or semi-daily intervals during the early weeks of flowback, and samples collected several months after the wells were brought on production. Samples of produced water were also collected from legacy wells in the field as well as offset wells being monitored for frac hits during completions. Results: Samples of the near surface and shallow aquifer source water collected prior to hydraulic fracturing fell on or near the global meteoric water line (GMWL) as defined by Craig (1961). This isotopic signature is expected for modern water in aquifers charged by precipitation. In contrast, samples collected during flowback and production were significantly enriched in H and O. Furthermore, the magnitude of the isotopic difference between the source and flowback water increased with time until equilibrating after several months. This equilibrated composition is consistent for Niobrara and Codell wells in the field, as well as legacy wells sampled and consequently is hypothesized to be indicative of native formation water. The study did find exceptions, particularly with wells known to be connected to major fault or fracture networks. These samples deviated from typical formation water signatures, potentially indicating the migration of deeper sourced fluids or the vertical mixing of shallower fluids with Cretaceous waters. Significance: The scale of this study is unique in the literature and provides novel and comprehensive insight into the dynamics of flowback and the sources of produced water in the Denver Basin. This study demonstrates that these data can clearly differentiate water injected during stimulation from native formation waters, as well as track the magnitude and duration of well cleanup. It can also identify wells that may be producing water with a unique composition due to fluid migration through faults or fracture networks or due to nearby well communication.
Rosenhagen, Nicolas M. (Colorado School of Mines) | Nash, Steven D. (Anadarko Petroleum Corporation) | Dobbs, Walter C. (Anadarko Petroleum Corporation) | Tanner, Kevin V. (Anadarko Petroleum Corporation)
Abstract The volume of stimulation fluid injected during hydraulic fracturing is a key performance driver in the horizontal development of the Niobrara formation in the Denver-Julesburg (DJ) Basin, Colorado. Oil production per well generally increases with stimulation fluid volume. Often, operators normalize both production and fluid volume based on stimulated lateral length and investigate relationships using "per-ft" variables. However, data from well-based approaches commonly display such wide distributions that no useful relationships can be inferred. To improve data correlations, multivariate analysis normalizes for parameters such as thermal maturity, depth, depletion, proppant intensity, drawdown, geology and completion design. Although advancements in computing power have decreased cycle times for multivariate analysis, preparing a clean dataset for thousands of wells remains challenging. A proposed analytical method using publicly available data allows interpreters to see through the noise and find informative correlations. Using a data set of over 5000 wells, we aggregate cumulative oil production and stimulation fluid volumes to a per-section basis then normalize by hydrocarbon pore volume (HCPV) per section. Dimensionless section-level Cumulative Oil versus Stimulation Fluid Plots ("Normalization" or "N-Plot") present data distributions sufficiently well-defined to provide an interpretation and design basis of well spacing and stimulation fluid volumes for multi-well development. When coupled with geologic characterization, the trends guide further refinement of development optimization and well performance predictions. Two example applications using the N-Plot are introduced. The first involves construction of predictive production models and associated evaluation of alternative development scenarios with different combinations of well spacing and completion fluid intensity. The second involves "just-in-time" modification of fluid intensity for drilled but uncompleted wells (DUC's) to optimize cost-forward project economics in an evolving commodity price environment.
Abstract In some basins, large scale development of unconventional stacked-target plays requires early election of well targeting and spacing. Changes to the initial well construction framework can take years to implement due to lead times for land, permitting, and corporate planning. Over time, as operators wish to fine tune their development plans, completion design flexibility represents a powerful force for optimization. Hydraulic fracturing treatment plans may be adjusted and customized close to the time of investment. With a practical approach that takes advantage of physics-based modeling and data analysis, we demonstrate how to create a high-confidence, integrated well spacing and completion design strategy for both frontier and mature field development. The Dynamic Stimulated Reservoir Volume (DSRV) workflow forms the backbone of the physics-based approach, constraining simulations against treatment, flow-back, production, and pressure-buildup (PBU) data. Depending on the amount of input data available and mechanisms investigated, one can invoke various levels of rigor in coupling geomechanics and fluid flow – ranging from proxies to full iterative coupling. To answer spacing and completions questions in the Denver Basin, also known as the Denver-Julesburg (DJ) Basin, we extend this modeling workflow to multi-well, multi-target, and multi-variate space. With proper calibration, we are able generate production performance predictions across the field for a range of subsurface, well spacing, and completion scenarios. Results allow us to co-optimize well spacing and completion size for this multi-layer column. Insights about the impacts of geology and reservoir conditions highlight the potential for design customization across the play. Results are further validated against actual data using an elegant multi-well surveillance technique that better illuminates design space. Several elements of subsurface characterization potentially impact the interactions among design variables. In particular, reservoir fluid property variations create important effects during injection and production. Also, both data analysis and modeling support a key relationship involving well spacing and the efficient creation of stimulated reservoir volumes. This relationship provides a lever that can be utilized to improve value based on corporate needs and commodity price. We introduce these observations to be further tested in the field and models.
Abstract Unconventional completions in North America have seen a paradigm shift in volumes of proppant pumped since 2014. There is a clear noticeable trend in both oil prices and proppant volumes – thanks to low product and service costs that accompanied the oil price crash in early 2015. As the industry continues to recover, operators are reevaluating completion designs to understand if these proppant volumes are beyond what is optimal. This paper analyzes trends in completion sizes and types across all major unconventional oil and gas plays in the US since 2011 and tracks their impact on well productivity. Completion and production data since 2011 from more than 70,000 horizontal wells in seven major basins (Gulf Coast, Permian, Appalachian, Anadarko, Haynesville, Williston and Denver Julesburg basins) and 11 major oil/gas producing formations were analyzed to examine developments in proppant and fluid volumes. Average concentration of proppant per gallon of fluid pumped was used to understand transitional trends in fracturing fluid types with time. Production performance indicators such as First month, Best 3 or Best 12 months of oil and gas production were mapped against completion volumes to evaluate if there are added economic advantages to pumping larger designs. In general, all major basins have seen progressive improvements in average well performance since 2011, with the Permian Basin showing the highest improvement, increasing from an average first-six-months oil production of 25,000 bbl in 2011 to 75,000 bbl in 2017. The Gulf Coast basin, where the Eagle Ford formation is located, has seen a 6-fold increase in proppant volumes pumped per foot of lateral since 2011 while the Permian and Appalachian basins hit peak proppant volumes in 2015 and 2016 respectively. In Permian and Eagleford wells, higher proppant volumes in general have resulted in better production up to a certain concentration. In Williston and Denver basins, most operators are moving away from gelled fluids, and reduced average proppant concentration per fluid volume pumped shows inclination toward hybrid or slickwater designs. While some of these observations are tied to reservoir quality, proppant volumes have begun to peak as operators have either reached an optimal point or are in the process of reducing volumes. Demand for proppant is expected to nearly double by 2020. As oil prices continue to recover, well AFEs continue to increase, despite multiple efforts to improve capital efficiency. The need for enhanced fracture conductivity and extended half-lengths on EURs are been discussed by combining actual observed production data and sensitivities using calibrated production models. The industry is moving toward large-volume slickwater fracturing operations using smaller proppants, but he operating landscape is expected to see a correction when such designs become less economical.
Abstract Accelerating the learning curve in the development of the Vaca Muerta utilizing lessons learned in North American unconventional resource plays is the focus of this paper. Reducing completion costs while maintaining high productivity has become a key objective in the current low-price environment. Completion diagnostics have been demonstrated to optimize stimulation and completion parameters that have shaped successful field developments. The paper reviews stimulation diagnostic data from wells completed in the Tuscaloosa Marine Shale, Eagle Ford, Wolfcamp and Niobrara shale formations. Case histories are presented in which proppant and fluid tracers were successfully employed in completion optimization processes. In the examples presented, diagnostic results were used to assess the stimulation of high productivity intervals within a target zone, evaluate various completion methods, and optimize stage and cluster spacing. The diagnostic data were compared with post-frac production rates in an effort to correlate completion changes with well performance. Results presented compare first, engineered perforations versus conventional geometrically spaced perforations to drive up effectiveness in cluster stimulation. Second, new chemistries, such as nanosurfactant, versus conventional chemistries to cut either completion cost or prove their profitability. Third, employing an effective choke management strategy to improve well productivity. Last, as in any stacked pay, determining fracture height growth in order to optimize well density, well spacing, field development and ultimately the recovery of the natural resources. Completion effectiveness is shown to be improved by landing laterals in high productivity target intervals, increasing proppant coverage across the lateral by utilizing the most effective completion methods, optimizing cluster spacing and decreasing the number of stages to reduce completion costs while achieving comparable production rates. Cluster treatment efficiency (CTE), in particular, has become a critical metric when optimizing hydraulic fracturing treatment designs based on current and future well densities. It can be used to rationalize well performance as well as to identify possible candidates for a refrac program. Using completion diagnostics, successful completion techniques were identified that led to production enhancements and cost reductions in prolific plays such as the Tuscaloosa Marine Shale, Eagle Ford, Wolfcamp and Niobrara.
ABSTRACT: Heterogeneity of an unconventional reservoir is one of the main factors affecting production. Well performance depends on the size and efficiency of the interconnected fracture “plumbing system”, as influenced by multistage hydraulic fracturing. A complex, interconnected natural fracture network can significantly increase the size of stimulated reservoir volume, provide additional surface area contact and enhance permeability. The purpose of this study was to characterize the natural fracture patterns occurring in the unconventional Niobrara reservoir and to determine the drivers that influenced fracture trends and distributions. Highly fractured areas/fracture swarm corridors were identified and integrated into a reservoir model though DFN (Discrete Fracture Network) application for further prediction of reservoir performance using reservoir simulations. The predictive capability of DFN models can aid in improved reservoir performance and hydrocarbon production through optimized well spacing, re-frac stage locations planning for existing wells as well as completion strategies design for new wells.
The Niobrara Shale in the United States has ramped up into a hot play that could soon bring an explosion of horizontal drilling in Colorado and Wyoming. The combination of horizontal drilling and multistage hydraulic fracturing is transforming the Niobrara from a target that has been drilled vertically and primarily for gas for nearly 100 years into a liquids-rich play that is capturing considerable attention. Speaking at the 2011 SPE Annual Technical Conference and Exhibition in Denver, John Ford, general manager of Colorado’s Wattenberg field at Anadarko, described the growing Niobrara activity as “really the next big thing.” That optimism was understandable. In November, Anadarko announced that its leases at Wattenberg may hold more than a billion barrels of recoverable oil and natural gas. The statement noted company drilling success in 11 recent wells at the field, including the Dolph 27-1HZ horizontal well that showed initial production of more than 1,100 B/D of oil and 2.4 MMcf/D of natural gas. These latest wells have given the company confidence that it can drill between 1,200 and 2,700 wells in northeast Colorado, with approximately 160 wells planned for this year. Based on results so far, the company expects ultimate recovery of between 500 million and 1.5 billion bbl of oil, natural gas liquids, and natural gas on an equivalent basis. Anadarko is not alone. Chesapeake Energy, Noble, Encana, and EOG Resources are among the largest acreage holders and the most active drillers of many companies—including numerous small independents—probing the Niobrara. Majors such as Shell and Marathon Oil have significant acreage. There are more than 50 operators in or near the Wattenberg field alone. Situated north/northeast of the Denver area, Wattenberg is the largest producing field in the Denver-Julesburg (D-J) Basin and one of the largest onshore oil and gas fields in the US. Reservoir Rock and Producing Regions Although the Niobrara is usually referred to as a shale, its reservoir rock consists primarily of limestone or chalk intervals, said Steve Sonnenberg, professor of petroleum geology at Colorado School of Mines in a recent edition of the AAPG Explorer (published by the American Association of Petroleum Geologists). “The formation demonstrates facies changes that range from limestone and chalk in the eastern end to calcareous shale in the middle and eventually transitioning to sandstone farther west,” said Sonnenberg, a past president of AAPG. “Depth and thickness are highly variable.”
Abstract A case study comparing the performance of wells fractured with crosslinked guar and hydroxypropyl guar (HPG) is presented. Data indicates that for a given crosslinked system, guar and HPG polymers yield comparable proppant pack impairment and fracture polymers yield comparable proppant pack impairment and fracture conductivity. Detailed laboratory conductivity and well performance data are presented for both low and high temperature conditions. Laboratory conductivity data is reported for proppant placed with guar and HPG crosslinked fracturing fluids under in-situ conditions. The effects of proppant embedment. the gel filter cake, and long-term exposure to reservoir temperature and closure stress were determined in this study. Additionally, the effect of crosslinker, breaker system, and polymer load on fracture conductivity is discussed in detail. Subsequent to laboratory testing, numerous fracture design and production simulations were performed to determine the effect of production simulations were performed to determine the effect of guar and HPG crosslinked fluids on well performance. The data indicates the forecasted cumulative production of wells fractured with guar and HPG are similar. However, due to the relatively lower cost of guar, the Net Present Value (NPV) of wells fractured using guar is greater due to lower treatment costs. A case study of sixteen high-temperature wells located in Weld County, Colorado was performed to determine the "actual" effect of the fracturing fluid on well performance. A comparison of post-frac well production data indicates guar and HPG crosslinked fluid yield comparable proppant pack impairment, and thus similar well performance. A detailed discussion is presented. performance. A detailed discussion is presented Introduction Previously researchers have reported natural polymers utilized in Previously researchers have reported natural polymers utilized in water-based fracturing fluids have adverse effects on proppant permeability. However, these viscous fluids provide an permeability. However, these viscous fluids provide an efficient means to create and propagate a fracture, and effectively transport proppant into the created fracture. Thus, it would be beneficial to develop methods to minimize proppant permeability impairment caused by the polymers. One of the earliest attempts to decrease proppant permeability damage was directed at the development of a "cleaner" polymer system. Guar, a naturally occurring polysaccharide, was reacted with proplylene oxide to form HPG. During this process, a large quantity of plant material (residue) was removed to yield a "cleaner" polymer. Laboratory tests indicated that HPG had only 1 to 3 weight percent (%w/w) residue, whereas guar exhibited 8 to 13 % w/w residue. Based on this information, it was concluded that HPG creates less proppant pack damage than guar polymers. Additionally, HPG offered improved compatibility with methanol and greater high-temperature stability. Consequently, in the early 1970's, the fracturing industry became very conscious of the fact that HPG had a lower residue than guar. Usage of guar fracturing fluids decreased dramatically (Fig. 1) while HPG usage increased. Thus, guar was perceived to be a "dirty" fluid and HPG became the standard frac fluid polymer. In 1984 a conductivity study was performed by Almond and Bland that indicated no correlation could be drawn between % w/w residue and proppant pack permeability impairment. In fact, it was reported that guar and HPG produced similar proppant pack damage (18 % HPG vs. 20 % guar @ 120 degrees F), even though the intermediate residue guar had 5 to 6%w/w residue compared to HPG's 1 to 2%w/w residue. Recently, conductivity studies performed under in-situ conditions by Pennys have shown that both guar and HPG yield similar conductivity impairment. Additionally, Penny's study indicates that polymer loading, type of crosslinker, and breaker system dramatically affect the conductivity of a proppant pack. In today's oilfield environment with depressed hydrocarbon prices, the optimization of all costs associated with the production prices, the optimization of all costs associated with the production of oil and gas is required. Since the fluid polymer costs may constitute 15 to 20% of hydraulic fracturing costs, guar warrants reevaluation as a cost effective alternative to more expensive, so-called "cleaner" polymers. This paper presents the results of extensive laboratory conductivity testing of proppants placed with various guar and HPG crosslinked systems. The laboratory data is supported by a case study of 16 wells fractured with guar and HPG crosslinked systems. P. 415