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Mondal, Somnath (Shell Exploration & Production Co.) | Zhang, Min (University of Texas at Austin) | Huckabee, Paul (Shell Exploration & Production Co.) | Ugueto, Gustavo (Shell Exploration & Production Co.) | Jones, Raymond (Shell Exploration & Production Co.) | Vitthal, Sanjay (Shell Exploration & Production Co.) | Nasse, David (Shell Exploration & Production Co.) | Sharma, Mukul (University of Texas at Austin)
Abstract This paper presents advancements in step-down-test (SDT) interpretation to better design perforation clusters. The methods provided here allow us to better estimate the pressure drop in perforations and near-wellbore tortuosity in hydraulic fracturing treatments. Data is presented from field tests from fracturing stages with different completion architectures across multiple basins including Permian Delaware, Vaca Muerta, Montney, and Utica. The sensitivity of near-wellbore pressure drops and perforation size on stimulation distribution effectiveness in plug-and-perf (PnP) treatments is modeled using a coupled hydraulic fracturing simulator. This advanced analysis of SDT data enables us to improve stimulation distribution effectiveness in multi-cluster or multiple entry completions. This analysis goes much further than the methodology presented in URTeC2019-1141 and additional examples are presented to illustrate its advantages. In a typical SDT, the injection flowrate is reduced in four or five abrupt decrements or "steps", each with a duration long enough for the rate and pressure to stabilize. The pressure-rate response is used to estimate the magnitude of perforation efficiency and near-wellbore tortuosity. In this paper, two SDTs with clean fluids were conducted in each stage - one before and another after proppant slurry was injected. SDTs were conducted in cemented single-point entry (cSPE) sleeves, which present a unique opportunity to measure only near-wellbore tortuosity using bottom-hole pressure gauge at sleeve depth, negligible perforation pressure drops, and less uncertainty in interpretation. SDTs were conducted in PnP stages in multiple unconventional basins. The results from one set of PnP stages with optic fiber distributed sensing were modeled with a hydraulic fracturing simulator that combines wellbore proppant transport, perforation size growth, near-wellbore pressure drop, and hydraulic fracture propagation. Past SDT analysis assumed that the pressure drop due to near-wellbore tortuosity is proportional to the flow rate raised to an exponent, β = 0.5, which typically overestimates perforation friction from SDTs. Theoretical derivations show that β is related to the geometry and flow type in the near-wellbore region. Results show that initial β (before proppant slurry) is typically around 0.5, but the final value of β (after proppant slurry) is approximately 1, likely due to the erosion of near-wellbore tortuosity by the proppant slurry. The new methodology incorporates the increase in β due proppant slurry erosion. Hydraulic fracturing modeling, calibrated with optic fiber data, demonstrates that the stimulation distribution effectiveness must consider the interdependence of proppant segregation in the wellbore, perforation erosion, and near-wellbore tortuosity. An improved methodology is presented to quantify the magnitude of perforation and near-wellbore tortuosity related pressure drops before and after pumping of proppant slurry in typical PnP hydraulic fracture stimulations. The workflow presented here shows how the uncertainties in the magnitude of near-wellbore complexity and perforation size, along with uncertainties in hydraulic fracture propagation parameters, can be incorporated in perforation cluster design.
Ugueto, Gustavo (Shell Exploration and Production) | Huckabee, Paul (Shell Exploration and Production) | Nguyen, Audrey (Shell Exploration and Production) | Daredia, Talib (Shell Canada Limited) | Chavarria, Jose (Shell Exploration and Production) | Wojtaszek, Magdalena (Shell Global Solutions International) | Nasse, Dave (Shell Exploration and Production) | Reynolds, Alan (Shell Exploration and Production)
Diversion has been widely promoted as a technology that can both, lower the cost and increase the efficiency of plug-and-perforating completions (PnP). There are many diversion materials and techniques available today including; balls, chemicals, etc. A new product, informally referred as "pods" consisting of knotted degradable fibers delivered in a capsule, has gained significant interest within the industry.
We tested this new diversion material, "pods", in four stages in one of our wells instrumented with a fiber optic cable deployed behind casing. The FO results clearly showed that although perforations were plugged following "pods" deployment, the diagnostics also revealed that the outcome was not the desired one, which is to divert a portion of the treatment to understimulated clusters. In all the stages tested, the material did not re-open screened-out clusters. Furthermore, the frac placement distribution effectiveness was worse after the deployment of the diverter material.
All the tested stages showed the expected treatment pressure increase at the surface corresponding to the "pods" blocking some of the perforations. It is important to highlight that in the absence of downhole FO technology all these tests would have been categorized as successful. However, when the number of "pods" was increased to try to improve their performance, we ended up blocking so many perforations that the stimulation could not continue due to pressure limitations. This integrated approach toward the testing of this new technology demonstrated that there was a clear downside risk in utilizing this diversion technology in many wells without a full understanding of how this diverter material was interacting downhole with the clusters and perforations. The paper highlights the pitfalls and risks of relying on a single diagnostic tool (surface treatment pressure) to evaluate emerging technologies.
Fundamentally, there are two ways to empirically test new completion designs and stimulation technologies: Production-only-Pilots (PoP) and Integrated-Frac-Diagnostics-Pilots (IFDP). While better PnP efficiency is not the only intended use for "pods", the IFDP approach and FO monitoring used in this test has enabled a rapid and cost-effective testing of this technology application at a fraction of the cost and time of a PoP test.
Ugueto C., Gustavo A. (Shell Exploration & Production Company) | Wojtaszek, Magdalena (Shell International) | Huckabee, Paul T. (Shell Exploration & Production Company) | Reynolds, Alan (Shell Exploration & Production Company) | Brewer, Jim (Shell Exploration & Production Company) | Acosta, Luis (Shell Canada)
Abstract Since the start of the "Shale Revolution" more than ten years ago, hydraulic fracturing stimulation providers have offered operators an increasing number of completion technologies and a large variety of stimulation designs. The evolution of completion practices across North America reveals a trend toward increasing stimulation intensity: more fracs, shorter stages and larger proppant volumes in all the unconventional plays. Although the result of this trend has generally been more productive wells, the optimization of completion and stimulation practices have been slow and in many cases resulted in significant over-capitalization. The question we need to answer for each of the unconventional resources is: Which combination of completion and stimulation options is the most cost effective and maximizes economic value? The traditional approach of industry towards stimulation de-risking has been through the implementation of "trials" comparing the well performance of several wells, completed with the new technology, against the production of a group of "reference" wells. While this empirical approach appears to be relatively straight forward, there are some obvious challenges associated with sample size and the cycle-time duration of these tests. Typically, this approach also requires a relatively large number of wells to compensate for uncertainties associated with the well-to-well subsurface variability. Experience has shown that this approach takes many years and some degree of over-capitalization to determine the optimum completion. This paper outlines an alternative approach that can be performed in a few wells and that allows accelerating the optimization process. It includes experimental design considerations, acquisition of stimulation distribution effectiveness information, as well as, production data obtained by continuously monitoring a well using Fiber Optics (FO). In the example, we used Distributed Acoustic Sensing (DAS) to derive discrete production profiling results over a period of more than two years. This has enabled us to track the gas production of two competing completion designs in a single well with minimum production deferral and Health Safety Environment (HSE) exposure. Continuously monitoring production of each stage, perforation cluster or sleeve-entry opens the possibility of testing different completion technologies or designs by comparing the performance of each type in different segments of the same well. This not only enables us to accelerate the completion optimization process and reduce over-capitalization risk but also the same FO cable can be interrogated to investigate other aspects of the stimulation that can impact stimulation quality and production results. This alternative approach towards completion de-risking using a few wells and continuous FO monitoring provides critical information that could make the evaluation of stimulation technology faster, with higher confidence, and more cost effective than traditional evaluation/optimization methods.
Mondal, Somnath (Shell International Exploration and Production) | Ugueto, Gustavo (Shell Exploration and Production Company) | Huckabee, Paul (Shell Exploration and Production Company) | Wojtaszek, Magdalena (Shell Global Solutions International) | Daredia, Talib (Shell Canada Limited) | Vitthal, Sanjay (Shell Exploration and Production Company) | Nasse, David (Shell Exploration and Production Company) | Todea, Felix (Shell Canada Limited)
Abstract In recent years, Step-Down Tests (SDTs) are being increasingly used for diagnosing completions effectiveness in plug-and-perf (PnP) fracturing in unconventional wells. SDT is primarily used to quantify pressure drop related to perforation friction, near-wellbore tortuosity (NWBT), and to estimate perforation efficiency (PE) i.e. the fraction of active perforations at the end of a hydraulic fracturing treatment of a stage. In the industry, perforation efficiency is generally considered to be the yardstick for evolving limited entry designs and perforating strategies. In a typical SDT, the injection flowrate is reduced in 3 to 4 abrupt steps, each of duration long enough for the rate and pressure to stabilize, to enable interpretation of the rate and pressure response. However, simple as it may appear to be, the interpretation of SDT as a stand-alone diagnostic test has several assumptions and inherent non-uniqueness that are often ignored. This paper presents integrated data, diagnostics, and analysis from multiple completion types across multiple basins that demonstrates the methodology and uncertainties associated with SDT analysis. In this paper, the SDT methodology was applied to 2 wells with different completion styles, and the interpretation was supplemented with fiber optics and bottomhole pressure gauges (BHPG). In the first well, SDTs were conducted on multiple stages of a cemented single-point entry (CSPE) sleeve completion that had well-defined, erosion-resistant openings to reduce uncertainties in the “perforation” pressure drop solution. In the second example, SDTs were conducted on multiple stages of a PnP well. Each PnP stage had two SDTs – one was conducted post pad but before proppant and another at the end of entire treatment, both with clean fluids. The authors have highlighted the uncertainties with traditional SDTs and the need for integration with additional diagnostics. The analysis shows that the exponent of flowrate commonly used to quantify pressure drop associated with NWBT is largely uncertain. It also demonstrates the non-uniqueness of the SDT interpretation, and that a range of perforation diameters and a / the number of active perforations can match the SDT unless constrained with fiber optics data and perforation imaging data. The interpretation with constant perforation diameter is found to generally overestimate the PE. The SDTs before and after proppant slurry placement, if correctly interpreted, show an increase in perforation diameter with a reduction in PE post proppant placement. This paper demonstrates that without constraints on either eroded perforation diameter or on a / the number of active perforations, the interpretation of SDT is non-unique. Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) analysis also illustrates the variable and non-unique tortuosity, and/or complex stimulation domain architecture, in the near-wellbore region. It is therefore recommended that SDTs be interpreted with consideration of the inherent complexities and uncertainties, and preferably supplemented either with perforation imaging or DAS and DTS data for more accurate analysis. To summarize, accurate interpretation of SDTs requires an interdisciplinary diagnostics approach, which is critical for optimization of limited entry designs.
Gustavo, A.. (Shell) | Ugueto, C.. (Shell) | Huckabee, Paul T. (Shell) | Reynolds, Alan (Shell) | Somanchi, Kiran (Shell) | Wojtaszek, Magda (Shell) | Nasse, Dave (Shell) | Tummers, Richard (Shell) | Stromquist, Marty (NCS Multistage) | Ravensbergen, John (NCS Multistage) | Brunskill, Doug (NCS Multistage) | Whyte, Rio (NCS Multistage) | Ellis, Dustin (NCS Multistage)
Abstract Cemented Single Point Entry (CSPE) has the potential to reduce or eliminate the non-uniformity and Hydraulic Frac Stimulation (HFS) placement uncertainties inherent in other completion systems. If entry-to-entry isolation can be achieved, HFS initiation and treatment allocation near the wellbore can be better controlled by a CSPE completion. Fiber Optics (FO) and other diagnostics can provide the means to evaluate the effectiveness and potential benefits of this and other completion systems. This paper describes the HFS placement findings of a FO instrumented Coil Tubing activated CSPE well (CTa-CSPE). Coil Tubing CSPE completions provide some additional frac diagnostic information. Pressure and Temperature (P/T) gauges located in the Coil Tubing Bottom Hole Assembly (CT-BHA) help to evaluate the isolation with prior stimulated stages. A newly developed sleeve, specially designed to accommodate a FO cable outside casing, allows the simultaneous acquisition of both P/T information from downhole gauges and high-resolution stimulation data from FO. This paper shows several examples from stages with variable entry-to-entry isolation quality in a wellbore with 6000 ft lateral section. The results from the P/T gauges, Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) are mostly consistent for all 69 stages in this well. Only stages where communication was observed toward the heel-side of the lateral, relative to treatment sleeve, show inconsistent but explainable results. CT-BHA P/T gauges are only capable of detecting communication toward the toe-side of the lateral. In this well some degree of communication occurred in 48% of all stages. Evaluation of the FO data across multiple stages shows that the path of communication between sleeves and slurry placement can be complicated. Integration of DAS and DTS indicates that the slurry, between adjacent and poorly isolated stages, travels behind the casing down to the prior sleeve and then inside the wellbore, where the slurry is partially re-injected into previously stimulated stages. This dataset clearly illustrates that no single HFS diagnostic provides all the necessary information to fully understand the complexities of HFS placement. In this well, the data from CT-BHA P/T gauges, DAS and DTS are clearly complementary. The data also indicate that there is an urgent need to improve isolation between stages. Cement quality seems to be the primary source of entry-to-entry communication in long horizontal wells for this and other completion systems. In this well alone we estimate several hundred thousand US$ were wasted from the misplacement of stimulation energy and materials (capital inefficiency). To capture the full value from CSPE "pinpoint-fracturing" and the corresponding more effective drainage of resource volumes between wells, the problems associated with entry-to-entry communication must be understood and corrected. Finally, we will introduce some new multicycle sleeves that will further enhance the capabilities of CSPE systems. These sleeves are specially designed to obtain production profiling information via FO. Deployment of such systems should provide the industry with the means to better evaluate and optimize completions and wellbore spacing.