bluuebunny/crossref_metadata_2025_split huggingface dataset:
Depletion-Induced Poroelastic Stress Changes in Naturally Fractured Unconventional Reservoirs and Implications for Hydraulic Fracture Propagation
Authors: Jin Lei , Zoback Mark 
Published: September 2019

Abstract
Numerous questions surround stimulation and depletion in unconventional reservoirs with many important implications. Understanding depletion-induced stress changes is critical for designing in-fill drilling and avoiding phenomenon such as hydraulic fracture growth into depleted areas and hydraulic fractures from in fill wells affecting pre-existing wells (the frac-hit or parent well/child well phenomenon). In this paper, we utilize a fully coupled fracture-poro-mechanical computational model described by Jin & Zoback (https://doi.org/10.1002/2017JB014892) to evaluate the pressure and stress changes associated with pore-scale flow from the low permeability matrix into a much more permeable discrete fracture network. These fractures represent pre-existing natural fractures stimulated in shear during hydraulic fracturing as well as the hydraulic fractures themselves. Because of the marked permeability contrast, depletion is rather heterogeneous and can be visualized as halos adjacent to the more permeable shear fractures and hydraulic fractures. While this might be expected, the calculations are helpful in understanding the extent of depletion and limitations of utilizing the concept of a stimulated reservoir volume to predicting production. To examine the evolutions and characteristics of depletion-induced stress changes, we consider three cases representing different initial pore pressure, horizontal stress anisotropy and pressure drawdown. We show that while the total normal stress decreases overall due to depletion as expected, the changes are anisotropic due to the pressure gradient oriented predominantly perpendicular to the well; the changes are also highly heterogeneous due the presence of fractures and unexpected local increases among fractures can occur. Additionally, newly induced shear stress also develops with heterogeneous distributions. These changes jointly produce complex magnitude variations and rotational patterns of the horizontal principal stresses. For the base case we consider (high initial stress anisotropy, low initial overpressure and insignificant depletion), rotations occur mostly surrounding the fractures and the degree of rotation is mild. In marked contrast to this, in a case in which there is high initial overpressure, little horizontal stress anisotropy and significant depletion, rotations become less dependent on fractures and is prominent throughout the domain to a degree such that the directions of the two horizontal principal stresses are essentially flipped. Taken together, these calculations help illustrate how depletion-induced stress changes can affect problems like in-fill drilling and re-stimulation and therefore provide insights into better drilling and completion designs.
Metal Expandable Annular Sealing Systems for High Pressure Open Hole Zonal Isolation and Stimulation
Authors: Esquitin Yosafat , Schwanitz Brian , Moreno Guido , Avella Natalia , Henao Oscar 
Published: September 2019

Abstract
Metal expandable annular sealing systems were used in a 4 ½" completion as an effective high-pressure isolation method inside 6" open hole mudstone formation in the Foothills Basin of Colombia. Effective isolation proved to be historically difficult to achieve.
The operator was approached with a solid metal expandable sealing system with rotation capabilities as an annular barrier for a preferred cementless completion. The sealing system needed to be assembled on a full-bore liner able to deliver robust deployment with a high-pressure seal in a worse case washed-out scenario. The deployment of the system consisted of one annular barrier placed above and one annular barrier placed below the mudstone zone.
Following careful job planning with the operator, the rotationally capable completion was deployed without any incidents. To achieve pressure integrity to set the metal expandable annular barriers, a ball seat sealing system was incorporated to allow the system to be closed and the annular barriers to be set.
After putting the well onto the pipeline, the client recorded a 52% increase in their expected produc-tion from previous wells. Successful results were accomplished as effective isolation was achieved and enhanced production was obtained because of the effective stimulation. This paper overviews the appli-cation, design, implementation and results of the use of new metal annular sealing systems in a 4 ½" completion as an effective high-pressure isolation method inside a 6" open hole, drilled in fractured sandstone and mudstone formations.
Developing an Integrated Real-Time Drilling Ecosystem to Provide a One-Stop Solution for Drilling Monitoring and Optimization
Authors: Cao Dingzhou , Ben Yuxing , James Chris , Ruddy Kate 
Published: September 2019

Abstract
The paper provides a technical overview of an operator's Real-Time Drilling (RTD) ecosystem currently developed and deployed to all US Onshore and Deepwater Gulf of Mexico rigs. It also shares best practices with the industry through the journey of building the RTD solution: first designing and building the initial analytics system, then addressing significant challenges the system faces (these challenges should be common in drilling industry, especially for operators), next enhancing the system from lessons learned, and lastly, finalizing a fully integrated and functional ecosystem to provide a one-stop solution to end users.
The RTD ecosystem consists of four subsystems as shown in architecture Figure 1. (I) The StreamBase RTD streaming system, which is the backbone of the ecosystem. It takes the real-time streaming log data as well as other contextual well data (for example, OpenWells), processes it through analytical models, generates results, and delivers them to the web-based user interface; (II) The analytics models, which include the Machine Learning (ML)/Deep Learning (DL) models, the physics-based models and the stream analytical/statistical models; (III) The digital transformation solution, which wasdesigned to address contextual well data digitization issues to enable real-time physics-based modeling. Contextual well data like bottom hole assemblies (BHAs) and casing programs are challenging to aggregate and deliver to models, as this data is often stored in locations across multiple systems and in various formats. The digital transformation applications are designed to fit into the drilling teams' workflows and collect this information during the course of normal engineering processes, enhancing both the engineering workflow and the data collection process; (IV) the cloud based ML pipeline, which streamlines the original ML workflows, as well as establishes an anomaly detection and re-training mechanism for ML models in production.
Figure 1 RTD ecosystem architecture
All of these subsystems are fully integrated and interact with each other to function as one system, providing a one-stop solution for real-time drilling optimization and monitoring. This RTD ecosystem has become a powerful decision support tool for the drilling operations team. While it was a significant effort, the long term operational and engineering benefits to operators designing such a real-time drilling analytics ecosystem far outweighs the cost and provides a solid foundation to continue pushing the historical limitations of drilling workflow and operational efficiency during this period of rapid digital transformation in the industry.
Application of Multizone Water Injection Downhole Flow Control Completions with Fibre-Optic Surveillance in Soft Sand Reservoirs
Authors: Nguyen Dzu , Macleod Innis , Taylor Donald , Murray Laurence , Zavyalov Denis , Booth Dave , Robertson Neil , Smith Robert , Joubran Jonathon , Allen Clifford , Shafei Sharil Mohd 
Published: September 2019

Abstract
The multiple zone water injection project (MZWIP) was initiated to deliver the following key objectives: deliver zonal injection with conformance control and reliable sand management across the major layered sands of the Balakhany unconsolidated reservoirs in the BP operated Azeri-Chirag-Gunashli (ACG) fields in Azerbaijan sector of the Caspian Sea.
Three years after MZWIP implementation, six wells with a total of 14 zones are injecting at required rates with zonal rate live-reporting. To achieve this multizone injection facility, the requirement for a standard ACG sand-control injector design was discounted and a non-standard sand management control technique developed using a cased & perforated (C&P) and downhole flow-control system (DHFC). During this program, BP ACG has successfully installed the world's first 10kpsi three-zone inline variable-choke DHFC wells with distributed temperature sensors (DTS) across all target injection zones.
The choking DHFC provides flexibility in operations and delivers the right rates to the right zones. The DTS provides conformance surveillance, fracture assessment, caprock integrity and sand ingress monitoring capability. A customized topside logic control system provides an automatic shutin of interval control valves (ICVs) during planned or unplanned shutins to stop crossflow and sand ingress and is the primary method of effectively managing sanded annuli.
The development of this MZWI solution has significantly changed the Balakhany development plan and has been quickly expanded across five ACG platforms. Accessing 2nd and 3rd zones in the same wellbore, this C&P DHFC well design is accelerating major oil volumes and will significantly reduce future development costs, maximizing wellbore utility in a slot-constrained platform.
Casing Rotation for Improved Cement Quality in Unconventional Horizontal Wellbores
Authors: Turner William , Adam Derek , Cowan Kenneth Mike , Tellez Diego , Willis John 
Published: September 2019

Abstract
Results from a long-term field study to improve zonal isolation show that rotating production casing in unconventional well laterals is possible and that it delivers excellent cement quality. This paper reports the results of the study. To date, 44 production strings have been rotated during cement jobs.
Specific details covered are cement bond evaluation results, methods used for modeling casing running, torque and drag forces for floated and rotated strings, torque estimation for casing connection selection, operational procedures, mud conversion cement additive, and best practices. Evaluation of cement bond is based on ultrasonic cement logs acquired in casing strings cemented with and without casing rotation. Advanced azimuthal ultrasonic logs were used to measure cement placement and quality. Trials with a mud conversion cement additive evaluated whether the cement quality could be achieved with additives instead of rotation. Both 6¾ in. and 8½ in. hole sizes in 10,000 ft lateral lengths were evaluated.
Prior studies demonstrated that casing movement is crucial for efficient mud removal (Hyatt et al. 1984; Gai et al. 1996), yet it is not a common practice on long horizontal sections in our company. The casing rotation initiative reported here was enabled by the availability of reliable high torque casing connections. The results shared in this paper demonstrate that it is necessary to rotate casing while cementing horizontal wells with 10,000 ft lateral lengths for effective cement isolation in the annulus. The cement bond resulting from rotated cement jobs is near-perfect. Long-term study is needed to evaluate the effect of optimal cement on hydraulic fracturing effectiveness, production, and the long-term health of the well.
Results reported include log data and modeled torque and drag values paired with operational data to validate the models. Log data is available for eight lateral wellbores evaluated during the base case and trial period. It is unique in that log data was acquired for both the base case and trial wells.
This paper supports well-known cementing best practices (McLean et al. 1967; Zurdo et al. 1986; Reiley 1987; Wilson et al. 1988; Sabins 1990; Torsvoll et al. 1991; Kettl 1993; McPherson 2000; Nelson et al. 2006; Al-Baiyat et al. 2019) with undisputable log data. The operational practices can be applied to many unconventional operations to implement casing rotating into their cementing programs. The method shared to estimate torque can be implemented by any drilling engineer with access to torque and drag software, enabling them to choose the right casing connection for their application.
Development and Application of Firebag SAGD Reservoir Simulation Platform
Authors: Xu Jinze , Wang Jin , Aghabarati Hossein , Zamani Amir , Cheung Kathy 
Published: September 2019

Abstract
Suncor's Firebag Project is one of the largest steam-assisted gravity drainage (SAGD) projects in the world. As a powerful tool for decision-making in the field, the Firebag SAGD reservoir simulation platform is based on an in-depth understanding of physics that controls thermal recovery process and meets the need for a practical solution. In this platform, standardized inputs and workflows are developed, and a good agreement with field data is achieved for all Firebag SAGD operating pads with production history. The Firebag SAGD reservoir simulation platform promotes the capacity to address existing Firebag SAGD challenges, capture unique Firebag reservoir features, and support reservoir management and future pad development.
Gas Relative Permeability and its Evolution During Water Imbibition in Unconventional Reservoir Rocks: Direct Laboratory Measurement and a Conceptual Model
Authors: Peng Sheng 
Published: September 2019

SummaryRelative permeability has a significant impact on gas or oil and water production, and is one of the most complicated properties in unconventional reservoirs. Current understanding of relative permeability for unconventional reservoir rocks is limited, mainly because of a lack of direct measurement of relative permeability for rocks that have a matrix permeability at the submicrodarcy level. Because of the difficulties related to direct measurement, most studies on relative permeability in unconventional reservoirs are based on indirect or modeling methods. In this paper, a modified gas–expansion method for shale matrix–permeability measurement (Peng et al. 2019) was adopted to measure gas relative permeability directly under the scenario of water imbibition for samples from different unconventional reservoir formations. Evolution of gas permeability, along with gas porosity and fracture/matrix interaction, during the process of water redistribution (which mimics what occurs in the shut–in period in real production) was also closely measured. Results show that gas relative permeability in the matrix decreases during water redistribution because of water imbibition from fractures to the matrix coupled with a water–block effect. The water–block effect is more significant at low water saturations than at higher water saturations, leading to a rapid–to–gradual drop of gas relative permeability with increasing water saturation.A conceptual model on water redistribution in a fracture/matrix system and the change of gas and water relative permeability is proposed on the basis of experimental results and observations. Influencing factors including pore size, shape, connectivity, and wettability are taken into account in this conceptual model. The combined effect of these four influencing factors determines the level of residual gas saturation, which is the most important parameter in defining the shape of relative permeability curves. Water relative permeability is predicted on the basis of the conceptual model and the measured gas relative permeability using modified Brooks–Corey equations. Deducing the oil/water relative permeability is also discussed. The implications of relative permeability for gas or oil and water production and potential strategies for optimal production are also discussed in the paper. The hysteresis effect is not included in this study but will be addressed in future work.
Orientation of Hydraulic Fracture Initiation from Perforated Horizontal Wellbores
Authors: Michael Andreas 
Published: September 2019

Abstract
The orientation of hydraulic fractures controls the productivity from hydrocarbon reservoirs. Productivity from low permeability formations is greatly improved having multiple fractures oriented transversely rather than longitudinally, relative to a horizontal wellbore. Analytical approximations from the literature for the longitudinal and transverse fracturing stresses are modified to incorporate pore pressure effects and then used to develop a criterion for the orientation of fractures initiating from perforated wells. The validity of this criterion is assessed numerically and is found to overestimate transverse fracture initiation, which occurs under a narrow range of conditions; when the formation tensile strength is below a critical value and the breakdown pressure within a "window."
In horizontal wells, it is easier to achieve longitudinal fracture initiation, as transverse fracture initiation only occurs over a narrow wellbore pressure-at-breakdown window, while longitudinal fracture initiation occurs at comparatively higher wellbore pressures. The numerical study shows that in contradiction with existing analytical approximations, the tangential stress which induces transverse fracture initiation, is a stronger function of wellbore pressure just as the stress inducing longitudinal fracture initiation is. This reduces the breakdown pressure window for transverse fracture initiation compared to what the derived analytical approximations predict. Furthermore, this creates an additional constraint for transverse fracture initiation; the critical tensile strength value, which determines the maximum tensile strength for which transverse fracture initiation is possible for a given stress state.
The range of the in-situ stress states where transverse fracture initiation is promoted can be visualized in dimensionless plots for perforated wells. This is useful for completion engineers; when targeting low permeability formations, wells must be made to induce multiple transverse fractures. A numerical simulation scheme performed on several stress states demonstrates frequent occurrence of longitudinal fracture initiation, implying that the propagating fracture re-orients in the near-wellbore region to become aligned perpendicular to the least compressive in-situ principal stress. This is the cause of near-wellbore tortuosity, which in turn is a cause completions and production-related problems, such as early screenouts and post-stimulation well underperformance.
Efficient Simulation and Analysis of the Effects of Permeability on the In-Situ Combustion of Heavy Oils
Authors: Aounallah Khaled 
Published: September 2019

Abstract
The simulation of the In Situ Combustion (ISC) process is a very challenging process due to the complexity and non-linear nature of the problem. In this work, we propose an efficient technique to simulate experimental procedures for the ISC process including heterogeneity. The effects of permeability on mass flow and heat transfer were studied through a series of numerical frameworks. Different approaches to model the reactions occurring during combustion were attempted and simulation results were validated using experimental results. We focus on two different key areas: the integration of chemical reaction kinetics obtained through kinetic cell experiments, and the analysis of efficient simulations of combustion tube experiments that account for the flow element. After establishing a robust framework that accurately matches lab-scale results, combustion tube simulation results using a commercial simulator were analyzed to corroborate conclusions. Through observing the propagation of the combustion front and the oil bank in heterogeneous zones, assessments around the effects of permeability on the ISC process were performed. This work provides valuable information that would be instrumental in understanding experimental behavior of in-situ combustion and upgrading results to field scale after matching numerical results with experimental data collected in our future work.
Polymer Viscosity: Understanding of Changes Through Time in the Reservoir and a Way to Predict Them
Authors: Katz Marquez Román E. 
Published: September 2019

Abstract
Polymer rheological behavior in an Enhanced Oil Recovery (EOR) project is one of the critical factors to determine whether the polymer injection would be effective to increase the oil production in a field. Due to complications on the measurement of this parameter and its variation within the reservoir, the challenge of understanding viscosity behavior relies on lab and field tests that become key factors to solve this issue.
This study was conducted during an injectivity test for an EOR project in Los Perales field (Santa Cruz, Argentina) in three wells with different operational and subsurface conditions, and tests were performed twice a day for 30 days each in order to obtain sufficient time span of data.
From lab rheology tests performed at reservoir conditions, where the main objective was to analyze viscosity changes through time, two different tendencies were observed: one that affects in early times and another that becomes preeminent at late times. With these results, a describing equation was developed to predict viscosity evolution over time. The equation consists of three terms including thermal variation, chemical degradation and the final viscosity towards which the polymer tends.
Although the equation properly describes both lab and field polymer solution, there is a considerable difference, especially when the effects mentioned become preponderant. This difference is attributed to both the water used for the mixture and the possible impurities that may be incorporated during the maturation or transfer of the polymer. Since most of the data used was obtained from field tests, this emphasizes the appliance of the equation on the field.
Impurities turn out to be crucial, specially oxygen (O2) and hydrogen sulfide (H2S) combined. Their presence highly impacts the asymptotic viscosity, so a correlation between H2S content and final viscosity was also developed.
Finally, an analysis of the temperature influence on the viscosity was conducted. A correlation between the final viscosity and temperature was found and used to incorporate temperature variations in the predictions and therefore to relate measurements performed at different conditions.
The primary advantage of this study is that the equation and correlations enable the prediction of the polymer solution viscosity at any time. This allows the estimation of actual polymer viscosity in the reservoir from a routine measurement at any temperature and impurities content. The versatility of this equation is what makes it novel and useful in an industry going towards EOR projects.