bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Stress-Dependent Fracture Permeability in Naturally Fractured Reservoirs Using a Fully Coupled Poroelastic Displacement Discontinuity Model
Authors: Tao Q. , Ehlig-Economides C. A. , Ghassemi A. 
Published: October 2009

Abstract
Fractures are the main channels of production/injection in naturally fractured reservoirs; therefore the fracture permeability is a key parameter to production optimization and reservoir management. Pressure depletion in naturally fractured reservoirs can result in effective stress change that, in turn, can change fracture permeability. We apply a fully coupled poroelastic displacement discontinuity method to model the fracture permeability change during production in naturally fractured reservoirs. The fully coupled poroelastic displacement discontinuity method employs a boundary element displacement discontinuity model for the behavior of rock discontinuities and fractures under changes in stress from pore pressure variations due to fluid flow in both the matrix and fractures. The nonlinear Barton-Bandis joint mechanical medel is applied to represent the fracture deformation including normal and shear deformation. Sensitivity studies using the numerical model show that fracture permeability decreases with pressure depletion during production in fractured reservoirs under isotropic stress conditions. However, in critical stress conditions the fracture permeability may increase with pressure depletion during production because of the fracture dilation caused by fracture slide, which may explain near well permeability improvement observed in shale gas reservoirs. Simulations of pressure transient behavior show that behavior characteristic of stress dependent fracture permeability can be identified in conventional pressure buildup data, and over a longer time frame the model can be used for production data analysis. Matching with field data enables quantification of external stress contrast and fracture stiffness, and the result can provide a more rigorous forecast of production decline and primary oil or gas recovery efficiency for wells in naturally fractured reservoirs.
Real-Time Long Distance Teaching: An Overview of Two Years of Tele-Teaching Between Texas and Germany
Authors: Teodoriu Catalin , Reinicke Kurt M. , Falcone Gioia 
Published: October 2009

Abstract
This paper presents the experience gained while using a very simple and efficient tele-teaching technique based on available systems integrated in Windows packages. In contrast to expensive, time-intensive systems that use high-end technologies, our system incorporates ordinary webcams on laptop computers, Microsoft NetMeeting online conferencing software, and remote control of a distant computer.
We show the advantages of these simple resources and the student response to the teaching process for a highly sophisticated petroleum engineering class delivered to students in Clausthal-Zellerfeld, Germany from offices in College Station, Texas. The experience over two years of tele-teaching using easily available standard internet messengers and MS Windows-integrated meeting packages has resulted in enthusiastic student acceptance and preference for our low-cost system over more expensive, complex approaches to distance learning. We include our recommendations for building a system that works efficiently yet minimizes the costs.
A Systematic Study of Alkaline-Surfactant-Gas Injection as an EOR Technique
Authors: Srivastava Mayank , Zhang Jieyuan , Nguyen Quoc P , Pope Gary A. 
Published: October 2009

AbstractAlkaline-Surfactant-Polymer (ASP) flooding is an attractive enhanced oil recovery method. However, some reservoir conditions are not favorable for the use of polymers or their use would not be economically attractive due to low permeability or other unfavorable conditions. Foam can be an alternative to polymer for improving the displacement efficiency in chemical-EOR process. The use of foam as a mobility control agent by co-injection or alternate injection of gas and chemical slug is termed, here, as Alkaline-Surfactant-Gas (ASG) Process. Foam reduces the relative permeability of the injected chemical slug that forms microemulsion at ultra-low oil-water interfacial tension (IFT) and generates sufficient viscous pressure gradient to drive the foamed chemical slug. The concept of ASG process as an enhanced oil recovery technique is relatively new, with very little experimental and theoretical work available on the subject. Polymer is replaced by foam in corefloods experiments as a mobility control agent. Phase behavior and ASG coreflood experiments were carried out to identify high performance chemicals, designed for both foaming and strong IFT reduction performance. The coreflood experiments were performed on sandstone and dolomite rock samples. Oil recovery and coreflood pressure response were evaluated to determine the success of the process. Different injection strategies for foam generation were investigated, and mechanisms of mobility control by foam were studied. Several promising surfactants, with dual properties of foaming and emulsification, were identified and used in the coreflood experiments. Maximum recovery of 95% of remaining oil after waterflood was observed. Oil recovery and pressure responses from ASG experiments are comparable to ASP coreflood experiments carried out under similar conditions. Experimental data show a strong synergic effect of foam and ultra-low oil-water IFT on oil recovery. Compared to polymer, foam has lower cost associated with its use and is less susceptible to biological, shear, and thermal degradation. The use of foam in chemical EOR can reduce the technical disadvantages associated with polymer in low permeability and fractured reservoirs.
A Theoretical Study of Acid Fracture Conductivity Under Closure Stress
Authors: Deng J. , Hill A. D. , Zhu D. 
Published: October 2009

Abstract
The conductivity of acid-etched fractures depends on spaces along the fracture created by uneven etching of the fracture walls remaining open after fracture closure. In this study, we have modeled the deformation of the irregular fracture surfaces created by acid etching and the resulting fracture conductivity as closure stress is applied to the fracture.
In our previous work, we modeled the dissolution of the fracture surfaces in a formation having small-scale heterogeneities in both permeability and mineralogy. This model yielded the geometry of the etched fracture at zero closure stress. Beginning with this profile of fracture width, we have modeled the deformation of the fracture surfaces as closure stress is applied to the fracture. At any cross-section along the fracture, we approximate the fracture shape as being a series of elliptical openings. Assuming elastic behavior of the rock, we calculate how many elliptical gaps remain open and their sizes as a function of the applied stress. The sections of the fracture that are closed are assigned a conductivity because of small-scale roughness features using a correlation obtained from laboratory measurements of acid fracture conductivity as a function of closure stress. The overall conductivity of the fracture is then obtained by numerically modeling the flow through this heterogeneous system.
Our previous work shows that high fracture conductivity can be created in acid fracturing if heterogeneity of the rock leads to the formation of channels along the fracture surfaces. In this study, we have determined how the channels in acid fracturing remain open as closure stress is applied. This model predicts the rock characteristics that are necessary for acid fracture conductivity to be sustainable under high closure stress.
The Variability of Gamma Ray Tool Response and Calibration as a Function of Tool Design
Authors: Pederson Raulie , Haecker Bill , Minette Daniel 
Published: October 2009

Abstract
In the last 5-10 years there has been a significant proliferation in the companies providing MWD gamma logging tools. A given MWD logging company might have 6 or more different gamma detector designs in their logging fleet. Historically, we know that different designs have produced different responses that need to be characterized. Calibration, dark current, detector sensitivity can all be affected by design.
In this paper, this question will be addressed through extensive API test pit logging, lab data, and Monte Carlo modeling. The foundation of the work is the running of five different detector designs from several different manufactures in the API gamma ray test pits. These tools are run in the API pits as bare sondes, and with a 4″ collar. They are also calibrated with two different types of gamma calibrators.
This work is extended with lab work with additional detectors. The laboratory procedure is directly tied to the API test pits through the use of tools and calibrators used at the API pit. Measurements are then made with different detector designs, as well as a number of different detectors of the same design.
Finally, the experimental work is complemented by Monte Carlo modeling. The Monte Carlo is benchmarked against the experimental results and then used to extend the range of investigation.
From this work, we are able to determine the variability of the following as a function of detector design: Dark Current (the count rate in a clean formation)Calibrator API ValuesCollar Shielding EffectsAbsolute API Pit ValuesEnvironmental Effects
In addition, we will be able to determine the variability of the dark current and the collar shielding effect between different detectors of the same design.
Finally, the effects on this on well logs will be addressed. First the effects of the uncorrected variation on the measured API values and the impact this has on formation evaluation will be discussed. Then means of minimizing these effects, and the resultant impact on formation evaluation will be presented.
Unified Model of Drainage and Imbibition in 3D Fractionally Wet Porous Media
Authors: Motealleh Siyavash , Ashouripashaki Mandana , DiCarlo David , Bryant Steven L. 
Published: October 2009

Abstract
We develop a grain based model for capillarity controlled displacement within 3D fractionally wet porous media. The model is based on a novel local calculation of the position of stable interfaces in contact with multiple grains. Each grain can have a different, arbitrary contact angle with the interface. The interface is assumed to be locally spherical for menisci separating the bulk non-wetting and wetting phases. The fluid/fluid interfaces between pairs of grains (surfaces of pendular rings) are assumed toroidal. Because the calculation of interface position is entirely local and grain-based, it provides a single, generalized, geometric basis for computing pore-filling events during drainage as well as imbibition. This generality is essential for modeling displacements in fractionally wet media. Pore filling occurs when an interface becomes unstable in a pore throat (analogous to Haines condition for drainage in a uniformly wet throat), when two or more interfaces come into contact and merge to form a single interface (analogous to the Melrose condition for imbibition in uniformly wet medium), or when a meniscus in a throat touches a nearby grain (a new stability criterion). The analytical solution for stable interface locations generalizes the Melrose and Haines criteria previously validated for pore-level imbibition and drainage events in uniformly wet media.
The concept of tracking the fluid/fluid interface on each grain means that a traditional pore network is not used in the model. The calculation of phase saturation or other quantities that are conveniently computed in a network can be done with any approach for defining pore bodies and throats (e.g. Delaunay tessellation, Voronoi tessellation, and medial axis methods). The fluid/fluid interfaces are mapped from the grain-based model to the network as needed. In addition, the model is robust as there is no difference in the model between drainage and imbibition, as all criteria are accounted for both increasing and decreasing capillary pressure.
To validate the model, we perform a series of drainage/imbibition experiments (oil/water) on fractionally wetted porous media prepared by mixing oil-wet grains with water-wet grains. In both experimental and simulation results, the drainage/imbibition curves shifts to lower capillary pressure with increasing fraction of oil-wet grains.
Using the model, we delineate which pore filling criteria occur as a function of initial wetting phase and wettability of grains. The shape and position of the pressure-saturation curve is shown to be a function of the pore filling types, and hysteresis arises naturally from the model.
Application of pH-Triggered Polymers for Deep Conformance Control in Fractured Reservoirs
Authors: Lalehrokh Farshad , Bryant Steven L. 
Published: October 2009

AbstractWater injection is commonly employed to increase the average reservoir pressure and displace the oil. However, water flooding is not always successful. The most important problem is channeling of the injected water into high permeability zones which occur in heterogeneous reservoirs. This is particularly true in naturally fractured reservoirs.Injecting low viscosity pH-triggered polymers into the reservoir to block the already swept fractures and high permeability zones is a promising solution. No injection of high viscosity gels or triggering agents is needed is this process. Polyacrylic acid microgels can swell a thousand fold as the pH of the surrounding solution changes, with an accompanying large increase in viscosity. In this paper we studied the factors affecting the feasibility and the placement of pH-triggered polymers into fractured reservoirs by performing several coreflood experiments in fractured cores.Polymer treatment reduced the overall core permeability in all cases in contact with different minerals in various sandstone and carbonate fractured cores. At polymer concentrations of 1% or greater, the permeability reduction was more than a factor of ten. The polymer microgels showed excellent consistency after being one month in reservoir condition at 58°C and resisted flow at pressure gradients up to 80 psi/ft. The selection of polymer and salt concentration in polymer solution depends on the application and desired PRF value. However, the 1% polymer concentration and 3% NaCl concentration is recommended due to the ease of polymer preparation, injectivity, reasonable geochemical buffering time and PRF values.
Predicting Depth of Penetration of Downhole Perforators
Authors: Gladkikh M. , Harvey W. B. , Halleck P. M. 
Published: October 2009

Abstract
Productivity of a cased-and-perforated well depends on completion parameters (charge, shot density and phasing), formation properties (lithology, anisotropy, permeability, fluid properties and saturations), and environmental conditions (pressure and temperature). A shaped charge produces a jet of dense, typically solid material traveling at very high velocity which penetrates casing, cement, and formation. This penetration process creates a tunnel in the rock connecting the reservoir and the wellbore. Stress waves generated during penetration damage the rock around the tunnel, creating a complex zone of mechanically deformed rock material. Explosive and metallic debris may mix with damaged rock material. Depending on the specific conditions (mechanical rock properties, permeability, fluid viscosities, interfacial tensions, pressures and fluid storage volumes), reverse surge flow following the jet penetration partially or completely clears the tunnel of the charge and rock debris. The resulting tunnel is a rugose, tapered cylinder roughly characterized by its diameter and total depth of penetration. The degree of cleanup and total depth of penetration are two of the most critical parameters influencing flow performance of a perforated well.
This work focuses on predicting penetration depth and providing a summary of recent progress and advances in this area. A review of industry penetration prediction methods is presented, including relationships based on surface perforation tests in concrete targets, as well as correlations of penetration depth with properties that could be measured by downhole logging tools. Despite a variety of available methods and published experimental data, penetration depth results are often inconsistent with each other and of questionable use in predicting actual downhole penetration. Moreover, most studies have concentrated on the influence of a single penetration variable. There have been no systematic studies of the interaction of parameters on perforation penetration.
This paper emphasizes the critical need for such a study, given the difficulty of downhole measurements of penetration depth to finally achieve reliable penetration predictions, and suggests future directions and conditions necessary for such a study.
Production Optimization Benefits through Application of Standardized Operating Procedures for Reservoir Monitoring
Authors: Bhushan Vikas , Lee Robert , Mukerji Parijat 
Published: October 2009

Abstract
The ultimate goal of excellence in brownfield management is to increase the value of a field through maximizing production and ultimate recovery within its remaining economic life. The ability to successfully apply reservoir management techniques is essential in meeting the challenges of optimizing late life production. Further, the standardization of operating procedures yields benefits both in terms of optimizing the use of technical resources and in successfully meeting well intervention objectives. It also facilitates and promotes an active collaboration between the operator and service provider, both during logging operations and later when the log data is evaluated and interpreted.
We will demonstrate the benefits that the successful development and implementation of robust Standard Operating Procedures (SOP's) for cased hole reservoir monitoring can have. These will be illustrated with recent examples from the Brent Field in the UK North Sea. Developing these SOP's was not a simple process, and required a detailed understanding of the rock & fluid properties, reservoir production mechanisms and contact movements, topsides constraints, and reservoir behavior coupled with experience in data acquisition & interpretation methods which are tailored to meet the specific challenges of the field.
The SOPs have been applied to meet a range of specific challenges such as the identification and perforation of gas zones, differentiating reservoir fluid type (e.g. formation/injection water and oil) to access bypassed oil, contact monitoring, and identifying impairment to increase production rates. Success in the development and application of SOPs requires service company involvement and cooperation in all aspects: program design, data acquisition (including real time support and monitoring to ensure data quality), processing, presentation and interpretation. Examples will be provided of how this involvement has contributed to the successful outcome of interventions in the Brent field.
The development of robust SOPs for reservoir monitoring yields benefits in terms of defining and streamlining data acquisition and interpretation methodologies, tailored to suit the specific field characteristics and challenges. Further, it facilitates knowledge transfer to staff unfamiliar with the tools & techniques captured within the SOPs and enables a more efficient interaction between operating company and service provider.
Monobore Completion System Provides Low-Cost Completion Option
Authors: Ingvardsen Don , Kritzler Jim 
Published: October 2009

Abstract
Many of the wells completed today could be classified as short life or harvest wells. Some of these would not be economically feasible using high end completion components, and methods. Monobore wells can be a solution to this dilemma.
This paper will discuss several methods in which monobore well design can save considerable time while lowering the overall completion cost. Several methods will be discussed, and case histories provided to substantiate the results and savings. Methods will include the following:
Disposable completions using minimal completion components. Cemented monobores using cement-tolerant components, and methods/procedures of completing wells. Staged cementing completion designs for openhole monobores. Two-trip monobore systems Detailed case histories of the methods above, discussing the advantages and disadvantages of each method. Results of pilot program with live gas lift valves in place during cement operations instead of dummy valves.
Illustrations along with detailed procedures will be discussed to better understand how each completion method can address the numerous opportunities, and problems associated in well completion design. Case histories will be provided to validate each method.
Development of a Comprehensive Rheological Property Database for EOR Polymers
Authors: Lee Seungjun , Kim Do Hoon , Huh Chun , Pope Gary A. 
Published: October 2009

Abstract
One of the most important factors in chemical enhanced oil recovery (EOR) is mobility control, for which partially hydrolyzed polyacrylamide (HPAM) and other polymers are extensively used. An accurate description of the polymer viscosity is needed to simulate field performance accurately. Rheological properties of the EOR polymer solutions depend on the polymer's molecular properties and concentration, salinity, shear rate and temperature.. Rheological measurements with commonly employed EOR polymers were made and the parameters in the rheological models that correlate polymer viscosity with these variables were determined and used to develop a polymer database.
The rheological measurements have been made to characterize the apparent viscosity of EOR polymers (mainly HPAM polymers) as a function of shear rate, polymer concentration, polymer molecular weight, degree of hydrolysis, salinity, hardness, and temperature. In addition to the steady shear viscosities, the oscillatory rheological properties have also been measured to better define the polymer behavior during flow in reservoir rocks. In view of the recent EOR applications to recover viscous oils and to offshore fields, the data were obtained for wider ranges of the polymer molecular weight and concentration, and salinity, than those reported in the literature. A comprehensive compilation of the rheological data and polymer parameters for currently available EOR polymers was needed since these polymers often have different properties than similar polymers that were studied during the earlier period of active chemical EOR research 20 to 30 years ago.