bluuebunny/crossref_metadata_2025 huggingface dataset:
A Chemical Potential Dominated Model for Fracturing-Fluid Flowback Simulation in Hydraulically Fractured Gas Shale
Authors: Fei Wang , Ziqing Pan , Hun Lin , Shicheng Zhang
Published: September 2016

High-clay shale formations could behave as a semi-permeable membrane, thus causing osmotic water molecules flow from low-salinity side to the high-salinity side. This chemical potential dominated flow, we believe, has non-negligible influence on water leak-off and flowback during the treatment of hydraulic fracturing, since there is a considerable salinity difference between the low-salinity fracturing-fluid and the high-salinity formation brine.

In this paper, we present the development of a comprehensive triple-porosity (organic materials, inorganic materials and fracture network), dual-permeability, chemical potential dominated water/gas flow model that uses experimentally determined formation properties to predict the fracturing fluid flowback of hydraulically fractured shale gas wells. The dual-permeability includes the chemical potential dominated flow within inorganic materials and the pressure dominated flow within fracture network. Fracture network is considered as an interconnected continuum embedded in shale matrix, where organic shale is interspersed within vast inorganic shale. The organic material is thus considered disconnected in the entire reservoir. The chemical potential dominated flow model accounts chemical osmosis, capillary and viscous forces.

The water saturation profiles for both osmosis-induced and capillary-induced cases are compared, revealing a region of saturation that effectively is immobile even though irreducible saturation has not been reached. The results indicate that chemical osmosis is a key mechanism for fluid loss during the hydraulic fracturing and should not be ignored under high clay content cases. This work provides a basis for flowback data analysis of hydraulically fractured shale gas wells and also helps define value adding laboratory measurements.
Effect of Well Trajectory on Liquid Removal in Horizontal Gas Wells
Authors: Brito R. , Pereyra E. , Sarica C.
Published: September 2016

A systematic experimental study on two-phase air-water was carried out to evaluate effect of well trajectory on liquid removal in horizontal gas wells. Experiments were conducted in a facility with a 2-in. ID and 62.6-ft. long lateral section and a 41-ft. vertical section, which mimics a horizontal well. Four well configurations were considered; namely, toe-down, toe-up, one-undulation with a sump and one-undulation with a hump. Additionally, different flow conditions were used to simulate the well production as the reservoir pressure depletes. The effect of well trajectory on the liquid removal was evaluated measuring the pressure gradient, liquid holdup, film reversal, and flow pattern.

Experimental results indicate that under stable conditions, toe-up is the best configuration for the displacement of the produced fluids from the toe to the kick-off point. However, at very low gas flow rates, severe slugging is observed in this configuration. Furthermore, for the toe-down, one-undulation with a sump, and one- undulation with a hump configurations liquid loading is observed in both lateral and vertical sections of the well. Consequently, significant liquid accumulation and an eventual slugging condition are observed in the well. It was observed that the measured critical gas velocity to avoid liquid loading is lower than gas velocity at the minimum pressure gradient, indicating that minimum pressure gradient criterion is not enough to determine whether the well will be under stable or unstable conditions. Finally, toe-down configuration presents the largest liquid accumulation in the lateral section, indicating lower efficiency to remove liquids from the toe to the kick-off point.
Geopolymer Composites as Efficient and Economical Plugging Materials in Peanuts Price Oil Market
Authors: Salehi S. , Ali N. , Khattak M. J. , Rizvi H
Published: September 2016

Optimization of well construction process by utilizing more economical and efficient materials can help in reducing overall well expenditure. Plug and Abandonment (P& A) process can be very costly depending on well's situation and materials used for P&A. Plugging materials for abandonment needs to have pumpability, good shear bond, and compressive strength and reasonable shrinkage. Previous research on application of geopolymers in oil/gas wells was mainly unsuccessful due to failure to achieve a reasonable thickening time. The results presented in this work propose different mixtures of Class F fly ash Geopolymer binder with controllable thickening times in temperatures up to 250 °F. Mixtures were tested for unconfined compressive strength (UCS), shear bond strength, shrinkage, thickening time, durability and contamination. The Geopolymer mixtures in this work compose class F fly ash rich in Silicate, Aluminum and have elements of Potassium, Calcium, Iron, Sodium and Titanium. Mixture of Sodium Hydroxide and Sodium Silicate was used to activate the Fly ash mixtures. Geopolymer mixture designs tested in this work showed high compressive strength, shear bond strength, low shrinkage and suitable thickening time for applications in well abandonment purposes. In addition to good resistance to Oilbased Mud (OBM) contaminants, these alternative P&A materials can be produced cheaper with less environmental impact which fits well for applications in the oil and gas well cementing.
Flow Rate Estimation of Downhole Leaks Using Acoustic Sensor Array
Authors: Lu Yinghui , Walters Darren , Hill Freeman
Published: September 2016

Well integrity is becoming a key area of focus for most operators during the entire well life cycle. Acoustic conformance-monitoring systems have been developed to detect undesired leaks in terms of depth and radial location and to estimate leak flow rates, enabling operators to assess the severity of the leak and to plan remedial action. If the leak flow rate were substantial based on a given threshold, the remedial action would be scheduled with high priority; otherwise, repair work would be deferred to a suitable maintenance time.

This paper presents a systematic statistical methodology to estimate leak flow rates using data acquired by an acoustic sensor array. The first stage of this methodology is data-level fusion through the beamforming technique, in which all signals acquired by an array of acoustic sensors are fused into a new signal. The second stage consists of feature-level fusion, in which representative and distinct features are extracted from the fused signal to construct the feature space. The third stage is decision-making, in which a statistical model is fitted in the feature space and then used to estimate flow rates in the sense of probability.

A series of experiments was conducted in which a variety of leak flow rates were simulated with various combinations of orifice sizes and differential pressures in various leak scenarios. A low-dimension, third-order logistic regression model was demonstrated that can be fitted to the data and used to effectively separate small/large flow rates (90.0% specificity and 91.7% sensitivity).
International Regulations and Compliance for Relief Well and Blowout Contingency Planning
Authors: Szemat Vielma W. E. , Mosti I. , Gallagher L. , Nergaard K.
Published: September 2016

Several countries have introduced new requirements to ensure that the well design has been evaluated for all well control possibilities, including drilling a relief well. However, without a single global standard, different approaches have been taken into consideration, and this situation merits a review of current legislative mandates for relief well planning (RWP) and/or blowout contingency planning (BCP).

Primarily through open source literature, a compilation of legislative requirements is provided, giving a short history of the legislative change that preceded relief well and blowout contingency planning as a requirement and noting specific technical requirements. The legislative review shows that RWP and/or BCP are becoming more prevalent for operators when seeking permission to drill.

A more detailed overview of the NORSOK D-010 Rev 4 standard (herein called NORSOK) is given because this is considered the most mature existing standard and is often used as a guideline by others. Based on the requirements in the NORSOK standard, an overview of the cross-disciplinary workflow necessary to model a blowout and relief well contingency plan is suggested: data gathering, relief well design, and dynamic multiphase simulation to determine worst case discharge and dynamic kill requirements to regain control of a blowout. The cross-disciplinary workflow for blowout and kill simulation modelling can lead to misinterpretation of the objectives. Drilling engineers are typically tasked with producing a BCP, but reservoir and/or production data drive the workflow.

This paper provides current regulations for RWP and BCP that operators can use as quick reference and compare and contrast for their ongoing or future operations, ensuring that compliance and maximum safety standards are adhered to at all times.
Appraising Unconventional Play from Mini-Frac Test Analysis, Actual Field Case
Authors: Ibrahim M. , Pieprzica C.
Published: September 2016

Unconventional reservoirs are an increasingly important worldwide resource. These reservoirs, generally defined by permeability values lower than 0.1 millidarcy, present today's engineer with unique challenges. To date, there are no available methods for evaluation of unconventional wells with respect to estimated ultimate recoveries (EURs). As a result, the conventional approach has been used resulting in initial well reserve and performance predictions containing large amounts of uncertainty. Ultimately, capital efficiency will suffer through these misinterpretations. A better understanding of completion efficiencies and of a well's performance in these new unconventional frontiers is needed.

This paper will present an optimized EUR prediction procedure for the ultra-low permeability unconventional reservoir. The data from a standard mini-frac test will be analyzed and interpreted to produce the desired results. Illustrated within is the integration of geological data, Mini-Frac test (DFIT) analysis, and logging data to predict EUR's and future performance profiles. The DFIT analysis shows itself to be the most influential in this predictive workflow. One should note that the critical step in the process is proper identification of the reservoirs parameters: initial reservoir pressure, permeability, fracture half-length, and reservoir boundary

A reservoir model was built using the results of the proposed workflow. Through multiple simulations, the model produced well-performance curves and EUR values that were in agreement. This procedure generates more accurate and reliable curves than the conventional decline curve analysis approach and properly applied, will improve individual well performance predictions with additional benefits including optimization of future completion metrics and spacing decisions.
Radio Frequency Identification RFID-Enabled Circulation Sub Improves Hole Cleaning in High-Angle Wells
Authors: Goodwin Alex , Reitsma Rienk , Osei-Kuffour Jonathan
Published: September 2016

Well cleanup operations require high fluid-circulation rates for efficient cuttings transport and hole cleaning. Conventional circulation subs are deployed in drilling applications such as slim-diameter wells to deliver higher circulation rates and cuttings removal. But because these subs require multiple trips downhole for mechanical or hydraulic actuation, they add rig time and costs while drilling complex, high-angle wells. This paper reviews a radio frequency identification (RFID) circulation sub that facilitates hole cleaning via remote actuation.

The RFID circulation sub is actuated using commands communicated by RFID tags as they pass through the inside diameter (ID) of the tool string, which replaces conventional actuation methods such as ball drop or darts. This sub can be selectively actuated any number of times during the same trip downhole for enhanced operational flexibility. And because no ball seats are present, the sub maintains a full-bore ID that facilitates higher annular velocity and turbulent flow.

This paper also reviews a field application in which the RFID sub was deployed in a multi-assembly tool string to clean out a perforated 7-in. liner section and cased-hole section for a North Sea well. Once the well reached total depth, the sub was opened, closed and reopened a number of times, on command, to facilitate hole cleaning and increase fluid circulation rates to remove the wellbore debris. The RFID circulation sub helped deliver a cleaned and conditioned hole that was ready for stimulation. By completing the entire operation in a single trip, the operator saved 1.5 days of rig time.
A Novel Test Automation Solution to Improve Petroleum Engineering Software Reliability and Development Efficiency
Authors: Chen Zhongming , Chaudhary Saleem , Xie Liangjun , Sui Xiaojing
Published: September 2016

Engineering software programs play a critical role in helping engineers understand complex engineering challenges and in analyzing engineering data to aid management in making the right decisions. Currently, it is almost impossible to present a job design without the help of engineering software. In petroleum industry this situation is especially true in the areas of reservoir study, drilling, hydraulic fracturing, cementing, and sand control, where the software is an integrated collection of the right technologies and is the "medium" used to transfer technology to end users.

Unlike a physical product, which has a solid touch and feel, the architectural design and detailed development of engineering software often seem like a mystery to users, because of the numerous, hidden algorithms. Ensuring the correctness of all the implemented logic and producing reliable software has always been the focus of software engineering. Theoretically, any change made to the software has the potential to affect the entire application and may require a full retesting of the application's functionality before release to the user. It is impossible to retest all logical combinations and algorithms by using traditional testing methodologies. A new automated test solution has been developed to revolutionize the process of software development and testing to improve software reliability. The new test automation technique enables the developer to record and document all testing on individual algorithms as well as algorithm combinations during early development phases. Most importantly, testing can be automatically repeated at a later stage as needed. This activity includes unit testing, module testing, integration testing, and the final entire application testing. The precision range can also be set in the proposed methodology.

Automated testing and retesting significantly improves the reliability of the software as it is developed during its lifecycle. The proposed methodology was validated by successful application of the new solution in our software development projects.
Use of Transient Tests to Monitor Progress of Flooding in IOR / EOR Operations
Authors: Kamal Medhat , Tian Chuan , Suleen Suleen
Published: September 2016

Improved and enhanced oil recovery methods (IOR and EOR, respectively) are used to increase recovery from proven reserves mainly following waterflooding. Monitoring and managing the progress of flood in IOR /EOR operations is currently a challenge to the oil industry especially in situations with large well spacing and cost prohibitive measures like drilling observation wells (e.g., offshore and deep water applications). Falloff tests have been proven successful under waterflooding operations to determine the reservoir properties in various banks around the injection wells and the location of the flood fronts (Abbaszadeh and Kamal 1989, Yeh and Agarwal 1992, and Kamal 2009). In this paper we share new development that extends transient testing and analysis technology to IOR and EOR operations during polymer flooding. With the expanded use of Permanent Downhole Pressure Gauges (PDHG), the new developed technique can be used without additional operational cost or interruption of field operations.

In this paper, the effects of polymer are described by shear rate dependent viscosity (non-Newtonian flow). We developed an analytical solution of wellbore pressure by combining the non-Newtonian fluids and the multi-composite reservoir models. The solution dose not only address the polymer region where the fluids follow either the power-law (Ostwald 1929) or the Meter model (Meter and Bird 1964), but also the Newtonian flow in the oil region with varying oil and polymer saturations in both regions. The developed solution was validated by analyzing synthetic data generated using a commercial numerical reservoir simulator. The solution provides a deeper understanding about the physics behind the transient pressure behaviors during polymer flooding, and can be applied to guide a better implementation of well tests. Interpretation method for falloff tests using the new solution and the conventional Bourdet derivative and Horner plots is presented indicating that existing commercial well testing software are sufficient to analyze data with the recent development. The new solution allows us to obtain the reservoir properties such as fluid mobilities in various banks and the location of the flood front.

The developed solution was applied to field data. The pressure behavior expected from the new solution was observed in field data validating our developed technique and yielding the characterization of reservoir parameters in various banks.

The novelty of this method of characterizing the dynamic properties of the various banks during injection of non-Newtonian fluids and the location of the flood fronts is that an analytical solution of pressure transient behavior in two phase flow of non-Newtonian fluids and Newtonian fluids was developed, validated and used to analyze field data. This is the first analytical solution developed for this type of problem.
Experimental and Numerical Investigation on Stress Dependence of Sandstone Electrical Properties and Deviations from Archie's Law
Authors: Farid M. F. , Arns J.-Y. , Pinczewski W. V. , Arns C. H.
Published: September 2016

Resistivity Index (RI) of Fontainebleau and Bentheimer sandstones was investigated at ambient and reservoir pressures down to low water saturations using the porous plate method. The measurements compared with computations directly on high-resolution three-dimensional images of the pore space using Digital Rock Physics. The numerical computations are in reasonable agreement with the experimental measurements down to water saturations as low as Sw = 10 %. The RI measurements show that both sandstones display Archie behavior at elevated pressure. However, at ambient pressure the RI for Fontainebleau sandstone deviates from Archie behavior at low water saturations. The pore-space images suggest that the deviation from Archie behavior is due to the presence of conductive percolating grain contact regions. Bentheimer sandstone for which grain contacts do not percolate, displays Archie behaviour both at ambient and elevated pressures. The present study extends previous work on RI of clean sandstones using micro-CT based analysis to high confining pressures and shows that for such sandstones the RI at elevated pressure displays Archie behavior down to low water saturations.
Combining Soluble Particle Diverter with Specially Engineered Proppant to Enhance Fracture Complexity and Post-Fracture Conductivity
Authors: Gomaa Ahmed M. , Spurr Naima , Pirogov Alexander , McCartney Elizabeth
Published: September 2016

The objective of this study is to introduce a technique of far-field diversion using a mixture of soluble solid particles and an engineered proppant that can ensure that the temporarily bridged fractures re-open and remain propped for hydrocarbon flow after the soluble material has fully dissolved. Far-field diversion is required inside the fracture network to increase complexity by creating additional branch fractures through overcoming stresses holding the natural fractures closed. Usually, diverter particles temporarily bridge inside the fracture to create a low-permeability zone that increases the net pressure within the fracture and enables redirection of the next fluid stage to previously unstimulated intervals. However, if the diversion does not include proppant, the created fracture may close after particle dissolution.

Two tests were performed in this study: solid bridging test to describe the bridging capabilities of solid particulate diverters as a function of fracture width (0.04 to 0.08 in.); and conductivity reduction tests to determine the reduction in the flow rate due to the particle pack permeability. Two types of particle diverters (Diverter A and B) were tested. Diverter A is typically used for low- to medium-temperature applications (less than 225°F) and Diverter B for high-temperature applications (greater than 225°F). The two diverters have nearly the same particle size and distribution, the only difference being a difference in particle shape.

Modeling performed before the experimental work indicated that a proppant size of 50 mesh or higher minimized the far-field segregation between the proppant and 20 mesh soluble particles under all modeled conditions. Modeling also showed that reducing the proppant size to a larger mesh number improved proppant placement in the far-field area with good vertical coverage. Based on this information, the diverter particles for the tests were selected to be in the medium-size range (10 to 50 mesh) while the proppant particles were selected to be in the fine size range (70 to 140 mesh). At a low injection rate, slickwater fluid (2 cP) may not have adequate transport characteristics to place soluble diverter particles for far-field application. Modeling indicated that a carrier fluid with viscosity of 10 cP could carry the soluble diverter at least 130 ft from the wellbore.

Experimental data, using the CFD recommended sizes of proppant-diverter mixture, confirmed that a loading of 0.5 ppga of Diverter A was needed to bridge and plug the 0.04-in. slot width, while only 0.25 ppga of Diverter B was needed to plug the same width. The spherical shape of Diverter B helps to bridge inside that fracture more than the flake shape of Diverter A. Finally, both diverters significantly reduced the conductivity of the test slot discs.
Methodology and Array Technology for Finding and Describing Leaks in a Well
Authors: Hill Freeman , Bond Andy , Biery Michael , Jagannathan Srinivasan , Walters Darren , Lu Yinghui
Published: September 2016

This paper presents a new technology and methods that can detect leak locations in a well and illustrate the flow profile of the leak. A substantial amount of time and effort can be used toward repairing leaks in wells, and these methods and technology can reduce that time. The paper shows results and compares them to other techniques for a well that had been shut in as a result of a small leak.

The new approach is based on a hydrophone array technology, modeling, and practices that can identify the depth and radial locations of a leak. The array uses beamforming to triangulate on the location of the noise caused by flow in the leak. In addition, with the configuration of the well, this method can be extended to map out the flow patterns, producing an image of the leak. The procedural methodology for locating a leak, combined with a technical description of this new technology, is provided to enable results to be duplicated on other wells.

Standard well practices for locating leaks are discussed, along with the methodology behind leak detection and obtaining leak flowing profiles. A field case study is presented for an Alaskan well in which a small leak was observed between annuli A and B, interrupting the production of the well. The leak was evasive as a result of its size and location. A combination of field practices and the new technology produced the location and a flow profile illustration of the leak. Other small leaks were found within the well, including a leaking gas lift mandrel and a suspected tubing thread leak. Most significantly, the annular leak was found less than 50 ft below surface. Because of its location and proximity to the surface, surface interference hampered standard practices, which prevented the identification of the leak point in the well. However, by using field practices and the array technology, the leak was identified, and its flow profile from annulus A to annulus B was mapped out, accurately describing the leak and providing a full understanding of it. This is significant because it is helpful for choosing the most economical method for addressing the issue and returning to normal production.

The methodology and new hydrophone array technology for detecting leaks is a novel approach. The ability to identify and present a leak profile in a well is highly beneficial because it can reduce time and repair costs. This paper presents field practices that support its relevance.
Remote Detection and Flow rates Quantification of Methane Releases Using Infrared Camera Technology and 3D Reconstruction Algorithm
Authors: Watremez Xavier , Labat Nadège , Audouin Grégoire , Lejay Bertrand , Marcarian Xavier , Dubucq Dominique , Marblé André , Foucher Pierre-Yves , Poutier Laurent , Danno Ronan , Elie Damien , Chamberland Martin
Published: September 2016

Hydrocarbon leaks in oil and gas installations present Health, Safety and Environmental risks. History of crisis management in oil and gas upstream has shown the value of efficient and accurate tools for quantifying the gas-leak rate and determining the perimeter of the hazardous areas.

In this context, Total initiated a multi-year R&D collaborative project designed to develop remote sensing technologies and architectures for remote detection, identification, quantification and visualization of gas leaks in the event of a crisis.

Total, the ONERA – The French Aerospace Lab – and ADCIS have developed a set of algorithms and software to measure, compute and visualize a methane plume using infrared optical imagers. Results are obtained in 3D and in real time. The following steps are involved: (1) Spectral images in the Long-Wavelength InfraRed (LWIR) region are captured by three hyper-spectral cameras located around a methane release point; (2) Concentrations of methane are measured linearly in ppm.m by comparing spectral images of the scene in the presence of gas and reference images acquired before the release; (3) An algorithm, drawing on tomography techniques, computes concentrations of methane in ppm from the linear concentrations; (4) Mass balance type equations finally help estimate the methane flowrates based on the set of concentrations and local wind data information.

A one-week test campaign was organized in September 2015 and consisted of performing twenty-six methane gas releases of 1 g/s to 50 g/s. Three Telops Hyper-Cam cameras were connected as part of a network to a main server which ran the tomography and flowrate estimation code. The real-time remote detection and quantification worked fully.

During the campaign, good accuracy was obtained at the low flowrates of 1 g/s and 10 g/s of methane. At the higher flowrate of 50 g/s, quantifications were underestimated due to an oversaturation phenomenon. Further works, the aim of which is to adapt the instrument sensing ranges to the maximum concentrations encountered, should help improve the accuracy of these quantifications.

The innovation lies in the fact that a 3D visualization of the methane plume can be computed and created in real time and that flowrates and concentrations can be quantified, also in real time. This technology could be applied in environmental monitoring and crisis management.
Extreme Expansion Openhole Packer with HP/HT Capabilities
Authors: Mills Aubrey , Deng Guijun , Wakefield John , Prieto Carlos
Published: September 2016

The increasing demand for annular isolation in openhole applications drives the need for tools to operate in non-controlled bores where large washouts can limit the reliability of sealing in fracturing, off-bottom cementing and other operations performed in openhole. The service industry has been developing technology to meet these challenges for years but these efforts have often resulted in costly solutions and less than desirable pressure ratings or production rates.

A milestone was recently achieved in openhole packer development due to collective advancement in design process, state-of-the-art polymeric material development and design validation utilizing fiber-optic sensors. In-house testing indicates superior results: HP/HT capacities with the enhanced capability of operating in ~288% larger radial gaps, 50% lower setting pressures and 67% lower swab-off pressure. An important discovery from the use of fiber-optics was confirmation of the self-energizing nature of the packer along with data directly relating setting pressure to casing stress and thus the near wellbore. This technology and methodology will fundamentally change packer design and could be the greatest breakthrough in this area over the last 50 years.

This paper elaborates on how the design process is integrated with concept evaluation, material selection and qualification, design optimization using structural analysis techniques, rapid design experimentation and design validation utilizing fiber-optic sensors to achieve 13,000 psi [89,632 kPas] and 5,000 psi [34,474 kPas] ratings at 350 °F [450 K] for gauge and large washout geometries, respectively. This technology is currently being evaluated in field trials in the Middle East.
The Next Generation of E&P Development Programs: Flipped, Blended and Mentored
Authors: Donohue David A , Bulath Zsolt , Kavanaugh Kimberly , Donohue Tim , Ogle Kenneth
Published: September 2016

Development programs for the next generation of E&P specialists will be considerably different from those of the past. Enhanced learning methods, improved virtual communications systems, expanded online learning resources, the use of competency based job models to guide learning design, new learning approaches which rely more on mentors than lecturers, increasingly realistic simulation games and other methods will all contribute to achieving more effective and less costly learning outcomes. These drivers will be enabled by a Millennials culture that is highly attuned to the use of technology and impatient to achieve outcomes. In this paper, the authors summarize how these drivers contribute to the design of the next generation of learning programs, list the various resources and communications systems that exist or need to be developed and outlines some potential program designs. They conclude with a case study that demonstrates a "next generation program" that has been designed by the authors and is currently being implemented by a European oil and gas company for its specialists who work on several continents. The cost-effectiveness of such programs relative to traditional programs—particularly in a low oil price environment—will be welcomed by employers who are looking for real and substantial development outcomes for their new employees.
A New Technique to Characterize Fracture Density Using Neutron Porosity Logs Enhanced by Electrically-Transported Contrast Agents
Authors: Tang Hewei , Killough John E. , Heidari Zoya , Sun Zhuang
Published: September 2016

Fracture density evaluation has always been challenging for the petroleum industry, although it is a required characteristic for reliable reservoir characterization. Production can be directly controlled by fracture density, especially in tight reservoirs. Previous publications introduced the method of using high thermal neutron capture cross-section contrast agents like boron carbide (CB4) to enhance the sensitivity of neutron logs to the presence of fractures. However, all of the studies focus on locating the proppants. In this paper, we propose to (a) enhance the propagation of the contrast agents into the secondary (natural and induced) fracture network using an externally applied electric field and (b) characterize the fracture density in un-propped area using the enhanced neutron porosity logs.

We perform numerical simulations to validate the feasibility of the proposed technique. A physical model derived from electrophoretic velocity and material balance formulations is proposed and solved to simulate the spatial distribution of contrast agents. Furthermore, we simulate neutron porosity logs by solving the neutron diffusion equation which significantly reduces the computing cost (from hours to a few seconds) compared to conventional use of the MCNP (Monte Carlo N-Particle Code) technique.

The simulation results confirmed that an external electric field can significantly enhance the transport of charged contrast agents into the secondary fracture network. Sensitivity analysis revealed that increasing particle zeta potential can efficiently decrease the transport time. Furthermore, we applied the introduced technique on synthetic cases with variable secondary fracture density ranging from 1% to 8%. The relative change of simulated neutron porosity before and after applying the electric potential field was up to 50% in a formation with 8% fracture density after applying an electric field for 6 hours. The proposed technique can potentially enable application of neutron porosity logs in fracture characterization, including assessment of secondary fracture density, if combined with other well logs.
Development of Permeability and Mechanical Properties of Class G Cement from Slurry to Set
Authors: Maharidge R. , Bottiglieri A. , Dighe S. S. , Holley A. , Zhang H. , Koch A.
Published: September 2016

As cement changes from liquid slurry to solid, its load-bearing response, strength and permeability characteristics are expected to change with time. Consequently the ability of any cement to withstand changes in wellbore pressure and temperature will be determined, in part, by the changes in elastic properties, failure criteria and permeability that occur over time. An experimental study of time evolution of mechanical and flow properties of Class G neat cement is presented in this study.

The objectives of this intra-laboratory test program were to answer the following questions: How rapidly do the mechanical and flow properties evolve over time? Can changes in microtexture be observed and correlated to those properties?What are the optimal times required to observe time-independent responses?What is happening to the water in the cement and does it correlate with the time evolution observed in mechanical properties and permeability?

Measurements of liquid permeability, static and dynamic elastic properties, compressive and tensile strengths, pore size distribution and microtexture and fabric photography were recorded over a 10 day interval.

The time evolution of mechanical and flow properties for 15.8 pound per gallon Class G cement and their relationships with water content are presented throughout the paper. Permeability is shown to dramatically decrease and equilibrate over the first 24-32 hours, while the mechanical properties continued to increase over a longer time period. The changes in mechanical/flow properties were strongly correlated to the decrease in water content and the shifting of pore size to smaller distribution functions. Complete stabilization of static elastic properties was not observed after 10 days, implying that, for certain cement formulations, these properties may need to cure for longer than industry standard times. From tests results, 96 hour cure times may be insufficient to characterize certain mechanical properties of wellbore cements. This study also sets a base standard for comparison with more complex cement chemistry's that are currently (and in the future) being used in oil-field operations. The authors also concluded that the use of NMR measurements of pore size and, in turn, water content correlate very well with conventionally used methods. Motivation for this study is based on limited data available on the simultaneous response of all critical wellbore cement properties from the very early stages of hydration to long-term set.
On the Exact Representation of Pressure Decay Tests: New Modeling and Experimental Data for Diffusivity Measurement in Gas - Oil/Bitumen Systems
Authors: Ratnakar R. R. , Dindoruk B.
Published: September 2016

Diffusion mixing is a dominant process in absence of convective mixing in various reservoir processes such as CO2 flooding of fractured reservoirs, heavy oil and bitumen recovery, solution gas drive processes, and gas re-dissolution process in depleted reservoir. In these processes, the diffusivity governs the rate and extent of mixing of light hydrocarbons/non-hydrocarbons with the oil that enhances the oil recovery through in-situ viscosities reduction. It is one of the key parameters for design and understanding of the displacement processes.

Due to its significance in various aspects of oil recovery processes, several experimental/theoretical studies are performed recently on the measurement of gas diffusivity in oils. Experimental work is most commonly based on the Pressure-decay concept due to its simplicity. The parameter estimation from these tests is based on the transient diffusion model, where the concentration/density gradient in gas phase is neglected or modelled with a transfer coefficient. However, these models are good for steady-state or late transient. Since the transfer coefficient concepts are validated only for steady-states (or near steady-state) in literature, its use in transient case must be investigated by analyzing the full diffusion model in both oil and gas phases. Therefore, in this article, the previous work [1] is extended and the diffusion process in pressure-decay set-up is experimentally investigatedthe transfer of gas from gas phase to the oil is captured properly through exact modeling based on the transient diffusion model in gas and oil phases coupled with continuity in state variable (using Henry's constant) and molar flux at the gas-oil interface;the exact solution of detailed pressure-decay (transient diffusion) model is developed and, the early and late transient solutions are analyzed;A robust inversion technique for parameter estimation is presented using exponentially decaying late transient data;Most importantly, the inversion technique is based on a linear regression and numerical integration rather than a non-linear regression. This integral based linear representation avoids the multiple solutions and can be used with limited dataset and/or when noise in the experimental data is significant.
Why Re-Fracturing Works and Under What Conditions
Authors: Asala H. I. , Ahmadi M. , Taleghani A. Dahi
Published: September 2016

Stimulated shale wells show sharp decline rates after several months of production imposing the need for rejuvenating production via re-fracturing or other methods. The sharp decline in production from shale gas/oil wells is attributed to full or partial closure and damage of the induced fracture network within the rock. The poor economic conditions stirred by low oil prices has persuaded operators to consider re-fracturing as an affordable option but the mechanisms behind this technique is not fully understood. In this paper, we utilize a fully coupled model to understand stress re-distribution and identify different modes of fracture closure during production from initial hydraulic fractures. Rock creep, proppant failure and differential fluid depletion are identified as primary causes of closure within shale fracture networks. We incorporate these phenomena into a poroelaso-plastic model that simulates fracture conductivity evolution during production, and re-fracturing treatments illustrated by re-fracture propagation, fracture coalesce or fracture extension along pre-existing fractures. This methodology provides a realistic initial condition to simulate varying re-fracture designs - different treatment schedules and fracturing fluids. The Influence of degradable mechanical and non-mechanical diverters is also incorporated in this model.

Our results reveal major stress redistribution in the fracture network especially at the intersections due to depletion. The results show how fracture closure at the fracture intersections causes abrupt or time dependent shrinkage of the drainage area. Under certain conditions, re-fracturing may effectively open up these bottlenecks while in extreme situations, it creates new fractures which reorient obliquely. Results also reveal the role of in-situ stress anisotropy, magnitude of depletion and complexity of fracture networks in the successful re-fracturing of lower- clay content naturally fractured formations such as the Barnett shale. The results do not suggest strong dependency on stress anisotropy and natural fractures orientation in high clay content reservoir rocks like Haynesville or Marcellus. It shows the quantifiable effect of creep on closure rate and conductivity loss. Results show diverters have a profound effect on the expansion of the re-fracture network, although it hinders reactivation of some clogged fractures. Using adaptive cohesive elements provides the opportunity to model longitudinal, transverse or oblique re-fracture propagation.

The Proposed model introduces a realistic fracture closure mechanism and stress re- distribution during drainage, prior to re-fracturing. This plays a vital role in explaining initial fracture extension, re-frac propagation, fracture coalesce, re-fracture re-orientation, and therefore the effectiveness of re-fracturing treatments. This model offers a practical tool for identifying potentially successful re-fracturing candidates.
New Wireline, In-situ, Downhole Fluid Compositional Analyses to Enhance Reservoir Characterization and Management
Authors: Hursan Gabor , Mark Ma S. , Soleiman Wael , Eyuboglu Sami , Sethi Neeraj , Guergueb Nacer
Published: September 2016

Physical fluid samples collected in situ provide evidence for verification of exploration prospects, optimization of formation evaluation and reservoir production. Downhole fluid analyzers (DFA) are developed essentially to ensure the quality of formation samples. Advanced DFA are emerging for more advanced fluid compositional analyses in situ, as well as for studying the effect of pressure on fluid physical and chemical properties, those typically determined in the laboratories. Laboratory tests such as PVT (pressure-volume-temperature) analysis are still used as reference in reservoir engineering, provided the sample tested is representative of formation fluid and also differences among different laboratories are minimized.

This study focuses on crude oil compositional analyses during pumpout with a wireline formation tester. It summarizes experience with the in-situ measurement of methane, ethane, propane, saturates, aromatics and GOR based on multivariate optical computing (MOC) conducted at over 200 pumpout stations in a total of 37 wells drilled with a variety of inclinations, bit sizes, drilling fluids in several oil and gas fields. The results and lessons learnt enhanced technology development including hardware improvements, capability expansion for new components, processing software upgrades and the foundation of a local center of excellence for operations and study support.

Examples of individual pumpout stations within the context of an integrated petrophysical analysis of wireline logs are presented to demonstrate data quality control and basic interpretation in oil and gas wells in the presence of water- and oil-based muds. The data are cross-validated by correlations with laboratory and other sensor data. Fine but consistent field-wide compositional variations suggest the possibility of new geological understanding and advanced reservoir fluid modeling from the newly acquired DFA data base.
New Pseudo-Pressure and Pseudo-Time Functions for Multiphase Flow
Authors: Shahenda Mahran , Ahmed H. El-Banbi
Published: September 2016

The development of pressure transient analysis was based on the assumption of a single phase slightly compressible fluid. This assumption was later relaxed to handle dry gas reservoirs and multiphase situations. The literature reported several methods for multiphase well test analysis [e.g., Perrine-Martin method (1956), pressure squared method proposed by A1-Khalifah (1987), and the two-phase pseudopressure function by Raghavan (1976), and 3-zone Fevang and Whitson approach (1995)].

In this paper, we develop new formulation for generalized multiphase pseudo-pressure and pseudo-time functions that can handle any type of multiphase flow system. In particular, the new formulation uses the modified black-oil (MBO) approach and can handle volatile oils and gas condensate reservoirs in more accurate ways than presented previously in the literature. These generalized multiphase pseudo-functions were validated through the analysis of many simulated drawdown and pressure buildup tests covering comprehensive inner (radial wells, partial penetration, fractured, and horizontal wells). The simulated cases also covered all multiphase flow situations. In every simulated case, analysis using the new functions was compared with single phase, Perrine-Martin, and the multiphase approaches proposed by Raghavan and Fevang and Whitson analyses. The new technique proved to be the most accurate among the other techniques. The new technique also uses one generalized form to handle any multiphase situation including volatile oils and gas condensates. As an example, application of the new generalized multiphase pseudo-functions to analyze transient data generated in gas-water multiphase flow system, at different water cut values; it was found that the new multiphase pseudo-function technique was able to predict the flow capacity with error percentage less than 10% when the water cut value was less than 50%. This was at least 2 folds better than other existing techniques. It was also found that this error percentage increased when the water cut value exceeded 80%.

Applying the new pseudo-functions techniques also improves the quality of data for analysis in multiphase flow situations.