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Research Papers: Air Emissions From Fossil Fuel Combustion

J. Energy Resour. Technol. 2016;138(3):031101-031101-9. doi:10.1115/1.4032617.

Many industrial sectors built cogeneration plants to secure their power supplies reliably and to efficiently produce the plant demand of steam through the associated heat. Due to the rise of fuel cost and tightening environmental regulations, the number of cogeneration plants will increase in lieu to individual boilers and steam turbine generators. Most of the recent cogeneration plants are equipped with hardware-based analyzer which is a continuous emission monitoring system (CEMS) to monitor the NOx emissions from the plant stack as per U.S. Environmental Protection Agency (EPA) regulations. The CEMS is unreliable due to high failure rates and requires high capital cost, high maintenance cost, high operational cost in addition to being subject to long lag time and having slow response. In this work, a software-based analyzer is designed by applying artificial neural networks (ANNs) on process data collected from cogeneration plant (156 MW X 2 combustion gas turbine generators (CGTGs)) equipped with CEMS for NOx monitoring. The developed soft analyzer will be used to verify the existing CEMS readings and used as a reliable tool to monitor the NOx emissions that will eventually replace the CEMS. By providing a relationship between the process and the emissions, the soft analyzer will also assist in understanding the NOx behavior in reference to the process variations and thus enables better emission control.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2016;138(3):032001-032001-8. doi:10.1115/1.4032238.

Considering the large variations of working fluid's properties in near-critical region, this paper presents a thermodynamic analysis of the performance of organic Rankine cycle in near-critical condition (NORC) subjected to the influence of evaporation temperature. Three typical organic fluids are selected as working fluids. They are dry R236fa, isentropic R142b, and wet R152a, which are suited for heat source temperature from 395 to 445 K. An iteration calculation method is proposed to calculate the performance parameters of organic Rankine cycle (ORC). The variations of superheat degree, specific absorbed heat, expander inlet pressure, thermal efficiency, and specific net power of these fluids with evaporation temperature are analyzed. It is found that the working fluids in NORC should be superheated because of the large slope variation of the saturated vapor curve in near-critical region. However, the use of dry R236fa or isentropic R142b in NORC can be accepted because of the small superheat degree. The results also indicate that a small variation of evaporation temperature requires a large variation of expander inlet pressure, which may make the system more stable. In addition, due to the large decrease of latent heat in near-critical region, the variation of specific absorbed heat with evaporation temperature is small for NORC. Both specific net power and thermal efficiency for the fluids in NORC increase slightly with the rise of the evaporation temperature, especially for R236fa and R142b. Among the three types of fluids, dry R236fa and isentropic R142b are better suited for NORC. The results are useful for the design and optimization of ORC system in near-critical condition.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032002-032002-12. doi:10.1115/1.4032241.

A scale-invariant model of statistical mechanics is applied to describe modified forms of zeroth, first, second, and third laws of classical thermodynamics. Following Helmholtz, the total thermal energy of the thermodynamic system is decomposed into free heat U and latent heat pV suggesting the modified form of the first law of thermodynamics Q = H = U + pV. Following Boltzmann, entropy of ideal gas is expressed in terms of the number of Heisenberg–Kramers virtual oscillators as S = 4 Nk. Through introduction of stochastic definition of Planck and Boltzmann constants, Kelvin absolute temperature scale T (degree K) is identified as a length scale T (m) that is related to de Broglie wavelength of particle thermal oscillations. It is argued that rather than relating to the surface area of its horizon suggested by Bekenstein (1973, “Black Holes and Entropy,” Phys. Rev. D, 7(8), pp. 2333–2346), entropy of black hole should be related to its total thermal energy, namely, its enthalpy leading to S = 4Nk in exact agreement with the prediction of Major and Setter (2001, “Gravitational Statistical Mechanics: A Model,” Classical Quantum Gravity, 18, pp. 5125–5142).

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032003-032003-5. doi:10.1115/1.4032427.

In recent years, more efforts have been made to improve new and more efficient nonmembrane-based methods for water desalination. Capacitive deionization (CDI), a novel technique for water desalination using an electric field to adsorb ions from a solution to a high-porous media, has the capability to recover a fraction of the energy consumed for the desalination during the regeneration process, which happens to be its most prominent characteristic among other desalination methods. This paper introduces a new desalination method that aims at improving the performance of traditional CDI systems. The proposed process consists of an array of CDI cells connected in series with buffer containers in between them. Each buffer serves two purposes: (1) averaging the outlet solution from the preceding cell and (2) securing a continuous water supply to the following cell. Initial evaluation of the proposed CDI system architecture was made by comparing a two-cell-one-buffer assembly with a two cascaded cells array. Concentration of the intermediate solution buffer was the minimum averaged concentration attained at the outlet of the first CDI cell, under a steady-state condition. The obtained results show that the proposed CDI system with intermediate solution had better performance in terms of desalination percentage. This publication opens new opportunities to improve the performance of CDI systems and implement this technology on industrial applications.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032004-032004-11. doi:10.1115/1.4032793.

Interconnected floaters could use relative rotations around connection joints to drive a power take-off (PTO) system, such that the ocean wave energy can be converted into a useful energy. In this paper, our attention is on the PTO optimization for the interconnected floaters. A fully linear dynamic system, including the linear hydrodynamics of the interconnected floaters and a linear PTO system, is considered. Under assumptions of linear theory, we present a mathematical model for evaluating the maximum wave energy conversion of two interconnected floaters based on the three-dimensional wave radiation–diffraction theory. The model is validated by comparison of the present results with the published data, and there is a good agreement. The model can be employed to calculate the maximum power absorbed by the interconnected floaters under motion constraints due to the restraints of pump stroke or/and collision problem between the floaters. The influence of wave frequency, PTO system, floater rotary inertia radius, and motion constraints on the power capture capability of the two interconnected floaters is also examined. It can be concluded that enlarging the rotary inertia of each floater by using mass nonuniform distribution can be seen as an alternative way of adding PTO inertia. The maximum relative power capture width of the two interconnected floaters with optimized PTO system under constraints is much smaller than that without any motion constraints for long waves.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032005-032005-11. doi:10.1115/1.4032770.

Low operating cost, comfort, sustainability, and environmental footprint are the key elements of robust space heating (SH) system. In quest for higher efficiencies, it is not always possible to meet all of these demands where environmental footprint often gets secondary attention. This paper presents a novel SH system which is capable of meeting all of the aforementioned elements while simultaneously proving SH and domestic hot water (DHW). The system comprises a geothermal sourced heat pump (HP) featuring “hot gas water” (HGW) technology which delivers higher efficiency. This paper gives a thorough thermodynamic assessment of the system covering component based first and second law analysis and provides test results based on two case studies at a house (W10/W35) and a renovated building (W10/W45). The results show that a theoretical efficiency gain by 11.02% is achievable where the source temperature is 10 °C and the water temperature for floor heating is 35 °C. For the same system, with the same source temperature but with a supply temperature of 45 °C for SH, an efficiency gain of 17.91% is achievable. From experimental testing of the system using the test stand at GeoTherma, 4.73% efficiency gain with water temperature of 35 °C and 3.59% efficiency gain with water temperature of 45 °C were obtained. Economic analysis results showed that savings of up to 10% on an annual basis is possible with HGW technology installed in an average family house, whereas it gets 4.36% for a small hotel with a payback time period of about 9 yrs.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2015;138(3):032201-032201-9. doi:10.1115/1.4031967.

Ignition and flame propagation in methane/O2 mixtures diluted with CO2 are studied. A laser ignition system and dynamic pressure transducer are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBVs) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation are recorded by using a high-speed camera in select experiments to visualize the effect of CO2 proportionality on the combustion behavior. The LBV is studied for a range of equivalence ratios (ϕ = 0.8–1.3, in steps of 0.1) and oxygen ratios, D = O2/(O2 + CO2) (26–38% by volume). It was found that the LBV decreases by increasing the CO2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO2 proportionality increases, where it was not possible to obtain LBV due to the deviation from spherical flame shape. Current LBV data are in very good agreement with existing literature data. The premixed flame model from chemkin pro (Reaction Design, 2011, CHEMKIN-PRO 15112, Reaction Design, San Diego, CA) software and two mechanisms (GRI-Mech 3.0 (Smith et al., 1999, “The GRI 3.0 Chemical Kinetic Mechanism,” http://www.me.berkeley.edu/gri_mech/) and ARAMCO Mech 1.3 (Metcalfe et al., 2013, “A Hierarchical and Comparative Kinetic Modeling Study of C1–C2 Hydrocarbon and Oxygenated Fuels,” Int. J. Chem. Kinetics, 45(10), pp. 638–675)) are used to simulate the current data. In general, simulations are in reasonable agreement with current data. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;138(3):032202-032202-6. doi:10.1115/1.4032140.

Conventional noncatalytic fuel reforming provides low efficiency, large amounts of char and tar and limited control on chemical composition of the syngas produced. The distributed reaction regime can be used to assist noncatalytic reforming. In this paper, volume distributed reaction technique is used to enhance reformate quality as compared to conventional noncatalytic reforming. This work examines the intermediate regimes between volume distributed reaction and conventional flame to reform JP8 with focus on the chemical and mixing time scales. Chemical time scales were controlled with air preheat temperatures while the mixing time scales were kept constant. Progressive shift toward distributed reaction regime resulted in higher quality reformate with increased amounts of hydrogen and carbon monoxide in the syngas, but with reduced acetylene concentrations and soot formation. Visible soot formation was observed on reactor walls only under the flamelets in eddies regime. Higher hydrogen and carbon monoxide without any catalyst for JP8 reformation offers significant advantages on cost-effective plant operation, reliability, and high yields of syngas. Air preheats of 600, 630, and 660 °C showed a distributed reaction regime wherein the Damkohler number was below the Damkohler criterion, and this condition provided high H2 and CO yields and no soot. At temperature of 690 °C, laminar flame thickness approximated the integral length scale (at the interface of distributed and traditional reforming flame) showed minor soot formation. At even higher temperature of 750 °C, conventional reforming occurred with increased soot observed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032203-032203-12. doi:10.1115/1.4032207.

In this study, a nonstoichiometric single-phase chemical equilibrium model was developed to simulate atmospheric circulating fluidized bed (CFB) coal gasifiers in reference to the available experimental and simulation data. In the literature, since the single-phase model assumes complete conversion of the solid particles to gas phase, the predictions for the resulting products of the gasifiers considerably deviate from the measured product concentrations. Two different model modifications for carbon conversion and temperature to improve the model results were tested. Particularly, carbon conversion modification has been found to improve the predictive ability significantly. The main reasons of the inaccuracy in the tested cases as well as the performance of some other modifications (quasi-equilibrium approach, empirical correlation for carbon conversion, etc.) were also discussed in comparison with the literature data. An alternative mathematical procedure that simplifies the formulation and numerical implementation was suggested as well.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032204-032204-8. doi:10.1115/1.4032239.

Given that sulfur contents of coals vary widely, this work investigated whether cofiring of high-sulfur coals with low-sulfur coals of different ranks has any distinct advantages on lowering the sulfur dioxide emissions of the former coals, beyond those predicted based on their blending proportions. Such cofiring intends to take advantage of documented evidence in previous investigations at the author's laboratory, which demonstrated that lignite coals of low-sulfur, high-calcium, and high-sodium content undergo massive bulk fragmentation during their devolatilization. This particular behavior generates a large number of small-sized char particles which, upon effective dispersion in the gas, can heterogeneously absorb the emitted sulfur dioxide gases, i.e., act as defacto sorbents, and then retain them in the ash. This study included two high- and medium-sulfur bituminous coals, two low-sulfur lignite coals, and a sub-bituminous coal. Results showed that bituminous coals burning under substoichiometric (fuel-lean) conditions release most of their sulfur content in the form of SO2 gases, whereas low-ranked coals only partly release their sulfur as SO2. Furthermore, the SO2 emission from coal blends is nonlinear with blend proportions, hence, beneficial synergisms that result in substantial overall reductions of SO2 can be attained. Finally, NOx emissions from coal blends did not show consistent beneficial synergisms under the implemented fuel-lean combustion conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032205-032205-10. doi:10.1115/1.4032771.

An n-dodecane spray flame was simulated using a dynamic structure large-eddy simulation (LES) model coupled with a detailed chemistry combustion model to understand the ignition processes and the quasi-steady state flame structures. This study focuses on the effect of different ambient oxygen concentrations, 13%, 15%, and 21%, at an ambient temperature of 900 K and an ambient density of 22.8 kg/m3, which are typical diesel-engine relevant conditions with different levels of exhaust gas recirculation (EGR). The liquid spray was treated with a traditional Lagrangian method. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. It is observed that the main ignitions occur in rich mixture, and the flames are thickened around 35–40 mm off the spray axis due to the enhanced turbulence induced by the strong recirculation upstream, just behind the head of the flames at different oxygen concentrations. At 1 ms after the start of injection (SOI), the soot production is dominated by the broader region of high temperature in rich mixture instead of the stronger oxidation of the high peak temperature. Multiple realizations were performed for the 15% O2 condition to understand the realization-to-realization variation and to establish best practices for ensemble-averaging diesel spray flames. Two indexes are defined. The structure-similarity index (SSI) analysis suggests that at least 5 realizations are needed to obtain 99% similarity for mixture fraction if the average of 16 realizations is used as the target at 0.8 ms. However, this scenario may be different for different scalars of interest. It is found that 6 realizations would be enough to reach 99% of similarity for temperature, while 8 and 14 realizations are required to achieve 99% similarity for soot and OH mass fraction, respectively. Similar findings are noticed at 1 ms. More realizations are needed for the magnitude-similarity index (MSI) for the similar level of similarity as the SSI.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032206-032206-8. doi:10.1115/1.4032978.

This paper aims at studying the combined effect of oxygen enrichment and dual fueling on performance, emission, and combustion characteristics of a mono cylinder diesel engine using a blend of cashew nut shell pyro oil (CSO) and conventional diesel oil (called BD—base diesel) as fuel. Experiments were initially conducted using 100% BD as fuel at variable power output conditions. Subsequently, experiments were repeated with CSO40D60 (blend of 40% of CSO and 60% of BD by volume) at different power outputs. In the third phase, the engine was run with oxygen enrichment of 24% by volume in the intake air using CSO40D60 as fuel. Finally, the engine was operated in dual fuel mode of operation with the oxygen concentrations of 24% using CSO40D60 as pilot fuel and ethanol as the primary inducted fuel. Ethanol induction was made up to the maximum possible limit until misfire or knock. The brake thermal efficiency (BTE) was found as 25% with CSO40D60 29.5% and 30.5% with BD at the rated power output of 3.7 kW. The smoke number was noted as 55 filter smoke number (FSN) and 40 FSN, respectively, with CSO40D60 and BD. Hydrocarbon (HC) and carbon monoxide (CO) emissions were found to be higher with CSO40D60 as compared to BD. Ignition delay (ID) and combustion duration (CD) were also noted to be higher with CSO40D60 at all power outputs. Combined oxygen enrichment and ethanol induction sufficiently increased the BTE using CSO40D60 as fuel at all power outputs. At peak power output, the BTE was noted as 34.5%. The lowest smoke number of 36 FSN was found for 24% of oxygen with 34.3% of ethanol energy share at peak power output with CSO40D60 as fuel, whereas it was 40 FSN with BD and 55 FSN with CSO40D60 for 21% of oxygen. Significant improvement in heat release rates was observed by combining ethanol induction and oxygen enrichment techniques using CSO40D60 as fuel. Overall, it is concluded that by combining oxygen enrichment and ethanol induction superior performance and reduced emissions can be achieved at all power outputs using CSO40D60 as fuel.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032207-032207-12. doi:10.1115/1.4032901.

In military propulsion applications, the characterization of internal combustion engines operating with jet fuel is vital to understand engine performance, combustion phasing, and emissions when JP-8 is fully substituted for diesel fuel. In this work, high-resolution large eddy simulation (LES) simulations have been performed in-order to provide a comprehensive analysis of the detailed mixture formation process in engine sprays for nozzle configurations of interest to the Army. The first phase examines the behavior of a nonreacting evaporating spray, and demonstrates the accuracy in predicting liquid and vapor transient penetration profiles using a multirealization statistical grid-converged approach. The study was conducted using a suite of single-orifice injectors ranging from 40 to 147 μm at a rail pressure of 1000 bar and chamber conditions at 900 K and 60 bar. The next phase models the nonpremixed combustion behavior of reacting sprays and investigates the submodel ability to predict auto-ignition and lift-off length (LOL) dynamics. The model is constructed using a Kelvin Helmholtz–Rayleigh Taylor (KH–RT) spray atomization framework coupled to an LES approach. The liquid physical properties are defined using a JP-8 mixture containing 80% n-decane and 20% trimethylbenzene (TMB), while the gas phase utilizes the Aachen kinetic mechanism (Hummer, et al., 2007, “Experimental and Kinetic Modeling Study of Combustion of JP-8, Its Surrogates, and Reference Components in Laminar Non Premixed Flows,” Proc. Combust. Inst., 31, pp. 393–400 and Honnet, et al., 2009, “A Surrogate Fuel for Kerosene,” Proc. Combust. Inst., 32, pp. 485–492) and a detailed chemistry combustion approach. The results are in good agreement with the spray combustion measurements from the Army Research Laboratory (ARL), constant pressure flow (CPF) facility, and provide a robust computational framework for further JP-8 studies of spray combustion.

Commentary by Dr. Valentin Fuster

Research Papers: Oil/Gas Reservoirs

J. Energy Resour. Technol. 2016;138(3):032801-032801-10. doi:10.1115/1.4032520.

The response of existing transient triple-porosity models for fractured horizontal wells do not converge to that of linear dual-porosity model (DPM) in the absence of natural/microfractures (MFs). The main reason is the assumption of sequential-depletion from matrix to MF, and from MF to hydraulic-fractures (HFs). This can result in unreasonable estimates of MF and/or HF parameters. Hence, the authors proposed a quadrilinear flow model (QFM) in a previous paper which relaxes this sequential-depletion assumption to allow simultaneous matrix–MF and matrix–HF depletion. Also, it is proved that QFM simplifies to both DPM and linear sequential triple-porosity model (STPM). This work considers the implications of applying QFM, STPM, and DPM type-curves and analysis equations on production data of two fractured horizontal wells completed in the Bakken and Cardium Formations. A comparative study of the reservoir parameters estimated from the application of these models to the same production data reveals two key results. First, the application of DPM on the production data from reservoirs with active MF could result in overestimation of HF half-length. This happens to compensate for the extra fluid depletion pathways provided by MF. Second, the application of STPM on the production data from the reservoirs with active matrix–HF communication could result in overestimation of the MF intensity. Results from this study are significant when selecting the appropriate model for interpreting production data from fractured horizontal wells completed in formations with or without active MF. The DPM is appropriate if analog studies (e.g., outcrop, microseismic and image log analyses) reveal high fracture spacing aspect ratio (negligible MF) in the reservoir. Fracture spacing aspect ratio is MF spacing divided by the HF spacing. The STPM is appropriate if analog studies reveal low spacing aspect ratio (e.g., matrix–HF face damage or high MF intensity within a given HF spacing). QFM is appropriate for all fracture spacing aspect ratios.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2015;138(3):032901-032901-10. doi:10.1115/1.4032121.

The drilling mud program contains many tests such as filtration rate and filter cake properties to select the proper drilling fluid additives that yield the standard ranges of the viscosity, filtration rate, etc. However, the physical and chemical changes in the mud composition during the mud circulating will cause changes to the filter cake properties. The changes in the filter cake properties should be considered in the mud design program to prevent the problems associated with the change in the drilling fluid properties. For long horizontal wellbores penetrating plastic formations, the two sources of solids in filter cake are drilling chemical additives and formation cuttings (sand particles in the case of sandstone reservoir). This study focuses on the effect of introducing sand particles from the drilled—formations on the filter cake properties. Real drilling fluid samples from the field were collected at different location during drilling a 3600 ft of the horizontal section of a sandstone formation. Calcium Carbonate (CaCO3) was used as weighting material in this filed. The drilling fluid samples were collected at two different points: the flow line coming from the well after shale shaker and the flow line going to the well to verify the effect of separation stages on filter cake properties. The primary drilling fluid properties of the collected samples were measured such as density and rheological parameters. High pressure high temperature (HPHT) filter press was used to perform the filtration and filter cake experiments at 300 psi differential pressure and room temperature (25 °C). The mineralogy of the external filter cake formed by fluid loss cell is determined using SEM (scanning electron microscopy) and XRD (X-ray diffraction). Finally, solubility test was conducted to evaluate the effect of sand particles on filter cake removal (containing Calcium Carbonate as weighting material) using chelating agent: glutamic diacetic acid (GLDA) at pH 4. The results showed that for long horizontal sections, the effect of introducing sand particles to the composition of the filter cake can cause significant change to the properties of filter cake such as mineralogy, thickness, porosity, and permeability. For instant the thickness of filter cake increased about 40% of its original thickness when drilling sandstone formation in horizontal well due to fine sand particle settling. The filter cake porosity and permeability increment in the first 2000 ft part of the horizontal section was observed clearly due to the irregular shape of the drilling particles. However for the points after the first 2000 ft of horizontal lateral, the porosity and permeability almost remained constant. Increasing the sand content up to 20% degrade the dissolution rate of calcium carbonate in the GLDA (pH = 3.8) to 80% instead of 100%.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032902-032902-11. doi:10.1115/1.4032227.

Particle transport has been an active area of research for many years. Despite many excellent experimental and modeling studies contributing to the fundamental understanding of particle transport, the effect of viscosity is still not well-understood. There are limited experimental studies addressing the effect of viscosity on particle transport. Even among those limited studies, contradictory conclusions have been reported in the literature. A review of the single-phase proposed models also reveals that fluid viscosity has not been well addressed in the models as well. The main focus of this study is to investigate the effect of viscosity on particle transport in laminar and turbulent flows. Experiments were performed using a 0.05 m diameter pipe. Comparisons of the obtained data with previously reported data in the literature show similar characteristics. The current study finds that liquid flow regime in the pipe plays an important role on how viscosity affects the particle transport phenomenon. Discussions presented in this work to explain the obtained experimental data shed light on this less addressed physical parameter.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032903-032903-6. doi:10.1115/1.4032226.

For gas condensate reservoirs, as the reservoir pressure drops below the dew point pressure (DPP), a large amount of valuable condensate drops out and remains in the reservoir. Thus, prediction of accurate values for DPP is important and leads to successful development of gas condensate reservoirs. There are some experimental methods such as constant composition expansion (CCE) and constant volume depletion (CVD) for DPP measurement but difficulties in experimental measurement especially for lean retrograde gas condensate causes to develop of different empirical correlations and equations of state for DPP calculation. Equations of state and empirical correlations are developed for special and limited data sets and for unseen data sets they are not generalizable. To mitigate this problem, in this paper we developed new artificial neural network optimized by particle swarm optimization (ANN-PSO) for DPP prediction. Reservoir fluid composition, temperature and characteristics of the C7+ considered as input parameters to neural network and DPP as target parameter. Comparing results of the developed model in this research with Gaussian processes regression by particle swarm optimization (GPR-PSO), previous models and correlations shows that the predictive model is accurate and is generalizable to new unseen data sets.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032904-032904-7. doi:10.1115/1.4032236.

Wellbore stability has plagued oil industry for decades. Inclusion of the mud in drilling and the effect of mud cake build up incorporate very complex chemical, thermal, mechanical, and physical phenomena. It is very difficult to quantify all these phenomena in one model. The after effects of mud cake buildup, its permeability and variation in thickness with time alter the actual stress profile of the formation. To see the impact of the whole mechanism, a combination of laboratory studies and numerical modeling is needed. This paper includes the procedure and results on stress profiles in near wellbore region based on laboratory studies of mud cake buildup in high pressure and high temperature environment using permeability plug apparatus (PPA). The damaged formation zone is very susceptible to drilling fluid and results in alteration of existing pore pressure and fracture pressure. This paper presents integrated experimental and analytical solutions for wellbore strengthening due to mud cake plastering. Conducting experiments on rock core disks has provided more realistic results which can resemble to field conditions. The experimental work here provides an insight to effect of mud cake build up at high pressure and high temperature conditions using a heterogeneous filtration medium prepared from different sandstone cores. Results were used in the analytical model to see the effect of stresses in the formation. The primary objective is to investigate the wellbore hoop stress changes due to formation of filter cake by mud plastering using the analytical models built upon the laboratory results. The models developed in this work provide insights to quantify on wellbore plastering effects by mud cake build up.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032905-032905-7. doi:10.1115/1.4032449.

Understanding the stress change in a reservoir generated by fluid production/injection is important for field development purposes. In this paper, we provide the Eshelby solution for stress and strain distribution inside and outside of an anisotropic poroelastic inhomogeneity due to pore pressure changes inside the inhomogeneity. The term anisotropic inhomogeneity refers to an inhomogeneity with anisotropic poroelastic constants. Some graphical results for strain and stress ratios for different material properties and geometries are presented as well. Anisotropy in elastic properties has been studied extensively in the last century; however, anisotropy in poroelastic properties, despite its potential significant impact in different engineering problems, has not been explored thoroughly. The results show how neglecting the effect of anisotropic poroelastic properties may result in large differences in calculated stresses. Due to the authors' primary interest in geomechanical problems, the discussions and examples are chosen for applications involving fluid withdrawal/injection into hydrocarbon reservoirs.

Topics: Stress , Pressure
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032906-032906-7. doi:10.1115/1.4032542.

This paper presents a comprehensive experimental evaluation to investigate the effects of adding iron-based and calcium-based nanoparticles (NPs) to nonaqueous drilling fluids (NAFs) as a fluid loss additive and for wellbore strengthening applications in permeable formations. API standard high-pressure-high-temperature (HPHT) filter press in conjunction with ceramic disks is used to quantify fluid loss reduction. Hydraulic fracturing experiments are carried out to measure fracturing and re-opening pressures. A significant enhancement in both filtration and strengthening was achieved by means of in situ prepared NPs. Our results demonstrate that filtration reduction is essential for successful wellbore strengthening; however, excessive reduction could affect the strengthening negatively.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032907-032907-7. doi:10.1115/1.4032546.

Well stimulation using acidic solutions is widely used to treat carbonate formations. The acidic fluids remove the near-wellbore damage and create channels around the wellbore by dissolving fraction of the carbonate rocks. Many stimulation fluids have been used such as hydrochloric acid (HCl) acid, organic acids, and chelating agents to stimulate carbonate reservoirs. Wormholes that are created by these fluids are very effective and will yield negative skin values and this will enhance the well productivity. In addition to the wormhole creation, the diffusion of these fluids inside the pores of the rock may create significant and permanent changes in the rock mechanical properties. These changes can eventually lead to weakening the rock strength, which may lead to future formation damage due to the wellbore instability. In this paper, the effect of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) chelating agents on the carbonate rocks elastic properties was investigated. The effect of wormholes created by chelating agent on the rock mechanical properties was investigated. Computed tomography (CT) scan and acoustic measurements were conducted on the core samples before and after matrix stimulation treatments. Experimental results showed that the mechanical properties of strong rocks such as Indiana limestone (IL) cores were not affected when chelating agents were used to stimulate those cores. On the other hand, less strong rocks such as Austin chalk (AC) show significant alteration on the rock elastic properties when chelating agents were used as stimulation fluids.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(3):032908-032908-9. doi:10.1115/1.4032886.

The Tahe reservoir, one of the largest scale carbonate reservoirs in western China, has very special cavities and fractures. The size of the cavities ranges from millimeter to meter scale, and the size of the fractures ranges from hundreds micrometers to millimeters scale. The length of some cavities can even reach kilometers. However, based on views of core testing results, there is insignificant flow in the rock matrix. This paper introduces a new and refined method to determine flow units in such Karst carbonate reservoirs. Based on fractal theory, fluid flow patterns can be divided into three types by using production data of the Tahe reservoir. Through porosity and permeability statistics of production layers on the established geological model, flow boundaries of different flow patterns were proposed. Flow units were classified in terms of the flow boundaries. As for refined flow units, subcategory flow units were determined by three graphical tools: the limit of dynamic synthesis coefficient (DSCL) method, modified flow coefficient (MS1 and MS2, which are derived by the Forchheimer equation) curve, and the stratigraphic modified Lorenz plot (SMLP). All the parameters of graphical tools help to reconcile geology to fluid flow by illustrating the important link between geology, petrophysics, and reservoir engineering. The use of this technique is illustrated with data from a specific block of the Tahe reservoir.

Commentary by Dr. Valentin Fuster

Expert View

J. Energy Resour. Technol. 2016;138(3):034701-034701-4. doi:10.1115/1.4032426.

This work has been done to recognize the various contributing disciplines in colleges and universities to achieving the global goals. One aim is to point out the many college disciplines internationally that would contribute to these goals. Only four out of the global goals seem not to be directly contributed to by sustainable engineering. A presentation of relevant publications has been made of the role of sustainable engineering in accomplishing the 17 global goals of the United Nations. The pervasiveness and long reach of the many branches of sustainable engineering are evident. The implied importance of good quality engineering schools and colleges worldwide cannot be refuted.

Commentary by Dr. Valentin Fuster

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