查看更多>>摘要：It is a widely used method to evaluate gas reservoirs by measuring inelastic gamma rays.A petrophysical parameter fast neutron cross section(FNXS)was proposed to describe the inelastic gamma for gas reservoir evaluation.FNXS is the 14 MeV neutron macroscopic elastic scattering cross section.However,the description of inelastic gamma using FNXS is only a first order approximation.Therefore,in some scenarios,the evaluation of gas saturation is not accurate enough.In this paper,we propose a new parameter total fast neutron cross section(TFNXS)based on the inelastic gamma generation and attenuation theory.TFNXS is the sum of macroscopic elastic and inelastic scattering cross sections of 14 MeV neutrons.The physical meaning of TFNXS is the probability of inelastic and elastic scattering between neutrons and formation.TFNXS is a new formation property independent of neutron macroscopic capture cross section(Sigma).TFNXS value of gas is quite different from that of matrix minerals,water,oil and clay,so TFNXS is more sensitive to gas-bearing formation and can identify gas reservoir more effectively.We compared the sensitivity of TFNXS and FNXS to gas.The sensitivity of TFNXS to gas is similar to that of FNXS.The effects of different formation conditions on the measurement accuracy of the TFNXS and the FNXS are analyzed with the Monte Carlo method.Compared with FNXS,TFNXS can be obtained more accurately in water and oil layers.Different clay minerals have different effects on TFNXS and FNXS.TFNXS is less affected by wellbore environment,such as well diameter and wellbore fluid,than that of FNXS.We evaluate the application results of TFNXS and FNXS in various model wells.Both TFNXS and FNXS can effectively identify gas-bearing formations.The accuracy of using TFNXS to obtain gas saturation is higher than that of FNXS.TFNXS can more accurately monitor reservoirs and evaluate low porosity gas reservoirs than FNXS.
查看更多>>摘要：Several researchers employed N2 to augment CH4 recovery efficiency and CO2 sequestration during the Enhanced Gas Recovery(EGR)process in consolidated rocks.To our knowledge,there has been limited data backing the reason why CO2 experienced a more extended breakthrough during the EGR process in the presence of N2 gas,This study investigated CO2 and N2 behaviour during the core flooding experiment by CO2 injection in Ben-theimer core plug.N2 was used as the continuous phase during the core flooding process,while CO2 was the dispersed phase.The experiment was designed with varying injection rates at 30 and 40 ℃ temperature points,The experimental findings showed that the dispersion and diffusion coefficient,CO2 storage,concentration profile and breakthroughs were highly influenced by temperature change,especially at lower injection rates,However,at high injections,those properties are less sensitive to change in temperature,with most of the curves overlapping in the concentration profile.The highest and most negligible dispersion and diffusion coefficients were recorded at the highest and lowest injection rates respectively.These results agree with those reported by several researchers for sandstone rocks.Thus,higher temperatures have a more substantial effect on dispersion and diffusion coefficient,which eventually led to higher mixing between CO2 and N2.The breakthrough time decreases with an increase in reservoir temperature,confirming the diffusion and dispersion coefficients are temperature dependent.The experiment at 30 ℃ recorded an extended breakthrough time over that at 40 ℃,The maximum breakthrough time at 0.52 PV was recorded at 30 ℃ at the lowest injection rate.The concen-tration profile highlighted the trend between the displacing and displaced gas during the core flooding experl-ment.From the range of injections and temperatures tested,the CO2 PV stored decreases as the rate of injection increases from 0.4 to 1.2 ml/min.However,the CO2 stored was more promising at higher rates,corresponding with high differential pressure,due to flow resistance within the tortuous flow channels in the porous mediunm.
查看更多>>摘要：The oil migration in nanoslits is essential to enhance oil recovery.In this study,the calcite was selected as typical representative of deep and medium-shallow reservoir,the effect of gas on oil migration behavior in calcite nanoslits is investigated at molecular level.Two types of migration behaviors,via overall migration and gas channel,were observed for oil in gas flooding,which was determining by the stability of oil adsorption region.Specifically,if the interaction of gas/nanoslits was more vigorous than that of oil/nanoslits,the oil adsorption region will remain stable and the oil would be overall migration;otherwise it formed gas channel.The influence of injected gas on oil migration had the sequence of CO2>C3H8>CH4>N2 under deep reservoirs,which is better than that under medium-shallow reservoirs.Our study highlighted the influence of injected gas and reservoir conditions on the oil migration at a molecular level,which might help facilitate the exploration of deep reservoirs.
查看更多>>摘要：As oil and gas production moves into deep-water,the effect of brine salinity in water produced with petroleum is an important factor to be considered for hydrate management in transport pipelines.In this work,methane hydrate formation was conducted in water-in-oil emulsions with various salinities in the aqueous phase by using a high-pressure rheometer.The viscosity evolution during hydrate formation was analyzed.The results suggested that the increase in salt concentration could significantly reduce the hydrate slurry viscosity,and improve the stability of the slurry.As the salinity increased from 0.3 wt% to 5 wt%,the relative viscosity of the final slurry after hydrate formation decreased from more than 300 to only 42.When the salinity was greater than 1 wt%,hydrate slurries could keep stable flow for a long time,and the relative viscosity was less than 100.Meanwhile,a shear ramp was conducted.The hydrate slurries exhibited shear-thinning,and the rheological properties were described with an established viscosity model.Good agreement was observed between the experiments and model calculations under different brine salinity,and the aggregation process of hydrate particle and viscosity change at different shear rates were analyzed.In addition,a rest and restart process was conducted,and the yield stress of time-dependent was analyzed.With increasing rest time,the yield stress increased gradually.A high brine salinity of 5 wt% in the aqueous phase could significantly decrease this yield stress value and slow its increase with the rest time.After 1280 min of rest,the yield stress increased to 83 Pa,which was only one third of the yield stress value of the hydrate slurry with 1 wt% NaCl.Particularly,with a high brine salinity,when the rest time was over 160 min,two-step yielding behaviors were first observed for the hydrate slurry in the stress sweep,and a possible mechanism for the two-step yielding in the hydrate slurry system was proposed.
查看更多>>摘要：One of the possible fluid-fluid interactions during water-flooding in oil reservoirs,that is still debated,is the effect of injected brine salinity on asphaltene destabilization.If asphaltene precipitation is induced by salinity changes in the oil reservoirs and surface facilities,this could have a massive impact on the economy of a low salinity water-flooding project.Therefore,this study aims to investigate the effect of brine salinity on the amount of asphaltene precipitation and the governing destabilization mechanisms.Direct asphaltene precipitation measurements,along with the analyses of optical microscopy images and ion chromatography(IC),indicate that the asphaltene precipitation mechanism is dependent on brine salinity.At a high brine salinity,ions play the primary role as possible nuclei for asphaltene aggregates and might promote asphaltene precipitation through asphaltene-ions bonding.While at low salinity,the polarity of the brine-oil interface causes the asphaltenes to be adsorbed toward the brine-oil interface,and this also might disrupt the stability of asphaltenes in the oil bulk Of all the brines investigated,the highest amount of asphaltene precipitation was observed for the case in which crude oil was in contact with formation water.Based on the IC results,sulfate and magnesium are the most active ions to play the role of the nucleus in the structure of asphaltene agglomerates.Results also showed that the presence of Naphthenic Acids(NAs)in crude oil composition can affect the amount of asphaltene precipitation.
Christina ApostolidouErnestos SardsAndreas Georgakopoulos
15页
查看更多>>摘要：This paper focuses on the development of a drilling fluid system that satisfies both environmental and technical requirements,acting as an environmentally appropriate alternative to oil or synthetic-based drilling fluids.The effectiveness of two types of low-rank coals(leonardite & lignite)as shear-thinning additives on the rheological behaviour and filtration control in drilling fluids after dynamic thermal aging is investigated.The most suitable model that best describes their rheology is the Herschel-Buckley model over the entire range of shear rates and all temperature levels.Dynamic thermal aging influences the yield stress at zero shear rates,the consistency index,the flow behaviour index of the Herschel-Buckley model as well as the yield point and plastic viscosity of the Bingham-Plastic model.Despite their geochemical differences,the addition of both low-rank coals in the drilling fluids improves the yield stress and yield point build-up with temperature increase and maintains them widiin acceptable values compared with coal-free drilling fluids.The highest aging temperature under dynamic conditions deteriorates significantly the rheological and filtration control parameters.For the specific concentration of additives and dynamic thermal aging,the temperature of 177 ℃ appears to be an upper thermal bound which the drilling fluids lose their design purpose.It is also demonstrated that considerable energy is required to change both the plastic viscosity and the yield point of the proposed drilling fluids with both low rank coals showing their effectiveness as shear thinning agents to maintain the desired low shear strength and yield point after dynamic thermal aging.
查看更多>>摘要：Recurrent neural networks(RNN),which are able to capture temporal natures of a signal,are becoming more common in machine learning applied to petroleum engineering,particularly drilling.With this technology come requirements and caveats related to the input data that play a significant role on resultant models.This paper explores how data pre-processing and attribute selection techniques affect the RNN models'performance.Re-sampling and down-sampling methods are compared;imputation strategies,a problem generally omitted in published research,are explored and a method to select either last observation carried forward or linear interpolation is introduced and explored in terms of model accuracy.Case studies are performed on real-time drilling logs from the open Volve dataset published by Equinor.For a realistic evaluation,a semi-automated process is proposed for data preparation and model training and evaluation which employs a continuous learning approach for machine learning model updating,where the training dataset is being built continuously while the well is being made.This allows for accurate benchmarking of data pre-processing mediods.Included is a previously developed and updated branched custom neural network architecture that includes both recurrent elements as well as row-wise regression elements.Source code for the implementation is published on GitHub.
查看更多>>摘要：This paper investigates the gas phase,including bubbles'and gas pockets'migration and evolution in gas-liquid flow in the pipelines,where the safe operation is severely influenced by the gas accumulations.To investigate the formation,as well as location and amount of these gas accumulations,a new transient model applied with the Population Balance Model(PBM),gas pockets capturing and tracking model are proposed,which are discretized and calculated in the collocated multi-grid with Eulerian-Lagrangian coupling scheme.The flow field of the pipeline is modeled with the Eulerian scheme,while the bubbles'migration,gas pockets'capturing and tracking can be modeled in the Lagrangian mesh.To couple the description of bubble-dimension and that of pipe-dimension,the Rayleith-Plesset equation and the Smooth Particle Hydrodynamics(SPH)are applied,thus,the changeable characteristics of bubbles along the pipes can be described.Based on that,the bubbles'transition to the gas pocket under specific conditions can be predicted.And the subsequent capturing and tracking process will work with the help of the collocated multi-grid,which provides the accurate and parallel calculation.The relative parameters are extracted from the published experimental data,and the simulation results are in good agreement with the measured results.Meanwhile,the case studies show the model has the prediction ability of the gas phase's migration and evolution,as well as the formation and location of gas accumulations in the pipeline.
Gabriela Souza ChavesHamidreza KaramiVirgilio Jose Martins Ferreira Filho
12页
查看更多>>摘要：In the oil industry,multiphase flow models are commonly used to simulate the flow from reservoir to the production unit.Flow simulations help in the production monitoring and optimization to support the decisionmaking process.Despite the need for accurate simulations to support production operations,multiphase flow models are mostly developed using laboratory data and rarely validated under field-scale conditions.To improve the understanding of multiphase flow models in field conditions,this work evaluates the performance of a large set of models for a dataset composed of two production units with 20 producing wells and 865 measured production points.The wells are divided and analyzed in two segments:the surface flowline and the wellbore.The evaluation compares the models'performances using various statistical parameters and trending charts.The evaluation analyzes the impacts of production parameters,well geometry,predicted flow pattern,and pressure drop components on the model performances.Overall,Ansari's model presented the best performance with 13.8% absolute average percent error for the flowline segment and 14.1% error for the wellbore segment.In addition,Gray can also generate good results for most but not all of the tested wellbores.From the production parameters evaluation,higher flow rate tests resulted in more stable outputs.Ansari and Beggs models showed a trend of increasing errors for wells with larger horizontal wellbore lengths.Also,Beggs model showed larger errors when the transition flow pattern was predicted.Finally,both Ansari and Beggs models showed larger overprediction errors for tests with higher pressure losses in the flowline segment,while Gray showed smaller errors for these cases.The conclusions can be used to select the best models given the production system's flow parameters,or be incorporated in systems to increase the accuracy.
查看更多>>摘要：It is crucial to ensure the safety and integrity of underground gas storage(UGS)infrastructure for energy reliability in California,and many other places around the world.To address the risk management need in UGS industry,we take advantage of recent advances in downhole fiber optic monitoring and coupled well-reservoir simulation to provide unprecedented understanding of gas flow in wells at UGS sites.We have combined advanced monitoring and simulation of UGS operations into a decision-support system called the Integrated Risk Management and Decision Support System(IRMDSS).The IRMDSS framework includes three components:(i)mechanistic models,(ii)continuous and frequent monitoring data,and(iii)a supervisory interface for performing analyses using the models and monitoring data.The goal of the IRMDSS is to equip UGS operators with real-time monitoring data and simulation tools that can alert them to potential failures,detect early leakage,and support mitigation decision-making to prevent otherwise larger failures.We demonstrate an application of the IRMDSS by analyzing the temperature and pressure response to a hypothetical leak.Through a review of distributed temperature sensing(DTS)data collected at an operating UGS facility we show that DTS can uniquely and precisely identify the depth of the gas-water-contact in the well annulus,and that DTS can provide an early warning signal of upward gas flow as would occur in a well blowout scenario.When combined with modeling analysis,a rough leak rate can be roughly estimated to understand the severity of the leakage conditions and to support the mitigation decision needed.
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