查看更多>>摘要：This paper studies the rheology and annular flow of a smart lost circulation material(LCM)at 160 ℃,using a high-temperature flow loop.The smart LCM is a shape memory polymer(SMP)that activates at high temper atures,and its particle size increases to seal fractures in geothermal formations.SMP was mixed with the base fluid in two different concentrations,1.0 and 3.0 wt%,to study rheology,wellbore hydraulics,activation process,and settling behavior under different testing conditions.The results of this study showed that the SMP could be activated at high temperatures.An increase of 80-100% in the particle size was observed at 160 ℃.The mud samples showed a high shear-thinning behavior at the two concentrations with a Power-law flow index(n)ranging between 0.025 and 0.101.No additional frie-tional pressure losses were observed when SMP was added to the base fluid.SMP particles showed an excellent suspension at 1.0 wt% while,at 3.0 wt%,a bed was formed at a low flow rate and without pipe rotation Increasing the drill pipe rotational speed or flow rate effectively removed the bed and homogeneously dispersed the SMP particles,ensuring a better sealing efficiency.SMP particle dispersion in inclined wells was better thar in horizontal wells.Moreover,the findings of this study help optimize the lost circulation treatment by considering a wide range of operating parameters that can further be extended to different systems and geometries.
查看更多>>摘要：A viscoelastic material exhibits both fluid(viscous)and solid(elastic)like properties simultaneously.The rheological behavior of drilling fluids is customarily measured under the assumption of pure viscous flow,yet they exhibit both viscous and elastic characteristics when subjected to deformation.Some imperative properties of drilling fluids such as gel strength,yield stress,and sag tendency at near-zero shear rate region are categorically under the influence of viscoelastic behavior and have not yet been completely understood due to the lack of appropriate measurement methods.Characterizing the complete rheological profile of material requires measuring linear and nonlinear viscoelastic responses at a wide range of stress/strain levels.The viscoelastic nonlinearity can be characterized under Large Amplitude Oscillatory Shear(LAOS)tests.This study presents a large amplitude oscillatory shear rheology investigation of two water-base(Lignosul-fonate and KCl/polymer)and two oil-base(low and high temperature)drilling fluids each in three states;unweighted,weighted,and weighted-contaminated.The viscoelastic nonlinearities of four fluid samples were investigated experimentally as a function of strain amplitude and strain-rate space at different temperatures.The results were described using Lissajous-Bowditch(L-B)plots and local nonlinear viscoelastic dynamic moduli through an oscillatory shear cycle.Structural stability of fluid samples was also studied using the creep-recovery test.The nonlinear viscoelastic behavior of drilling fluids was comprehensively compared and distinguished to understand their nonlinear shear mechanism.As a result of the creep-recovery test at 150 ℃,high-temperature oil base mud provided higher thermo-structural stability and zero shear viscosity than those of Lignosulfonate,KCl/polymer,and low-temperature oil-base muds.While the elastic nonlinearity was found to be strain/strain rate softening,the nonlinear viscous character was recorded as shear/shear rate thinning at large strain rates for all drilling fluid systems.Quite a different shear mechanism was detected at low and moderate strain rates.Shear rate thinning was found to be the dominant mechanism for all fluids except Lignosulfonate mud samples that demonstrated shear-thickening behavior at moderate strain rates at 25 ℃.At high temperatures(100 ℃ and 150 ℃),shear rate thickening followed by shear rate thinning behavior was governing mechanism under the low and moderate strain rates in all mud samples except KCl/polymer muds.An inverse behavior(shear rate thinning followed by shear rate thickening)was observed through low and moderate strain rates in KCl/polymer muds at 100 ℃ and 150 ℃.Therefore,as revealed from the LAOS test results,shear rate thickening behavior at low to moderate strain rates is in contradiction of the commonly known shear thinning behavior for a drilling fluid undergoing viscous deformation.This finding explains the facts underlying some important properties of drilling fluids such as gel structure formation,hole cleaning ability,and sag tendency.
查看更多>>摘要：A newly developed CO2-brine interfacial tension(IFT)correlation has been successfully developed to more accurately estimate the CO2-brine IFT for a wide range of reservoir pressure,temperature,and formation water salinity.The new CO2-brine correlation is expressed as a function of CO2-water density difference(function of pressure and temperature),temperature,and the valence-weighted molality of the cations.The novel aspect of the approach was to both correlate with density difference and include accurate temperature dependence of the parameters.This prediction model originated from a CO2-brine IFT database from the literature that covers 1298 CO2-brine IFT data including 484 for pure water and CO2.To examine its predictive capacity,the new CO2-brine IFT correlation is compared with four commonly used IFT correlations in the literature.It is found that the new CO2-brine IFT correlation provides more comprehensive and accurate reproduction of the literature pure CO2-pure water IFT data with an average absolute relative error(AARE)of 2.4% and standard deviation(SD)of 3.2%.In addition,the newly developed CO2-brine IFT correlation results in the accurate prediction of the CO2-brine IFT with an AARE of 2.4% and a SD of 3.4%.
查看更多>>摘要：Drilling more infill multi-fractured horizontal wells(MFHWs)is one of the most direct oil and gas production methods in unconventional reservoirs with high recovery.MFHWs in the multi-horizontal-well pad can be easily interfered by the adjacent wells during well testing.Unfortunately,most of the existing well testing models for MFHWs are limited to a single well.A semi-analytical well testing model for transient pressure analysis in a multi-horizontal-well pad is presented in this work.In the proposed model,the entire formation is divided into three domains,namely matrix,natural fracture,and hydraulic fracture,to describe unconventional reservoirs comprehensively.With Laplace transform and Stehfest numerical inversion techniques,the reservoir models with matrix and natural fracture systems are solved analytically.The solutions of the hydraulic fracture model for multiple MFHWs are obtained by the finite difference method.The pressure superposition method and production rate relationship are used to characterize the impact from the adjacent wells.The general solutions of the multi-well reservoir model and hydraulic fracture model are then coupled to obtain the tested well's bottom-hole pressure.The results of the proposed model are in good agreement with the commercial numerical software.The multi-horizontal-well pad's integrated flow regimes can be divided into a bilinear flow,linear formation flow,the pseudo radial flow of hydraulic fracture,multi-MFHW effect,cross-flow between matrix and natural fracture,and formation pseudo radial flow.The pseudo radial flow of hydraulic fracture,the multi-MFHW effect,cross flow,and formation pseudo radial flow have unique characteristics in the multi-horizontal-well pad,and these flow regimes are highly affected by the adjacent MFHWs properties and well-spacing.With the change of well-spacing,the multi-MFHW effect is characterized by the linear flow inside the multi-horizontal-well pad or the multi-well pad's biradial flow.The comparison of pseudo-steady-state(PSS)flow and transient flow indicates that different cross-flow conditions from the matrix to natural fracture will only affect the derivative curve's cross-flow behavior.The case study shows that the proposed model can obtain a more accurate interpretation result of the tested well under the adjacent well's effect.
查看更多>>摘要：The hydrate saturation is a critical parameter in the evaluation of gas hydrate reservoirs.The complex characteristics of hydrate-bearing sediments pose challenges to the reliability of conventional geophysical techniques for hydrate saturation evaluation.In this paper,we present a study on developing a novel approach to characterize the electrical properties of hydrate-bearing porous media and to evaluate the hydrate saturation quantitatively based on parameters of the complex electrical conductivity.In the laboratory experiments we prepared samples with the tetrahydrofuran hydrate forming in sands to simulate the hydrate-bearing sediments and for measuring the complex conductivity at frequencies from 20 Hz to 100 kHz.The frequency-dispersion characteristics of complex conductivity of the hydrate-bearing samples with different saturations were analyzed,and then three types of hydrate-saturation evaluation models,denoted as the conductance-based,polarization-based and fusion models,were developed based on the in-phase conductivity,frequency-dispersion characteristic parameters of the phase angle and the combination of those two,respectively.A critical frequency(fc = 2 kHz)can be identified,where both the phase angle and imaginary component of the complex conductivity reach their minima.The Archie's formula shows its capability to model the relationship between the in-phase conductivity and hydrate saturation(i.e.,conductance-based model),but the frequency higher than fc is preferred because stable Archie parameters can only be obtained in that frequency range.Linear correlations between the hydrate saturation and frequency-dispersion characteristic parameters(i.e.,the logarithms of FE(frequency effect)and slope of the relation between FE and FR(frequency ratio)of the phase angle can be obtained,serving as the polarization-based models in the frequency range higher than fc.The fusion model performs the best in the perspective of low errors and high reliability for predicting the hydrate saturation,because more parameters of the complex conductivity and underlying physics of the conductance and polarization have been incorporated.In the frequency range lower than fc in contrast to that of the phase angle,me quadrature conductivity shows remarkable frequency-dispersion characteristics with the variation of the hydrate saturation,showing the great potential for developing new saturation-evaluation models in future.
查看更多>>摘要：A novel formula of anionic surfactants with propoxy(PO)and ethoxy(EO)groups and cationic surfactants was developed and temperature and salt resistance performance of the formula has been studied with both model oil and crude oil.An obvious synergistic effect was evidenced by CMC values and interaction parameters of non-ylphenol polyether carboxylate,hexadecyltrimethylammonium chloride and their mixtures.Effect of molar ratio of anionic surfactant and cationic surfactant,temperature,salinity,concentration and oil-water ratio on phase behavior and interfacial tension were investigated systematically.The results demonstrate that ultra-low interfacial tension and excellent phase behavior were obtained at temperature up to 120 ℃ and a wide range of salinity,which shows promising for enhanced oil recovery.
查看更多>>摘要：In this study,a thixotropic and high-strength gel system(THSG)is developed,which is experimentally proven to be feasible for conformance control in fractured reservoirs.The THSG is based on in-situ polymerization of the acrylamide monomer,incorporating a weak gel system.It is found that the superior rheological properties of THSG are beneficial for injection and placement of gelant into the fractures.The viscosity of THSG at varying shear rates can be well fit by the Carreau-Yasuda model,and its shear thinning behavior contributes to low injection pressure during the gelant injection.Moreover,this THSG system exhibits much better thixotropy than the traditional Cr(III)-acetate-HPAM gel system(HPAM/Cr(III)gel),which would enable the THSG an easier access to the small apertures.It is also found that the injection pressure is greatly increased with decreasing of the diameter of aperture during injection of the HPAM/Cr(III)gel,while little effect of the aperture size on injection pressure was observed during THSG injection.Additionally,the yield stress of the thixotropic gelant is noticeably high,which would greatly mitigate the adverse effect of gravity segregation in fractures during well shut-off.This would be also beneficial for plugging the whole fractures.To better understand the properties of THSG,the gelation performance,the microstructure of the gel and the blocking ability of gel in the tubes were investigated.The results show that the clay particles strengthened gel exhibits a large storage modulus and excellent thermal stability.Scanning electron microscopy(SEM)results show that the clay particles were readily distributed on the polymer chains,and the clay particles could facilitate the gel to form a firm and uniform network.Consequentiy,the clay particles strengthened THSG gels have relatively high rupture pressure,which would be exceedingly favorable for efficient gel treatments in fractured reservoirs.
查看更多>>摘要：Formation damage can significantly defer hydrocarbon production.Formation damage is one of the key parameters used to evaluate the quality of various operations during the life of a well.The evolution of formation damage over time is rarely studied.This paper presents the pressure transient analysis(PTA)used to derive a correlation between skin factor increase and the length of time for which a well was left exposed to drilling fluid.Multiple field examples are analyzed and modeled comparatively to evaluate the magnitude of the time-lapse formation damage.A quantitative relationship between the increase in mechanical skin as a function of exposure to drilling mud is constructed by a polynomial fitting.This gives us an insight on the how the well skin increases with exposure to drilling mud.Several mathematical models have been developed to model formation damage mechanisms.However,it is cumbersome to isolate and compute the individual mechanisms contributing to observed damage.Formation damage results from a combination of the pore size distribution,fines migration,fluid compatibility problems,wettability,presence of inorganic salts deposition,insufficient well cleanup,organic substance deposition,multiphase flow effects,etc.The proposed approach uses the skin factor derived from pressure transient analysis(PTA)to track the time-lapse evolution of formation damage during exposure time to mud,from drilling to production.The methodology has been applied to various reservoir rocks to quantify the impact for a specific rock type.Results from pressure transient tests conducted immediately after drilling,casing,and perforating are compared with production tests performed multiple years after drilling confirm that there is a mathematical relation between the formation damage,type of drilling and completion fluid,formation rock type,and exposure time to such fluids.The formation damage increase is more severe for longer duration of exposure,and also more severe for higher formation permeability.
查看更多>>摘要：Fractured-vuggy reservoir is characterized by various reservoir spaces,large multi-scale differences,uneven connectivity,and strong spatial heterogeneity,all of which bring great challenges to the understanding of the remaining oil distribution.Therefore,we built a visual physical model based on typical well groups,and intuitively simulated the remaining oil distribution of the fractured-vuggy reservoir through experiments.Then,we discussed the influence of the key parameters,including the injection-production position,injection rate,and bottom water intensity,on waterflooding development and remaining oil distribution.The results show that extending the injection-production distance and avoiding water injecting above the side with a deep dominant pathway is beneficial to enhance oil recovery.In a certain range,the swept area of injected water and displacement efficiency can be increased by appropriately increasing the injection rate.When the development depends on bottom water,the reserves between production wells cannot be effectively used.Based on the experiment results,five types of remaining oil distribution can be summarized:attic-type oil,blocked-type oil,retained-type oil,occluded-type oil,and shielded-type oil.There are multiple types of remaining oil in a fractured-vuggy system,so when tapping the remaining oil,it is necessary to comprehensively analyze the distribution and reserves scale to optimize the tapping scheme and maximize the recovery degree of the reservoir.
查看更多>>摘要：Well placement optimization is important in reservoir management,but it is challenging to implement due to the high-dimensional solution space and large number of reservoir simulations required.Surrogate models may assist to alleviate the computational burden by efficiently approximating full-order models.Although deep learning has been proven to be effective for surrogate modeling,most deep learning surrogates are purely data-driven,and underlying physical principles or theories of subsurface flows are not considered.In this work,a theory-guided convolutional neural network(TgCNN)framework is extended as a surrogate for subsurface flows with position-varying sink/source terms(well locations),which is further utilized for well placement optimization.In TgCNN,the physical constraints are incorporated to guide the training process of the surrogate by adding the residual of governing equations(and boundary/initial conditions)into the loss function.Guided by theory,the TgCNN surrogate can achieve better accuracy and generalizability,even when trained with limited data.The trained TgCNN surrogate can be further used for well placement optimization by combining it with the genetic algorithm(GA).The TgCNN surrogate also achieves satisfactory extrapolation performance for scenarios with different well numbers,and thus joint optimization of well number and placement can also be implemented with the TgCNN surrogate.The performance of the proposed optimization strategy is compared with the optimization framework that uses the simulator directly,and the results verify the accuracy of the TgCNN surrogate-based GA.Moreover,using the TgCNN surrogate can improve the efficiency of optimization significantly compared with running the simulators repeatedly.The effect of geologic uncertainty for the optimization is also investigated,and the results demonstrate that the optimization results may deviate from the optimal well placements as the degree of uncertainty increases.
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