查看更多>>摘要：Wellbore failure is the most headache and common problem in drilling engineering.Wireline loggings like caliper log and image log are usually used to identify wellbore failure.However,it is impossible to discern the failure types and take steps in real-time using the post-drilling methods.During the drilling process,various cavings will circulate to the ground with drilling fluid when wellbore instability occurs.These cavings are the foremost indicator of wellbore deterioration and have a potential link to the mechanism of borehole failure.Unfortunately,the use of cavings to understand borehole instability and its mechanism requires correct descriptions of caving which are inclined to be qualitative and fragmentary in previous studies,as well as proper interpretation which entails a wealth of field experience and comprehensive understanding of drilling,geo-mechanics and geology.This paper proposes a new method for caving characterization and a caving interpretation workflow based on image processing and machine learning.Firstly,we thoroughly analyze all modes of borehole failures and the corresponding cavings they generate,and make clear the significant characteristics to distinguish different types of cavings.Then the morphologies of caving contour and surface are quantitatively characterized using Speeded-Up Robust Features(SURF)algorithm and 2D-Discrete Wavelet Transform(DWT),respectively.These two categories of characteristics are used as the input of Light Gradient Boosting Machine(LightGBM)-based classification model,and the mode of borehole failure that generates the caving can be inferred from the classification results.We demonstrate the application of this interpretation workflow utilizing the cavings from the T oilfield,Xinjiang,China.The result shows that the average accuracy of classification is 90.9 %,which reflects that the workflow has a satisfactory performance in caving interpretation as well as that the features have high representativeness and robustness for caving characterization.This method opens up a new path to the early warning of borehole instability and real-time diagnosis of instability mechanism,thus corresponding remedies can be taken in time to avoid serious downhole accidents.
查看更多>>摘要：To investigate the corrosion behavior of gas-injection well of CO2 flooding and dien to take measures to inhibit the corrosion of casing,firstly an HTHP autoclave and surface characterization technology are applied to analyzing the corrosion behavior of casing and then a new type of oil-based annulus protection fluid has been developed to avoid the casing corrosion issue.The results show that the casing in the simulated supercritical CO2-saturated aqueous brine phase(SC CO2-saturated aqueous phase)has severe uniform corrosion,while that in the simulated water-saturated supercritical CO2(SC CO2 phase)has severe pitting corrosion.The temperature and CO2 partial pressure can promote the water film adsorbed on the steel surface,further inducing the corrosion of casing.In order to prevent casing corrosion,an oil-based annulus protection fluid suitable for gas-injection well in CO2 flooding is developed,and the preparation process of oil-based annulus protection fluid is proposed.The oil-based annulus protection fluid is composed of white oil and 1000 mg/L imidazoline inhibitor.The flash point of the oil-based annulus protection fluid is over 160 ℃,the freezing point-23 ℃,and the density 0.85 g/cm~3.The corrosion inhibition rate is more than 80% when PI 10 steel is in SC CO2 phase with oil-based annulus protection fluid,and it is more than 95% when P110 steel is in SC CO2-saturated aqueous phase.It proves that the newly developed oil-based annulus fluid can effectively solve the corrosion problem of PI 10 steel as casing in gas-injection well of CO2 flooding.
查看更多>>摘要：With the advancement of technology,various types of downhole tools have been developed.It is necessary to ensure that downhole tools can be tripped to the predetermined well depth dirough a drilling and completion string without any damage.However,mathematical models to predict the downhole tool deformation under axial loading are lacking.In this paper,an eccentric tube deflection model is established according to the geometric characteristics of downhole tools.First,six contact cases of an eccentric tube under axial loading in a curved wellbore are considered.The model solves the eccentric tube deflection in the different contact cases dirough the beam-column model and energy method.Second,using this model,the critical axial load in the contact cases is examined along with the deflection,bending moment,and contact force of the eccentric tube.The results show that the deflection,bending moment,and contact force of the eccentric tube are related to the contact case.The bending moment and contact force of the eccentric tube in wrap contact under axial compression are higher than those in other contact cases.In particular,when the eccentric tube is subjected to wrap contact under axial compression,the maximum bending moment and contact force increase sharply,and this aspect can help evaluate the accessibility of the downhole tool.Finally,this paper proposes a new method based on the eccentric tube deflection model to analyze the accessibility of a completion string in the context of eccentric downhole tools.The effectiveness of the proposed method is demonstrated dirough a field case.
查看更多>>摘要：Emulsions are widely produced and handled in the petroleum industry,particularly in the recovery of heavy oil and bitumen by steam flooding enhanced oil recovery(EOR)techniques.Production of emulsions has been detected from the very early stages of steam-assisted gravity drainage(SAGD)operations,and the literature suggests emulsification occurs in the reservoir.The model fluids employed in the current SAGD sand pack testing,such as sand retention test(SRT)and flow line testing,do not account for emulsions and their properties.This study introduces model emulsions formulated to mimic some essential features of the SAGD in-situ emulsion properties in terms of droplet size,viscosity,kinetic stability,and asphaltene precipitation.Moreover,a workflow is presented which can be used to synthesize model emulsions of any desired properties.Additionally,the effects of gilsonite,sorbitan sesquioleate,oil composition,electrolyte,and water content on the emulsion properties were investigated.It was found that the addition of light n-alkanes with a smaller atomic number in the oil blend results in the formation of emulsions with lower viscosity,weaker kinetic stability,and larger droplet sizes.It was also found that gilsonite which is a rich source of asphaltenes can be used in model emulsions to enhance the emulsions'stability.Molecular dynamic simulation results verified by bottle tests,interfacial tension measurements,and optical microscopy demonstrate that π-π bonding,along with asphaltene-asphaltene and water-asphaltene hydrogen bonding results in face-to-face stacking of asphaltene molecules which in turn leads to the asphaltene aggregation.It was observed that the asphaltene molecules tend to settle at the oil-water interface due to the insolubility of asphaltene in the n-alkane oil and the tendency to associate with water molecules and forming hydrogen bonds.Better kinetic stability was achieved when a blend of non-ionic surfactant was used with gilsonite to prepare emulsions.Moreover,the viscosity of emulsions increased when a larger concentration of gilsonite was used in the emulsion recipes.The electrolyte's presence in the emulsions yielded lower stability.However,a higher dosage of gilsonite dominates the detrimental effect of the NaCl on the emulsion kinetic stability.
查看更多>>摘要：Three-dimensional CFD-DEM-IBM simulations of sand production in a sandstone formation,using periodic boundaries,were performed using 10000 frictional elastic spheres bonded together and compressed at 1 MPa of overburden pressure.Sand production simulation geometry and procedures are proposed,in which the cone penetration test(CPT)has been used to investigate the physical perforation penetration of the cemented sandstone material with the real-world grain size distribution from the Ustyurt-Buzachi Sedimentary Basin.The Immersed Boundary Method(IBM)was adapted for the sand production simulation geometry to simulate the fluid flow near the well casing.Oil with low viscosity and density was used as an injection fluid(reservoir fluid).This study shows what happens in the first 0.1 s immediately after perforating of the cased horizontal oil well.Erosion near the perforation tunnel was triggered due to the pressure drawdown,where the production of sand particles was initiated during the first flow due to the drag force that lifted the sand particles from the perforation damage zone.At the beginning of the simulation a sand arch was captured around the perforation tunnel and due to the fluid flow it collapsed and the perforation cavity became larger.The amount and mass of produced sand particles were calculated.The research findings provide insight into the sanding process and could be helpful for practicing engineers to understand the sanding mechanism at micro and macro scales.The results show that the proposed model is promising,and the innovative CFD-DEM-IBM-based system should be further elaborated to simulate the sand production in a sandstone formation.
查看更多>>摘要：In the petroleum industry,the transport of offshore crude oil via pipelines may suffer damage known as wax precipitation.This reduces the flow capacity of the crude oil,reducing its transport efficiency.Under extreme conditions,this may also result in serious damage to equipment.To help alleviate this problem,the petroleum transport and flow characteristics of offshore waxy crude oil in pipelines are investigated,together with the development of several options to help minimize wax precipitation.This paper reviews the current research status for reducing wax precipitation and enhancing crude oil flow in offshore pipelines.Specifically,reducing the viscosity of waxy crude oil,strengthening the process technology of the pipeline and the related flow mechanisms are each investigated.This paper also identifies and discusses areas of study that require further investigation.
查看更多>>摘要：Replicating initial reservoir wettability conditions in core restoration by core cleaning and fluid restoration in the laboratory is of great importance.There are several core cleaning and restoration protocols used in the oil industry and academia that include the usage of different equipment,techniques,and materials.Strong solvents used in core cleaning can remove material that is part of the rock phase leading to more water-wet behavior.Large volumes of crude oil exposure in core restorations can result in high adsorption of polar organic components onto the mineral surfaces giving less water-wet behavior.Therefore,sufficient core cleaning should be targeted,involving no physical damage to the solid rock phase and effective crude oil exposure securing realistic water saturations,avoiding overexposure of crude oil.The objective of this study was to establish an optimum core restoration process in terms of cleaning solvents and the amount of crude oil exposure,to re-establish the same core wettability from one core restoration to the next.Seven sandstone cores from a reservoir on the Norwegian Continental Shelf underwent a series of core restorations.Two different core cleaning procedures were used,in which mild(kerosene/heptane)and strong(toluene/methanol)solvents were involved,and furthermore,the cores were exposed to various volumes of crude oil.Spontaneous imbibition experiments showed that mild core cleaning in combination with 5 pore volumes or more crude oil exposure rendered the cores less water-wet in successive core restorations.More rigorous cleaning with 5 pore volumes of crude oil exposure rendered the cores more water-wet in successive core restorations.From spontaneous imbibition results it was concluded that an optimum core restoration procedure involving mild cleaning and only 1 pore volume of crude oil exposure successfully reproduced core wettability in successive experiments.
查看更多>>摘要：Nanoparticles(NPs)of various types have gained attention for utilization in chemical enhanced oil recovery(CEOR)studies.This is because they can potentially take part in interfacial interactions due to their tiny size and unique characteristics,which would otherwise lead to more efficient EOR operations.Among various NPs,multi-walled carbon nanotubes(MWCNTs),due to functionalization capability,the abundance of carbon sources,and reasonable price,could be a promising option.In this study,a novel nano-complex was synthesized based on the surface modification of the functionalized MWCNTs(f-MWCNTs)with cetyltrimethylammonium bromide(CTAB).The synthesized f-MWCNT-CTAB nano-complex was then used,for the first time,in low salinity(12-fold diluted)seawater(LSSW)to discern interfacial interactions between LSSW and crude oil/dolomite.The results showed great potential of the nano-complex to reduce the crude oil/brine interfacial tension(IFT).Accordingly,the critical micelle concentration(CMC)of the nano-complex in the LSSW/crude oil interface was obtained to be 20 ppm of the nano-complex,for which a low IFT value of 0.33 mN/m was recorded.Moreover,despite the low adsorption of nano-complex on the dolomite surface,a profound wettability alteration of the dolomite rock surface from oil-wet to water-wet state was also observed.Finally,a tertiary flooding study resulted in 21% increase in oil recovery after secondary water injection,which is assumed to be due to the integrating effect of nano-complex and low salinity brine.
查看更多>>摘要：This study analyses three-dimensional(3D)effects during steady-state tests in short cores,primarily used to determine relative permeability(Kr)and capillary pressure(Pc).Here we concentrate on steady-state transition tests(SSTTs),which allows simultaneous determination of Kr and Pc from the steady-state data and the transition data measured between the steady states.Comparison between three-and one-dimensional(ID)modelling in short cores shows a significant difference in measured water-cut and pressure-drop data.This difference has been observed for cores with different inlet distributor geometries,aspect ratios,and anisotropy.Despite the influence of 3D flow effects on measurement data,the agreement between Kr and Pc as obtained from the 3D and ID models is close.This phenomenon of conservative inverse-solution results has been demonstrated for different inlet distributor geometries.The Spiral distributor exhibits lower 3D flow effects and more accurate determination of relative permeability and capillary pressure from SSTT tests.
查看更多>>摘要：When drilling long horizontal wells,the axial vibration generated by the drilling string at the bottom hole will effectively alleviate the phenomenon of"frictional drag of the drill bit",which can reduce the friction and enhance the penetration rate.Based on the principle of vibration impact,the axial vibratory tool for friction reduction with a diameter of 127 mm was designed,and the mechanical structure and working principle of this tool were also introduced in detail.First,the planar planetary motion of the throttle valve was described,and a model for calculating the cross-flow area at different moving valve and fixed valve sizes was established.Then,considering the effect of local head loss,the mechanical analysis of the working pressure drop generated by the fluid at each site within the dynamic short connector was carried out,and the relationship curves of the working pressure drop with time and cross-flow area were obtained.After that,the Viscous-Realizable k-e turbulence model was used to simulate the water hammer pressure of the dynamic short connector,and the variation of water hammer pressure with time,cross-flow area,and cross-sectional flow velocity under 3D/2D conditions was obtained.Based on the undamped vibration differential equation,the axial impact force and axial vibration displacement generated by the vibratory tool were solved.The calculated results are in good agreement with the experimental test results.The field test of this vibratory tool was conducted in well FNHW4084 of the Mahu oil field in Xinjiang,China.The tool was in the well for 10.68 days.The drilling fluid was circulated for 202 h.The pure drilling time was 125.83 h.The drilling footage of a single tool is 596 m with an average penetration rate of 4.74 m/h.Rate of penetration in the test section was increased by 254% compared with the upper section.Compared with the same kick-off section of the neighboring well FNHW4026,the one-trip drilling footage of the test section was increased by 150% and the penetration rate was increased by 126%.The field test results present that this vibratory tool can significantly increase the drilling footage and penetration rate of horizontal kick-off section.
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