This work investigated the dynamic behavior of vertical pipes conveying gas-liquid two-phase flow when subjected to external excitations at both ends.Even with minimal excitation amplitude,resonance can occur when the...This work investigated the dynamic behavior of vertical pipes conveying gas-liquid two-phase flow when subjected to external excitations at both ends.Even with minimal excitation amplitude,resonance can occur when the excitation frequency aligns with the natural frequency of the pipe,significantly increasing the degree of operational risk.The governing equation of motion based on the Euler-Bernoulli beam is derived for the relative deflection with stationary simply supported ends,with the effects of the external excitations represented by source terms distributed along the pipe length.The fourth-order partial differential equation is solved via the generalized integral transform technique(GITT),with the solution successfully verified via comparison with results in the literature.A comprehensive analysis of the vibration phenomena and changes in the motion state of the pipe is conducted for three classes of external excitation conditions:same frequency and amplitude(SFSA),same frequency but different amplitudes(SFDA),and different frequencies and amplitudes(DFDA).The numerical results show that with increasing gas volume fraction,the position corresponding to the maximum vibration displacement shifts upward.Compared with conditions without external excitation,the vibration displacement of the pipe conveying two-phase flow under external excitation increases significantly.The frequency of external excitation has a significant effect on the dynamic behavior of a pipe conveying two-phase flow.展开更多
Rocking the drillstring at the surface during slide drilling is a common method for reducing drag when drilling horizontal wells.However,the current methods for determining the parameters for rocking are insufficient,...Rocking the drillstring at the surface during slide drilling is a common method for reducing drag when drilling horizontal wells.However,the current methods for determining the parameters for rocking are insufficient,limiting the widespread use of this technology.In this study,the influence of rocking parameters on the friction-reduction effect was investigated using an axialetorsional dynamic model of the drillstring and an experimental apparatus for rocking-assisted slide drilling in a simulated horizontal well.The research shows that increasing the rocking speed is beneficial improving the friction-reduction effect,but there is a diminishing marginal effect.A method was proposed to optimize the rocking speed using the equivalent axial drag coefficienterocking speed curve.Under the influence of rocking,the downhole weight on bit(WOB)exhibits a sinusoidal-like variation,with the predominant frequency being twice the rocking frequency.The fluctuation amplitude of the WOB in the horizontal section has a linear relationship with the rocking-affected depth.Based on this,a method was proposed to estimate the rockingaffected depth using the fluctuation amplitude of the standpipe pressure difference.Application of this method in the drilling field has improved the rate of penetration and toolface stability,demonstrating the reliability and effectiveness of the methods proposed in this paper.展开更多
Natural gas hydrates (NGH)is one of key future clean energy resources.Its industrialized development will help remit the huge demand of global natural gas,relieve the increasing pressure of the environment, and play a...Natural gas hydrates (NGH)is one of key future clean energy resources.Its industrialized development will help remit the huge demand of global natural gas,relieve the increasing pressure of the environment, and play a vital role in the green sustainable growth of human societies.Based on nearly two decades' studying on the reservoir characteristics in the South China Sea (SCS)and the knowledge of reservoir system,the China Geological Survey (CGS)conducted the first production test on an optimal target selected in Shenhu area SCS in 2017.Guided by the "three-phase control"exploitation theory which focused on formation stabilization,technologies such as formation fluid extraction,well drilling and completing, reservoir stimulating,sand controlling,environmental monitoring,monitoring and preventing of secondary formation of hydrates were applied.The test lasted for 60 days from May 10^th when starting to pump, drop pressure and ignite to well killing on July 9^th,with gas production of 3.09×10^5 m^3 in total,which is a world record with the longest continuous duration of gas production and maximal gas yield.This successful test brings a significant breakthrough on safety control of NGH production.展开更多
Clayey silt reservoirs bearing natural gas hydrates(NGH)are considered to be the hydrate-bearing reservoirs that boast the highest reserves but tend to be the most difficult to exploit.They are proved to be exploitabl...Clayey silt reservoirs bearing natural gas hydrates(NGH)are considered to be the hydrate-bearing reservoirs that boast the highest reserves but tend to be the most difficult to exploit.They are proved to be exploitable by the first NGH production test conducted in the South China Sea in 2017.Based on the understanding of the first production test,the China Geological Survey determined the optimal target NGH reservoirs for production test and conducted a detailed assessment,numerical and experimental simulation,and onshore testing of the reservoirs.After that,it conducted the second offshore NGH production test in 1225 m deep Shenhu Area,South China Sea(also referred to as the second production test)from October 2019 to April 2020.During the second production test,a series of technical challenges of drilling horizontal wells in shallow soft strata in deep sea were met,including wellhead stability,directional drilling of a horizontal well,reservoir stimulation and sand control,and accurate depressurization.As a result,30 days of continuous gas production was achieved,with a cumulative gas production of 86.14×104 m3.Thus,the average daily gas production is 2.87×10^4 m^3,which is 5.57 times as much as that obtained in the first production test.Therefore,both the cumulative gas production and the daily gas production were highly improved compared to the first production test.As indicated by the monitoring results of the second production test,there was no anomaly in methane content in the seafloor,seawater,and atmosphere throughout the whole production test.This successful production test further indicates that safe and effective NGH exploitation is feasible in clayey silt NGH reservoirs.The industrialization of hydrates consists of five stages in general,namely theoretical research and simulation experiments,exploratory production test,experimental production test,productive production test,and commercial production.The second production test serves as an important step from the exploratory production test to experimental production test.展开更多
Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the pr...Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the proppant-transport behavior of CO_(2)is required to better apply this technique in the engineering field.In the present paper,we adopted a coupled Computational Fluid Dynamics and Discrete Element Method(CFD-DEM)approach to simulate the proppant transport in a fracking fracture with multiple perforation tunnels.Previous experiments were first simulated to benchmark the CFD-EDM approach,and then various pumping schedules and injection parameters(injection location,multi-concentration injection order,multi-density injection order and injection temperature)were investigated to determine the placement characteristics of proppant.Results indicate that the swirling vortex below the injection tunnels dominates the proppant diffusion in the fracture.The velocity of fluid flow across the proppant bank surface in multi-concentration injection shows a positive correlation with the proppant concentration.Injecting high-density proppant first can promote the transportation of low-density proppant injected later in the fracture to a certain extent.Decreasing the initial injection temperature of supercritical CO_(2)slurry helps enhance the particle-driving effect of fluid and improve the performance of supercritical CO_(2)in carrying proppant.展开更多
To meet the requirements of marine natural gas hydrate exploitation,it is necessary to improve the penetration of completion sand control string in the large curvature borehole.In this study,large curvature test wells...To meet the requirements of marine natural gas hydrate exploitation,it is necessary to improve the penetration of completion sand control string in the large curvature borehole.In this study,large curvature test wells were selected to carry out the running test of sand control string with pre-packed screen.Meanwhile,the running simulation was performed by using the Landmark software.The results show that the sand control packer and screen can be run smoothly in the wellbore with a dogleg angle of more than 20°/30 m and keep the structure stable.Additionally,the comprehensive friction coefficient is 0.4,under which and the simulation shows that the sand control string for hydrate exploitation can be run smoothly.These findings have important guiding significance for running the completion sand control string in natural gas hydrate exploitation.展开更多
With the increasing complexity of prospecting objectives,reverse time migration( RTM) has attracted more and more attention due to its outstanding imaging quality. RTM is based on two-way wave equation,so it can avoid...With the increasing complexity of prospecting objectives,reverse time migration( RTM) has attracted more and more attention due to its outstanding imaging quality. RTM is based on two-way wave equation,so it can avoid the limits of angle in traditional one-way wave equation migration,image reverse branch,prism waves and multi-reflected wave precisely and obtain accurate dynamic information. However,the huge demands for storage and computation as well as low frequency noises restrict its wide application. The normalized cross-correlation imaging conditions based on wave field decomposition are derived from traditional cross-correlation imaging condition,and it can eliminate the low-frequency noises effectively and improve the imaging resolution. The practical procedure includes separating source and receiver wave field into one-way components respectively,and conducting cross-correlation imaging condition to the post-separated wave field. In this way,the resolution and precision of the imaging result will be promoted greatly.展开更多
Over the past 80 years,dozens of underground coal gasification(UCG)mine field tests have been carried out around the world.However,in the early days,only a small number of shallow UCG projects in the former Soviet Uni...Over the past 80 years,dozens of underground coal gasification(UCG)mine field tests have been carried out around the world.However,in the early days,only a small number of shallow UCG projects in the former Soviet Union achieved commercialised production.In this century,a few pilot projects in Australia also achieved short-term small-scale commercialised production using modern UCG technology.However,the commercialisation of UCG,especially medium-deep UCG projects with good development prospects but difficult underground engineering conditions,has not progressed smoothly around the world.Considering investment economy,a single gasifier must realise a high daily output and accumulated output,as well as hold a long gasification tunnel to control a large number of coal resources.However,a long gasification tunnel can easily be affected by blockages and failure,for which the remedial solutions are difficult and expensive,which greatly restricts the investment economy.The design of the underground gasifier determines the success or failure of UCG projects,and it also requires the related petroleum engineering technology.Combining the advantages of the linear horizontal well(L-CRIP)and parallel horizontal well(P-CRIP),this paper proposes a new design scheme for an“inclined ladder”underground gasifier.That is to say,the combination of the main shaft of paired P-CRIP and multiple branch horizontal well gasification tunnels is adopted to realise the control of a large number of coal resources in a single gasifier.The completion of the main shaft by well cementation is beneficial for maintaining the integrity of the main shaft and the stability of the main structure.The branch horizontal well is used as the gasification tunnel,but the length and number of retracting injection points are limited,effectively reducing the probability of blockage or failure.The branch horizontal well spacing can be adjusted flexibly to avoid minor faults and large cracks,which is conducive to increasing the resource utilisation rate.In addition,for multi-layer thin coal seams or ultra-thick coal seams,a multi-layer gasifier sharing vertical well sections can be deployed,thereby saving investment on the vertical well sections.Through preliminary analysis,this gasifier design scheme can be realised in engineering,making it suitable for largescale deployment where it can increase the resource utilisation rate and ensure stable and controllable operations.The new gasifier has outstanding advantages in investment economy,and good prospects for application in the commercial UCG projects of medium-deep coal seams.展开更多
During offshore deepwater drilling,the strata with abnormal pressure are often encountered and gas invasion and overflow occur easily.If they cannot be detected and controlled in time,blowout may happen and even get o...During offshore deepwater drilling,the strata with abnormal pressure are often encountered and gas invasion and overflow occur easily.If they cannot be detected and controlled in time,blowout may happen and even get out of control,which will cause considerable economic loss and irreparable casualties and may even damage the marine ecologic environment seriously.How to monitor overflow early during deepwater drilling is a global research hot,focus and difficulty at present.In order to provide theoretical guidance for the early monitoring of overflow in the riser during offshore deepwater drilling,this paper designed an experimental device for the early monitoring of gas invasion based on the propagation principle of Doppler ultrasonic wave.Then,the installation mode and angle of Doppler probe were optimized.Finally,the propagation of Doppler ultrasonic wave in the gaseliquid two-phase flow with a void fraction of 0-46% and a liquid flow velocity of 0-0.7 m/s was experimentally studied,and the change laws of Doppler ultrasonic wave with void fraction were revealed.And the following research results are obtained.First,when the void fraction changes,the signal voltage will jump up and down at different amplitudes and frequencies on the basis of initial curve.The signal voltage amplitude increases firstly and then decreases with the increase of void fraction.Second,when the increase amplitude of mean signal voltage caused by multiple reflection is greater than the attenuation degree of ultrasonic wave,the mean signal voltage increases.Otherwise,the signal voltage decreases.Third,the fitting curve of mean signal voltage scatters and void fraction under different flow velocities and void fractions during pump stopping and starting present a change law of quadratic function.In conclusion,void fraction can be quantitatively predicted based on the measured signal voltage,so as to provide guidance for the early monitoring of riser overflow and well kill operation during offshore deepwater drilling.展开更多
Natural gas hydrate(NGH)is generally produced and accumulated together with the underlying conventional gas.Therefore,optimizing the production technology of these two gases should be seen as a relevant way to effecti...Natural gas hydrate(NGH)is generally produced and accumulated together with the underlying conventional gas.Therefore,optimizing the production technology of these two gases should be seen as a relevant way to effectively reduce the exploitation cost of the gas hydrate.In this study,three types of models accounting for the coexistence of these gases are considered.Type A considers the upper hydrate-bearing layer(HBL)adjacent to the lower conventional gas layer(CGL);with the Type B a permeable interlayer exists between the upper HBL and the lower CGL;with the type C there is an impermeable interlayer between the upper HBL and the lower CGL.The production performances associated with the above three models are calculated under different conditions,including only a depressurized HBL(only HBL DP);only a depressurized CGL(only CGL DP);and both the HBL and the CGL being depressurized(HBL+CGL DP).The results show that for Type A and Type B coexistence accumulation models,when only HBL or CGL is depressurized,the gas from the other layer will flow into the production layer due to the pressure difference between the two layers.In the coexistence accumulation model of type C,the cumulative gas production is much lower than that of Type A and Type B,regardless of whether only HBL DP,only CGL DP,or HBL+CGL DP are considered.This indicates that the impermeable interlayer restricts the cross-flow of gas between HBL and CGL.For three different coexistence accumulation models,CGL DP has the largest gas-to-water ratio.展开更多
Poor investment economy under current technical level In terms of economy and due to the factors including environmental protection,coal quality,coal seam thickness,geological conditions and mining scope,the potential...Poor investment economy under current technical level In terms of economy and due to the factors including environmental protection,coal quality,coal seam thickness,geological conditions and mining scope,the potential of UCG business in China is mainly in mediumdeep coal seams.Due to its low calorific value and low value,brown coal has basically no open-pit mining or underground mining value,and can only be exploited and utilised by UCG once its burial depth exceeds 500 m.Most of the bituminous coal with a burial depth of less than 1,000 m also exceeds the economic lower limit of underground mining,and“underground coal gasification”becomes an important option.展开更多
China is rich in tight sandstone gas resources(“tight gas”for short).For example,the Sulige Gasfield in the Ordos Basin and the Upper Triassic Xujiahe Fm gas reservoir in the Sichuan Basin are typical tight gas rese...China is rich in tight sandstone gas resources(“tight gas”for short).For example,the Sulige Gasfield in the Ordos Basin and the Upper Triassic Xujiahe Fm gas reservoir in the Sichuan Basin are typical tight gas reservoirs.In the past decade,tight gas reserve and production both have increased rapidly in China,but tight gas reservoirs are always managed as conventional gas reservoirs without effective fiscal,taxation and policy supports.The potential of sustainable tight gas production increase is obviously restricted.The tight gas development projects represented by the Sulige Gasfield have failed to make profit for a long period,and especially tight gas production has presented a slight decline since 2015.In this paper,a new economic evaluation method was proposed for tight gas development projects.The new method was designed to verify the key parameters(e.g.production decline rate and single-well economic service life)depending on tight gas development and production characteristics,and perform the depreciation by using the production method.Furthermore,the possibility that the operation cost may rise due to pressure-boosting production and intermittent opening of gas wells is considered.The method was used for the tight gas development project of Sulige Gasfield,showing that its profit level is much lower than the enterprise's cost level of capital.In order to support a sustainable development of tight gas industry in China,it is recommended that relevant authorities issue value-added tax(VAT)refund policy as soon as possible.It is necessary to restore the non-resident gas gate price of the provinces where tight gas is produced to the fair and reasonable level in addition to the fiscal subsidy of CNY0.24/m^(3),or offer the fiscal subsidy of CNY0.32/m^(3) directly based on the on-going gate price.With these support policies,tax income is expected to rise directly,fiscal expenditure will not increase,and gas consumption cost in China will be significantly cut down.展开更多
Liquid nitrogen fracturing is one of the potential feasible technologies for improving the stimulation efficiency of coalbed methane(CBM)reservoirs.At present,the visualization of pore-throat connectivity and microsco...Liquid nitrogen fracturing is one of the potential feasible technologies for improving the stimulation efficiency of coalbed methane(CBM)reservoirs.At present,the visualization of pore-throat connectivity and microscopic seepage characteristics in coal rocks under liquid nitrogen thermal shock is still lack of studying.Hence,the influence of liquid nitrogen thermal shock on the micro-nano pore structure and mechanical property of coal rocks are not understood clearly.In order to provide theoretical basis for the stimulation behavior of liquid nitrogen fracturing in coal beds,this paper investigates the change of micro-nano pore structure and mechanical property of coal rocks before and after liquid nitrogen treatment means of CT scanning and atomic force microscope(AFM).In addition,the influence of liquid nitrogen thermal shock on the seepage routes of coal rock are revealed.The following research results can be obtained.First,the number and scales of pores in the coal increase after liquid nitrogen thermal shock.In this experiment,porosity is increased by 200%,micro-fracture is dominant and its volume proportion is increased to 90.0% from 7.7% before liquid nitrogen treatment.Second,the three-dimensional pore structure reconstruction model obtained by CT shows that after the liquid nitrogen treatment,the number,total length and total volume of throats in the coal rock are increased by 170%,140% and 130% and the pore connectivity is improved greatly.Third,after liquid nitrogen treatment,the sample's absolute permeability is improved significantly.In this experiment,the absolute permeability of coal after liquid nitrogen treatment is 77 times higher than that before liquid nitrogen cooling.The micro-fractures induced by thermal stress are the main percolation routes in coal after liquid nitrogen cooling.Fourth,pores and fractures are newly formed on both matrix and mineral domains,and the surface roughness is increased.In the meantime,the elastic modulus in matrix and mineral domains of coal drops,and the average elastic modulus drops by 81% and 91%,respectively.In conclusion,liquid nitrogen thermal shock leads to the increase of microscopic defects in coal and the deterioration of mechanical property.Liquid nitrogen fracturing is expected to be a new kind of efficient and green CBM reservoir stimulation technology.展开更多
The nonlinear dynamic behaviors of viscoelastic axially functionally graded material(AFG)pipes conveying pulsating internal flow are very complex.And the dynamic behavior will induce the failure of the pipes,and resea...The nonlinear dynamic behaviors of viscoelastic axially functionally graded material(AFG)pipes conveying pulsating internal flow are very complex.And the dynamic behavior will induce the failure of the pipes,and research of vibration and stability of pipes becomes a major concern.Considering that the elastic modulus,density,and coefficient of viscoelastic damping of the pipe material vary along the axial direction,the transverse vibration equation of the viscoelastic AFG pipe conveying pulsating fluid is established based on the Euler-Bernoulli beam theory.The generalized integral transform technique(GITT)is used to transform the governing fourth-order partial differential equation into a nonlinear system of fourth-order ordinary differential equations in time.The time domain diagram,phase portraits,Poincarémap and power spectra diagram at different dimensionless pulsation frequencies,are discussed in detail,showing the characteristics of chaotic,periodic,and quasi-periodic motion.The results show that the distributions of the elastic modulus,density,and coefficient of viscoelastic damping have significant effects on the nonlinear dynamic behavior of the viscoelastic AFG pipes.With the increase of the material property coefficient k,the transition between chaotic,periodic,and quasi-periodic motion occurs,especially in the high-frequency region of the flow pulsation.展开更多
The structural behavior of mechanically lined pipes （MLPs） during the spooling-on phase is investigated in this paper, motivated by their promising offshore applications relying on reel installation. By applying qua...The structural behavior of mechanically lined pipes （MLPs） during the spooling-on phase is investigated in this paper, motivated by their promising offshore applications relying on reel installation. By applying quasi 2D models, we first investigated the gripping stresses preserved in the MLP after the hydraulic expansion manufacturing process and the detachment of the liner under spooling-on curvatures. Furthermore, a comparative 3D finite element （FE） analysis for the liner wrinkling behaviors of MLP with different wall thicknesses of outer layers was performed and indicated that when the wall thickness of outer layer increases from 14.3 mm to 17.9 mm, MLP＇s critical spooling-on curvature increased more than 47%, reachin0.1432 rdd/m.展开更多
Pipeline inner inspection technology based on Pipeline Inspection Gauge(PIG),is the primary means for ensuring the safety of submarine pipelines.The dynamic characteristics of a PIG can change abruptly with the excita...Pipeline inner inspection technology based on Pipeline Inspection Gauge(PIG),is the primary means for ensuring the safety of submarine pipelines.The dynamic characteristics of a PIG can change abruptly with the excitation of obstacles such as girth welds inside the pipeline,which would result in failure or inaccuracy of the inspection results.This study establishes a dynamic model of the PIG sealing disc based on Kelvin spring damping in the circumferentially confined space.The axial vibration differential equations of the PIG is examined in detail.MSC/ADAMS is used to conduct the dynamic simulation of the PIG at different motion velocities and center of mass positions while passing through the girth weld process.Results indicate that the axial vibration caused by the girth weld intensifies substantially as the speed of the PIG increases,while the pitch and vertical vibrations exhibit a significant decline with an increase in the motion velocity.The change in the PIG’s center of mass positions has little effect on its axial vibration,while the pitch and vertical vibration conditions are significantly different in the same circumstances.展开更多
A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account the circular configuration of the pipe, the pipe embedment, and the pipe-so...A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account the circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe limit to those for the conventional rectangular strip footing while the pipe embedment approaches zero. Parametric studies indicate that, the pipe-soil interfacial properties have much influence on the bearing capacity for the pipe foundation on clayedy soils.展开更多
In the exploitation process of offshore natural gas hydrate(“hydrate”for short),it is necessary to take into consideration the wear of wellbore equipment caused by micron-sized sand particles after their breaking th...In the exploitation process of offshore natural gas hydrate(“hydrate”for short),it is necessary to take into consideration the wear of wellbore equipment caused by micron-sized sand particles after their breaking through the sand control facility of the wellbore.At present,however,there is no literature on the migration,deposition and blockage of micron-sized sand particles(<44 μm)after their flowing into the wellbore with the formation fluid.To deal with this situation,this paper took the sand particles in a throttling helical tube section for water transport in the process of depressurization hydrate exploitation as the research object.After a geometric model of flow channel was established for numerical simulation,the migration and deposition laws of micron-sized sand particles were analyzed and the critical non-deposition water velocity of micronsized sand particles under different conditions was obtained.And the following research results were obtained.First,micron-sized sand particles are mainly accumulated in the helical tube section of a complex pipeline,and the deposition of sand particles decreases with the increase of water velocity.The sand particles deposited in the upper part of the helical tube section are more difficult to clean than those in the lower part.Second,the critical non-deposition water velocity increases gradually with the increase of sand particle size and sand production concentration.Third,the variables are nondimensionalized by applying the Buckingham-P theorem.And the model for predicting the sand deposition concentration in the local complex wellbore section during hydrate production test can be obtained using the OriginPro 2019 non-linear fitting tool.Fourth,based on the proposed concept of sand deposition concentration ratio,combined with the deposition prediction model,it is convenient to calculate critical non-deposition water velocity of micron-sized sand particles and to judge the situation of sand deposition in the wellbore.In conclusion,a method for determining the critical non-deposition water velocity of micron-sized sand particles in the local complex wellbore section during the hydrate production test is proposed.And by virtue of this method,the critical non-deposition water velocity of micron-sized sand particles under three particle sizes and three sand production concentrations is obtained respectively.And the research results provide a basis for the reasonable arrangement of hydrate production system and pressure reduction range.展开更多
It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because o...It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because of the high risk of well construction and low production efficiency,they are difficult to be recovered by using conventional oil production methods.As a result,this paper proposes an alternative design based on a combination of radial drilling,heat injection,and backfilling methods.Multi-branch holes are used to penetrate shallow gas hydrate reservoirs to expand the depressurization area,and heat injection is utilized as a supplement to improve gas production.Geotechnical information collected from an investigation site close to the offshore production well in the South China Sea is used to assess the essential components of this plan,including well construction stability and gas production behavior.It demonstrates that the hydraulic fracturing of the 60mbsf overburden layer can be prevented by regulating the drilling fluid densities.However,the traditional well structure is unstable,and the suction anchor is advised for better mechanical performance.The gas produc-tion rate can be significantly increased by combining hot water injection and depressurization methods.Additionally,the suitable produc-tion equipment already in use is discussed.展开更多
基金financially supported by the Key Research and Development Program of Shandong Province(Grant Nos.2022CXGC020405,2023CXGC010415 and 2025TSGCCZZB0238)the National Natural Science Foundation of China(Grant No.52171288)the financial support from CNPq,FAPERJ,ANP,Embrapii,and China National Petroleum Corporation(CNPC).
文摘This work investigated the dynamic behavior of vertical pipes conveying gas-liquid two-phase flow when subjected to external excitations at both ends.Even with minimal excitation amplitude,resonance can occur when the excitation frequency aligns with the natural frequency of the pipe,significantly increasing the degree of operational risk.The governing equation of motion based on the Euler-Bernoulli beam is derived for the relative deflection with stationary simply supported ends,with the effects of the external excitations represented by source terms distributed along the pipe length.The fourth-order partial differential equation is solved via the generalized integral transform technique(GITT),with the solution successfully verified via comparison with results in the literature.A comprehensive analysis of the vibration phenomena and changes in the motion state of the pipe is conducted for three classes of external excitation conditions:same frequency and amplitude(SFSA),same frequency but different amplitudes(SFDA),and different frequencies and amplitudes(DFDA).The numerical results show that with increasing gas volume fraction,the position corresponding to the maximum vibration displacement shifts upward.Compared with conditions without external excitation,the vibration displacement of the pipe conveying two-phase flow under external excitation increases significantly.The frequency of external excitation has a significant effect on the dynamic behavior of a pipe conveying two-phase flow.
基金sponsored by the National Natural Science Foundation of China,China(No.52304002).
文摘Rocking the drillstring at the surface during slide drilling is a common method for reducing drag when drilling horizontal wells.However,the current methods for determining the parameters for rocking are insufficient,limiting the widespread use of this technology.In this study,the influence of rocking parameters on the friction-reduction effect was investigated using an axialetorsional dynamic model of the drillstring and an experimental apparatus for rocking-assisted slide drilling in a simulated horizontal well.The research shows that increasing the rocking speed is beneficial improving the friction-reduction effect,but there is a diminishing marginal effect.A method was proposed to optimize the rocking speed using the equivalent axial drag coefficienterocking speed curve.Under the influence of rocking,the downhole weight on bit(WOB)exhibits a sinusoidal-like variation,with the predominant frequency being twice the rocking frequency.The fluctuation amplitude of the WOB in the horizontal section has a linear relationship with the rocking-affected depth.Based on this,a method was proposed to estimate the rockingaffected depth using the fluctuation amplitude of the standpipe pressure difference.Application of this method in the drilling field has improved the rate of penetration and toolface stability,demonstrating the reliability and effectiveness of the methods proposed in this paper.
文摘Natural gas hydrates (NGH)is one of key future clean energy resources.Its industrialized development will help remit the huge demand of global natural gas,relieve the increasing pressure of the environment, and play a vital role in the green sustainable growth of human societies.Based on nearly two decades' studying on the reservoir characteristics in the South China Sea (SCS)and the knowledge of reservoir system,the China Geological Survey (CGS)conducted the first production test on an optimal target selected in Shenhu area SCS in 2017.Guided by the "three-phase control"exploitation theory which focused on formation stabilization,technologies such as formation fluid extraction,well drilling and completing, reservoir stimulating,sand controlling,environmental monitoring,monitoring and preventing of secondary formation of hydrates were applied.The test lasted for 60 days from May 10^th when starting to pump, drop pressure and ignite to well killing on July 9^th,with gas production of 3.09×10^5 m^3 in total,which is a world record with the longest continuous duration of gas production and maximal gas yield.This successful test brings a significant breakthrough on safety control of NGH production.
基金This study is supported by the offshore NGH production test projects under the Marine Geological Survey Program initiated by the China Geological Survey(DD20190226,DD20190218)the Major Program of National Natural Science Foundation of China(41730528,51991365)。
文摘Clayey silt reservoirs bearing natural gas hydrates(NGH)are considered to be the hydrate-bearing reservoirs that boast the highest reserves but tend to be the most difficult to exploit.They are proved to be exploitable by the first NGH production test conducted in the South China Sea in 2017.Based on the understanding of the first production test,the China Geological Survey determined the optimal target NGH reservoirs for production test and conducted a detailed assessment,numerical and experimental simulation,and onshore testing of the reservoirs.After that,it conducted the second offshore NGH production test in 1225 m deep Shenhu Area,South China Sea(also referred to as the second production test)from October 2019 to April 2020.During the second production test,a series of technical challenges of drilling horizontal wells in shallow soft strata in deep sea were met,including wellhead stability,directional drilling of a horizontal well,reservoir stimulation and sand control,and accurate depressurization.As a result,30 days of continuous gas production was achieved,with a cumulative gas production of 86.14×104 m3.Thus,the average daily gas production is 2.87×10^4 m^3,which is 5.57 times as much as that obtained in the first production test.Therefore,both the cumulative gas production and the daily gas production were highly improved compared to the first production test.As indicated by the monitoring results of the second production test,there was no anomaly in methane content in the seafloor,seawater,and atmosphere throughout the whole production test.This successful production test further indicates that safe and effective NGH exploitation is feasible in clayey silt NGH reservoirs.The industrialization of hydrates consists of five stages in general,namely theoretical research and simulation experiments,exploratory production test,experimental production test,productive production test,and commercial production.The second production test serves as an important step from the exploratory production test to experimental production test.
基金National Natural Science Foundation of China(Grant No.51874318,51922107,and41961144026)support from the National Key Scientific Research Instrument Research Project of NSFC(Grant No.51827804)
文摘Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the proppant-transport behavior of CO_(2)is required to better apply this technique in the engineering field.In the present paper,we adopted a coupled Computational Fluid Dynamics and Discrete Element Method(CFD-DEM)approach to simulate the proppant transport in a fracking fracture with multiple perforation tunnels.Previous experiments were first simulated to benchmark the CFD-EDM approach,and then various pumping schedules and injection parameters(injection location,multi-concentration injection order,multi-density injection order and injection temperature)were investigated to determine the placement characteristics of proppant.Results indicate that the swirling vortex below the injection tunnels dominates the proppant diffusion in the fracture.The velocity of fluid flow across the proppant bank surface in multi-concentration injection shows a positive correlation with the proppant concentration.Injecting high-density proppant first can promote the transportation of low-density proppant injected later in the fracture to a certain extent.Decreasing the initial injection temperature of supercritical CO_(2)slurry helps enhance the particle-driving effect of fluid and improve the performance of supercritical CO_(2)in carrying proppant.
基金supported jointly by one of the major projects of Basic and Applied Basic Research in Guangdong Province“Key Basic Theory Research for Natural Gas Hydrate Trial Production in Shenhu Pilot Test Area”(2020B0301030003)the project from Southern Marine Science&Engineering Guangdong Laboratory Guangzhou City“Research on New Closed Circulation Drilling Technology without Riser”(GML2019ZD0501)the special project for hydrate from China Geological Survey“Trial Production Implementation for Natural Gas Hydrate in Shenhu Pilot Test Area”(DD20190226)。
文摘To meet the requirements of marine natural gas hydrate exploitation,it is necessary to improve the penetration of completion sand control string in the large curvature borehole.In this study,large curvature test wells were selected to carry out the running test of sand control string with pre-packed screen.Meanwhile,the running simulation was performed by using the Landmark software.The results show that the sand control packer and screen can be run smoothly in the wellbore with a dogleg angle of more than 20°/30 m and keep the structure stable.Additionally,the comprehensive friction coefficient is 0.4,under which and the simulation shows that the sand control string for hydrate exploitation can be run smoothly.These findings have important guiding significance for running the completion sand control string in natural gas hydrate exploitation.
文摘With the increasing complexity of prospecting objectives,reverse time migration( RTM) has attracted more and more attention due to its outstanding imaging quality. RTM is based on two-way wave equation,so it can avoid the limits of angle in traditional one-way wave equation migration,image reverse branch,prism waves and multi-reflected wave precisely and obtain accurate dynamic information. However,the huge demands for storage and computation as well as low frequency noises restrict its wide application. The normalized cross-correlation imaging conditions based on wave field decomposition are derived from traditional cross-correlation imaging condition,and it can eliminate the low-frequency noises effectively and improve the imaging resolution. The practical procedure includes separating source and receiver wave field into one-way components respectively,and conducting cross-correlation imaging condition to the post-separated wave field. In this way,the resolution and precision of the imaging result will be promoted greatly.
文摘Over the past 80 years,dozens of underground coal gasification(UCG)mine field tests have been carried out around the world.However,in the early days,only a small number of shallow UCG projects in the former Soviet Union achieved commercialised production.In this century,a few pilot projects in Australia also achieved short-term small-scale commercialised production using modern UCG technology.However,the commercialisation of UCG,especially medium-deep UCG projects with good development prospects but difficult underground engineering conditions,has not progressed smoothly around the world.Considering investment economy,a single gasifier must realise a high daily output and accumulated output,as well as hold a long gasification tunnel to control a large number of coal resources.However,a long gasification tunnel can easily be affected by blockages and failure,for which the remedial solutions are difficult and expensive,which greatly restricts the investment economy.The design of the underground gasifier determines the success or failure of UCG projects,and it also requires the related petroleum engineering technology.Combining the advantages of the linear horizontal well(L-CRIP)and parallel horizontal well(P-CRIP),this paper proposes a new design scheme for an“inclined ladder”underground gasifier.That is to say,the combination of the main shaft of paired P-CRIP and multiple branch horizontal well gasification tunnels is adopted to realise the control of a large number of coal resources in a single gasifier.The completion of the main shaft by well cementation is beneficial for maintaining the integrity of the main shaft and the stability of the main structure.The branch horizontal well is used as the gasification tunnel,but the length and number of retracting injection points are limited,effectively reducing the probability of blockage or failure.The branch horizontal well spacing can be adjusted flexibly to avoid minor faults and large cracks,which is conducive to increasing the resource utilisation rate.In addition,for multi-layer thin coal seams or ultra-thick coal seams,a multi-layer gasifier sharing vertical well sections can be deployed,thereby saving investment on the vertical well sections.Through preliminary analysis,this gasifier design scheme can be realised in engineering,making it suitable for largescale deployment where it can increase the resource utilisation rate and ensure stable and controllable operations.The new gasifier has outstanding advantages in investment economy,and good prospects for application in the commercial UCG projects of medium-deep coal seams.
基金Project supported by the Major Program of National Natural Science Foundation of China“Formation mechanism and safety control of barriers for multi-phase flow in natural gas hydrate wellbores”(No.:51991363)the National Program on Key Basic Research Project“Basic study on safe and efficient drilling for offshore deepwater petroleum development”(No.:2015CB251200)the Natural Science Foundation of Shandong Province“Flow pattern conversion mechanism of gaseliquid reverse multi-phase flow in annulus during bullheading”(No.:ZR2020ME095).
文摘During offshore deepwater drilling,the strata with abnormal pressure are often encountered and gas invasion and overflow occur easily.If they cannot be detected and controlled in time,blowout may happen and even get out of control,which will cause considerable economic loss and irreparable casualties and may even damage the marine ecologic environment seriously.How to monitor overflow early during deepwater drilling is a global research hot,focus and difficulty at present.In order to provide theoretical guidance for the early monitoring of overflow in the riser during offshore deepwater drilling,this paper designed an experimental device for the early monitoring of gas invasion based on the propagation principle of Doppler ultrasonic wave.Then,the installation mode and angle of Doppler probe were optimized.Finally,the propagation of Doppler ultrasonic wave in the gaseliquid two-phase flow with a void fraction of 0-46% and a liquid flow velocity of 0-0.7 m/s was experimentally studied,and the change laws of Doppler ultrasonic wave with void fraction were revealed.And the following research results are obtained.First,when the void fraction changes,the signal voltage will jump up and down at different amplitudes and frequencies on the basis of initial curve.The signal voltage amplitude increases firstly and then decreases with the increase of void fraction.Second,when the increase amplitude of mean signal voltage caused by multiple reflection is greater than the attenuation degree of ultrasonic wave,the mean signal voltage increases.Otherwise,the signal voltage decreases.Third,the fitting curve of mean signal voltage scatters and void fraction under different flow velocities and void fractions during pump stopping and starting present a change law of quadratic function.In conclusion,void fraction can be quantitatively predicted based on the measured signal voltage,so as to provide guidance for the early monitoring of riser overflow and well kill operation during offshore deepwater drilling.
基金supported by the National Natural Science Foundation of China (Nos.52074334,51991365)the National Key R&D Program of China (2021YFC2800903),which are gratefully acknowledged.
文摘Natural gas hydrate(NGH)is generally produced and accumulated together with the underlying conventional gas.Therefore,optimizing the production technology of these two gases should be seen as a relevant way to effectively reduce the exploitation cost of the gas hydrate.In this study,three types of models accounting for the coexistence of these gases are considered.Type A considers the upper hydrate-bearing layer(HBL)adjacent to the lower conventional gas layer(CGL);with the Type B a permeable interlayer exists between the upper HBL and the lower CGL;with the type C there is an impermeable interlayer between the upper HBL and the lower CGL.The production performances associated with the above three models are calculated under different conditions,including only a depressurized HBL(only HBL DP);only a depressurized CGL(only CGL DP);and both the HBL and the CGL being depressurized(HBL+CGL DP).The results show that for Type A and Type B coexistence accumulation models,when only HBL or CGL is depressurized,the gas from the other layer will flow into the production layer due to the pressure difference between the two layers.In the coexistence accumulation model of type C,the cumulative gas production is much lower than that of Type A and Type B,regardless of whether only HBL DP,only CGL DP,or HBL+CGL DP are considered.This indicates that the impermeable interlayer restricts the cross-flow of gas between HBL and CGL.For three different coexistence accumulation models,CGL DP has the largest gas-to-water ratio.
文摘Poor investment economy under current technical level In terms of economy and due to the factors including environmental protection,coal quality,coal seam thickness,geological conditions and mining scope,the potential of UCG business in China is mainly in mediumdeep coal seams.Due to its low calorific value and low value,brown coal has basically no open-pit mining or underground mining value,and can only be exploited and utilised by UCG once its burial depth exceeds 500 m.Most of the bituminous coal with a burial depth of less than 1,000 m also exceeds the economic lower limit of underground mining,and“underground coal gasification”becomes an important option.
文摘China is rich in tight sandstone gas resources(“tight gas”for short).For example,the Sulige Gasfield in the Ordos Basin and the Upper Triassic Xujiahe Fm gas reservoir in the Sichuan Basin are typical tight gas reservoirs.In the past decade,tight gas reserve and production both have increased rapidly in China,but tight gas reservoirs are always managed as conventional gas reservoirs without effective fiscal,taxation and policy supports.The potential of sustainable tight gas production increase is obviously restricted.The tight gas development projects represented by the Sulige Gasfield have failed to make profit for a long period,and especially tight gas production has presented a slight decline since 2015.In this paper,a new economic evaluation method was proposed for tight gas development projects.The new method was designed to verify the key parameters(e.g.production decline rate and single-well economic service life)depending on tight gas development and production characteristics,and perform the depreciation by using the production method.Furthermore,the possibility that the operation cost may rise due to pressure-boosting production and intermittent opening of gas wells is considered.The method was used for the tight gas development project of Sulige Gasfield,showing that its profit level is much lower than the enterprise's cost level of capital.In order to support a sustainable development of tight gas industry in China,it is recommended that relevant authorities issue value-added tax(VAT)refund policy as soon as possible.It is necessary to restore the non-resident gas gate price of the provinces where tight gas is produced to the fair and reasonable level in addition to the fiscal subsidy of CNY0.24/m^(3),or offer the fiscal subsidy of CNY0.32/m^(3) directly based on the on-going gate price.With these support policies,tax income is expected to rise directly,fiscal expenditure will not increase,and gas consumption cost in China will be significantly cut down.
基金Project supported by the National Natural Science Foundation of China for Research and Development Program for Major Research Instruments“Synthetic experimental system of radial jet drilling technology”(No.:51827804).
文摘Liquid nitrogen fracturing is one of the potential feasible technologies for improving the stimulation efficiency of coalbed methane(CBM)reservoirs.At present,the visualization of pore-throat connectivity and microscopic seepage characteristics in coal rocks under liquid nitrogen thermal shock is still lack of studying.Hence,the influence of liquid nitrogen thermal shock on the micro-nano pore structure and mechanical property of coal rocks are not understood clearly.In order to provide theoretical basis for the stimulation behavior of liquid nitrogen fracturing in coal beds,this paper investigates the change of micro-nano pore structure and mechanical property of coal rocks before and after liquid nitrogen treatment means of CT scanning and atomic force microscope(AFM).In addition,the influence of liquid nitrogen thermal shock on the seepage routes of coal rock are revealed.The following research results can be obtained.First,the number and scales of pores in the coal increase after liquid nitrogen thermal shock.In this experiment,porosity is increased by 200%,micro-fracture is dominant and its volume proportion is increased to 90.0% from 7.7% before liquid nitrogen treatment.Second,the three-dimensional pore structure reconstruction model obtained by CT shows that after the liquid nitrogen treatment,the number,total length and total volume of throats in the coal rock are increased by 170%,140% and 130% and the pore connectivity is improved greatly.Third,after liquid nitrogen treatment,the sample's absolute permeability is improved significantly.In this experiment,the absolute permeability of coal after liquid nitrogen treatment is 77 times higher than that before liquid nitrogen cooling.The micro-fractures induced by thermal stress are the main percolation routes in coal after liquid nitrogen cooling.Fourth,pores and fractures are newly formed on both matrix and mineral domains,and the surface roughness is increased.In the meantime,the elastic modulus in matrix and mineral domains of coal drops,and the average elastic modulus drops by 81% and 91%,respectively.In conclusion,liquid nitrogen thermal shock leads to the increase of microscopic defects in coal and the deterioration of mechanical property.Liquid nitrogen fracturing is expected to be a new kind of efficient and green CBM reservoir stimulation technology.
基金supported by the National Natural Science Foundation of China(52171288,51890914)the Key Research and Development Program of Shandong Province(Major Innovation Project)(2022CXGC020405)+3 种基金the National Ministry of Industry and Information Technology Innovation Special Project-Engineering Demonstration Application of Subsea Oil and Gas Production System-Subject 4“Research on Subsea Christmas Tree and Wellhead Offshore Testing Technology”[MC-201901-S01-04]the Fundamental Research Funds for the Central Universities(20CX02410A)the Development Fund of Shandong Key Laboratory of Oil&Gas Storage and Transportation SafetyCNPq,CAPES and FAPERJ of Brazil。
文摘The nonlinear dynamic behaviors of viscoelastic axially functionally graded material(AFG)pipes conveying pulsating internal flow are very complex.And the dynamic behavior will induce the failure of the pipes,and research of vibration and stability of pipes becomes a major concern.Considering that the elastic modulus,density,and coefficient of viscoelastic damping of the pipe material vary along the axial direction,the transverse vibration equation of the viscoelastic AFG pipe conveying pulsating fluid is established based on the Euler-Bernoulli beam theory.The generalized integral transform technique(GITT)is used to transform the governing fourth-order partial differential equation into a nonlinear system of fourth-order ordinary differential equations in time.The time domain diagram,phase portraits,Poincarémap and power spectra diagram at different dimensionless pulsation frequencies,are discussed in detail,showing the characteristics of chaotic,periodic,and quasi-periodic motion.The results show that the distributions of the elastic modulus,density,and coefficient of viscoelastic damping have significant effects on the nonlinear dynamic behavior of the viscoelastic AFG pipes.With the increase of the material property coefficient k,the transition between chaotic,periodic,and quasi-periodic motion occurs,especially in the high-frequency region of the flow pulsation.
基金supported by the Science Foundation of China University of Petroleum,Beijing (2462015YQ0415)the Specialized Research Fund for the Doctoral Program of Higher Education of China (20120007120002)
文摘The structural behavior of mechanically lined pipes （MLPs） during the spooling-on phase is investigated in this paper, motivated by their promising offshore applications relying on reel installation. By applying quasi 2D models, we first investigated the gripping stresses preserved in the MLP after the hydraulic expansion manufacturing process and the detachment of the liner under spooling-on curvatures. Furthermore, a comparative 3D finite element （FE） analysis for the liner wrinkling behaviors of MLP with different wall thicknesses of outer layers was performed and indicated that when the wall thickness of outer layer increases from 14.3 mm to 17.9 mm, MLP＇s critical spooling-on curvature increased more than 47%, reachin0.1432 rdd/m.
基金financially supported by the National Natural Science Foundation of China(No.51805542)the Strategic Cooperation Technology Projects of CNPC and CUPB(ZLZX2020-05)the Science Foundation of China University of Petroleum,Beijing(No.2462020YXZZ046 and 2462020XKJS01)
文摘Pipeline inner inspection technology based on Pipeline Inspection Gauge(PIG),is the primary means for ensuring the safety of submarine pipelines.The dynamic characteristics of a PIG can change abruptly with the excitation of obstacles such as girth welds inside the pipeline,which would result in failure or inaccuracy of the inspection results.This study establishes a dynamic model of the PIG sealing disc based on Kelvin spring damping in the circumferentially confined space.The axial vibration differential equations of the PIG is examined in detail.MSC/ADAMS is used to conduct the dynamic simulation of the PIG at different motion velocities and center of mass positions while passing through the girth weld process.Results indicate that the axial vibration caused by the girth weld intensifies substantially as the speed of the PIG increases,while the pitch and vertical vibrations exhibit a significant decline with an increase in the motion velocity.The change in the PIG’s center of mass positions has little effect on its axial vibration,while the pitch and vertical vibration conditions are significantly different in the same circumstances.
基金the National Natural Science Foundation of China(Grant No.12072347)the Excellent Training Plan of the Institute of Mechanics,Chinese Academy of Sciences,and CNPC New Energy Key Project(Grant No.2021DJ4902).
基金supported by the National Natural Science Foundation of China(10872198,50509022)
文摘A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account the circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe limit to those for the conventional rectangular strip footing while the pipe embedment approaches zero. Parametric studies indicate that, the pipe-soil interfacial properties have much influence on the bearing capacity for the pipe foundation on clayedy soils.
基金supported by the National Major Science and Technology Project“Drilling hydraulics and borehole cleaning supporting techniques for complex structural cluster wells”(No.:2017ZX05009-003)National Natural Science Foundation Project of China“Rotary drive mechanism study on the hydraulicmagnetic coupling self-rotation borehole cleaning tools”(No.:51674087)Innovative Science and Research Project for the Postgraduates of Northeast Petroleum University“Cohesion mechanism and flow assurance study on the natural gas hydrates during deep-water drilling”(No.:YJSCX2017-008NEPU).
文摘In the exploitation process of offshore natural gas hydrate(“hydrate”for short),it is necessary to take into consideration the wear of wellbore equipment caused by micron-sized sand particles after their breaking through the sand control facility of the wellbore.At present,however,there is no literature on the migration,deposition and blockage of micron-sized sand particles(<44 μm)after their flowing into the wellbore with the formation fluid.To deal with this situation,this paper took the sand particles in a throttling helical tube section for water transport in the process of depressurization hydrate exploitation as the research object.After a geometric model of flow channel was established for numerical simulation,the migration and deposition laws of micron-sized sand particles were analyzed and the critical non-deposition water velocity of micronsized sand particles under different conditions was obtained.And the following research results were obtained.First,micron-sized sand particles are mainly accumulated in the helical tube section of a complex pipeline,and the deposition of sand particles decreases with the increase of water velocity.The sand particles deposited in the upper part of the helical tube section are more difficult to clean than those in the lower part.Second,the critical non-deposition water velocity increases gradually with the increase of sand particle size and sand production concentration.Third,the variables are nondimensionalized by applying the Buckingham-P theorem.And the model for predicting the sand deposition concentration in the local complex wellbore section during hydrate production test can be obtained using the OriginPro 2019 non-linear fitting tool.Fourth,based on the proposed concept of sand deposition concentration ratio,combined with the deposition prediction model,it is convenient to calculate critical non-deposition water velocity of micron-sized sand particles and to judge the situation of sand deposition in the wellbore.In conclusion,a method for determining the critical non-deposition water velocity of micron-sized sand particles in the local complex wellbore section during the hydrate production test is proposed.And by virtue of this method,the critical non-deposition water velocity of micron-sized sand particles under three particle sizes and three sand production concentrations is obtained respectively.And the research results provide a basis for the reasonable arrangement of hydrate production system and pressure reduction range.
基金financially supported by the Natural Science Foundation of Shandong Province(No.ZR202011030013)the National Natural Science Foundation of China(No.41976205)+1 种基金the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(No.2021QNLM020002)the China Geological Survey Program(No.DD20221704).
文摘It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because of the high risk of well construction and low production efficiency,they are difficult to be recovered by using conventional oil production methods.As a result,this paper proposes an alternative design based on a combination of radial drilling,heat injection,and backfilling methods.Multi-branch holes are used to penetrate shallow gas hydrate reservoirs to expand the depressurization area,and heat injection is utilized as a supplement to improve gas production.Geotechnical information collected from an investigation site close to the offshore production well in the South China Sea is used to assess the essential components of this plan,including well construction stability and gas production behavior.It demonstrates that the hydraulic fracturing of the 60mbsf overburden layer can be prevented by regulating the drilling fluid densities.However,the traditional well structure is unstable,and the suction anchor is advised for better mechanical performance.The gas produc-tion rate can be significantly increased by combining hot water injection and depressurization methods.Additionally,the suitable produc-tion equipment already in use is discussed.
