Permeability sensitivity to stress experiments were conducted on standard core samples taken from Wen 23 Gas Storage at multi-cycle injection and production conditions of the gas storage to study the change pattern of...Permeability sensitivity to stress experiments were conducted on standard core samples taken from Wen 23 Gas Storage at multi-cycle injection and production conditions of the gas storage to study the change pattern of stress sensitivity of permeability.A method for calculating permeability under overburden pressure in the multi-cycle injection and production process was proposed,and the effect of stress sensitivity of reservoir permeability on gas well injectivity and productivity in UGS was analyzed.Retention rate of permeability decreased sharply first and then slowly with the increase of the UGS cycles.The stress sensitivity index of permeability decreased with the increase of cycle number of net stress variations in the increase process of net stress.The stress sensitivity index of permeability hardly changed with the increase of cycle number of net stress variations in the decrease process of net stress.With the increase of cycle number of net stress variation,the stress sensitivity index of permeability in the increase process of net stress approached that in the decrease process of net stress.The lower the reservoir permeability,the greater the irreversible permeability loss rate,the stronger the cyclic stress sensitivity,and the higher the stress sensitivity index of the reservoir,the stronger the reservoir stress sensitivity.The gas zones with permeability lower than 0.3’10-3 mm2 are not suitable as gas storage regions.Stress sensitivity of reservoir permeability has strong impact on gas well injectivity and productivity and mainly in the first few cycles.展开更多
Tight sandstone gas reservoirs have poorer porosityepermeability relationships,so conventional reservoir classification schemes can hardly satisfy the classification and evaluation demand of this type of reservoirs.To...Tight sandstone gas reservoirs have poorer porosityepermeability relationships,so conventional reservoir classification schemes can hardly satisfy the classification and evaluation demand of this type of reservoirs.To solve this problem,this paper took the Permian tight sandstone gas reservoir in the Linxing Block along the eastern margin of the Ordos Basin as an example to describe the micro-structures of the tight sandstone reservoirs by means of high-pressure mercury injection,nuclear magnetic resonance(NMR),scanning electron mi-croscope(SEM)and so on.Then,the control effect of micro-structure parameters on the macrophysical properties was studied.Finally,classification and evaluation of tight sandstone reservoirs were carried out on this basis.And the following research results were obtained.First,NMR can identify the distribution of pores of different sizes,and high-pressure mercury injection can reflect the poreethroat configuration and percolation capacity of a reservoir.Second,both methods are better coincident in the description results.With an in-crease of the right peak of T2 spectra,the mercury intrusion curve presents a concave shape and the pore throat radius increases while the pore type gradually changes from intragranular dissolution pores and intercrystalline pores to intergranular pores and intergranular disso-lution pores and the reservoir quality gets better.Third,micro-pore structure controls reservoir physical properties andfluid mobility.And the porosity of large pores is best correlated with the effective porosity,so it can be used to evaluate the reservoir capacity of tight sandstone.Fourth,the throat radius R15 obtained by high pressure mercury injection is in the best correlation with porosity and permeability,so it can be used to evaluate the percolation capacity of tight sandstone.Fifth,by combining the porosity of large pores with the R15,the tight sandstone reservoirs in the Linxing Block are classified into 4 categories,and the classification results are in a good agreement with the on-site well test data.It is concluded that the combination of high-pressure mercury injection and NMR can effectively identify the key parameters which reflect the reservoir capacity and percolation capacity of tight sandstone,and improve the reliability and integrity of reservoir classification.And by selecting the key parameters that reflect reservoir capacity and percolation capacity,it can provide guidance for the classification and evaluation of tight sandstone reservoirs.展开更多
Critical erosionflow rate is the key factor restricting the injection/production capacity of an injection/production well.At present,it is commonly calculated according to API RP 14E standard and its calculation resul...Critical erosionflow rate is the key factor restricting the injection/production capacity of an injection/production well.At present,it is commonly calculated according to API RP 14E standard and its calculation result tends to be conservative.So far,however,there is no definite laboratory experiment orfield data that can prove that critical erosionflow rate can be increased on the basis of API RP 14E.To deal this end,the concept of critical erosionflow rate was proposed based on corrosion rate for thefirst time in this paper.Then,a laboratory equivalent simulation experiment under real injection and production conditions was carried out by comprehensively taking into account the factors influencing string erosion(including temperature,pressure,gas component,water content,solid particle content and string material)while introducing the wall shear stress.Accordingly,the critical erosion coefficient(C)under experimental working conditions was calculated.Finally,a C value chart for three kinds of strings that are commonly used onfield(N80,SM80S and S13Cr)was established.And the following research results are ob-tained.First,solid particle content,water content,CO_(2)differential pressure and wall shear stress are the main erosion controlling factors.Second,solid particle content is the most significant factor that affects the erosion of N80,SM80S and S13Cr strings,and erosion of N80 and SM80S strings is more sensitive to wall shear stress and water content.Third,as for S13Cr string,the C value can be 100 when the solid particle content is lower than 250 mg/L,180 when thefluid contains liquid but no solid particles,and 275 when thefluid is gas phase.Fourth,as for N80 and SM80S strings,the C value can be in the range of 100e180 based on different water content and wall shear stress when thefluid contains liquid but no solid particles,and 275 when thefluid is in gas phase.Fifth,in view that thefluid produced from the injection/production wells of Hutubi gas storage has a water content of 0.0010‰without solid particles,S13Cr is adopted as string material and the C value is set at 180.It is shown in the laboratory erosion experiments that no erosion trace occurs on the string samples under injection and production conditions and the erosion rate is extremely low without point erosion.In conclusion,the C value chart established in this paper is reliable and can provide the guidance for the scientific and reasonable determination of critical erosionflow rate.展开更多
Water injection for oil displacement is one of the most effective ways to develop fractured-vuggy carbonate reservoirs.With the increase in the number of rounds of water injection,the development effect gradually fail...Water injection for oil displacement is one of the most effective ways to develop fractured-vuggy carbonate reservoirs.With the increase in the number of rounds of water injection,the development effect gradually fails.The emergence of high-pressure capacity expansion and water injection technology allows increased production from old wells.Although high-pressure capacity expansion and water injection technology has been implemented in practice for nearly 10 years in fractured-vuggy reservoirs,its mechanism remains unclear,and the water injection curve is not apparent.In the past,evaluating its effect could only be done by measuring the injection-production volume.In this study,we analyze the mechanism of high-pressure capacity expansion and water injection.We propose a fluid exchange index for high-pressure capacity expansion and water injection and establish a discrete model suitable for high-pressure capacity expansion and water injection curves in fractured-vuggy reservoirs.We propose the following mechanisms:replenishing energy,increasing energy,replacing energy,and releasing energy.The above mechanisms can be identified by the high-pressure capacity expansion and water injection curve of the well HA6X in the Halahatang Oilfield in the Tarim Basin.By solving the basic model,the relative errors of Reservoirs I and II are found to be 1.9%and 1.5%,respectively,and the application of field examples demonstrates that our proposed high-pressure capacity expansion and water injection indicator curve is reasonable and reliable.This research can provide theoretical support for high-pressure capacity expansion and water injection technology in fracture-vuggy carbonate reservoirs.展开更多
In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement proce...In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement process for oil recovery.Asynchronous injection-production modes can use supercritical CO_(2)to enhance oil recovery but may also worsen the injection capacity.Cores with high permeability have higher oil recovery rates and better injection capacity,however,gas channeling occurs.Supercritical CO_(2)flooding has a higher oil recovery at high pressure levels,which delays the occurrence of gas channeling.Conversely,gas injection has lower displacement efficiency but better injection capacity at the high water cut stage.This study analyzes the displacement characteristics of supercritical CO_(2)flooding with a series of experiments under different injection and production parameters.Experimental results show that the gas breakthrough stage has the fastest oil production and the supercritical CO_(2)injection capacity variation tendency is closely related to the gas-oil ratio.Further experiments show that higher injection rates represent significant ultimate oil recovery and injection index,providing a good reference for developing low-permeability reservoirs.展开更多
The Chinese C-Sight team aims to restore vision to blind patients by means of stimulating the optic nerve with a penetrating microelectrode array. A biocompatible, implantable microwire array was developed having four...The Chinese C-Sight team aims to restore vision to blind patients by means of stimulating the optic nerve with a penetrating microelectrode array. A biocompatible, implantable microwire array was developed having four platinum-iridium shafts, each 100μm in diameter. This penetrating microwire array is described in this paper, including its fabrication techniques and its in-vitro electrical characteristics. Every set of four shafts was spaced 0.4mm from center to center, comprising two short shafts that were 0.3mm long and two that were 0.9mm long. This design was intended to stimulate ganglion cell axons at different depths within the optic nerve. In-vitro electrochemical impedance testing results showed that the impedance at 1kHz ranged from 8 to 10kΩ at room temperature. The voltage responses of the arrays to current pulse stimulation indicated a charge-injection capacity of 210μC/cm2. Finally, in-vivo acute animal experiments showed that the amplitude of the electrically evoked potentials (EEPs) measured in primary visual cortex could be as large as 100 μV upon direct stimulation of the optic nerve.展开更多
基金Supported by the Chongqing Technical Innovation and Application&Development Special Project(cstc2020jscx-msxmX0189)。
文摘Permeability sensitivity to stress experiments were conducted on standard core samples taken from Wen 23 Gas Storage at multi-cycle injection and production conditions of the gas storage to study the change pattern of stress sensitivity of permeability.A method for calculating permeability under overburden pressure in the multi-cycle injection and production process was proposed,and the effect of stress sensitivity of reservoir permeability on gas well injectivity and productivity in UGS was analyzed.Retention rate of permeability decreased sharply first and then slowly with the increase of the UGS cycles.The stress sensitivity index of permeability decreased with the increase of cycle number of net stress variations in the increase process of net stress.The stress sensitivity index of permeability hardly changed with the increase of cycle number of net stress variations in the decrease process of net stress.With the increase of cycle number of net stress variation,the stress sensitivity index of permeability in the increase process of net stress approached that in the decrease process of net stress.The lower the reservoir permeability,the greater the irreversible permeability loss rate,the stronger the cyclic stress sensitivity,and the higher the stress sensitivity index of the reservoir,the stronger the reservoir stress sensitivity.The gas zones with permeability lower than 0.3’10-3 mm2 are not suitable as gas storage regions.Stress sensitivity of reservoir permeability has strong impact on gas well injectivity and productivity and mainly in the first few cycles.
基金supported by the National Natural Science Foundation of China"Full-borchole pore throat characterization and modeling of tight sandstone based on the combination of image method and fluid method"(No.41602141)"Mechanism and effects of imbibition and retention of fracturing fluid in in-situ shale gas reservoirs"(No.41972139)the Independent Innovation Foundation of Universities(No.18CX02069A).
文摘Tight sandstone gas reservoirs have poorer porosityepermeability relationships,so conventional reservoir classification schemes can hardly satisfy the classification and evaluation demand of this type of reservoirs.To solve this problem,this paper took the Permian tight sandstone gas reservoir in the Linxing Block along the eastern margin of the Ordos Basin as an example to describe the micro-structures of the tight sandstone reservoirs by means of high-pressure mercury injection,nuclear magnetic resonance(NMR),scanning electron mi-croscope(SEM)and so on.Then,the control effect of micro-structure parameters on the macrophysical properties was studied.Finally,classification and evaluation of tight sandstone reservoirs were carried out on this basis.And the following research results were obtained.First,NMR can identify the distribution of pores of different sizes,and high-pressure mercury injection can reflect the poreethroat configuration and percolation capacity of a reservoir.Second,both methods are better coincident in the description results.With an in-crease of the right peak of T2 spectra,the mercury intrusion curve presents a concave shape and the pore throat radius increases while the pore type gradually changes from intragranular dissolution pores and intercrystalline pores to intergranular pores and intergranular disso-lution pores and the reservoir quality gets better.Third,micro-pore structure controls reservoir physical properties andfluid mobility.And the porosity of large pores is best correlated with the effective porosity,so it can be used to evaluate the reservoir capacity of tight sandstone.Fourth,the throat radius R15 obtained by high pressure mercury injection is in the best correlation with porosity and permeability,so it can be used to evaluate the percolation capacity of tight sandstone.Fifth,by combining the porosity of large pores with the R15,the tight sandstone reservoirs in the Linxing Block are classified into 4 categories,and the classification results are in a good agreement with the on-site well test data.It is concluded that the combination of high-pressure mercury injection and NMR can effectively identify the key parameters which reflect the reservoir capacity and percolation capacity of tight sandstone,and improve the reliability and integrity of reservoir classification.And by selecting the key parameters that reflect reservoir capacity and percolation capacity,it can provide guidance for the classification and evaluation of tight sandstone reservoirs.
基金supported by PetroChina Major Scientifie Research&Techno-logical Development Project"Research on Key Technologies of Injection and Production Engincering of Underground Gas Storage"(No:2015E-4004).
文摘Critical erosionflow rate is the key factor restricting the injection/production capacity of an injection/production well.At present,it is commonly calculated according to API RP 14E standard and its calculation result tends to be conservative.So far,however,there is no definite laboratory experiment orfield data that can prove that critical erosionflow rate can be increased on the basis of API RP 14E.To deal this end,the concept of critical erosionflow rate was proposed based on corrosion rate for thefirst time in this paper.Then,a laboratory equivalent simulation experiment under real injection and production conditions was carried out by comprehensively taking into account the factors influencing string erosion(including temperature,pressure,gas component,water content,solid particle content and string material)while introducing the wall shear stress.Accordingly,the critical erosion coefficient(C)under experimental working conditions was calculated.Finally,a C value chart for three kinds of strings that are commonly used onfield(N80,SM80S and S13Cr)was established.And the following research results are ob-tained.First,solid particle content,water content,CO_(2)differential pressure and wall shear stress are the main erosion controlling factors.Second,solid particle content is the most significant factor that affects the erosion of N80,SM80S and S13Cr strings,and erosion of N80 and SM80S strings is more sensitive to wall shear stress and water content.Third,as for S13Cr string,the C value can be 100 when the solid particle content is lower than 250 mg/L,180 when thefluid contains liquid but no solid particles,and 275 when thefluid is gas phase.Fourth,as for N80 and SM80S strings,the C value can be in the range of 100e180 based on different water content and wall shear stress when thefluid contains liquid but no solid particles,and 275 when thefluid is in gas phase.Fifth,in view that thefluid produced from the injection/production wells of Hutubi gas storage has a water content of 0.0010‰without solid particles,S13Cr is adopted as string material and the C value is set at 180.It is shown in the laboratory erosion experiments that no erosion trace occurs on the string samples under injection and production conditions and the erosion rate is extremely low without point erosion.In conclusion,the C value chart established in this paper is reliable and can provide the guidance for the scientific and reasonable determination of critical erosionflow rate.
基金supported by the China Postdoctoral Science Foundation(No.M2019650965)Major R&D Plan of Sichuan Province(No.2020YFQ0034)the National Natural Science Fund Projects(Grant No.51804253).
文摘Water injection for oil displacement is one of the most effective ways to develop fractured-vuggy carbonate reservoirs.With the increase in the number of rounds of water injection,the development effect gradually fails.The emergence of high-pressure capacity expansion and water injection technology allows increased production from old wells.Although high-pressure capacity expansion and water injection technology has been implemented in practice for nearly 10 years in fractured-vuggy reservoirs,its mechanism remains unclear,and the water injection curve is not apparent.In the past,evaluating its effect could only be done by measuring the injection-production volume.In this study,we analyze the mechanism of high-pressure capacity expansion and water injection.We propose a fluid exchange index for high-pressure capacity expansion and water injection and establish a discrete model suitable for high-pressure capacity expansion and water injection curves in fractured-vuggy reservoirs.We propose the following mechanisms:replenishing energy,increasing energy,replacing energy,and releasing energy.The above mechanisms can be identified by the high-pressure capacity expansion and water injection curve of the well HA6X in the Halahatang Oilfield in the Tarim Basin.By solving the basic model,the relative errors of Reservoirs I and II are found to be 1.9%and 1.5%,respectively,and the application of field examples demonstrates that our proposed high-pressure capacity expansion and water injection indicator curve is reasonable and reliable.This research can provide theoretical support for high-pressure capacity expansion and water injection technology in fracture-vuggy carbonate reservoirs.
基金financial support from the National Natural Science Foundation of China(No.51904324,51974348,U19B6003)
文摘In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement process for oil recovery.Asynchronous injection-production modes can use supercritical CO_(2)to enhance oil recovery but may also worsen the injection capacity.Cores with high permeability have higher oil recovery rates and better injection capacity,however,gas channeling occurs.Supercritical CO_(2)flooding has a higher oil recovery at high pressure levels,which delays the occurrence of gas channeling.Conversely,gas injection has lower displacement efficiency but better injection capacity at the high water cut stage.This study analyzes the displacement characteristics of supercritical CO_(2)flooding with a series of experiments under different injection and production parameters.Experimental results show that the gas breakthrough stage has the fastest oil production and the supercritical CO_(2)injection capacity variation tendency is closely related to the gas-oil ratio.Further experiments show that higher injection rates represent significant ultimate oil recovery and injection index,providing a good reference for developing low-permeability reservoirs.
基金the National Natural Science Foundation of China (Nos. 30700217 and 60971102)the National Basic Research Program (973) of China(Nos. 2011CB707502 and 2011CB707505)
文摘The Chinese C-Sight team aims to restore vision to blind patients by means of stimulating the optic nerve with a penetrating microelectrode array. A biocompatible, implantable microwire array was developed having four platinum-iridium shafts, each 100μm in diameter. This penetrating microwire array is described in this paper, including its fabrication techniques and its in-vitro electrical characteristics. Every set of four shafts was spaced 0.4mm from center to center, comprising two short shafts that were 0.3mm long and two that were 0.9mm long. This design was intended to stimulate ganglion cell axons at different depths within the optic nerve. In-vitro electrochemical impedance testing results showed that the impedance at 1kHz ranged from 8 to 10kΩ at room temperature. The voltage responses of the arrays to current pulse stimulation indicated a charge-injection capacity of 210μC/cm2. Finally, in-vivo acute animal experiments showed that the amplitude of the electrically evoked potentials (EEPs) measured in primary visual cortex could be as large as 100 μV upon direct stimulation of the optic nerve.
