Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production pe...Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production performance.According to matrix properties,fracture development degree and configuration between matrix and fractures,the reservoirs are classified into three types:single porosity single permeability system,dual porosity dual permeability system,and dual porosity single permeability system.These three types of gas reservoirs show remarkable differences in different scales of permeability,the ratio of dynamic reserves to volumetric reserves and water invasion risk.It is pointed out that the key factors affecting development efficiency of these gas fields are determination of production scale and rapid identification of water invasion.Figuring out the characteristics of the gas fields and working out pertinent technical policies are the keys to achieve efficient development.The specific strategies include reinforcing early production appraisal before full scale production by deploying high precision development seismic survey,deploying development appraisal wells in batches and scale production test to get a clear understanding on the structure,reservoir type,distribution pattern of gas and water,and recoverable reserves,controlling production construction pace to ensure enough evaluation time and accurate evaluation results in the early stage,in line with the development program made according to the recoverable reserves,working out proper development strategies,optimizing pattern and proration of wells based on water invasion risk and gas supply capacity of matrix,and reinforcing research and development of key technologies.展开更多
Considering the characteristics that the fracture conductivity formed by hydraulic fracturing varies across space and time, a new mathematical model was established for seepage flow in tight gas fractured vertical wel...Considering the characteristics that the fracture conductivity formed by hydraulic fracturing varies across space and time, a new mathematical model was established for seepage flow in tight gas fractured vertical wells which takes into account the effects of dual variable conductivity and stress sensitivity. The Blasingame advanced production decline curves of the model were obtained using the finite element method with hybrid elements. On this basis, the effects of fracture space and time dual variable conductivity and stress sensitivity on Blasingame curve were analyzed. The study shows that the space variable conductivity mainly reduces decline curve value at the early stage; the time variable conductivity can result in drops of the production and the production integral curves, leading to a S-shaped curve; dual variable conductivity is the superposition of the effects given by the two variable conductivities; both time and space variable conductivities cannot delay the time with which the formation fluid flow reaches the quasi-steady state. The stress sensitivity reduces the curve value gradually rather than sharply, delaying the time the flow reaching the quasi-steady state. Ignoring the effects of variable conductivity and stress sensitivity will not affect the estimation on well controlled dynamic reserves. However, it can result in large errors in the interpretation of fractures and reservoir parameters. Conventional advanced production decline analyses of a tight gas fractured well in the Sulige gas field showed that the new model is more effective and reliable than the conventional model, and thus it can be widely applied in advanced production decline analysis of wells with the same characteristics in other gas fields.展开更多
Multi-stage volume fracturing of horizontal wells is the main means to develop tight gas reservoirs.Complex fracture networks of various shapes are generated around the wellbore after volume fracturing.At present,howe...Multi-stage volume fracturing of horizontal wells is the main means to develop tight gas reservoirs.Complex fracture networks of various shapes are generated around the wellbore after volume fracturing.At present,however,most of the well test models suitable for fracturing horizontal wells take all hydraulic fractures as single main fractures,which results in a large error between well test interpretation result and actual situation.As a result,the fracture network characteristic parameters of the stimulated areas cannot be obtained accurately.To this end,a well test model for complex fracture networks in tight-gas fracturing horizontal wells was established on the basis of the non-structural discrete fracture model.Then,this model was solved by using thefinite element method with combined triangular elements and linear elements.And accordingly,the well test type curves of a horizontal well under different fracture network patterns(rectangular,elliptical and hyperbolic)were prepared.Based on this,well test type curves were analyzed from the aspects of characteristics and influential factors and were compared with those obtained from the conventional single-fracture model.Finally,the new model was applied in well test interpretation of one multi-stage volume fracturing horizontal well in the gas reservoir of Permian Shan 1 formation in the Qingyang Gas Field of the Ordos Basin.And the following research results were obtained.First,the biggest difference of well test type curve between the fracture network model and the conventional single-fracture model occurs in the early stage,the characteristics offirst linearflow regime are replaced with the characteristics of pseudo-radialflow regime in the stimulated area.Second,the end time of the pseudo-radialflow regime in the stimulated area is mainly dominated by the size and shape of the stimulated area.The larger the stimulated area is,the longer the pseudo-radialflow regime lasts.As the shape of the stimulated area approaches to be elongated,the characteristics of the well test type curve obtained by the new model are more consistent with those by the single-fracture model.Third,the pressure derivative value of the pseudo-radialflow regime in the stimulated area is mainly dependent on the conductivity and density of the fracture network.The higher the density or the conductivity of fracture network in the stimulated area is,the earlier the wellbore storage effect regime ends,the lower the pressure derivative value of the pseudo-radialflow regime in the stimulated area is and the more obvious the characteristics of the horizontal line are.In conclusion,case study results confirm that the new model is reliable and practical and can provide accurate reservoir parameters as well as the size of the effectively stimulated area by volume fracturing and the conductivity of fracture network,which is conducive to evaluating the stimulation effect of volume fracturing and predicting the postfrac production performance.展开更多
Gas well deliverability evaluation and analysis are challenging due to the frequent abnormalities of deliverability test data of gas condensate wells caused by seepage of oil and gas phases in the reservoirs.To this e...Gas well deliverability evaluation and analysis are challenging due to the frequent abnormalities of deliverability test data of gas condensate wells caused by seepage of oil and gas phases in the reservoirs.To this end,based upon the pseudo-single-phase seepage equation and the oilegas two-phase seepage equation,a new deliverability evaluation method was established which is applicable to the following two cases when the flow of a gas well reaches the quasi-steady stage,i.e.,the pseudo-single-phase stable point deliverability evaluation for the case when the formation pressure is above the dew pressure;the gaseliquid two-phase stable point deliverability evaluation for the case when the formation pressure is below the dew pressure.Using this established deliverability evaluation method,based on the basic parameters of the Yaha gas field,Tarim Basin,the IPR curves were first obtained of gas wells do not get this at the same production gaseoil ratio and at the formation pressure above and below the dew point pressure;then,according to the four condensate gas fields,such as Yaha,Tazhong I,Qianmiqiao and Dina 2,the absolute open flow(AOF)potentials of condensate gas wells under different gaseoil production ratios were calculated.Finally,through statistical analysis of the calculation results from typical wells,the following findings were obtained.This new deliverability evaluation method under the two states of condensate gas wells with quasi-single-phase and gaseliquid two-phase stable points can be used to avoid cases due to the oilegas flow in a condensate gas well which has remained unresolved by the classical deliverability evaluation methods.Also,with the increase of gaseoil ratios in gas condensate wells,a variable discrepancy is gradually reduced in AOF potentials calculated respectively by the quasi-single-phase and gaseliquid two-phase stable point deliverability evaluation equations.For the condensate gas wells with high condensate content and low condensate gas production rates,the AOF potentials calculated by the gaseliquid two-phase stable point deliverability equation is more appropriate and reliable compared with that obtained by classical methods.展开更多
It is difficult to determine the effective reservoir rock compressibility,aquifer volume and water influx of high pressure and ultra-high pressure gas reservoirs,so when the traditional apparent reservoir pressure and...It is difficult to determine the effective reservoir rock compressibility,aquifer volume and water influx of high pressure and ultra-high pressure gas reservoirs,so when the traditional apparent reservoir pressure and cumulative gas production curve extrapolation method and its modified version are used to calculate the initial gas in-place of such gas reservoirs,the calculation accuracy is lower.The material balance equation in the form of power function for such gas reservoirs was established based on Gonzalez method to improve the accuracy and reliability of reserve evaluation.Then,based on 20 high pressure and ultra-high pressure reservoirs that had been developed abroad,the empirical value of the power exponent was defined,and the influences of the depletion degree of apparent reservoir pressure and the degree of reserve recovery on the reliability of reserve calculation were analyzed.Besides,the critical value of the key parameter affecting the reliability of reserve evaluation(depletion degree of apparent reservoir pressure)was determined and compared with the critical value of the two-linear trends.Finally,an example calculation was carried out.And the following research results were obtained.First,the empirical value of the power exponent calculated using the material balance method in the form of power function is 1.02847,with an upper limit of 1.11567.Second,the depletion degree of apparent reservoir pressure corresponding to the inflection point of the classical two-linear trends ranges from 0.14 to 0.38 with an average of 0.23,while that corresponding to the extrapolation point of the second straight line is between 0.23 and 0.50 with an average of 0.33,and the corresponding degree of reserve recovery is in the range of 33%-65%with an average of 45%.Third,the reserves of such high pressure gas reservoirs calculated with this new method has an error rate less than 10%if the depletion degree of apparent reservoir pressure is greater than 0.33.In conclusion,for such high pressure gas reservoirs and the stress-sensitive fractured gas reservoirs,the material balance method in the form of power function proposed in this paper can avoid the uncertainty parameters(e.g.effective reservoir rock compressibility,aquifer volume and water influx)and it is advantageous with simple calculation process,better practicability and small error.展开更多
In order to quickly and accurately evaluate gas well deliverability,it is necessary to clarify the applicable conditions of the simplified laminarinertial-turbulent gas well deliverability evaluation method(i.e.,press...In order to quickly and accurately evaluate gas well deliverability,it is necessary to clarify the applicable conditions of the simplified laminarinertial-turbulent gas well deliverability evaluation method(i.e.,pressure-squared method and pressure method).In this regard,this paper analyzes the PVT data,simulation wells and field case wells of typical gas reservoirs in China by reviewing the formal evolution of the flow control equation for the real gases in porous media.Then,the applicable conditions of binomial pressure-squared method and pressure method are discussed.And the following research results were obtained.First,when the pressure is lower than 14 MPa,p/(μZ) is basically a constant;and when the pressure is higher than 42 MPa,μZ is basically a constant.Second,the applicable range of the pressure-squared method can be increased from 14 to 20 MPa.In this case,the relative error of absolute open flow potential calculated using the pressure-squared method is less than 5%compared with the pseudo-pressure method.If the pressure is between 20 and 30 MPa,the relative error of the absolute open flow potential calculated using the pressure-squared method is less than 10%.Third,when the pressure exceeds 80 MPa,the relative error of the absolute open flow potential calculated using the pressure method is less than 10%compared with the pseudo-pressure method.If the pressure-squared method is used in the case of high pressure,the calculated absolute open flow potential is lower and the relative error is close to 25%.Fourth,in the case of low pressure,if the pressure is constant,the higher the temperature is,the smaller the relative error between the pressure-squared method and the pseudo-pressure method is.In the case of high pressure,if the pressure is constant,the higher the temperature is,the greater the relative error between the pressure method and the pseudo-pressure method.In conclusion,it is recommended to adopt the pseudo-pressure method in laminareinertial-turbulent gas well deliverability analysis.In the case of low pressure(below 30 MPa),the pressure-squared method can be used.In the case of high pressure(above 80 MPa),the pressure method can be applied.展开更多
Ultra-deepmajor gas fields are typically characterized by high and ultra-high pressure,tightmatrix and developed fractures,so the reserve estimation is of higher uncertainty.In order to accurately estimate the reserve...Ultra-deepmajor gas fields are typically characterized by high and ultra-high pressure,tightmatrix and developed fractures,so the reserve estimation is of higher uncertainty.In order to accurately estimate the reserves of this type of gas reservoir,this paper analyzed the correlation between the effective rock compressibility and the cumulative effective rock compressibility based on the material balance equation of high and ultra-high pressure gas reservoirs,and accordingly selected the material balance based analysis method suitable for the reserves estimation of high and ultra-high pressure gas reservoirs.Then,the starting calculation conditions of reserve estimation were determined using the non-linear regressionmethod.In addition,a semilogarithmic type curvematchingmethodwas established for the caseswhere the starting conditions could not bemet.Finally,thismethodwas applied to calculate the reserves of three ultra-high pressure gas fields(reservoirs)to verify its reliability.And the following research results were obtained.First,the cumulative effective compressibility of gas reservoir in thematerial balance equation of high and ultra-high pressure gas reservoir is a key parameter influencing its reserves,and it is the function of original formation pressure and current average formation pressure,but its numerical value can be hardly obtained by core experiments.Second,it is recommended to adopt the nonlinear regressionmethod without compressibility to estimate the reserves of high and ultra-high pressure gas reservoirs.Third,the calculation starting point of reserves by the nonlinear regression method(the starting point of dimensionless apparent formation pressure-cumulative gas production curve deviating from the straight line relationship)cannot be theoretically calculated.The calculation starting point for different dimensionless linear coefficients(uD)obtained fromthe statistical results by the graphic method corresponds to the dimensionless apparent pressure depletion degree of 0.06-0.38,and that obtained based on the data statistics of the example gas reservoir falls within this interval.Fourth,when the starting conditions are not satisfied,the semi-logarithmic type curve matching method can be used for reserve estimation.The ratio of the reserves to the apparent geological reservesG/G_(app) is a function of uD.The higher the uD,the lower the G/G_(app).Fifth,for the high and ultra-high pressure gas reservoirs in the production test stage,the test production time shall be extended as long as possible to improve the reliability of reserve estimation.And for those in the middle and late stages of development,it is necessary to prepare the comprehensive treatment measures on the basis of reserves so as to improve the development effects of gas reservoirs continuously.展开更多
A new model called semi-permeable wall model is presented for multilayer gas reservoir. The model is used to study the influence of crossflow on pressure transient well tests and other single-phase flow problems. It i...A new model called semi-permeable wall model is presented for multilayer gas reservoir. The model is used to study the influence of crossflow on pressure transient well tests and other single-phase flow problems. It is suggested here to use this model to approximate the actual multilayer gas reservoir, so that the problem is greatly simplified mathematically. Its differential equation is established here for multilayer gas reservoirs, and is linearized by normalized pseudo pressure and pseudo time. Simulation program is developed by finite-difference method when all layers are perforated. The feature of wellbore pressure and rate is clarified by analyzing the results of numerical simulation.展开更多
文摘Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production performance.According to matrix properties,fracture development degree and configuration between matrix and fractures,the reservoirs are classified into three types:single porosity single permeability system,dual porosity dual permeability system,and dual porosity single permeability system.These three types of gas reservoirs show remarkable differences in different scales of permeability,the ratio of dynamic reserves to volumetric reserves and water invasion risk.It is pointed out that the key factors affecting development efficiency of these gas fields are determination of production scale and rapid identification of water invasion.Figuring out the characteristics of the gas fields and working out pertinent technical policies are the keys to achieve efficient development.The specific strategies include reinforcing early production appraisal before full scale production by deploying high precision development seismic survey,deploying development appraisal wells in batches and scale production test to get a clear understanding on the structure,reservoir type,distribution pattern of gas and water,and recoverable reserves,controlling production construction pace to ensure enough evaluation time and accurate evaluation results in the early stage,in line with the development program made according to the recoverable reserves,working out proper development strategies,optimizing pattern and proration of wells based on water invasion risk and gas supply capacity of matrix,and reinforcing research and development of key technologies.
基金Supported by the China National Science and Technology Major Project(2016ZX05015-005)
文摘Considering the characteristics that the fracture conductivity formed by hydraulic fracturing varies across space and time, a new mathematical model was established for seepage flow in tight gas fractured vertical wells which takes into account the effects of dual variable conductivity and stress sensitivity. The Blasingame advanced production decline curves of the model were obtained using the finite element method with hybrid elements. On this basis, the effects of fracture space and time dual variable conductivity and stress sensitivity on Blasingame curve were analyzed. The study shows that the space variable conductivity mainly reduces decline curve value at the early stage; the time variable conductivity can result in drops of the production and the production integral curves, leading to a S-shaped curve; dual variable conductivity is the superposition of the effects given by the two variable conductivities; both time and space variable conductivities cannot delay the time with which the formation fluid flow reaches the quasi-steady state. The stress sensitivity reduces the curve value gradually rather than sharply, delaying the time the flow reaching the quasi-steady state. Ignoring the effects of variable conductivity and stress sensitivity will not affect the estimation on well controlled dynamic reserves. However, it can result in large errors in the interpretation of fractures and reservoir parameters. Conventional advanced production decline analyses of a tight gas fractured well in the Sulige gas field showed that the new model is more effective and reliable than the conventional model, and thus it can be widely applied in advanced production decline analysis of wells with the same characteristics in other gas fields.
文摘Multi-stage volume fracturing of horizontal wells is the main means to develop tight gas reservoirs.Complex fracture networks of various shapes are generated around the wellbore after volume fracturing.At present,however,most of the well test models suitable for fracturing horizontal wells take all hydraulic fractures as single main fractures,which results in a large error between well test interpretation result and actual situation.As a result,the fracture network characteristic parameters of the stimulated areas cannot be obtained accurately.To this end,a well test model for complex fracture networks in tight-gas fracturing horizontal wells was established on the basis of the non-structural discrete fracture model.Then,this model was solved by using thefinite element method with combined triangular elements and linear elements.And accordingly,the well test type curves of a horizontal well under different fracture network patterns(rectangular,elliptical and hyperbolic)were prepared.Based on this,well test type curves were analyzed from the aspects of characteristics and influential factors and were compared with those obtained from the conventional single-fracture model.Finally,the new model was applied in well test interpretation of one multi-stage volume fracturing horizontal well in the gas reservoir of Permian Shan 1 formation in the Qingyang Gas Field of the Ordos Basin.And the following research results were obtained.First,the biggest difference of well test type curve between the fracture network model and the conventional single-fracture model occurs in the early stage,the characteristics offirst linearflow regime are replaced with the characteristics of pseudo-radialflow regime in the stimulated area.Second,the end time of the pseudo-radialflow regime in the stimulated area is mainly dominated by the size and shape of the stimulated area.The larger the stimulated area is,the longer the pseudo-radialflow regime lasts.As the shape of the stimulated area approaches to be elongated,the characteristics of the well test type curve obtained by the new model are more consistent with those by the single-fracture model.Third,the pressure derivative value of the pseudo-radialflow regime in the stimulated area is mainly dependent on the conductivity and density of the fracture network.The higher the density or the conductivity of fracture network in the stimulated area is,the earlier the wellbore storage effect regime ends,the lower the pressure derivative value of the pseudo-radialflow regime in the stimulated area is and the more obvious the characteristics of the horizontal line are.In conclusion,case study results confirm that the new model is reliable and practical and can provide accurate reservoir parameters as well as the size of the effectively stimulated area by volume fracturing and the conductivity of fracture network,which is conducive to evaluating the stimulation effect of volume fracturing and predicting the postfrac production performance.
基金supported by the PetroChina Major Science and Technology Project(No.2014E-3203)。
文摘Gas well deliverability evaluation and analysis are challenging due to the frequent abnormalities of deliverability test data of gas condensate wells caused by seepage of oil and gas phases in the reservoirs.To this end,based upon the pseudo-single-phase seepage equation and the oilegas two-phase seepage equation,a new deliverability evaluation method was established which is applicable to the following two cases when the flow of a gas well reaches the quasi-steady stage,i.e.,the pseudo-single-phase stable point deliverability evaluation for the case when the formation pressure is above the dew pressure;the gaseliquid two-phase stable point deliverability evaluation for the case when the formation pressure is below the dew pressure.Using this established deliverability evaluation method,based on the basic parameters of the Yaha gas field,Tarim Basin,the IPR curves were first obtained of gas wells do not get this at the same production gaseoil ratio and at the formation pressure above and below the dew point pressure;then,according to the four condensate gas fields,such as Yaha,Tazhong I,Qianmiqiao and Dina 2,the absolute open flow(AOF)potentials of condensate gas wells under different gaseoil production ratios were calculated.Finally,through statistical analysis of the calculation results from typical wells,the following findings were obtained.This new deliverability evaluation method under the two states of condensate gas wells with quasi-single-phase and gaseliquid two-phase stable points can be used to avoid cases due to the oilegas flow in a condensate gas well which has remained unresolved by the classical deliverability evaluation methods.Also,with the increase of gaseoil ratios in gas condensate wells,a variable discrepancy is gradually reduced in AOF potentials calculated respectively by the quasi-single-phase and gaseliquid two-phase stable point deliverability evaluation equations.For the condensate gas wells with high condensate content and low condensate gas production rates,the AOF potentials calculated by the gaseliquid two-phase stable point deliverability equation is more appropriate and reliable compared with that obtained by classical methods.
基金Project supported by Major Special Science and Technology Project of PetroChina Company Limited“Study and application of key technologies for developing deepeultra-deep gas in Kuqa depression”(No.:2018E-1803).
文摘It is difficult to determine the effective reservoir rock compressibility,aquifer volume and water influx of high pressure and ultra-high pressure gas reservoirs,so when the traditional apparent reservoir pressure and cumulative gas production curve extrapolation method and its modified version are used to calculate the initial gas in-place of such gas reservoirs,the calculation accuracy is lower.The material balance equation in the form of power function for such gas reservoirs was established based on Gonzalez method to improve the accuracy and reliability of reserve evaluation.Then,based on 20 high pressure and ultra-high pressure reservoirs that had been developed abroad,the empirical value of the power exponent was defined,and the influences of the depletion degree of apparent reservoir pressure and the degree of reserve recovery on the reliability of reserve calculation were analyzed.Besides,the critical value of the key parameter affecting the reliability of reserve evaluation(depletion degree of apparent reservoir pressure)was determined and compared with the critical value of the two-linear trends.Finally,an example calculation was carried out.And the following research results were obtained.First,the empirical value of the power exponent calculated using the material balance method in the form of power function is 1.02847,with an upper limit of 1.11567.Second,the depletion degree of apparent reservoir pressure corresponding to the inflection point of the classical two-linear trends ranges from 0.14 to 0.38 with an average of 0.23,while that corresponding to the extrapolation point of the second straight line is between 0.23 and 0.50 with an average of 0.33,and the corresponding degree of reserve recovery is in the range of 33%-65%with an average of 45%.Third,the reserves of such high pressure gas reservoirs calculated with this new method has an error rate less than 10%if the depletion degree of apparent reservoir pressure is greater than 0.33.In conclusion,for such high pressure gas reservoirs and the stress-sensitive fractured gas reservoirs,the material balance method in the form of power function proposed in this paper can avoid the uncertainty parameters(e.g.effective reservoir rock compressibility,aquifer volume and water influx)and it is advantageous with simple calculation process,better practicability and small error.
基金Project supported by Major Science&Technology Project of PetroChina Company Limited“Research and application of key technologies for development of deepeultra-deep gas reservoirs in Kuqa Depression”(No.:2018E-1803).
文摘In order to quickly and accurately evaluate gas well deliverability,it is necessary to clarify the applicable conditions of the simplified laminarinertial-turbulent gas well deliverability evaluation method(i.e.,pressure-squared method and pressure method).In this regard,this paper analyzes the PVT data,simulation wells and field case wells of typical gas reservoirs in China by reviewing the formal evolution of the flow control equation for the real gases in porous media.Then,the applicable conditions of binomial pressure-squared method and pressure method are discussed.And the following research results were obtained.First,when the pressure is lower than 14 MPa,p/(μZ) is basically a constant;and when the pressure is higher than 42 MPa,μZ is basically a constant.Second,the applicable range of the pressure-squared method can be increased from 14 to 20 MPa.In this case,the relative error of absolute open flow potential calculated using the pressure-squared method is less than 5%compared with the pseudo-pressure method.If the pressure is between 20 and 30 MPa,the relative error of the absolute open flow potential calculated using the pressure-squared method is less than 10%.Third,when the pressure exceeds 80 MPa,the relative error of the absolute open flow potential calculated using the pressure method is less than 10%compared with the pseudo-pressure method.If the pressure-squared method is used in the case of high pressure,the calculated absolute open flow potential is lower and the relative error is close to 25%.Fourth,in the case of low pressure,if the pressure is constant,the higher the temperature is,the smaller the relative error between the pressure-squared method and the pseudo-pressure method is.In the case of high pressure,if the pressure is constant,the higher the temperature is,the greater the relative error between the pressure method and the pseudo-pressure method.In conclusion,it is recommended to adopt the pseudo-pressure method in laminareinertial-turbulent gas well deliverability analysis.In the case of low pressure(below 30 MPa),the pressure-squared method can be used.In the case of high pressure(above 80 MPa),the pressure method can be applied.
基金supported by the Major Science and Technology Project of PetroChina Company Limited“Research and Application of Key Technologies for Development of Deep and Ultra-deep Gas Fields in Kuqa Depression”(No.2018E-1803).
文摘Ultra-deepmajor gas fields are typically characterized by high and ultra-high pressure,tightmatrix and developed fractures,so the reserve estimation is of higher uncertainty.In order to accurately estimate the reserves of this type of gas reservoir,this paper analyzed the correlation between the effective rock compressibility and the cumulative effective rock compressibility based on the material balance equation of high and ultra-high pressure gas reservoirs,and accordingly selected the material balance based analysis method suitable for the reserves estimation of high and ultra-high pressure gas reservoirs.Then,the starting calculation conditions of reserve estimation were determined using the non-linear regressionmethod.In addition,a semilogarithmic type curvematchingmethodwas established for the caseswhere the starting conditions could not bemet.Finally,thismethodwas applied to calculate the reserves of three ultra-high pressure gas fields(reservoirs)to verify its reliability.And the following research results were obtained.First,the cumulative effective compressibility of gas reservoir in thematerial balance equation of high and ultra-high pressure gas reservoir is a key parameter influencing its reserves,and it is the function of original formation pressure and current average formation pressure,but its numerical value can be hardly obtained by core experiments.Second,it is recommended to adopt the nonlinear regressionmethod without compressibility to estimate the reserves of high and ultra-high pressure gas reservoirs.Third,the calculation starting point of reserves by the nonlinear regression method(the starting point of dimensionless apparent formation pressure-cumulative gas production curve deviating from the straight line relationship)cannot be theoretically calculated.The calculation starting point for different dimensionless linear coefficients(uD)obtained fromthe statistical results by the graphic method corresponds to the dimensionless apparent pressure depletion degree of 0.06-0.38,and that obtained based on the data statistics of the example gas reservoir falls within this interval.Fourth,when the starting conditions are not satisfied,the semi-logarithmic type curve matching method can be used for reserve estimation.The ratio of the reserves to the apparent geological reservesG/G_(app) is a function of uD.The higher the uD,the lower the G/G_(app).Fifth,for the high and ultra-high pressure gas reservoirs in the production test stage,the test production time shall be extended as long as possible to improve the reliability of reserve estimation.And for those in the middle and late stages of development,it is necessary to prepare the comprehensive treatment measures on the basis of reserves so as to improve the development effects of gas reservoirs continuously.
基金the National NatualScience Foundation of China (No.59995460).
文摘A new model called semi-permeable wall model is presented for multilayer gas reservoir. The model is used to study the influence of crossflow on pressure transient well tests and other single-phase flow problems. It is suggested here to use this model to approximate the actual multilayer gas reservoir, so that the problem is greatly simplified mathematically. Its differential equation is established here for multilayer gas reservoirs, and is linearized by normalized pseudo pressure and pseudo time. Simulation program is developed by finite-difference method when all layers are perforated. The feature of wellbore pressure and rate is clarified by analyzing the results of numerical simulation.
