Production decline analysis has been considered as an important method to obtain the flow parameters, reservoir properties and original gas in place. Although advanced Blasingame production decline analysis methods fo...Production decline analysis has been considered as an important method to obtain the flow parameters, reservoir properties and original gas in place. Although advanced Blasingame production decline analysis methods for vertical wells, fractured wells and horizontal wells are widely used, limited study has conducted on Blasingame production decline type curves for multi-fractured horizontal well(MFHW). Based on the perpendicular bisection(PEBI) grids, a numerical model was developed and the solution was obtained using control volume finite element method and the fully implicit method. Blasingame production decline-type curves of the infinitely conductive MFHW were plotted through computer programming. A field case was presented to analyse and verify the model developed. Five flow regimes, including early formation linear flow, early radial flow, compound linear flow, transient flow and pseudo-radial flow, are recognized. Fracture spacing is the main factor that affects early radial flow, compound linear flow and transient flow, the distance from the well to the circular boundary affects the pseudo-radial flow, and the type curves are also significantly affected by the formation permeability, fracture number and fracture half-length. The validation of field case suggests that the Blasingame production decline type curves proposed in this work can be applied to the production decline analysis for MFHW in tight gas reservoirs.展开更多
Based on the results of drilling,tests and simulation experiments,the shales of the Cretaceous Qingshankou Formation in the Gulong Sag of the Songliao Basin are discussed with respect to hydrocarbon generation evoluti...Based on the results of drilling,tests and simulation experiments,the shales of the Cretaceous Qingshankou Formation in the Gulong Sag of the Songliao Basin are discussed with respect to hydrocarbon generation evolution,shale oil occurrence,and pore/fracture evolution mechanism.In conjunction with a substantial amount of oil testing and production data,the Gulong shale oil enrichment layers are evaluated and the production behaviors and decline law are analyzed.The results are drawn in four aspects.First,the Gulong shales are in the stage of extensive hydrocarbon expulsion when R_(0) is 1.0%-1.2%,with the peak hydrocarbon expulsion efficiency of 49.5%approximately.In the low-medium maturity stage,shale oil migrates from kerogen to rocks and organic pores/fractures.In the medium-high maturity stage,shale oil transforms from adsorbed state to free state.Second,the clay mineral intergranular pores/fractures,dissolution pores,and organic pores make up the majority of the pore structure.During the transformation,clay minerals undergo significant intergranular pore/fracture development between the minerals such as illite and illite/smectite mixed layer.A network of pores/fractures is formed by organic matter cracking.Third,free hydrocarbon content,effective porosity,total porosity,and brittle mineral content are the core indicators for the evaluation of shale oil enrichment layers.Class-I layers are defined as free hydrocarbon content equal or greater than 6.0 mg/g,effective porosity equal or greater than 3.5%,total porosity equal or greater than 8.0%,and brittle mineral content equal or greater than 50%.It is believed that the favourable oil layers are Q2-Q3 and Q8-Q9.Fourth,the horizontal wells in the core area of the light oil zone exhibit a high cumulative production in the first year,and present a hyperbolic production decline pattern,with the decline index of 0.85-0.95,the first-year decline rate of 14.5%-26.5%,and the single-well estimated ultimate recovery(EUR)greater than 2.0×10^(4)t.In practical exploration and production,more efforts will be devoted to the clarification of hydrocarbon generation and expulsion mechanisms,accurate testing of porosity and hydrocarbon content/phase of shale under formation conditions,precise delineation of the boundary of enrichment area,relationship between mechanical properties and stimulated reservoir volume,and enhanced oil recovery,in order to improve the EUR and achieve a large-scale,efficient development of shale oil.展开更多
Based on dynastic period division and AMS ^14 C dating performed on the sedimentary layers at Zhongba and Yuxi sites,and also the analysis of Na,Ca and Mg of 201 sedimentary samples from Zhongba site and that of Ca an...Based on dynastic period division and AMS ^14 C dating performed on the sedimentary layers at Zhongba and Yuxi sites,and also the analysis of Na,Ca and Mg of 201 sedimentary samples from Zhongba site and that of Ca and Na in 47 sedimentary samples from Yuxi by using an inductively coupled plasma-mass spectrometry（ICP）,we found that there were 35 time periods when the contents of Ca and Na were reversely correlated,i.e.whenever the content of Ca was the highest,the content of Na was the lowest,and vice versa. Among them,there were 21 time periods when the content of Ca was the highest,and Na was the lowest,indicating that there were about 21 prosperous periods of ancient salt production at Zhongba site since 3000BC.Other 14 time periods with the peak values of Na while the low values of Ca indicate 14 declined periods of salt production at Zhongba site since 3000BC.The conclusion obtained from the reverse relationship between Ca and Na contents in this paper is consistent with that＂the salt production at Zhongba site started in the new stone age,developed in the Xia and Shang dynasties,reached at the heyday in periods from the Western Zhou to the Han Dynasties,maintained stable to develop in the Tang and the Song dynasties,and gradually declined after the Song Dynasty because the sea salt were conveyed into Sichuan region,however,still had production in the 1970s-1980s＂,educed from archeological exploration.All the above mentioned results indicate that there is a reverse relationship obviously between the contents of Na and Ca in sediments at Zhongba site for ancient salt production,which can be used to reveal the process of rise and decline of ancient salt industry at Zhongba site.展开更多
Prediction of shale gas production is a challenging task because of the complex fracture-pore networks and gas flow mechanisms in shale reservoirs.Empirical methods,which are used in the industry to forecast the futur...Prediction of shale gas production is a challenging task because of the complex fracture-pore networks and gas flow mechanisms in shale reservoirs.Empirical methods,which are used in the industry to forecast the future production of shale gas,have not been assessed sufficiently to warrant high confidence in their results.Methane carbon isotopic signals have been used for producing gas wells,and are controlled by physical properties and physics-controlling production;they serve as a unique indicator of the gas production status.Here,a workable process,which is combined with a gas isotope interpretation tool(also known as a numerical simulator),has been implemented in Longrnaxi shale gas wells to predict the production decline curves.The numerical simulator,which takes into account a convection-diffu-sion-adsorption model for the matrix and a convection model for fractures in^(13)CH_(4) and ^(12)CH_(4) isotopologues,was used to stabilize the carbon isotope variation in the produced gas to elucidate gas recovery.Combined with the production rates of the four developing wells,the total reserves ranged from 1.72×10^(8) to 2.02×10^(8) m^(3),which were used to constrain the trend of two-segment produc-tion decline curves that exhibited a transition from a hyperbolic equation to an exponential one within 0.82-0.89 year.Two-segment production decline curves were used to forecast future production and estimate ultimate recovery.展开更多
The monitoring results of production logging show that almost one third of perforation clusters produce no or less gas after volumetric fracturing is initially applied in shale gas reservoirs.Besides,the production de...The monitoring results of production logging show that almost one third of perforation clusters produce no or less gas after volumetric fracturing is initially applied in shale gas reservoirs.Besides,the production decline after the commissioning is commonly faster.In this paper,a fracture network prediction model and a fracturing well productivity prediction model were established based on microseismic interpretation data and hydraulic fracture network propagation results.After petrophysics,microseism,production performance were taken into consideration comprehensively,shale re-fracturing development potential evaluation index(RDPEI)was proposed.Then,a re-fracturing design and evaluation method was developed and targeted interval selection and evaluation was realized and applied on site.And the following research results were obtained.First,due to the heterogeneity of natural fractures,hydraulic fracture networks are more different,so an obvious“dead gas zone”can be easily formed and its re-fracturing potential is high.Second,the initial hydraulic fracture network is more affected by natural fractures.The main part of a fracture network propagates along the direction of maximum horizontal major stress,the fractures in regional stimulated intervals propagate in the form of double wing,and the length of a liquid swept fracture network is 52e70%of seismic interpretation result.Third,the RDPEI model avoids the limitations of single factor analysis and realizes the quantitative prediction on three types of indexes of recoverability,compressibility and re-fracturing.Fourth,re-fracturing of the case well is remarkable in stimulation effect.Its shale gas productivity is increased by 38.9%,and its cumulative gas production in one year is increased by 62.5%.In conclusion,re-fracturing is an effective and feasible method for improving the single well ultimate recovery reserves of shale gas.This method provides a theoretical and technical support for the selection and effect evaluation of re-fracturing intervals in shale-gas horizontal wells.展开更多
As shale gas development is advancing continuously and rapidly,how to deeply analyze the production performance of shale gas wells and evaluate their production characteristics has become an urgent problem in the eval...As shale gas development is advancing continuously and rapidly,how to deeply analyze the production performance of shale gas wells and evaluate their production characteristics has become an urgent problem in the evaluation of shale gas productivity construction zone,the formulation of new area development scheme and the preparation of planning program.Some scholars have applied the Logical Growth Model(LGM)in the production decline analysis of unconventional gas wells,but the influences of shale gas reservoir and development characteristics are not taken into consideration.Therefore,this method still has some space of further development and improvement.In this paper,a Logistic Growth Model considering shale gas reservoirs and development characteristics(RB-LGM)was established based on the previous research results.Then,it was applied to the shale gas development wells in the Changning Block of the Sichuan Basin to analyze their production performance,and the analysis results were compared with thefitting and prediction results provided by the Arps hyperbolic decline model.Finally,the optimal well spacing of horizontal wells was determined using RB-LGM.And the following research results were obtained.First,shale gas is produced by deploying horizontal wells in the clustered pattern in a large number,so on the basis of LGM,RB-LGM takes shale gas reservoir parameters(thickness,shale density,gas content)and development parameters(horizontal section length,well spacing and recovery factor)as the logic control factors of horizontal-well gas productionfitting,so that the production prediction result of gas well is more reasonable.Second,RB-LGM can not only wellfit the early production data of gas well,but ensure the convergence of the later prediction results under the control of logical conditions.Third,RB-LGM takes into account the influence of shale gas reservoir and development characteristics so as to optimize the horizontal well pattern and analyze the change trend of reservoir parameters in the development area through data inversion.展开更多
基金Project(2013CB228005)supported by the National Basic Research Program of China
文摘Production decline analysis has been considered as an important method to obtain the flow parameters, reservoir properties and original gas in place. Although advanced Blasingame production decline analysis methods for vertical wells, fractured wells and horizontal wells are widely used, limited study has conducted on Blasingame production decline type curves for multi-fractured horizontal well(MFHW). Based on the perpendicular bisection(PEBI) grids, a numerical model was developed and the solution was obtained using control volume finite element method and the fully implicit method. Blasingame production decline-type curves of the infinitely conductive MFHW were plotted through computer programming. A field case was presented to analyse and verify the model developed. Five flow regimes, including early formation linear flow, early radial flow, compound linear flow, transient flow and pseudo-radial flow, are recognized. Fracture spacing is the main factor that affects early radial flow, compound linear flow and transient flow, the distance from the well to the circular boundary affects the pseudo-radial flow, and the type curves are also significantly affected by the formation permeability, fracture number and fracture half-length. The validation of field case suggests that the Blasingame production decline type curves proposed in this work can be applied to the production decline analysis for MFHW in tight gas reservoirs.
基金Supported by the National Natural Science Foundation Project(42090020,42090025)Strategic Research of Oil and Gas Development Major Project of Ministry of Science and TechnologyPetroChina Scientific Research and Technological Development Project(2019E2601).
文摘Based on the results of drilling,tests and simulation experiments,the shales of the Cretaceous Qingshankou Formation in the Gulong Sag of the Songliao Basin are discussed with respect to hydrocarbon generation evolution,shale oil occurrence,and pore/fracture evolution mechanism.In conjunction with a substantial amount of oil testing and production data,the Gulong shale oil enrichment layers are evaluated and the production behaviors and decline law are analyzed.The results are drawn in four aspects.First,the Gulong shales are in the stage of extensive hydrocarbon expulsion when R_(0) is 1.0%-1.2%,with the peak hydrocarbon expulsion efficiency of 49.5%approximately.In the low-medium maturity stage,shale oil migrates from kerogen to rocks and organic pores/fractures.In the medium-high maturity stage,shale oil transforms from adsorbed state to free state.Second,the clay mineral intergranular pores/fractures,dissolution pores,and organic pores make up the majority of the pore structure.During the transformation,clay minerals undergo significant intergranular pore/fracture development between the minerals such as illite and illite/smectite mixed layer.A network of pores/fractures is formed by organic matter cracking.Third,free hydrocarbon content,effective porosity,total porosity,and brittle mineral content are the core indicators for the evaluation of shale oil enrichment layers.Class-I layers are defined as free hydrocarbon content equal or greater than 6.0 mg/g,effective porosity equal or greater than 3.5%,total porosity equal or greater than 8.0%,and brittle mineral content equal or greater than 50%.It is believed that the favourable oil layers are Q2-Q3 and Q8-Q9.Fourth,the horizontal wells in the core area of the light oil zone exhibit a high cumulative production in the first year,and present a hyperbolic production decline pattern,with the decline index of 0.85-0.95,the first-year decline rate of 14.5%-26.5%,and the single-well estimated ultimate recovery(EUR)greater than 2.0×10^(4)t.In practical exploration and production,more efforts will be devoted to the clarification of hydrocarbon generation and expulsion mechanisms,accurate testing of porosity and hydrocarbon content/phase of shale under formation conditions,precise delineation of the boundary of enrichment area,relationship between mechanical properties and stimulated reservoir volume,and enhanced oil recovery,in order to improve the EUR and achieve a large-scale,efficient development of shale oil.
基金The Key Project of National Natural Science Foundation of China, No.90411015 University Doctoral Foundation of China, Grand No.20050284011+2 种基金 The Prior study project for Key Basic Scientific Issue of Nanjing University, Grand No. 0209005206 Open Foundation of the State Key Laboratory of Loess and Quaternary Geology from the Institute of Earth Environment, CAS, No.SKLLQG0503 Foundation of Modern Analyses Center of Nanjing University, No.0209001309.
文摘Based on dynastic period division and AMS ^14 C dating performed on the sedimentary layers at Zhongba and Yuxi sites,and also the analysis of Na,Ca and Mg of 201 sedimentary samples from Zhongba site and that of Ca and Na in 47 sedimentary samples from Yuxi by using an inductively coupled plasma-mass spectrometry（ICP）,we found that there were 35 time periods when the contents of Ca and Na were reversely correlated,i.e.whenever the content of Ca was the highest,the content of Na was the lowest,and vice versa. Among them,there were 21 time periods when the content of Ca was the highest,and Na was the lowest,indicating that there were about 21 prosperous periods of ancient salt production at Zhongba site since 3000BC.Other 14 time periods with the peak values of Na while the low values of Ca indicate 14 declined periods of salt production at Zhongba site since 3000BC.The conclusion obtained from the reverse relationship between Ca and Na contents in this paper is consistent with that＂the salt production at Zhongba site started in the new stone age,developed in the Xia and Shang dynasties,reached at the heyday in periods from the Western Zhou to the Han Dynasties,maintained stable to develop in the Tang and the Song dynasties,and gradually declined after the Song Dynasty because the sea salt were conveyed into Sichuan region,however,still had production in the 1970s-1980s＂,educed from archeological exploration.All the above mentioned results indicate that there is a reverse relationship obviously between the contents of Na and Ca in sediments at Zhongba site for ancient salt production,which can be used to reveal the process of rise and decline of ancient salt industry at Zhongba site.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA14050201).
文摘Prediction of shale gas production is a challenging task because of the complex fracture-pore networks and gas flow mechanisms in shale reservoirs.Empirical methods,which are used in the industry to forecast the future production of shale gas,have not been assessed sufficiently to warrant high confidence in their results.Methane carbon isotopic signals have been used for producing gas wells,and are controlled by physical properties and physics-controlling production;they serve as a unique indicator of the gas production status.Here,a workable process,which is combined with a gas isotope interpretation tool(also known as a numerical simulator),has been implemented in Longrnaxi shale gas wells to predict the production decline curves.The numerical simulator,which takes into account a convection-diffu-sion-adsorption model for the matrix and a convection model for fractures in^(13)CH_(4) and ^(12)CH_(4) isotopologues,was used to stabilize the carbon isotope variation in the produced gas to elucidate gas recovery.Combined with the production rates of the four developing wells,the total reserves ranged from 1.72×10^(8) to 2.02×10^(8) m^(3),which were used to constrain the trend of two-segment produc-tion decline curves that exhibited a transition from a hyperbolic equation to an exponential one within 0.82-0.89 year.Two-segment production decline curves were used to forecast future production and estimate ultimate recovery.
基金supported by the National Major Science and Technology Project“Optimization system of horizontal well fracturing design”(No.:2016ZX05023-001).
文摘The monitoring results of production logging show that almost one third of perforation clusters produce no or less gas after volumetric fracturing is initially applied in shale gas reservoirs.Besides,the production decline after the commissioning is commonly faster.In this paper,a fracture network prediction model and a fracturing well productivity prediction model were established based on microseismic interpretation data and hydraulic fracture network propagation results.After petrophysics,microseism,production performance were taken into consideration comprehensively,shale re-fracturing development potential evaluation index(RDPEI)was proposed.Then,a re-fracturing design and evaluation method was developed and targeted interval selection and evaluation was realized and applied on site.And the following research results were obtained.First,due to the heterogeneity of natural fractures,hydraulic fracture networks are more different,so an obvious“dead gas zone”can be easily formed and its re-fracturing potential is high.Second,the initial hydraulic fracture network is more affected by natural fractures.The main part of a fracture network propagates along the direction of maximum horizontal major stress,the fractures in regional stimulated intervals propagate in the form of double wing,and the length of a liquid swept fracture network is 52e70%of seismic interpretation result.Third,the RDPEI model avoids the limitations of single factor analysis and realizes the quantitative prediction on three types of indexes of recoverability,compressibility and re-fracturing.Fourth,re-fracturing of the case well is remarkable in stimulation effect.Its shale gas productivity is increased by 38.9%,and its cumulative gas production in one year is increased by 62.5%.In conclusion,re-fracturing is an effective and feasible method for improving the single well ultimate recovery reserves of shale gas.This method provides a theoretical and technical support for the selection and effect evaluation of re-fracturing intervals in shale-gas horizontal wells.
基金Project supported by the National Major Science and Technology Project“Evaluation of industrial shale gas productivity construction zone and research on main factors controlling high yield”(No.2017ZX05035-004)。
文摘As shale gas development is advancing continuously and rapidly,how to deeply analyze the production performance of shale gas wells and evaluate their production characteristics has become an urgent problem in the evaluation of shale gas productivity construction zone,the formulation of new area development scheme and the preparation of planning program.Some scholars have applied the Logical Growth Model(LGM)in the production decline analysis of unconventional gas wells,but the influences of shale gas reservoir and development characteristics are not taken into consideration.Therefore,this method still has some space of further development and improvement.In this paper,a Logistic Growth Model considering shale gas reservoirs and development characteristics(RB-LGM)was established based on the previous research results.Then,it was applied to the shale gas development wells in the Changning Block of the Sichuan Basin to analyze their production performance,and the analysis results were compared with thefitting and prediction results provided by the Arps hyperbolic decline model.Finally,the optimal well spacing of horizontal wells was determined using RB-LGM.And the following research results were obtained.First,shale gas is produced by deploying horizontal wells in the clustered pattern in a large number,so on the basis of LGM,RB-LGM takes shale gas reservoir parameters(thickness,shale density,gas content)and development parameters(horizontal section length,well spacing and recovery factor)as the logic control factors of horizontal-well gas productionfitting,so that the production prediction result of gas well is more reasonable.Second,RB-LGM can not only wellfit the early production data of gas well,but ensure the convergence of the later prediction results under the control of logical conditions.Third,RB-LGM takes into account the influence of shale gas reservoir and development characteristics so as to optimize the horizontal well pattern and analyze the change trend of reservoir parameters in the development area through data inversion.
