For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures,an acidizingfluidflow and reaction model taking the multiple leak-off effec...For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures,an acidizingfluidflow and reaction model taking the multiple leak-off effect of natural fracture,wormhole and matrix into account was established according to the liquid phase reaction equilibrium principle and the local reaction equilibrium principle after the dynamic change of fracture geometry in the process of fracture created by prepadfluid was simulated in the classical pseudo-three dimensional mathematical model of fracture propagation.Then,the acid fracturing stimulation of a case well on site was taken as an example.The newly developed model was used to simulate thefiltration process of acidizingfluid in fractures and the dynamic etching morphology of acidic rocks during the acidizingfluid injection of prepad acid fracturing.The effective length of etched fractures was determined by analyzing the concentration change of acidizingfluid along the direction of hydraulic fracture length and the threshold concentration of residual acidizingfluid comprehensively,and then it was compared with the interpretation result of pressure buildup test.And the following research results were obtained.First,in the process of acid fracturing in fracturedeporous reservoirs,the acidizingfluidfiltration velocity along the direction of fracture length is not constant and thefiltration velocity curvefluctuates in a serrated shape.And the acidizingfluidfiltration velocity where etched wormholes meet natural fractures is commonly higher than that in matrix.Second,acidizingfluid is lost seriously and the effective distance of acidizingfluid gets short significantly during the acid fracturing of fracturedeporous reservoirs.Third,acid fracturing in the verification well is remarkable in blockage removing and stimulation,and its well test interpretation results are consistent with the simulation interpretation results provided by the newly developed mathematical model.It is indicated that this newly developed model is reliable.In conclusion,the mathematical model of prepad acid fracturing which considers multiple leak-off effect is more suitable for acid fracturing simulation of fracturedeporous reservoirs.展开更多
Post-fracturing evaluation by using limited data is of great significance to continuous improvement of the fracturing programs.In this paper,a fracturing curve was divided into two stages(i.e.,prepad fluid injection a...Post-fracturing evaluation by using limited data is of great significance to continuous improvement of the fracturing programs.In this paper,a fracturing curve was divided into two stages(i.e.,prepad fluid injection and main fracturing)so as to further understand the parameters of reservoirs and artificial fractures.The brittleness and plasticity of formations were qualitatively identified by use of the statistics of formation fracture frequency,and average pressure dropping range and rate during the prepad fluid injection.The composite brittleness index was quantitatively calculated by using the energy zones in the process of fracturing.It is shown from the large-scale true triaxial physical simulation results that the complexity of fractures is reflected by the pressure fluctuation frequency and amplitude in the main fracturing curve,and combined with the brittleness and plasticity of formations,the fracture morphology far away from the well can be diagnosed.Well P,a shale gas well in SE Chongqing,was taken as an example for post-fracturing evaluation.It is shown that the shale beds are of stronger heterogeneity along the extension directions of horizontal wells,and with GR 260 API as the dividing line between brittleness and plasticity in this area,complex fracture systems tend to form in brittleness-prone formations.In Well P,half of the fractures are single fractures,so it is necessary to carry out fine subsection and turnaround fracturing so as to improve development effects.This paper provides a theoretical basis for improving the fracturing well design and increasing the effective stimulated volume in this area.展开更多
基金supported by the National Major Science and Technology Project“Demonstrative development project of large carbonate gas field in Sichuan Basin”(No.:2016ZX05052).
文摘For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures,an acidizingfluidflow and reaction model taking the multiple leak-off effect of natural fracture,wormhole and matrix into account was established according to the liquid phase reaction equilibrium principle and the local reaction equilibrium principle after the dynamic change of fracture geometry in the process of fracture created by prepadfluid was simulated in the classical pseudo-three dimensional mathematical model of fracture propagation.Then,the acid fracturing stimulation of a case well on site was taken as an example.The newly developed model was used to simulate thefiltration process of acidizingfluid in fractures and the dynamic etching morphology of acidic rocks during the acidizingfluid injection of prepad acid fracturing.The effective length of etched fractures was determined by analyzing the concentration change of acidizingfluid along the direction of hydraulic fracture length and the threshold concentration of residual acidizingfluid comprehensively,and then it was compared with the interpretation result of pressure buildup test.And the following research results were obtained.First,in the process of acid fracturing in fracturedeporous reservoirs,the acidizingfluidfiltration velocity along the direction of fracture length is not constant and thefiltration velocity curvefluctuates in a serrated shape.And the acidizingfluidfiltration velocity where etched wormholes meet natural fractures is commonly higher than that in matrix.Second,acidizingfluid is lost seriously and the effective distance of acidizingfluid gets short significantly during the acid fracturing of fracturedeporous reservoirs.Third,acid fracturing in the verification well is remarkable in blockage removing and stimulation,and its well test interpretation results are consistent with the simulation interpretation results provided by the newly developed mathematical model.It is indicated that this newly developed model is reliable.In conclusion,the mathematical model of prepad acid fracturing which considers multiple leak-off effect is more suitable for acid fracturing simulation of fracturedeporous reservoirs.
基金Project supported by the National Natural Science Funds“Mechanism of dynamic stochastic fracture control and theory of waterless fracturing for shale formations”(Grant No.51490653)the Sinopec S&T Researches“Optimal stimulation technology for shale gas formations in Fuling Block”(Grant No.P14091)the National Major S&T Projects“Demonstration of shale gas exploration and development under normal pressure in Pengshui region”(Grant No.2016ZX05061)。
文摘Post-fracturing evaluation by using limited data is of great significance to continuous improvement of the fracturing programs.In this paper,a fracturing curve was divided into two stages(i.e.,prepad fluid injection and main fracturing)so as to further understand the parameters of reservoirs and artificial fractures.The brittleness and plasticity of formations were qualitatively identified by use of the statistics of formation fracture frequency,and average pressure dropping range and rate during the prepad fluid injection.The composite brittleness index was quantitatively calculated by using the energy zones in the process of fracturing.It is shown from the large-scale true triaxial physical simulation results that the complexity of fractures is reflected by the pressure fluctuation frequency and amplitude in the main fracturing curve,and combined with the brittleness and plasticity of formations,the fracture morphology far away from the well can be diagnosed.Well P,a shale gas well in SE Chongqing,was taken as an example for post-fracturing evaluation.It is shown that the shale beds are of stronger heterogeneity along the extension directions of horizontal wells,and with GR 260 API as the dividing line between brittleness and plasticity in this area,complex fracture systems tend to form in brittleness-prone formations.In Well P,half of the fractures are single fractures,so it is necessary to carry out fine subsection and turnaround fracturing so as to improve development effects.This paper provides a theoretical basis for improving the fracturing well design and increasing the effective stimulated volume in this area.
