In this work,a flowing material balance equation(FMBE) is established for under saturated coalbed methane(CBM) reservoirs,which considers immobile free gas expansion effect at the dewatering stage.Based on the establi...In this work,a flowing material balance equation(FMBE) is established for under saturated coalbed methane(CBM) reservoirs,which considers immobile free gas expansion effect at the dewatering stage.Based on the established FMBE,five straight-line methods are proposed to determine the control area,initial water reserve,initial free gas reserve,initial adsorbed gas reserve,original gas in place,as well as permeability at the same time.Subsequently,the proposed FMBE methods for undersaturated CBM reservoirs are validated against a reservoir simulation software with and without considering free gas expansion.Finally,the proposed methods are applied in a field case when considering free gas expansion effect.Validation cases show that the straight-line relationships for the proposed five FMBE methods are excellent,and good agreements are obtained among the actual reserves and permeabilities and those evaluated by the proposed five FMBE methods,indicating the proposed five FMBE methods are effective and rational for CBM reservoirs.Results show that a small amount of free gas will result in a great deviation in reserve evaluation;hence,the immobile free gas expansion effect should be considered when establishing the material balance equation of undersaturated CBM reservoirs at the dewatering stage.展开更多
Permeability is an important index in reservoir evaluation,oil and gas accumulation control,and production effi ciency.At present,permeability can be obtained through several methods.However,these methods are not suit...Permeability is an important index in reservoir evaluation,oil and gas accumulation control,and production effi ciency.At present,permeability can be obtained through several methods.However,these methods are not suitable for tight sandstone in general because the pore type in tight sandstone is mainly secondary pores and has the characteristics of low porosity and permeability,high capillary pressure,and high irreducible water saturation.Mud invasion depth is closely related to permeability during drilling.In general,the greater the permeability,the shallower the mud invasion depth,and the smaller the permeability,the deeper the mud invasion depth.Therefore,this paper builds a model to predict the permeability of tight sandstone using mud invasion depth.The model is based on the improvement of the Darcy flow equation to obtain permeability using mud invasion depth inversion of array induction logging.The influence of various permeability factors on the model is analyzed by numerical simulation.The model is used to predict the permeability of tight sandstone in the south of the Ordos Basin.The predicted permeability is highly consistent with the core analysis permeability,which verifi es the reliability of the method.展开更多
基金supported by the National Science and Technology Major Projects of China (No. 2016ZX05042 and No. 2017ZX05039)the National Natural Science Foundation Projects of China (No. 51504269 and No. 51490654)Science Foundation of China University of Petroleum, Beijing (No.C201605) to support part of this work。
文摘In this work,a flowing material balance equation(FMBE) is established for under saturated coalbed methane(CBM) reservoirs,which considers immobile free gas expansion effect at the dewatering stage.Based on the established FMBE,five straight-line methods are proposed to determine the control area,initial water reserve,initial free gas reserve,initial adsorbed gas reserve,original gas in place,as well as permeability at the same time.Subsequently,the proposed FMBE methods for undersaturated CBM reservoirs are validated against a reservoir simulation software with and without considering free gas expansion.Finally,the proposed methods are applied in a field case when considering free gas expansion effect.Validation cases show that the straight-line relationships for the proposed five FMBE methods are excellent,and good agreements are obtained among the actual reserves and permeabilities and those evaluated by the proposed five FMBE methods,indicating the proposed five FMBE methods are effective and rational for CBM reservoirs.Results show that a small amount of free gas will result in a great deviation in reserve evaluation;hence,the immobile free gas expansion effect should be considered when establishing the material balance equation of undersaturated CBM reservoirs at the dewatering stage.
基金supported by the National Natural Science Foundation of China project(No.41504103 and No.41804097).
文摘Permeability is an important index in reservoir evaluation,oil and gas accumulation control,and production effi ciency.At present,permeability can be obtained through several methods.However,these methods are not suitable for tight sandstone in general because the pore type in tight sandstone is mainly secondary pores and has the characteristics of low porosity and permeability,high capillary pressure,and high irreducible water saturation.Mud invasion depth is closely related to permeability during drilling.In general,the greater the permeability,the shallower the mud invasion depth,and the smaller the permeability,the deeper the mud invasion depth.Therefore,this paper builds a model to predict the permeability of tight sandstone using mud invasion depth.The model is based on the improvement of the Darcy flow equation to obtain permeability using mud invasion depth inversion of array induction logging.The influence of various permeability factors on the model is analyzed by numerical simulation.The model is used to predict the permeability of tight sandstone in the south of the Ordos Basin.The predicted permeability is highly consistent with the core analysis permeability,which verifi es the reliability of the method.