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
Coal Bed Methane(CBM)is natural gas occurring in coal seams.It can be used for domestic(heating and cooking)and industrial purposes,electricity generation,transportation(as compressed natural gas or liquefied natural ...Coal Bed Methane(CBM)is natural gas occurring in coal seams.It can be used for domestic(heating and cooking)and industrial purposes,electricity generation,transportation(as compressed natural gas or liquefied natural gas),and in boilers supporting mining operations.It is established that Zimbabwe has CBM in the North-Western region.At the time of this study,only one organization(Industrial Development Corporation)has reported an Original Gas in Place(OGIP)estimate for the region as 765 Bm3.In this study we use Monte Carlo Simulation(MCS)to estimate the range of OGIP values for the region.MCS is a widely used probabilistic method,preferred over deterministic methods in which only best-estimate values of parameters are used to predict a single OGIP value.This single OGIP value may be either positively(overestimated)or negatively skewed(underestimated).However,the probabilistic approach using MCS accounts for the uncertainty in values of parameters.This is done by incorporating appropriate range and probability distributions(e.g.triangular,normal,uniform,etc.)of input parameters(e.g.target area,formation thickness,coal bulk density,and adsorbed methane content),and repeating calculations to generate a cumulative distribution curve for the OGIP.The generated curve provides statistical confidence levels represented as probability distributions,i.e.P10,P50,and P90 represents low,mid,and high probability estimates,respectively.Our results show that P10,P50,and P90 values for the North-Western region OGIP are 5699 Bm3,2347 Bm3,and 706 Bm3,respectively.The Resource Density(RD)estimation is found to range from 0.015 Bm3/km2 to 0.113 Bm3/km2 over the geographic area.This range is comparable to Alberta plains shallow and deep basins in Canada which boosts a higher level of confidence for CBM potential in Zimbabwe.The results are encouraging for further exploration and planning of exploitation of CBM in Zimbabwe.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.
文摘Coal Bed Methane(CBM)is natural gas occurring in coal seams.It can be used for domestic(heating and cooking)and industrial purposes,electricity generation,transportation(as compressed natural gas or liquefied natural gas),and in boilers supporting mining operations.It is established that Zimbabwe has CBM in the North-Western region.At the time of this study,only one organization(Industrial Development Corporation)has reported an Original Gas in Place(OGIP)estimate for the region as 765 Bm3.In this study we use Monte Carlo Simulation(MCS)to estimate the range of OGIP values for the region.MCS is a widely used probabilistic method,preferred over deterministic methods in which only best-estimate values of parameters are used to predict a single OGIP value.This single OGIP value may be either positively(overestimated)or negatively skewed(underestimated).However,the probabilistic approach using MCS accounts for the uncertainty in values of parameters.This is done by incorporating appropriate range and probability distributions(e.g.triangular,normal,uniform,etc.)of input parameters(e.g.target area,formation thickness,coal bulk density,and adsorbed methane content),and repeating calculations to generate a cumulative distribution curve for the OGIP.The generated curve provides statistical confidence levels represented as probability distributions,i.e.P10,P50,and P90 represents low,mid,and high probability estimates,respectively.Our results show that P10,P50,and P90 values for the North-Western region OGIP are 5699 Bm3,2347 Bm3,and 706 Bm3,respectively.The Resource Density(RD)estimation is found to range from 0.015 Bm3/km2 to 0.113 Bm3/km2 over the geographic area.This range is comparable to Alberta plains shallow and deep basins in Canada which boosts a higher level of confidence for CBM potential in Zimbabwe.The results are encouraging for further exploration and planning of exploitation of CBM in Zimbabwe.
