鄂尔多斯盆地中生界特低—超低渗透油藏递减规律

Decline law of extra-low—ultra-low permeability of mesozoic reservoir in the Ordos basin

密切结合油田开发实际,综合运用动态分析、典型曲线拟合以及公式法等,对鄂尔多斯盆地南部长6特低—超低渗透油藏的自然开采特征及递减规律进行了分析.结果表明:特低—超低渗透油藏开发阶段可大致划分为滚动建产、快速递减、减速递减、缓慢衰减等四个阶段.滚动建产阶段持续时间很短,油藏投产后2个月内即可实现最大产能;随后开发进入一个漫长的递减历程.递减初期为快速递减阶段,亦称指数递减阶段,历时约5个月,月均综合递减率5.8%;之后为减速递减阶段,亦称双曲递减阶段,历时约7个月,月均综合递减率3.7%;再后为缓慢衰减阶段,亦称调和递减阶段,历时70个月以上,月均综合递减率0.92%,折合年递减率为11%.缓慢衰减阶段几乎贯穿了特低—超低渗透油藏开发阶段的始终,成为其开发历程中最主要的开发阶段,其递减率大致代表了特低—超低渗透油藏的综合递减率.滚动建产和快速递减阶段该油藏以溶解气驱动为主,减速递减阶段以弹性—溶解气混合驱动为主,缓慢衰减阶段以弹性驱动为主.

Combined with actual oil field development,the dynamic analysis method,typical curve fitting,the formula method and other methods were synthetically used to analyze in-depth production characteristics and the decline law of special extra-low—ultra-low permeability of mesozoic reservoir of Chang 6 in the Ordos basin.The results show that the development phase of extra-low—ultra-low permeability reservoirs could be divided into roughly four stages,i.e.,the production-building phase,fast decline phase,deceleration decline phase and slow decay decline phase.The duration of production-building phase was short and the reservoir production could achieve the maximum capacity within 2 months;then the reservoir development entered a long degression process.Decreasing the initial stage for the rapid decline,also known as exponential decrease,which lasted about 5 months,the average monthly decline rate of the exponential declining stage （fast decline phase） was 5.8%.Afterwards,for the deceleration decline phase,also known as hyperbolic decline phase,which lasted about 7 months,the average monthly decline rate of the hyperbolic decline stage （deceleration decline phase） were 3.7%.After a further slow decay phase,also known as harmonic decrease,which lasted for more than 70 months,the average monthly decline rate of the harmonic decline stage （slow decay stage） were 0.92%,equivalent to the average annual decline rate of 11%.The slow decay （harmonic decline） phase became the major and most characteristic development phase of extra-low—ultra-low permeability of the reservoir because it nearly went through the entire period of the reservoir development.The decline rate of this stage represented roughly a synthesized decreasing rate of extra-low—ultra-low permeability of the reservoir.The reservoir was driven mainly by the dissolved gas in the production-building phase and fast decline phase,and driven mainly by a combination drive of flexible-dissolved gas in the deceleration decline phase and by an elastic drive in slow decay phase.