鄂尔多斯盆地姬塬地区长8段孔隙度演化定量模拟

摘要

Based on the analysis of characteristics and major controlling factors of Chang-8 section sandstone reservoir in Jiyuan area of Ordos Basin and the study on corresponding stratigraphic and diagenetic history, combined with petroleum geology theory and mathematical statistics method, porosity evolution was divided into two processes including the decrease and increase of the porosities under the condition of the restriction of present porosity, and a model for the porosity evolution of Chang-8 section sandstone reservoir in the research area was built. Porosity varied with the depth of burial and geological time from the initial burial to the present in the model. The results showed that the model with quantitative porosity evolution was a piecewise function with four sections. Mechanical compaction stage was a model with the decrease of porosity, which was a continuous function with the independent variable of burial depth; compaction and cementation stage was a model with the decrease of porosity, which was a continuous function with the variables of geological time and burial depth; the secondary porosity increase was caused by the dissolution of acid fluid within a temperature range of 70℃ -110℃ , so that dissolution stage was a model with the increase of porosity, which was a composite function of depth and burial time; after the dissolution stage, formation porosity was in compaction and maintenance stage, which was a model with the decrease of porosity, and the model was a superimposed composite function of depth, burial time and the porosity increase amount. Finally, taking one well in the research area as an example, it was verified that the model with quantitative porosity evolution was consistent with actual geological condition, and could be applied to calculate the porosity of any strata.%在对鄂尔多斯盆地姬塬地区长8段砂岩储层特征、主控因素及地层埋藏史和成岩史研究的基础上,结合石油地质理论,应用数理统计方法,以现今孔隙度为约束条件,将孔隙度演化分为孔隙度减小和孔隙度增大2个过程,分别建立研究区长8段砂岩储层从埋藏初始至现今的孔隙度随埋藏深度和地史时间变化的演化模型.结果表明:孔隙度定量演化模型为一个四段式分段函数.机械压实阶段为孔隙度减小模型,是以埋深为自变量的连续函数；压实和胶结作用阶段为孔隙度减小模型,是对埋深和埋藏时间的连续函数；次生增孔是由于地层酸性流体的溶蚀作用而产生的,主要发生在70℃～110℃的温度窗口内,因此溶蚀阶段为孔隙度增大模型,是对埋深和埋藏时间的复合函数；溶蚀阶段结束后,地层孔隙度处于压实和保持阶段,该阶段为孔隙度减小模型,是对埋深、埋藏时间及增孔量的叠加复合函数.最后进行实例验证,发现在研究区建立的砂岩孔隙度定量演化模型符合地质实际,可以推广应用到研究区任一地层孔隙度计算,为孔隙度预测提供定量计算方法.