鄂尔多斯盆地白豹—华池地区长8段孔隙度演化定量模拟

Quantitative Simulation on Porosity-evolution in Member 8 of Yanchang Formation of Baibao-Huachi Area,Ordos Basin

在对鄂尔多斯盆地白豹—华池地区长8段砂岩储层特征、主控因素分析及地层埋藏史和成岩史研究的基础上,应用数理统计的方法,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,分别建立了鄂尔多斯盆地白豹—华池地区长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4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80～100℃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为压实和保持阶段,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。实例验证结果表明在研究区建立的该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相似岩性、埋藏年代和沉积类型的地层孔隙度计算中,为孔隙度预测提供定量计算方法,以期对该区油气勘探提供借鉴意义。

Combining with the mathematical statistics method, we describe of tight sandstone reservoir char- acteristics and simulate the burial history and diagenetie history of the Member 8 of Yanchang Formation in the Baibao-Huachi area,Ordos basin. According to present porosity as boundary constraint conditions,geo- logical times and burial depths, the whole porosity evolution from initial burial until present is divided into two independent processes of porosity decrease and porosity increase and establish two mathematical rood els,respectively. The quantitative simulation result indicates that the whole porosity evolution quantitative simulation is a piecewise function with four sections. That is, the porosity decrease model of mechanical compaction stage is a continuous function with burial depth as the independent variable function,the coin paction-cementation comprehensive stages is a continuous function with geological time and burial depth as the variables;the secondary porosity increase is caused by organic acid dissolution within a temperature window of 80-100℃. Therefore,the dissolution phase is the porosity increase model,which is a composite function of depth and burial time. After the dissolution phase,the porosity is in the phase of compaction and maintenance. The model of porosity decrease is a superimposed composite function of depth, burial time,and the porosity increase. Finally,by a case study,it is verified that the established porosity evolution quantitative simulation is consistent with actual geological conditions and can be applied to the porosity cal culation of similar lithology, burial history and sedimentary type strata in the study area. Meanwhile, this approach provides quantitative calculation method for porosity prediction and it will be helpful for oil-gas exploration of this area.