一种厘定复合辫状河道砂体期次的新方法

在对辫状河发育的地层进行小层划分对比研究过程中,常常遇到某些单井钻遇的厚层辫状河道砂体无法分期的情况,给辫状河道的平面组合和识别带来很大困难。为此,通过分析研究岩心、测井录井、野外露头剖面和现代卫星图片等资料,总结出了一套简单且行之有效的方法,就是在标志层顶拉平的基础上,呆用"去压实效应邻井单期河道标定法",用邻井的期次可明显划分的单期河道去标定复合河道,最终完成复合河道的分期。以鄂尔多斯盆地苏里格气田西区下二叠统石盒子组8段下亚段2小层为研究对象,基于连续取心的岩心标定法验证结果表明:①该方法分期精度较高,有助于揭示砂体空间叠置与局部砂体富集规律,提高砂体的钻遇率;②在消除压实效应过程中,采用了"松弛回弹技术"对因泥岩段的大量压实造成的河道上拉进行了拉伸复位,从而提高了同期河道对比的准确性,避免了误判。结论认为:该方法能够对切叠较严重、分期难度较大的复合辫状河道进行准确分期,可为后续小层地层精确对比和同期河道砂体的平面预测提供技术支撑。

A new method for determining the phases of composite braided river channel sand bodies

In substratum division and correlation of strata with braided river developed, the phases of thick-bedded braided river channel sand bodies encountered by a certain individual well often cannot be divided. This makes planar assembling and identification of braided river channels very difficult. Thus, a simple and effective method was figured out by analyzing core data, well-logging and mud-logging data, field outcrop section and modern satellite images. This is a decompaction adjoining well single-period channel calibration methodology, which, based on a section flatted on the top marker bed, calibrates the composite channel with adjoining well-encountered single-phase channel, and eventually divide its phases. This methodology has been applied in the 8^th Member of Lower Permian Shihezi Formation(P₁x_{8 1}²). The results verified by using the continuous coring-based core calibration method show that ① this method provides a high-precision division of phases, which is useful in revealing the spatial sand body superimposition and local sand body enrichment law, thus to improve the ratio of encountering sand bodies; and ② in compaction-eliminating application, this method provides a higher accuracy for correlating channels of the same phase and eliminates the mistakes by stretching and restoring the channel pulled due to the great compaction of mudstone member through a relaxation springback technique. It is concluded that, this method provides a precise division of phases for greatly segmented and superimposed composite braided river channels that are commonly difficult to be divided, and hence can provide technical support for subsequent fine substratum correlation and planar prediction of channel sand bodies of the same phase.