三角洲外前缘亚相储层井间连通性定量评价——以大庆长垣萨尔图油田南二区东部为例

三角洲外前缘亚相储层井间连通性研究对于高含水期油田井网优化和剩余油挖潜具有重要意义。以大庆长垣萨尔图油田南二区东部为靶区,利用122个时间单元的密井网资料,首先构建出三角洲外前缘亚相储层井间连通性定量评价模型,进而开展不同砂地比和井距条件下的三角洲外前缘亚相储层井间连通性定量评价。结果表明:(1)砂地比为评价储层井间连通性的宏观评价参数,即存在一个"渗流阈值",当砂地比低于渗流阈值时,井间连通性不超过20%变为不连通,当砂地比达到渗流阈值后,井间连通性迅速增长至80%以上变为完全连通,整个过程反映的砂地比和井间连通性函数图像呈S形曲线;(2)通过对砂体最大横截面面积沿垂直于井钻进方向的投影和井距的空间耦合关系分析,建立了以井距为变量的三角洲外前缘亚相储层井间连通概率模型,同时提出各微相砂体所占比例影响储层井间连通性整体变化趋势;(3)储层井间连通性渗流阈值与井距呈正相关,随着井距变小,砂地比与井间连通性的S形曲线函数图像趋于"线性",当平均井距为70 m(1倍井距)条件下三角洲外前缘亚相储层井间连通性的渗流阈值为0.20,平均井距为140 m(2倍井距)和210 m(3倍井距)条件下储层井间连通性的渗流阈值分别为0.24和0.30。

Q uantitative evaluation on the interwell connectivity of reservoirs in delta outer-front subfacies:a case study of the eastern Nan'er block,Saertu oilfield,Daqing placanticline

A research on the interwell connectivity of reservoirs in delta outer-front subfacies is of great importance to well pattern optimization and residual oil tapping for oilfields in a high water-cut period. Taking the eastern Naner block, Seartu oilfield, Daqing placanticline as a target region, based on the dense well pattern data of 122 time units, this study firstly establishes the quantitative evaluation model on the interwell connectivity of reservoirs in delta outer-front subfacies, followed by quantitative evaluations under different net to gross ratios and well spacing conditions. The results show that firstly, the net to gross ratio is a macro-evaluation parameter for the interwell connectivity of reservoirs, i.e., a "porous flow threshold" exists. When the net to gross radio is lower than the porous flow threshold, the interwell connectivity is no more than 20% and changed into disconnection. But when the net to gross ratio reaches the porous flow threshold, the interwell connectivity is increased sharply to over 80% and changed into complete connection. The functional image of net to gross ratio and interwell connectivity reflected in the whole process is shown as a S-shaped curve. Secondly, through analyzing the spatial coupling relationship between the well spacing and the projection of maximum sand-body cross sectional area perpendicularly to well drilling direction, the interwell connectivity probability model of reservoirs in delta outer-front subfacies is created using well spacing as a variable. Meanwhile, it is put forward that the overall variation tendency of reservoir interwell connectivity is influenced by the proportion of each microfacies sand body. Thirdly, the porous flow threshold of reservoir interwell connectivity shows a positive correlation to well spacing. As the well spacing gets smaller, the S-shaped-curve functional image of the net to gross ratio and interwell connectivity tends to be "linear". When the average well spacing is 70 m (simple well spacing), the porous flow threshold of the interwell connectivity of reservoirs in delta outer-front subfacies is 0.20; when the average well spacing is 140 m (double well spacing) and 210 m (triple well spacing), the porous flow thresholds of reservoir interwell connectivity are 0.24 and 0.30, respectively.