姬塬油田长8油层组短期基准面旋回与储层成因分析

Short-term base level cycle and reservoir genesis analysis of Chang 8 oil reservoir set in Jiyuan Oilfield

运用高分辨率层序地层学原理将鄂尔多斯盆地姬塬油田长8油层组三角洲前缘短期基准面旋回分为对称型和非对称型两大类,其中非对称型旋回包含向上变深和向上变浅2种类型,对称型旋回包含上升半旋回厚度大于下降半旋回厚度、上升半旋回厚度小于下降半旋回厚度和上升半旋回厚度近似等于下降半旋回厚度3种类型。长8油层组储集砂体按成因可分为水下分流河道、河口坝、复合式坝和远砂坝砂体四大类,水下分流河道砂体包含削截式和完整式2种类型,河口坝砂体包含孤立式和叠加式2种类型,复合式坝砂体为水下分流河道砂体直接叠加在河口坝砂体之上形成,它们明显受基准面升降引起的可容纳空间(A)和沉积物补给量(S)之间变化关系的影响。在基准面上升过程中,主要形成削截式和完整式水下分流河道砂体,前者A/S<1,后者A/S>1;在基准面下降过程中,主要形成孤立式、叠加式河口坝和远砂坝砂体,前者A/S<1,后两者A/S>1;在一个完整的基准面升降旋回中,如果既保留了短期基准面上升期的沉积,又保留了下降期的沉积,则形成复合式坝砂体。姬塬油田长8油层组属岩性油藏,搞清短期基准面旋回的变化规律及其对砂体的控制作用,预测水下分流河道、叠加式坝和河口坝等砂体将是下一步油气勘探的重点。

Based on the theory of high resolution sequence stratigraphy, the short-term base level cycle of delta tront ot Chang 8 oil reservoir set in Jiyuan Oilfield was divided into two types, including non-symmetric short-time cycle and symmetric short-time cycle. The non-symmetric short-time cycle includes upward-deepening and upward-shallowing cycles, and the symmetric short-time cycle includes three kinds of cycle： the ascending half cycle thickness is greater than the descending half cycle thickness, the ascending half cycle thickness is less than the descending half cycle thickness, and the ascending half cycle thickness is ap proximately equal to the descending half cycle thickness.According to the forming reason, the reservoir sand bodies of Chang 8 oil reservoir set were divided into three categories and six types, and each kind of sand body is obviously controlled by relationship between the accommodate space （A） and sediment supply （S）. In the process of the base Xevel rising, when the A/S 〈 1, mainly formed cutting distributa^y channel sandbody, while when the A/S 〉 1, mainly formed complete type channel sand body. In the process of base level falling, when the A/S〈 1, mainly formed isolated type mouth bar sand body, while when A/S〉 1, mainly formed super- position type mouth bar sand body and far bar sand body. In a complete base level cycle, if there not only kept rising short-term base level of deposition, but also retained the decline phase deposition, so the composite dam sand bodies formed. Chang 8 oil reservoir set in Jiyuan Oilfield belongs to lithologic reservoir. Therefore, further study on short- term base level change rule and its control effect on sand bodies, forecasting and looking for underwater distributary channel, the superposition type sand dam and mouth bar sand bodies will be the main direction of next exploration.