陇东地区长8油层组短期基准面旋回与储层成因

SHORT-TERM BASE-LEVEL CYCLE AND RESERVOIR ORIGIN OF CHANG-8 RESERVOIR GROUP IN LONGDONG AREA

以陕甘宁盆地延长组长8油层组为例，运用高分辨率层序地层学的短期基准面旋回原理，详细分析了以水下分流河道和河口坝沉积为主体的辫状河三角洲前缘厚层储集砂体的成因。研究表明，各种成因砂体的发育受沉积基准面升降、可容纳空间增加与沉积物补给通量比值变化的控制。在基准面上升过程中，A／S〈1时以多期叠加型和废弃型河道砂体为主，A／S〉1时则为完整型河道砂体；在基准面下降过程中，A／S〈1时以完整型河口坝砂体为主，A／S〉l时则以叠加型河口坝为主。在此基础上，讨论了各种成因砂体在高分辨率层序地层学格架内的时空分布规律。

Taking the Chang-8 reservoir group in Yanchang Formation in Shanganning Basin for example, using the short-term base-level cycle theory of high-resolution sequence stratigraphy, this paper analyzes the origin of thick reservoir sandbodies in braided-river delta front that is dominated by the underwater distributary channel and mouth bar in detail. The research indicates that the development of sandbodies with different origins is controlled by the fluctuation of depositional base-level and changes of the ratio of admittable space improvement to sediment recharge flux. In the process of base-level rising, when A/S 〈 1, the multi-phase superposition and abandoned channel sandbodies are taken as the dominant factor; when AZS 〉 1, the integrated channel sandbodies are taken as the dominant factor. In the process of base-level dropping, when A/S 〈 1, the integrated mouth bar sandbodies are taken as the dominant factor; when A/S 〉 1, the stacked mouth bar sandbodies are taken as the dominant factor. Based on this, the time and space distribution laws of sandbodies with different origins in high-resolution sequence stratigraphy framework are discussed.