硬石膏结核白云岩沉积微相——以鄂尔多斯盆地东部马五1^3小层为例

Sedimentary microfacies of anhydrite concretion dolomite rock： Take Majiagou Formation Ma5_1~3 layer in the eastern Ordos Basin as an example

鄂尔多斯盆地奥陶系古风化壳顶部发育的马五13小层是盆地东部的主要产层之一,小球状硬石膏结核白云岩是其重要的储集层。对马五13小层岩石学特征及微相标志研究表明,这套小球状硬石膏结核白云岩及与其间互的含硬石膏白云岩和白云岩均属潮坪沉积,自中央隆起边缘向东,硬石膏结核含量逐渐减少,含盐度降低,水体变得更开阔,自西向东依次发育硬石膏结核白云岩坪—含硬石膏结核白云岩坪—白云岩坪,3个沉积相带呈环状弧形展布。硬石膏结核白云岩坪是马五13小层最有利的沉积微相,含硬石膏结核白云岩坪次之,靖边大气田分布于硬石膏结核白云岩坪中。沉积微相是控制靖边气田及榆林—米脂地区有利储集层展布的基本因素。

Layer Ma513 developed in the top of Ordovician weathering crust is one of the main pay zones in the eastern Ordos Basin,and the coccoid anhydrite concretion dolomite is the important reservoir bed of it.Research on the lithologic characteristics and microfacies signs of layer Ma513 demonstrates that the coccoid anhydrite concretion dolomite and its interbedded dolomites with or without anhydrite are tidal flat deposits.From the central uplift to the east,the amount of anhydrite concretion tapers off,saltness decreases,and the water body becomes wider.From west to east develops successively anhydrite concretion dolomite flat-dolomite flat with anhydrite concretion-dolomite flat,and the three depositional facies-belts present a circular arc-like distribution.Anhydrite concretion dolomite flat is the optimum sedimentary microfacies of layer Ma513,secondarily the dolomite flat with anhydrite concretion.The Jingbian large gas field is distributed in the anhydrite concretion dolomite flat.Sedimentary microfacies is the fundamental factor controlling the distribution of favorable reservoirs in the Jingbian gas field and Yulin-Mizhi area.