柴西南区湖相碳酸盐岩勘探潜力评价

Exploration potential evaluation of lacustrine carbonate rock in Southwest Qaidam Basin

近年来,柴达木盆地英西下干柴沟组上段碳酸盐岩储层成功钻探了多口千吨井。研究区柴西南区与英西地区毗邻,广泛发育碳酸盐岩,其成藏地质条件与英西地区相似。为了进一步了解柴西南区碳酸盐岩油藏分布规律及勘探潜力,文中利用岩心、测井、地震、试油等资料,对柴西南区下干柴沟组上段的构造、源岩、储层、油藏进行了详细解剖和刻画,认为下干柴沟组上段具备4个有利成藏的地质条件:1)成藏期古构造背景为邻凹古斜坡,位于生烃中心附近,古今构造继承性好,相对稳定;2)该区发育了盆地分布最广、最优质的烃源岩,有机碳质量分数最高达4.32%,厚度最大超过1 000 m,面积达到2 000 km^2;3)有利储集岩石类型包括颗粒灰岩、藻灰岩、泥晶灰岩,原生孔、次生溶蚀孔、微裂缝发育;4)源储配置条件好,有利于形成源内或近源型油藏。通过综合评价,落实下干柴沟组上段碳酸盐岩有利勘探面积480 km^2,确定该区为下一步增储上产的有利区带。

In recent years, several kiloton wells have been drilled in the upper part of Lower Ganchaigou Formation in Yingxi area ot Qaidam Basin. In this paper, carbonate rocks are widely developed in the study area, Southwest Qaidam Basin, which is adjacent to Yingxi area, and the geological conditions are similar to Yingxi area. In order to thrther reveal the distribution pattern and exploration potential of carbonate reservoir in the study area, based on drilling core, logging, seismic, oil well testing data, we studied the characteristics of structure, hydrocarbon source rocks, reservoir stratum and reservoir in the upper part of Lower Ganchaigou Formation in details. The resuhs indicate that there are tbur favorable geological conditions. Firstly, the paleotectonic background in study area is ancient slope which was located near the hydrocarbon generation center during accunrmation period. And the tectonic enviromnent is relatively stable. Secondly, high-quality source rocks with organic carbon content up to 4.32% are widely developed in the study area. The maximum thickness of source rocks exceeds 1,000m, and the acreage is 2,000 km^2. Thirdly, tavorable reservoir rock Upes include grain limestone （dolomite）, algal limestone （dolomite） and micrite. In addition, the reservoir rocks developed much primary pore, secondary pore and microfracture. Fourthly, good allocation conditions of source and reservoir are conducive to form in-source or near-source reservoirs. Comprehensive evaluation indicated that the favorable exploration area of the upper part of Lower Ganchaigou Formation is about 480 km^2, which is the hopeful zone for the further exploration.