古洞穴型碳酸盐岩储层特征研究——以塔河油田奥陶系古洞穴为例

RESERVOIR CHARACTERISTICS OF PALEOCAVE CARBONATES—A CASE STUDY OF ORDOVICIAN PALEOCAVE IN TAHE OILFIELD,TARIM BASIN

古洞穴型碳酸盐岩储层都具有显著的非均质性和预测难度大的特点。通过对比巴楚五道班野外露头剖面上的洞穴 ,结合岩溶理论建立了古洞穴型储层的地质模型。以塔里木盆地塔河油田奥陶系古洞穴型储层为例 ,系统分析和归纳了该类储层在钻井、录井、测井、试井、地震等资料上的响应特征和识别标志。在垂向上 ,可将洞穴划分为洞穴顶部相、洞穴充填相与下部垮塌相 ,其中洞穴顶部相和下部垮塌相对油气储集十分有利。而多层洞穴的发育则主要受控于构造抬升和海平面升降。影响古洞穴碳酸盐岩储层的平面非均质性的主要因素有古构造、古断裂、古水文系统、古岩溶地貌等 ,其中与古岩溶地貌关系最为密切。研究结果表明 ,储集性能较好的古洞穴型碳酸盐岩储层为未充填洞穴储层和大型洞穴充填孔隙型砂岩储层。

Paleocave carbonate reservoirs are characterized by their heterogeneity ,and they are very difficult to predict. For the sake of building a realistic geological model of the paleocave carbonate reservoir, correlation has been made with the paleocaves occurred in Wudaoban outcrop sections in Bachu area. The shape, size, structure, cave deposit, genesis and reservoir properties of the Ordovician paleocaves in Tahe oilfield , Tarim basin ,have been studied on the basis of the theory of karst and the paleocave marks identified by means of drilling, logging, well logging, testing and seismic methods. The vertical and lateral heterogeneities of paleocave carbonate reservoir have also been discussed. Vertically , paleocave sediments can be divided into the top facies, filling facies and the lower sloughing facies. The top facies and the lower sloughing facies are quite favorable for hydrocarbon entrapment. But the development of multiple paleocaves have mainly been controlled by tectonic uplift and sea-level fluctuation. Ancestral structures, such as paleofault, paleodrainage system and paleokarst topography etc. have mainly been influencing the lateral heterogeneity of paleocave carbonate reservoirs, among which the paleokarst topography has the closest relation to lateral heterogeneity of paleocave carbonate reservoir. The study indicates that the relatively good paleocave carbonate reservoirs include the unfilled paleocave reservoirs and large paleocave-filling deposits—porous sandstone reservoirs.