鄂尔多斯盆地西缘克里摩里组白云岩储层特征及成因

Characteristics and genesis of the Ordovician Kelimoli dolomite reservoirs in the western edge of the Ordos Basin

鄂尔多斯盆地西缘奥陶系发育多期台缘礁滩体沉积,其中对于中奥陶统桌子山组厚层块状白云岩的研究较多,而对于中奥陶统克里摩里组中薄层状白云岩的研究则较少。为此,在分析该区克里摩里组储层发育背景的基础上,基于露头、岩心、岩石薄片观察资料和测井解释成果,研究了克里摩里组的岩石学特征、孔隙结构特征、储层物性和地球化学特征;结合碳氧同位素、锶同位素、稀土元素、微量元素、阴极发光等资料,明确了该组白云岩成因和储层成因模式,进而预测了该区克里摩里组白云岩储层的展布情况。研究结果表明:①该区克里摩里组白云岩储层发育晶间孔隙型、溶蚀孔洞型和裂缝型等3种储层类型,其中前两者孔喉分布均匀、孔渗性较好,是主要的储层类型;②克里摩里组主力储层白云岩以浅埋藏交代成因为主,局部经受了后期深埋热液改造作用;③高频层序和埋藏白云岩化控制了克里摩里组的储层发育,其中构造运动形成的古沉积地形控制了滩体的平面展布,海平面的短期升降变化控制了储层的纵向差异性,而埋藏白云岩化作用使岩石骨架得以强化、孔隙得以保存。结论认为,该区克里摩里组白云岩储层主要沿台缘带呈南北向断续分布,厚度介于0.8~43.0m,总面积为6512km^2,可以形成规模有效的储集体。

In the Ordos Basin, the Ordovician developed multi-stage platform edge reefs and beach deposits. The thick and massive dolomite of the Zhuozishan Fm of Middle Ordovician has been widely studied, but the thin–medium dolomite of the Kelimoli Fm of Middle Ordovician is seldom studied. Based on outcrop, core, thin section observation and well logging interpretation results, and through the analysis of the development background of reservoir of the Kelimoli Fm in this area, the petrological characteristics, pore structure characteristics, reservoir physical properties and geochemical characteristics of the Kelimoli Fm were studied. Based on the data of carbon and oxygen isotopes, strontium isotopes, rare earth elements, trace elements and cathode luminescence etc., the dolomite genesis and reservoir genesis models in this area were confirmed, and the dolomite reservoir distribution of the Kelimoli Fm in this area was predicted. The results indicate that:(1) there are three types of dolomite reservoirs in the Kelimoli Fm: intercrystalline pore, dissolution pore and cave, and fracture. The pore throats of intercrystalline pores and dissolution pores and caves which are the main reservoirs are evenly distributed with better porosity and permeability;(2) the main dolomite reservoir of the Kelimoli Fm is mainly formed by shallow burial metasomatism, and part of it has undergone deep burial hydrothermal transformation during the later stage;(3) high-frequency sequence and buried dolomitization control the reservoir development of the Kelimoli Fm. Hereinto, the ancient sedimentary terrain formed by tectonic movement controls the planar distribution of the beach, while the short-term fluctuation of sea level controls the longitudinal difference of the reservoir, and buried dolomitization strengthens the rock skeleton and pore preservation. It is concluded that the discontinuous dolomite reservoir of the Kelimoli Fm in this area is mainly distributed along the platform edge in an SN direction, with a thickness of 0.8–43.0 m and a total area of 6 512 km^2, which makes it possible to form an effective scale reservoir.