鄂尔多斯盆地西北部奥陶系“三元”主控成藏规律

Analysis of three controlling regularities on the Ordovician gas accumulation in the northwest Ordos Basin,China

通过对鄂尔多斯盆地西北部奥陶系烃源岩、储集层及天然气展布规律的研究,探讨其天然气成藏规律。奥陶系烃源岩主要分布在上统乌拉力克组和拉什仲组,以海相泥岩为主;储层主要发育在中统克里摩里组和桌子山组,依据岩石类型、孔隙结构,可分为岩溶孔洞型储层和白云岩晶间溶孔型储层;天然气藏的形成受烃源岩、储层和圈闭的"三元"主控,具有有效烃源岩控制天然气区域分布、优质储层控制天然气聚集带展布、有效圈闭控制气藏分布特征。鄂尔多斯盆地西北部的西侧气藏主要为油型气,东侧主要为煤型气,均为上生下储的成藏模式。

The gas accumulation regularity is analyzed by studying the hydrocarbon source rocks, the characteristics of reservoir and the distribution of Ordovician oil and gas in the northwest Ordos Basin. The Ordovician hydrocarbon source rocks mainly distribute in the Upper Ordovician Wulalike Formation and Lashizhong Formation with mud and grey mud as main lithology, and reservoirs occur in the Kelimoli Formation and Zhuozishan Formation of Middle Ordovician. Based on the rock type and pore combination characteristics, the Ordovician reservoirs can be divided into the karst vug reservoir and dolomite intergranular pore reservoir. The gas accumulation is mainly controlled by 3 factors of hydrocarbon source rock, reservoir and trap, respectively. The effective hydrocarbon source rocks control the regional distribution of the gas, the high quality reservoirs control the gas zones and the effective trap controls the gas accumulation characteristics. It shows that the oil type gas is in the west of the study area and the coal type gas is in the east. The gas mainly formed in the upper stratum and trapped and accumulated in the lower stratum.