Bitumen and hydrocarbon generation potential of paleo-reservoirs in the Ordovician, south Ordos Basin

Bitumen is distributed extensively but not even in the Ordovician, south Ordos Basin. Core observation and slice identification indicate that it is distributed horizontally in the Yongcan 1-Xuntan 1-Chuntan 1-Yaocan 1 wellblock and concentrated vertically in the Majiagou Formation Ma6 Member top-Pingliang Formation bottom and the Ma3 Member top-Ma4 Member bottom. It exists largely in fractures, intercrystalline pores, and solution pores or stylolites. Optical characteristics and bituminous reflectivity reveal that bitumen charging has two phases in this area. According to the solid bitumen amount, abundance degree and thermal simulation experiment, paleo-reservoirs exist in the studied area. They are divided into three types, Ma6 Member pore filling, Ma3-Ma4 Member pore filling and Liangjiashan Formantion (?). Their source rock was developed in a deepwater slope depositional environment of the middle Ordovician period. The hydrocarbon potential was evaluated by solid bitumen content and geological features. The amount of cracking gas is probably 3.6×1012−7.7×1012 m3, providing sufficient gas source for hydrocarbon accumulation in the Ordovician, south Ordos Basin.