鄂尔多斯盆地南部奥陶系沥青及古油藏生气潜力

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

鄂尔多斯盆地南部地区奥陶系固体储集层沥青分布较为普遍但不均匀。岩心观察和镜下薄片鉴定表明,奥陶系固体沥青平面上主要分布在永参1井—旬探1井—淳探1井—耀参1井区,剖面上主要集中在马家沟组马六段顶—平凉组底部和马三段顶—马四段底部;其赋存形式常见有3种：赋存于裂缝、晶间孔和溶蚀孔隙/缝合线中。结合光性特征和沥青反射率分析,确定该区发育两期充注的沥青。固体沥青的数量、富集程度和热模拟实验资料证实了研究区古油藏的存在,其可分为3类：马六段孔隙充填型、马三段—马四段孔隙充填型和亮甲山组古油藏（？）。沉积环境分析表明古油藏烃源岩（平凉组泥页岩）发育于中奥陶世的深水斜坡沉积环境。依据固体沥青含量和古油藏的地质特征评价古油藏生烃潜力,总裂解生气量约为3.6×1012~7.7×1012m3,为南部地区奥陶系成藏提供了充足的气源。

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 we]Iblock and concentrated vertically in the Majiagou Formation Ma6 Member top -- Pingliang Formation bottom and the Mas 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 ×10^12-7. 7 × 10^12 m3 , providing sufficient gas source for hydrocarbon accumulation in the Ordovician, south Ordos Basin.