准噶尔盆地北三台地区清水河组低渗透储层成因机制

Genetic mechanisms of low permeability reservoirs of Qingshuihe Formation in Beisantai area,Junggar Basin

碎屑岩低渗透储层成因机制包括低渗透储层物性主控因素和储层致密史-油藏成藏史匹配关系两个方面。综合利用岩心观察、薄片鉴定、图像分析、扫描电镜观察、压汞与岩石物性测试等多种技术方法,对准噶尔盆地北三台地区下白垩统清水河组低渗透储层进行了研究。储层低渗透特征具有沉积作用主控、压实作用主导、溶蚀作用改善、胶结作用强化的特点。针对砂质砾岩—细砾岩、细砂岩、粉砂岩和泥质粉砂岩,以"储层成岩作用演化序列-储层孔隙结构"为约束进行地质历史时期储层物性的恢复,确定不同区带、不同岩性储层的低渗透形成时间,结合油藏成藏史及原油分布特征,分析清水河组低渗透储层成因机制。清水河组存在3类不同成因类型的储层,Ⅰ类为中渗成藏-现今中渗储层、Ⅱ类为中渗成藏-现今(特)低渗储层、Ⅲ类为(特/超)低渗成藏-现今(特/超)低渗储层;其中Ⅱ类细分出2个亚类,Ⅲ类细分出4个亚类。针对不同成因类型的(低渗透)储层,结合成藏时期储层渗透率特征、储层含油级别、原油特征及试油试采成果等,进行了钻前勘探潜力分析及有效开发增产措施的优选。

Genetic mechanisms of low-permeability clastic reservoirs include many controlling factors, such as low-permeability reser- voir properties and a matching relationship between the reservoir compaction history and the hydrocarbon accumulation history. Cur- rently, studies on the controlling factors of low-permeability reservoir properties have been relatively mature, while the matching re- lationship between the reservoir compaction history and the hydrocarbon accumulation history has been less studied. Therefore, we studied the Lower Cretaceous Qingshuihe Formation low-permeability reservoirs of the Beisantai area, Junggar Basin by means of core observation, thin section identification, image analysis, scanning electron microscopy observation, mercury penetration, petro- physical property testing and other technical methods. The result showed that the low-permeability reservoirs are characterized of be- ing controlled by deposition, predominated by compaction, improved by dissolution and enhanced by cementation. Confined by ＂res- ervoir diagenesis evolutionary sequence and reservoir pore structure＂ conditions, physical properties of sandy-fine conglomerate, fine sandstone, siltstone and argillaceous siltstone reservoirs in geological history were restored, respectively, and the geological time when reservoirs with different lithology in different zones form low-permeability properties was determined based on the reservoir property evolutionary history. Genetic mechanisms of the Qingshuihe Formation low-permeability reservoirs were investigated in combination with the reservoir property evolutionary history, hydrocarbon accumulation history and distribution features of crude oils. The results showed that there exist three different genetic types of reservoirs in the Qingshuihe Formation. Type I had medi- um permeability in the hydrocarbon accumulation period and remains in this permeability now. Type Ⅱ had medium permeability in the hydrocarbon accumulation period and shows low （extra- or super-low） permeability now. Type Ⅲ had low （extra- or super-low） permeability in the hydrocarbon accumulation period and remains in the permeability now. Moreover, type Ⅱ can be subdivided into two sub-types and type Ⅲ into four sub-types. Integrated with reservoir physical properties in the hydrocarbon accumulation period, oil-bearing grades of reservoirs, characteristics of crude oils and oil testing results, we analyzed the exlaloration potential of different genetic types of reservoirs before drilling, and optimized effective development and stimulation methods.