Abstract:

Two types of oil reservoirs, related to Cenozoic igneous rocks, exist in Qikou depression,i.e., basic volcanic rock reservoir and diabase alteration zone reservoir, both of them are tectonic-lithological oil reservoirs. Horizontally, they are affected by distribution of igneous rocks and hydrocarbon source rocks, and are mainly focused on the transformation belt related to NE and EW fractures. Vertically, they are controlled by regional cap rocks, and are almost kept in Es^z_１ and Ed. In these two strata within the transformation belt, whether hydrocarbon can accumulate into igneous rocks or not mainly depend on the type of reservoir system. As for open storage system, on one hand reservoir spaces can be protected by fluid replacement to discharge mineralized water and reduce the formation of secondary minerals, on the other hand the reservoir spaces can be increased and expanded to further improve reservoir conditions by the way that: organic acid fluids get into the spaces and dissolve amygdale, fracture fillings and unstable minerals in igneous rock. In addition, open storage system provides the necessary conducting channel for hydrocarbon，through which hydrocarbon can seep from source rocks to accumulate into igneous rock to form oil reservoirs. In closed reservoir system, there are no these conditions mentioned above, the reservoir property has been lost partly because mineralized water can not be expelled out of igneous rocks and result in the formation of secondary minerals to fill reservoir space. Moreover, part of the unfilled spaces have no intercommunication channel between igneous reservoir and hydrocarbon source rock and become dead spaces, which makes it difficult to accumulate oil and gas in the closed reservoir system.

Key words: Qikou depression, volcanic reservoir, diabase alteration zone reservoir, closed storage system, open storage system