Geological Setting

Liaohe Basin in Northeast China has been divided into several depressions (Wang & Wang, 1988; Hu, et al.,2005) and Olituoz of Liaohe Oilfield resides in the middle segment of Eastern Depression (Fig.1a). Liaohe basin is a Cenozoic rift basin which experienced pre-rift in Paleocene, chief rift stage in Eocene, and post-rift subsidence stage since Miocene (Fig.1c and Fig.2). Shahejie formation of Eocene was the main strata in the region (Fig.1c and Fig.2) and was subdivided into 4 members - Es1 to Es4. Es4 is absent in the region, while Es2 is narrowly distributed in Olituoz block. Es3 is most important strata in the region and the target layer for oil exploration. Volcanic activities were intensive and widespread in the region during the phase of rifting (Fig1.b) and many episodes could be recognized.

Figure 2. Stratigraphy of Olituoz area.

Stratigraphy of Olituoz area.

Three stages of volcanic activities are shown, with each stage data after Sun (1999). Es4 is absent in the region, while Es2 is narrowly distributed.

Tan-Lu Fault system plays a key role in the evolution of the area. The strike-slip motion of Tan-Lu Fault Zone transferred from dextral strike slip to left-lateral strike slip at 42 Ma is a key turning point for the region (Hou, et al., 1998; Hou et al., 2001). Detail structural and volcanic events are presented in Fig. 2.

Research has proved that the trachyte of Es3 is the main reservoir layer in Olituoz area (Gu, et al.,2002). Judging from structural evolution, these volcanic rocks only experienced the structural events of Dongying Formation time (Ed). And their development of structural fractures should be chiefly controlled by the stress field in Ed stage.