1. College of Geoscience and Surveying Engineering��China University of Mining and Technology��Beijing 100083��China; 2. Langfang Branch of ��esearch Institute of Petroleum Exploration and Development��PetroChina��Langfang 065007��Hebei�� China

Shahezi Formation of Lower Cretaceous is the main source rock in the deep fault- depression of Songliao Basin�� The present drilling data reveal that it is large in thickness ( �� 700 m) and deep in burial ( ��3 500 m)�� However��most wells are located in the margin of the deep fault depression��which brought about relatively rare information on the source rocks in the internal fault basin�� On the basis of the structural style and seismic reflection feature of the fault depression��two development models of source rocks in Shahezi Formation are summarized��including the dustpan shape unilateral fault depression and graben bilateral fault depression�� Mean- while�� there exist five types of deep source rocks�� The source rocks in the central fault depression which have paral- lel structural��stratified and continuous seismic reflections are most reliable�� These source rocks are characterized by deep and semi- deep lacustrine facies with large thickness and big ratio of dark mudstone and stratum (45% ��70%)�� The quantity of gas generating in the studied area is 148. 38 ×10 12 m 3 ��which indicates a huge po- tential of gas��