Abstract: By horizon-controlled method, the velocity fields of Kulongshan and Jinhaizi 3-D areas are mapped,the characteristics ofvertical and transversial distribution of velocity are discussed. The analyzed result shows that distinct velocity layering feature occurs invertical direction, and velocity reversion is found in near surface-shallow zone and mid-deep zone; the velocity of overthrust nappe is ofclear block feature in lateral direction; the variation of lateral velocity tends to grow ing from north to south, with gradient of north-low andsouth-high; the contour of velocity assumes distributing along the north-west direction roughly, and there are abnormal-velocity regionsfor these two 3-D areas. It is shown that differences in deep-shallow lithology, thickness and compaction degrees are the essential causesfor the velocity anomaly in these areas.

Key words: Jiuquan basin, Qingxi oilfield, velocity analysis, formation, rock, thickness, compaction