THE SEDIMENTARY FACIES AND THEIR BEARING OIL- GAS PROPERTY IN THE LOWER PART OF THE THIRD MEMBER OF SHAHEJIE FORMATION, ZHUANGXI DEPRESSION IN SHANDONG PROVINCE

To coordinate the exploration of oil-gas traps in nonanticline. this paper studies the reservoir in the lower part of the third member of Shahejie Formation in Neogene. Zangxi depression. Through observation of cores, electric logging, lithoiogy and useing of over 10 laboratory test data and studies of samaple data more than 2700 in 24 wells, this paper gives details or the distributions, forming conditions, sedimentary features, genesis. sedinentary microfacics, influnce factors of ability for reservoir, and evaluation of bearing oil- gas for the sandbodies. Authors consider that the sandbody type belongs to the submarine fan which comes from the deposition of gravity current. The sandbodies develop in the center of the depression. Those can be classified into 6 fans which occur in the same region. The area of the sixth fan is the largest one. The major part of sandbodies is the thickest in the deepest place of the depression. From the bottom to the top of the formation, the distributions of the sandbodies become little and thin. During the formation of sandbodies, the paleoclimate wsa warm and humid, the paleotopography steep on the eastern and western coastline of the lake. The center of the lake was underground paleouplift. Its east and west pans were depression favorable to the sedimentation of subaqueous fan. The lake filled fresh water with a little salinity. During the drop of the crust continuously, the water became larger, from semi-deep lake to deep lake, with plenty of algae. The lake became a good source area. Gravity clastic sediment, which genesis was mainly mixed with type of grain- fragment current, derived from mesozoic, paleozoic group of the east and west area of the lake, and from the shore and sallow lake. The subaqueous fan can be classified into 5 microfacies, i.e. main channel, subaqueous levee, braided channle, and interchannel. Evaluation of reservoir in studying area is following. There are the best reservoirs in the center of the eastern depression; The fourth, fifth, sixth fans are the most favorable reservoirs; the second and third rather good, the first bad; Braided channle is the best and main channel is good for reservoir. The lower part of the third member of Shahejie is in the middle age of late diagenesis. The primary porosity or the sandstone has decreased, but the secondary interparticle porosity well developed in the lower than the upper of the sandstone. The control factors of rich oil-gas in studying area are followings: 1. Havine plenty source rock with large distribution, the source rock has matured in the depression, which produced a lot of oil-gas; 2. Having good associations of source rock, reservoir, and cover, the numerous grav ci rent subaqeous fan has been separated by the mature source rock, contituting combination of self-genents of oil self-reservoir, and self-cover; 3. the braided channel of the middle fan is a favorable facieszonc for reservoir, with a large thickness and area; 4. The depositional mechcnism and diagenesis are major factors controlling oil-gas. The sandbodies formed from mechanism of grain-fragment current have the texture of grain supported, bearing oil-gas high level in the place of strong secondary solution, but bearing oil-gas is low level in the sandbodies of matrix supported producing from the low density flow; 5. Having favorable lithological oil-gas traps. The fourth member of Shanhcjie Formation-Kongdian-Formation, and mesozoic group have been deduced to be benefical to exploration. The west of the depression and Gunan depression may have the same depositional condition as the east of the depression. It is possible to find a oilfield like, Wuhuazhuang oilfield.