| Chang7member of Yanchang formation in Huachi-Heshui area is typical tight reservoir which belongs to turbidity current deposits of shallow lake and deep lake, and oil distribution is charaterized by large-scale, extensive accumulation without obviously oil-water boundary. Chang7member is usually treated as main source rock of Yanchang formation, systematic reaserch about accumulation controlling factors are almost absent. Accumuation characters of Chang7member are discussed and cntrolling factors are summrised through compensive anylysis about distribution and generation characters of source rock, reservoir characters, migration pathway and abnormal pressure in the reaserch area in the paper.Chang7source rocks are developed in the research area and Zhangjiatan shale is the main source rocks. Based on characters of turbidity current deposits, Chang71and Chang72source rocks are also develop in local areas. The Chang7peak mature stage source rocks which have high organic content provide a firm material foundation for reservoir in the research area. On one hand, thick source rocks of Chang73and the bottom of Chang72provide abudent oil source for oil accumulation. Furthermore, sorce rock of Chang72and Chang71can provide guarantee for Chang71oil accumulation at the same time and forming oil extensive distribution characteristics in Chang7j.The distribution of sand body is stable in the study area, and mainly composed of lithic arkoses and feldspathic litharenite sandstones with high content of interstitial matter, various types of pores and poor property&permeability. The property is mainly between6%to12%and permeability is mainly ranges from0.1×10-3μm2to0.3×10-3μm2. Plate-shaped and pipe-sharped throats are main pore-throats with small radii, belongs to typical tight reservoir. Reservoirs with good are well oil-bearing, else are not oil-bearing. The better property&permeability, the higher oil saturation.Chang7source rocks in the study area which begin to grow into maturity at late Jurassic and lasting generating with the increase of depth. But the densificationc of the reservoir is so fast that the the reservoir tighten before peak hydrocarbon generation of source rock. Dissolution caused by hydrocarbon charging took place during the whole period, so the oil accumulation present the character of" eraly tighten, lasting charing in the later period’Oil distribution in Huachi-Heshui area is controlled by source rock obviously, belongs to typical accumulation nera source rock, and the thick and distribution of source rock have a direct influence on oil distribution and enrichment. The oil distribution area is controlled by distribution of sandbody, and the oil enrichment is mainly controlled by reservior property&permeability. Overlay sandbodys and fracture are the main migration pathway, abnormal pressure in Chang7is the motivation for oil accumulation after generated. |
