The Unconformity Structures And Transfortation Mechanism Of Tertiary Unconformity In Jiyang Depression

Based on the seismic data, core data, logging data, microscopy, mineralogy content and element content test etc., the geological feature of unconformity structures and transportation mechanism of unconformity in Jiyang Depression were detailedly analyzed. It is considered that the Tertiary unconformity in Jiyang Depression can be divided into three types: typeⅠ1, typeⅠ2 and typeⅡ. Unconformity generally consists of weathered clay, semi-weathered rock and unweathered rock. The weathered rock is characteristic of Feldspar and calcite leached out, while quartz and clay minerals concentrated, and is rich in Fe, Al, Mn and Ti while lack of Ca, Mg in terms of the element content, especially in the weathered clay. So established the Al-CN-K triangle chart board and Q-PL+CA-CL triangle chart board to identify the unconformity structures. The applicability and the threshold value of the chemical weathering indices in Jiyang Depression were sudied. The development model and the main controlling factors (such as time, lithology, palaeogeomorphology, palaeoclimate, conservation) of unconformity were established. The forecasting model of unconformity structure in Jiyang Depression was erected using fuzzy comprehensive evaluation method. By the transportation element analysis of the unconformity,found that the reservoir space of non-clastical unconformity (carbonatite, metamorphics, magmatite) contains fractures and dissolved pores, and calcite ,mudstone, dolomite are found in cave filling, and mostly are typeⅠ-Ⅱreservoir. It can be divided into four zones vertically:Including tight zone(crust), high permeability zone, low permeability zone and non-reservoir zone, in which the high permeability zone is the main reservoir and transporting layer of the unconformity. The reservoir space of clastical unconformity is dominated by primary pore and the dissolved pores of feldspar or calcite. The permeability of the weathered rock is improved in certain degree, and the improvement degree is mainly controlled by lithology of mother rock, mudstone barrier, the buried depth of the unconformity and the unconformity level etc. In order to clarify the transportation mechanism of the unconformity, the aggregation process of the Taiping oilfield and Gaoqing oilfield are studied, it indicates that the unconformity can be taken as not only pathways for oil and gas migration, but also barrier for oil and gas accumulation. There are three kinds of pool-controlling models existed in Jiyang Depression: lateral migration pattern, clearstory-like vertical migration pattern and barrier pattern. According to the influencing factors: the features of the transporting layer, the dynamics and resistance for oil and gas migration,a quantitative formula of unconformity transportation capability is erected: T=(-1)biΔP×K×H×L×ρ/μ, it is a Comprehensive evaluation index, which can evaluate the transportation capability of the unconformity precisely.