Research On Migration And Accumulation Conditions Of Mesozoic Buried-hills In GuDong Oil Field

Gudong buried hill is a monoclinal hill sloping down to the northwest controlled by Gudong faultage and Kendong faultage. It is adjacent to Gunan sub-sag in south and Zhuangdong depression in north. It is abundant in oil source, the Tertiary overlying is the main oil and gas region, and rich oil had been explored in Zhuangdong buried hill, so the research on the accumulation condition of Gudong buried hill is important for the deep exploration in Gudong. Conducted by the modern theory of petroleum accumulation, we launched the hydrocarbon accumulation conditions research in Gudong buried hills, which concentrated on the secondary migration. The effective migration path is analyzed by systematical study on the conducting validity of sand-bodies, faults and E/Mz unconformity. After these researches, the controlling factors, rules and potentials for oil accumulation in Gudong buried hills are analyzed and revealed.The conduit's effectiveness of the Paleogene sand-bodies located in the oil source region is the precondition of oil and gas migration to the buried hills. In the southwest part, sand-bodies are developed in Es3 and Es2 members, characterized by stable distribution, good interconnection, high sand percentage, high porosity and permeability, are the main conduit systems for oil from Gunan sub-sag. Sand-bodies of Es1 member is the main conduit system for oil from Zhuangdong depression.Research on the types of unconformity, lithology composition and conduit effectiveness are conducted on the basis of seismic and log data. The E/Mz conformity is classified into migration path, dissipating path and seal-capping according to the lithology composition and buried depth distribution. Different conduit types have different control actions on hydrocarbon migration. The east slope zone has developed Structural ridge and favorable lithology composition, and is the main direction for charging. The E/Mz of south step-fault zone acts as seal-capping, and the western step-fault zone can't form a main migration path, for it lacks of structural development.Gunan faultage and Gudong faultage controlled the development of Gudong buried hills, and their fault-sealing is the controlling factor of oil migration and charging to buried hills. A systemic research on the vertical and lateral fault-sealing of hill-formed faults and their secondary faults are carried on. The effective conduit paths are clearly defined integrate with fault activity and fault surface pattern. The potential of oil charge in the west step-fault zone are higher than the south zone, because F78 seal laterally. Oil has the potential of charging into hill through F67 in the east slope zone.Conditions of oil sources, conduit system effectiveness and cap condition are the main factors in controlling the hydrocarbon accumulation in Gudong buried hills. The west step- fault zone has favorable migration conditions and the No.1 and No.2 traps have a relatively higher potential for accumulation. Oil charges into buried hill mainly through sandbody-unconformity, and has the possibility of accumulate in the updip direction of GD20 wellblock. The GD33 wellblock have no potential of oil accumulation for the lack of cap and the high sealing grade of F78.