Studying On Sealing Capacity Of Cap Rock In East Of Changyuan,Daqing

To study the hydrocarbon preservation conditions in east area of Daqing placanticline, the caprock development and distribution characteristics in each layer were studied first on the basis of making full use of geological and logging data. The caprocks of the area were determined. The regional caprocks are Qingshankou Formation caprock and Kn1, Kn2 interval caprocks. The local caprocks are mudstone layers in Quantou Formation, Denglouku Formation and Upper Jurassic. Based on the analysis of the laboratory test data,we established the caprock sealing mechanism, and studied the ability of caprock restraining water-sobublehydrocarbon and free hydrocarbon from escaping. It proves that the two sets of regional caprocks excepting those in Kn1, Kn2 intervals of Chaoyang groove Changchun ridge area,pervasive exist formation overpressure. It effectively prevents or restrains hydrocarcons from escaping through regional caprock in water soluble state.The displacement pressure of Kqn1 and Kn1 base caprocks are all quite high which illustrates that the two sets of caprocks in the whole area have strong ability to seal free hydrocarbons. Meanwhile, by researching the caprock micro-parameter and clay mineral longitudinal variation characteristics, it comes that : besides the influence of sand content, caprock’s quality was mainly influenced by diagenesis as they have the same sandy content. As diagenesis enhance, the quality of caprock gets better. By adopting the way of combining macro and micro, cap rock sealing capacity evaluation standard was established. By adopting the way of combining macro and micro, cap rock sealing capacity evaluation standard was established. Evaluated the caprock sealing ability of the research area we found that Kn1, Kn2 interval’s caprocks are regional caprocks which have II~I level,strong to very strong sealing ability. The caprock in Changchun ridge area of Qingshankou Formation has the sealing ability of II~III level,strong to medium grade.Others in this formation has the ability of I level, very strong grade. Aegillaceous rock in Quantou and Denglouku Formations are local caprocks which have III~I level, medium to very strong sealing ability. Quantou Formation has II~I level caprocks in the majority, while Denglouku Formation has II~III level’s in majority. In Upper Jurassic,only in several intervals in fault depression middle area may developed local II~III level sealing ability thin caprock.Then used numerical simulation method and Dynamic balance theory detemined each area’s caprock valid sealing critical value, got the sealing thinkness lower limit value of Kn1 and Kn2 interval was 20 m,the homologous burial depth was 1050 m. Actually,when the bottom boundary buried depth got 200 m, it has reached the valid sealing ability. Qingshankou Formation’s sealing thinkness lower limit value is 150 m, valid depth is 150 m.Finally, by the matching relation between each caprock’s certain sealing capacity formation time and source rock’s hydrocarbon expulsion history,we evaluated each caprock’s sealing validity in east area of placanticline and found that Kn1, Kn2 interval’s caprock sealing history has the best matching relation with Kqn1 interval source rock hydrocarbon-expulsion, while Qingshankou Formation’s caprock has bad matching relation with Upper Jurassic’s expulsion history, it can only seal 10-20% of the total gas which expeled from Upper Jurassic. Based on the analysis of the above, it proof that: the growth characteristics of caprocks in placanticline east area has important contol action to hydrocarbon’s distribution.