关键词: 砂泥岩薄互层, 断层封闭性, 断层岩, 排替压力, 定量评价

Abstract:

The sealing ability of faults in the sandstone and mudstone thin interbed is mainly determined by the displacement pressure contrast of fault rock against reservoir, while the displacement pressure of fault rock is controlled by shale content and diagenetic grade of fault rock. The proportion of mudstone thickness in faulted formation decides the shale content of fault rock, and the positive pressure exerted on the fracture surface determines the diagenetic grade of fault rock. The positive pressure of fractured surface has relation with the fault dip and buried depth of the fault rock, while the displacement pressure of reservoir is controlled by the shale content and buried depth of reservoir. A new quantitative method for evaluating fault sealing ability is proposed on the basis of sealing rule of displacement pressure contrast in the sandstone and mudstone thin interbed. The evaluating procedure is as follows: ①regarding the shale content of fault rock as being equal to the proportionality of mudstone thickness to faulted formation thickness; ②setting the alternation relationship between displacement of different shale content rock and burial depth; ③calculating the positive pressure on the fracture surface; ④calculating the positive pressure in the break point and the buried depth of strata corresponding to the pressure exerted on the fracture surface according to the relationship between geostatic pressure and buried depth of strata; ⑤defining the displacement pressure of fault rock according to the relationship between displacement pressure and buried depth of strata; ⑥calculating the reservoir displacement pressure on the objective plate according to the shale content and buried depth of the reservoir, and determining the displacement pressure contrast to the reservoir displacement pressure using the fault rock displacement pressure. The displacement pressure contrast expresses quite right the sealing ability of the fault in the break point. This method is feasible by means of actual verification in Beir Depression of Hailar Basin.

Key words: sandstone and mudstone thin interbed, fault sealing ability, fault rock, displacement pressure, quantitative evaluation