莺歌海盆地莺歌海组二段泥岩盖层封闭性综合评价

摘要

Through measuring the displacement pressure of mudstone cap rock in member 2 of Yinggehai Formation of Yinggehai Basin, the linear relation between displacement pressure of cap rock and acoustic time was demonstrated, and the method to calculate the displacement pressure with acoustic time and seismic velocity data was put forward to. Then, based on acoustic time and seismic velocity data, the overpressure distribution of mudstone cap rock in the lower of member 2 of Yinggehai Formation was determined by means of equivalent depth method. Considering the cap rock thickness, displacement pressure, overpressure, pressure of the gas reservoir, the damage of fracture to cap rock and the characteristic of gas (such as flow viscosity), the comprehensive index to evaluate the sealing ability of cap rock was put forward to, and was applied in member 2 of Yinggehai Formation. The results showed that the area with the best sealing ability of cap rock included most part of Ledong District, southern part of Lingao District and the region between eastern part of Dongfang District and No. 1 fracture; the area with the better sealing ability included southern part of No. 1 fracture, eastern and southern parts of Dongfang District; the sealing ability of cap rock in the edge of studied area gradually deceased because the formation exposed on the surface. Cap rock with the sealing ability above middle level could be considered as the effective one; according to the distribution of gas reservoir, the sealing ability of mudstone cap rock in member 2 of Yinggehai Formation and the sealing condition of gas reservoir in middle-deep layer were Favorable.%通过实测莺歌海盆地莺歌海组二段泥岩盖层的排替压力,建立了盖层排替压力与声波时差的线性关系,进而提出了利用声波时差及地震速度资料求取排替压力的方法.接着,利用测井声波时差和地震速度资料,按等效深度法确定莺歌海组二段下部泥岩盖层的超压分布.综合考虑盖层累计厚度、排替压力、剩余压力、气藏内部压力、断裂对盖层破坏程度和天然气本身性质(比如流动黏度),提出了盖层封闭能力综合评价指数,并据此对莺歌海组二段泥岩盖层综合封闭能力进行评价.结果表明:莺歌海组二段泥岩盖层封闭能力强的地区分布在乐东区大部、临高区南部及东方区东部到一号断裂之间的地区,一号断裂南段、东方区东部和北部地区则为盖层封闭能力较强的地区,研究区边部由于地层上倾出露地表,盖层封闭能力逐渐减弱.莺歌海组二段泥岩盖层封闭能力中等及以上地区可作为天然气的有效盖层；由现有气藏分布可知,莺歌海组二段泥岩盖层封盖能力良好,中深层的天然气保存条件优越.