应力对超深层碳酸盐岩气藏孔喉结构的影响

Effects of stress on pore and throat structures of ultra-deep carbonate gas reservoirs

超深层碳酸盐岩气藏埋藏深,应力状态复杂,非均质性极强,应力变化前后孔喉结构的变化规律尚不明确。选取高石梯-磨溪区块台内灯四气藏储层岩心,通过CT扫描得到应力实验和压裂实验前后不同类型储层的孔喉尺寸分布、缝洞占比和连通性等,研究应力和压裂对超深层碳酸盐岩储层孔喉结构的影响规律。结果表明:在受压恢复后,孔洞型和缝洞型岩心的孔隙和喉道个数均大幅度下降且主要集中在半径在1 mm以下的微孔、中孔和0.04mm以下的微喉,孔隙平均半径、喉道平均半径和喉道平均长度均大幅度增加,缝洞比例大幅度增加,孔隙和喉道总体积趋于减小;孔洞型岩心连通孔喉体积占比大幅下降,而缝洞型岩心由于裂缝发育,其连通孔喉体积占比维持原有水平。压裂后,孔洞型岩心孔隙个数大幅度下降,减少的孔隙半径主要集中在0.5 mm以下的微孔和中孔,孔隙平均半径大幅度上升,增加的孔隙半径主要集中在0.5~0.8 mm,孔隙体积总体呈上升趋势,喉道个数、喉道平均半径、喉道平均长度和喉道总体积均趋于增加,缝洞比例大幅度增加,连通孔喉体积大幅度提高。实验表明超深层碳酸盐岩储层受压恢复后,渗流能力不降反而大幅度提升,压裂主要通过提高孔喉空间中裂缝占比来改善孔喉连通性。

Ultra-deep carbonate gas reservoirs are deeply buried,with complex stress states and extremely strong heterogeneity,and the change laws of pore and throat structures before and after stress changes is not clear. In this paper,the cores from Deng4 gas reservoir in Gaoshiti-Moxi block were selected,and CT experiments were conducted to obtain the size distribution of pores and throats,the proportion of pores and vugs,and the connectivity of various reservoirs before and after the stress experiment and fracturing experiment. In addition,the effects of stress and fracturing on the pore and throat structures of ultra-deep carbonate reservoirs were studied. The research results reveal that the pores and throats in the pore-vug and fracture-vug cores decrease obviously after recovery from stress,and most of them are the micropores and mesopores with a radius of less than1 mm and the micro-throats with a radius of less than 0.04 mm. The average pore radius,average throat radius,average throat length,as well as the proportion of fractures and vugs all rise significantly,while the total volume of pores and throats tends to decline. The volume ratio of connected pores and throats in the pore-vug cores decreases significantly,while the volume ratio of connected pores and throats in the fracture-vug cores remains at the original level due to the development of fractures. After fracturing,the pores in the pore-vug cores decrease sharply and the reduced pores are mainly micropores and mesopores with a radius below 0.5 mm. The average pore radius greatly increases,while the most increased pore radii are in 0.5-0.8 mm. There is an upward trend in the pore volume,the throats,average throat radius,average throat length as well as total throat volume,and the proportion of fractures and vogs and the volume of connected pores and throats increase drastically. The experiments indicate that after recovery from stress,the flow capacity of the ultra-deep carbonate reservoir does not decrease but greatly increases,and fracturing mainly improves the connectivity of pores and throats by increasing the proportion of fractures in the pore-throat space.