沁水盆地永乐南区块煤储层聚煤前后沉积相预测及其控气作用

沉积环境通过控制储盖分布特征进而控制煤层气的聚集成藏,是煤储层开发评价的重要影响因素.含煤岩系中砂岩、泥岩、煤薄互层特征突出,且砂岩分布横向变化快,使得砂体预测难度大.运用地震沉积学方法,建立地震地质等时格架,对目标层序进行地层切片并优选融合反映岩性、沉积相变化的敏感地震属性,结合单井岩性与微相特征精细刻画聚煤前后沉积相展布特征,在钻测井数据基础上分析顶底板所处沉积相带对含气富集的控制作用,进而划分沉积控气有利区.研究结果表明:地震沉积学可以研究解释研究区含煤岩系四级层序内沉积现象;弧长、瞬时频率属性在该区可有效反映岩性变化;太原组9+10煤聚煤前为障壁-泻湖相,山西组2+3煤聚煤前后为三角洲前缘相;泻湖泥坪相、分流间湾相有利于煤层气保存,障壁砂坪相及分流河道相不利于煤层气成藏.

The Prediction of Sedimentary Facies before and after Coal Accumulation of and Its Controlling Effects in Block Yonglenan, Qinshui Basin

The sedimentary environment is a key factor for gas prediction of coal reservoir, , which controls the coalbed methane accumulation. In the coal-bearing strata, sandstone, mudstone and coal were interactively distributed, and the transverse distribution of sandstone changes rapidly, leading to a more difficult prediction of sand body. Seismic sedimentology method was used to set up the seismic geological isochronous framework in this paper. The target sequence was analyzed by strata slicing and the sensitive seismic attributes, which reflect the changes of lithology and sedimentary facies, were optimized. Combining with single-well lithology interpretation and microfacies characteristics, distribution characteristics of sedimentary facies in the study area were interpreted. Meanwhile, the relationship between gas content and sedimentary facies belt facies was statistically analyzed. The results show that seismic sedimentology can be used to study and explain the sedimentary phenomena in the fourth order sequence of coal-bearing strata. The properties of arc length and instantaneous frequency can reflect the change of lithology effectively. The sedimentary facies before the accumulation of 9+10 coal in Taiyuan formation were barrier-lagoon facies. The sedimentary facies before and after the accumulation of 2+3 coal in Shanxi formation were delta front facies. Moreover, lagoon-mudflat facies and interdistributary bay are conducive to reserve coal-bed methane, and barrier bar sandstone facies and distributary channel facies have negative influence on the reservation of coal-bed methane.