198 / 2022-02-28 21:14:35

川南低阻页岩沉积-成岩-构造耦合控制作用分析及其储层物性评价

页岩气，电阻率，四川盆地，重力流，峨眉山玄武岩

低阻页岩的成因机制以及低阻效应对于页岩储层条件的影响目前受到学者们的广泛关注。川南地区五峰组-龙马溪组电阻率低于20Ω·m的页岩广泛发育，许多学者认为电阻率过低往往会影响页岩储层的含气性，从而影响勘探有利区的选取。基于川南地区的八口钻井中1036个低阻页岩样品矿物组成、有机地化以及物性参数的分析，本文在明确了泸州地区以及长宁地区低阻页岩成因差异的基础上，探讨了3类低阻页岩储层的物性条件以及含气性差异。导致川南地区部分页岩电阻率偏低的主要原因有三点：重力流沉积广泛发育、构造保存条件差以及峨眉山玄武岩造成的页岩石墨化。浊流沉积在长宁地区西部以及泸州地区东南部广泛发育，与电阻率低于20Ω·m的低阻页岩分布区域基本重合。浊流沉积中高含量碎屑粘土矿物（尤其是伊利石）增加了页岩储层的阳离子交换量以及束缚水饱和度，造成页岩电阻率降低。复杂的断层-裂缝系统附近页岩电阻率总是低于20Ω·m，构造保存条件变差导致页岩气大量散失，从而造成电阻率降低。长宁地区发育规模最大的北东向断层对低阻页岩控制作用最强，而泸州地区低阻页岩常分布于穿层断裂较为发育的紧闭背斜顶部。峨眉山玄武岩溢流造成长宁地区西部页岩发生广泛石墨化，电阻率普遍低于5Ω·m，泸州地区页岩电阻率却不受影响。在3类低阻页岩中，III类低阻页岩储层具有相对较高的石英、TOC、孔隙度以及含气量，页岩几乎没有发生石墨化，是川南地区低阻页岩储层的有利勘探目标。

The genetic mechanism of low resistivity shale and the influence of the characteristic of low-resistivity effect on shale reservoir quaility have aroused wide public concern. Shales with resistivities lower than 20 Ω· m is widely developed in the Wufeng-Longmaxi formation of the Southern Sichuan Basin. Many scholars believed that the gas- bearing property of low- resistivity shale is poor, thus the distribution of low- resistivity shales affecting the selection of favorable exploration areas.Based on the analysis of mineral composition, organic geochemistry and physical property parameters of 1036 low-resistivity shale samples from eight shale gas wells in the Southern Sichuan Basin, this paper discussed the petrophysical properties and gas bearing properties of three types of low-resistivity shale reservoirs on the basis of clarifying the genetic differences of low-resistivity shales in the Luzhou area and Changning area. There are three main reasons controlling the distribution of low-resistivity shales in the Southern Sichuan Basin: extensive development of gravity flow deposits, poor structural preservation conditions and the graphitization of shale caused by Emeishan basalt. Turbidite flow deposits are widely developed in the west of the Changning area and the southeast of Luzhou area, and basically coincided with the distribution area of low-resistivity shale with resistivity lower than 20 Ω· M. The high content of detrital clay minerals (especially illite) in turbidite flow deposits increased the cation exchange capacity and irreducible water saturation of shale reservoir, resulting in the decrease of electrical resistivity. The resistivity of shale developed near the complex fault-fracture system is always lower than 20 Ω· m and the poor structural preservation conditions lead to a large loss of shale gas, resulting in the reduction of resistivity. The NE trending fault with the largest development scale in the Changning area has the strongest control effect on the low resistivity shale, while the low resistivity shale in the Luzhou area is often distributed on the wing of the tight anticline with well-developed trans-layer faults. Emeishan basalt caused extensive graphitization of shales in the western of the Changning area, and the resistivities were generally lower than 5 Ω· m, but the resistivities of shales in the Luzhou area was not affected. Among the three types of low-resistivity shale, Type III low-resistivity shale reservoirs have relatively high quartz, TOC, porosity and gas content, and the graphitization degree of type III low- resistivity shales are low. It is a favorable exploration target for low resistivity shale reservoirs in the southern Sichuan Basin.