鄂尔多斯盆地上古生界砂岩储集层控制因素分析

Analysis on control factors of sandstone reservoir of the Upper Paleozoic in Ordos Basin

同沉积期火山作用、物源条件、构造作用、气候条件、沉积作用及成岩作用,是控制鄂尔多斯盆地上古生界砂岩储集层发育的主要因素。同沉积期火山作用提供的易溶火山碎屑组分(包括颗粒和凝灰质填隙物),对区内中高渗次生溶孔型储集层的形成起决定性控制作用。盆地北部物源区巨厚的、富含中粗粒石英颗粒的风化母岩层集中剥露,是导致盆地内山西—石盒子期中粗粒砂质沉积物集中堆积、形成厚层砂岩沉积的主要原因。局部构造的控制主要表现为:奥陶系被下切较深的继承性洼陷,往往是河流长期作用的厚砂层发育区。气候因素主要通过影响母岩的化学风化作用强度来控制岩石的成分成熟度,盆地二叠系山西组煤系地层中石英砂岩的形成与该区二叠纪潮湿的气候条件有密切的关系。沉积控制包括沉积相带控制和沉积微相控制两方面,前者主要表现在对砂体分布的宏观控制上,后者主要表现为不同砂体微相的物性差异。成岩作用的控制是多方面的,主要分析了该区砂岩在成岩早期的碳酸盐矿物的充填交代和胶结作用对储集层致密化的影响,其形成可能与砂层长期处在近地表潜水面附近的暴露环境有关。

The control factors of the sandstone reservoir development of the Upper Paleozoic in the Ordos Basin include the synsedimentary volcanism, provenance conditions, tectonism, climate conditions, sedimentation and diagenesis. The easily dissolved volcanic elastic components （including grains and matrix） , which were derived from the synsedimentary volcanism, have dominant controls on the formation of the high-permeabale and secondary dissolved-porous reservoirs in the study area. The thickly bedded weathered rocks abounding with medium-coarse grained quartz were eroded in the provenance area to the north of the Ordos Basin, thus the medium-coarse grained sandy sediments accumulated in the basin during the deposition of the Shanxi Formation and Shihezi Formation and thickly bedded sandstones were developed. The regional tectonic control is mainly represented by that the areas where incision of the inherited sags of the Ordovician occurred are usually the thickly bedded sandstones developing areas which were in- fluenced by the river for a long period. Climate mainly influences the degree of the chemical weathering of source rocks and thus controls the composition maturity of rocks. The formation of the quartz sandstones in the coal-bearing Shanxi Formation of Permian in the basin is closely related with the humid climate condi- tions in the Permian. Sedimentary controls include sedimentary facies belts and sedimentary microfacies control. The former mainly controls the macro distribution of sandbodies, while the latter is shown as the difference of petrophysical properties of different microfacies. Diagenesis has various influences. Influences of filling, replacement and cementation of the carbonate minerals on the reservoir＇s tightening are analyzed in this paper. The tightening of the reservoir is probably due to the reason that the sandstones are distributed in the exposed environments near the ground surface.