塔巴庙气田上古生界致密储层裂缝系统基本特征及其在天然气成藏中的作用

Basic Characteristics of Natural Fracture Systems in the Upper Paleozoic Tight Sand Reservoirs in Tabamiao area,North Ordos Basin and Its Role in the Process of Gas Reservoir Formation

塔巴庙地区位于鄂尔多斯盆地北部伊陕斜坡构造带上,构造平缓,一般认为不具备裂缝发育条件,然而大量岩心观察、薄片分析、物性测试、测井及试井资料证实,研究区上古生界发育以垂直或高角度裂缝为主的区域性分布构造裂缝系统,与区域构造变形具有同序性;其次为与地层局部挠曲变形有关的低角度构造裂缝系统。我们结合研究区裂缝系统的形态、产状、密度及裂缝分布范围等表观特征和前人区域应力场演化研究成果后认为,与区域水平挤压应力为主的多期隆升构造有关的区域性裂缝系统在塔巴庙地区天然气成藏过程中起双重作用,在自生自储组合中区域性裂缝以输导作用为主,在下生上储组合中储集作用为主。天然气成藏模式的建立,无疑对塔巴庙主力目的层盒2+3的勘探开发提供一定指导作用。

The Tabamiao block is located in the northeastern part of Yishan slope in northern Ordos basin. Its tectonic setting is of gentle monoclinal structure with dip angle only 1° and hence is commonly regarded as unfavorable for natural fracture growth. However, many natural tectonic fractures in reservoirs of Upper Paleozoic were found on the basis of such means as core analysis, thin section analysis, well testing and imaging logging interpretation. The natural fracture systems in the area include two types, namely regional fractures and local fractures, related respectively to the regional stress field and the stratigraphic flexibility. These regional fractures, formed in the same period of regional deformation, are mostly vertical fractures and high-angle tectonic fractures. Comparatively, local fractures are mostly low-angle tectonic fractures. Based on studies of shapes, attitudes, densities and distribution areas of natural regional fractures as well as stress researches made by previous researchers, the authors consider that regional tectonic fractures related to repeated lithosphere upheaval resulting from regional and horizontal compressed stress have played double important roles in the process of gas reservoir formation. That is to say, regional fractures function as gas-migration channels in the combination of self-production and self-conglomeration, and as gas accumulation in the combination of under-production and upper-conglomeration. According to the double roles played by regional fractures, a model for gas-forming reservoirs has been established, which will undoubtedly provide a good guidance for gas exploration and development of the H- 2+3 segment in Tabamiao block.