鄂尔多斯盆地北部塔巴庙地区上古生界致密砂岩气藏天然裂缝形成机理浅析

MECHANISM OF NATURAL FRACTURE FORMATION IN THE UPPER PALEOZOIC TIGHT SAND GAS RESERVOIRS IN THE TABAMIAO AREA, NORTH ORDOS BASIN

鄂尔多斯盆地北部塔巴庙地区上古生界致密砂岩气藏的低孔、低压、低渗特点给开发带来了相当大的难度。天然裂缝的存在对致密砂岩气藏经济开发意义重大,致密砂岩中裂缝发育层段往往是天然气富集区,天然裂缝能大大改善致密砂岩储层渗透性,研究其发育状况及分布规律对储层压裂改造及水平井开发技术的实施具有积极的指导意义。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,地层倾角仅1°左右,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,研究区的确不同程度地发育垂直裂缝和高角度裂缝。对裂缝的形态、产状、密度及裂缝分布范围研究后认为,天然裂缝主要是在区域应力、差异压实和异常高流体压力综合作用下形成的,断裂作用不是该区裂缝发育的主导因素。

It is very hard to develop effectively the Upper Paleozoic low-pressure, low-porosity, low-permeability tight sand gas reservoir in the Tabamiao area, northern Ordos basin. The existence of natural fractures in tight gas sand can change the situation dramatically by improving greatly the permeability of the tight sand reservoir. The study of the development and distribution of natural fractures may help to determine the design of hydraulic stimulation and horizontal drilling program in tight gas development. The Tabamiao block is located on a slope in the north of the Ordos basin, and the strata occur as a gentle monoclinal structure with a stratigraphic dip angle of only 1° and it is generally thought that they have no conditions for natural fracture growth. However, many vertical fractures and high-angle fractures have been found through core observations, thin-section analysis and tests of physical properties, as well as well testing and logging. Studies of the shape, attitude, density and distribution of natural fractures indicate that natural fractures result from combined effects of the tectonic stress, differential compaction and very high fluid pressure, whereas faulting is the leading factor responsible for the development of the natural fractures in the area.