低孔低渗背景下砂体输导物性下限及其对石油运聚的影响:以鄂尔多斯盆地胡尖山地区延长组长4+5段和长6段为例

The Physical Properties , Lowest Limit Values in Sandstone Conducting System and Their Affections to Oil Accumulation in the Setting of Low Porosity and Permeability: Taking Chang(4+5) and Chang 6 Sections of Yanchang Formation in Hujianshan Area of Ordos

以鄂尔多斯盆地胡尖山地区上三叠统延长组长4+5段和长6段为例,对砂体石油输导物性下限特征及其与石油聚集的关系进行了分析。砂岩的油气输导物性下限与砂岩的排替压力有关,在油气注入动力相近时,砂岩物性数值越高,油气越容易注入。同一地区、相近深度、相近层位油气能够注入的砂岩物性往往有一最低值(下限值),只有砂岩物性数值高于该值,油气才能注入;低于该值,油气因动力不足而不能注入砂层。排替压力与砂岩物性数值呈正相关,而物性随深度增加而降低。当深度变化较大时,砂岩的油气有效输导物性下限值随深度增加而降低。低孔低渗背景下,砂体在纵向与横向上都有较强的非均质性。在相近流体动力条件下,不同的砂体和同一砂体的不同部位因物性差异,油气输导物性下限和富集的程度不同。对胡尖山地区来说,深度主要变化于1700-2400m,相应地,砂岩孔隙度和渗透率下限值分别变化于6%～3.2%和(0.062～0.019)×10-3μm2。

Taking the layer Chang （4＋5） and the layer Chang 6 of Yanchang Formation in Hujianshan area of Ordos basin for example, the authors analyze the oil-transporting petrophysical lowest limit values in sandstone conducting system and their affections to the oil migration and accumulation. These values are related to the displacement pressure. When the oil-driving force is similar, the higher the permeability and porosity of sandstones are, the easier the oil filling in them. In the same area, for the similar depth and similar layer, there is a lowest value of sandstones , permeability and porosity at which oil can fill in them. Only when the permeability and porosity of sandstones are higher than their lowest limit values, the oil filling can be possible. Otherwise, the oil can , t do so because of the higher resistance force. The displacement pressure is positively correlated to permeability and porosity properties of sandstones. Because the permeability and porosity of sandstones decrease while the depth increases, when the depth increases greatly, the permeability and porosity lowest limit values of effective transporting properties of sandstones would decrease by depth increasing. Generally, the sandstones have strong anisotropism both in vertical and horizontal directions. Under the similar dynamic conditions, there are different lowest limit values of porosity and permeability in different sandstones and different places of the same sandstone layer, and therefore, the oil accumulation degree would be different. For the Hujianshan area, the formation depth varies mainly from 1 700 m to 2 400 m. Correspondingly, the lowest limits of porosity and permearbility of sandstones change from 6% to 3.2% and from 0.062×10 -3 μm 2 to 0.019×10 -3 μm 2 , respectively.