致密砂岩油优质储层形成机理--以鄂尔多斯盆地合水地区长7油层组为例

有别于国内外大多数致密油藏呈异常高压的特征,鄂尔多斯延长组长7油层组(简称长7)致密砂岩油呈异常低压的特征。因此,创新致密砂岩油藏的开发地质研究思路和方法是成功开发鄂尔多斯盆地长7致密砂岩油的前提。文中以鄂尔多斯盆地合水地区长7致密砂岩油为例,研究其储层现状特征、致密化成因和优质储层的形成机理,最终认为合水长7砂岩原始组成中的杂基含量高、塑性岩屑发育、火山灰物质丰富是导致储层致密化的内因,强烈的压实作用与泥质胶结作用是导致长7储层致密化的外因,烃源岩演化过程中的有机酸侵入溶解作用和区域构造应力控制下的破裂作用是长7致密砂岩油藏中存在优质储层的成因机制。研究结论为合水长7致密砂岩油的经济有效开发奠定理论基础,其研究思路和方法对于国内外其他致密油储层评价具有一定的借鉴意义。

Formation Mechanism for High-Quality Reservoir in Tight Sandstone Reservoir--A Case Study of Chang 7 Formation in Ordos Basin Heshui Area

Tight oil is one of the hotspots for global oil and gas exploration and development, the successful development of tight oil in the US helped them reverse the declining trend of oil production. By relying on the effective development of ultra-low permeability reservoir, the oil production increases to a certain extent, but the rapid development of economy has led to the crude oil demand gap expanding in our country. Tight oil resource is rich in our country and which would be the substitute resource for oil and can also ensure the energy safety and rapid development of economy. Different from the abnormal high pressure character in most tight oil reservoir, tight sandstone oil reservoir in Ordos Basin Yanchang formation Chang 7 oil formation (Chang 7 for short) is abnormal low pressure. Therefore, bring forth new geology development research ideas and methods for tight sandstone oil reservoir is the premise for Ordos Basin Chang 7 oil reservoir successfully developing. Taking Chang 7 tight sandstone oil in Ordos Basin Heshui area as an example, this paper make a study of present characters and causes of densification for the formation, and formation mechanism for high quality reservoir, eventually considered that the internal cause of the formation densification is high content of matrix, plastic debris and volcanic ash, and the external causes are strong compaction and cementation, the formation mechanisms for high quality reservoir in Chang 7 tight sandstone reservoir are the dissolution effect by organic acid from source rock and fracturing controlled by regional tectonic stress. The conclusions lay theory foundation for Heshui Chang 7 tight sandstone oil economically and effectively developing, and the research ideas and methods have great significance on the formation evaluation for both domestic and foreign tight oil.