鄂尔多斯盆地陕北斜坡东南部长7段致密砂岩油藏成藏物性下限

Lower limits of porosity and permeability for tight oil accumulations in the Chang 7 member,southeastern Shaanbei Slope,Ordos Basin

成藏物性下限研究可为致密砂岩储层的含油有效性评价提供重要参数,可为资源潜力较大的鄂尔多斯盆地致密油勘探发现提供重要指导。运用录井、测井、试油试采、物性、压汞、流体包裹体、铸体薄片、扫描电镜等资料,综合确认了鄂尔多斯盆地陕北斜坡东南部长7段有效储层物性下限和油气的关键成藏时期,进一步对现今有效储层物性下限进行关键成藏时期以来成岩作用对物性的改变量校正,得到了研究区长7段致密砂岩油气成藏物性下限。结果表明,研究区长7段有效储层孔隙度下限为5.0%,渗透率下限为0.038×10^(-3)μm^2;关键成藏时期主要为早白垩世中晚期,关键成藏时期与现今时期储层物性存在较大差异,研究区Ⅳ_a型、Ⅳ_n型、Ⅴ型3种储层类型在2个时期的物性差异大小平均值分别为5.15%、3.46%、2.32%;研究区Ⅳ_b型、Ⅴ型储层的物性大小多分布在现今有效储层物性下限值附近,这2种储层类型的关键成藏与现今时期孔隙度相差平均为2.79%,进而得到研究区长7段致密砂岩油气成藏孔隙度下限约为7.79%、成藏渗透率下限约为0.10×10^(-3)μm^2。

Lower limits of porosity and permeability for oil accumulations can provide major parameters for the oiliness evaluation of tight sandstone reservoir, and important guidance for exploration discovery of tight oil of Ordos Basin which has big exploration potential. Many data including mud logging, log data, well test and production test, physical property, mercury intrusion, fluid inclusion, thin section examina- tion,SEM and so on were applied to determine porosity and permeability cutoffs of effective reservoir in the Chang 7 member, southeastern Shaanbei Slope, Ordos Basin, and critical accumulation period. By adding the loss of porosity after oil accumulation to current lower limit value of effective reservoir, lower limits of porosity and permeability for tight oil accumulations in the Chang 7 member, southeastern Shaan- bei Slope,Ordos Basin were determined. The results show that the lower limit values of porosity and per meability of effective reservoir are 5 % and 0.038 × 10^-3 μm^2. The critical accumulation periods are mainly the mid-late stage of Early Cretaceous. The physical properties of Chang 7 member reservoir are different between the critical accumulation period and nowadays, and the average differences of porosity between the two ages in the IV,, Igb and V reservoir type are 5.15%,3.46% ,2.32% ,respectively. The physical property values of Igb and V reservoir type are nearly the current lower limit value of effective reservoir,the average differences of porosity of the two reservoir type between the critical accumulation period and nowadays are 2.79% ,and then the lower limit value of porosity and permeability of oil accumulations of Chang 7 member in the study area are 7.79% and 0.10×103μm^2.