Abstract:

Based on the data such as cast thin section, scanning electron microscope, Xray diffractometry and mercuryinjection, this paper has researched the micropore structure classification and evaluation of tight oil reservoir Chang 6 in Daijiaping area according to the feature and genetic analysis. The results showed that the reservoir space of reservoir Chang 6 is mainly characterized by intragranular dissolved pore and residual intergranular pore, and secondly by intergranular dissolved pore and debris dissolved pore associating with flaky, curved lamellar throat and necking throat mainly. The differences between rock fabric and clastic composition during sedimentation decided the original porosity and permeability, and influenced the diagenesis type and strength in the later stage. The results of the quantity calculation about the influence of diagenesis on reservoir quality suggest that compaction and cement of carbonate are the principal reason causing the damage of primary pore; whereas tectonic compression strengthened the heterogeneity of reservoir pore.We divided the porosity evolution into four stage, such as shallow burial cement, middle burial compaction porosity decrease, deep burial dissolve porosity increase and deep burial cement porosity decrease according to burial history analysis. Based on the correlation analysis among pore structure parameters and physical properties, we selected the largest connected throat radius, the main flow throat radius, sorting coefficient, displacement pressure and median pressure as the basis parameters for classification of reservoir. Further, this paper divides the reservoir of Chang 6 member into four types by Qcluster analysis, in which Ⅰ and Ⅱ types of reservoir pore structure are more favorable to be as development target play.

Key words: Ordos Basin, oil bearing layer Chang 6, tight oil, pore structure, reservoir evaluation