Keywords: 
• diagenesis reservoir facies classification /
• quantitative classification model /
• reservoir with extremely low permeability /
• diagenesis process /
• evolution of porosity /
• secondary porosity /
• relatively high quality reservoirs

Abstract: The reservoir in Shannbei structural slope is affected by the depositional environment, diagenesis and structural factor, so the compaction and cementation effects are intense in Shanbei slope center. In this paper relative high quality reservoirs of hyposmosis reservoir were filtered, in which diagenetic reservior facies mode of quantitative classification of Chang 61 reservoir in AS oilfield of extralow permeability was used. With the work of sandstone diagenesis and porosity evolution analysis of Chang 61, different types of diagenetic reservoir facies model of quantitative classification and comprehensive evaluation index system of diagenesis reservoir facies was established. The evolution parameter of diagenesis in different diagenetic reservior facies and the characteristic of reservoir & flow are obviously not the same. The compaction porosity loss rate of I, II diagenetic reservior facies is 5.1%~6.6%; cement prosity loss rate is 30.1%~36.0%; dissolution of secondary porosity increased up to 9.7% with an average of increasing porosity of 5.1%~6.5%. It can be the standard of diagenetic reservior facies "dessert" because of less loss of pore compaction cementation and great increase of dissolution porosity. And these can be used to quantitatively evaluate reservior. 
〓〓Diagenetic stage of pore evolution parameter of different wells in Chang 61 could get by the results' deduction of pore evolution analysis along diagenetic process, and the results come from the material analysis and the identification of pore space of different samples in Chang 61. Though the integration of gray theory of the following parameters, compaction loss porosity, cementation loss porosity, dissolution increased porosity, porosity, permeability and thin section porosity, the matrix analysis of evaluation parameters and evaluation indicator can be normalized, the absolute difference extreme of standard indicators could be weighted combination & amplification and integrated analysis and processing. With the integration of multiple information in diagenesis, theⅠ,Ⅱtype diagenesis reservoir facies “dessert” was filtered. They mainly distributed in the vicinity of generating rock of the centre of acidic lake basin, and were located in favorable reservoir sand in overlying location of the underwater distributary channel of delta front subfacies, more primary porosity was remained in the formation of organic acids water period in diagenetic process, diffluent clastic particles and cementing material were dissolved by acidic water, secondary laumontite and feldspar pore was generated. Thus, relative highquality reservoirs which controlled and blocked out favorable oilbearing areas in extralow permeability Chang 61 reservoir were formed.
〓〓The scale and scope of favorable oil field with the direction from the center to the southwest in the lake area could be identified by the above mentioned highquality reservoir. Using sedimentation, diagenesis, posttectonic and the role of fluid transformation draw the scope of favorable diagenetic reservoir unit, the geological features of highquality reservoir could be reflect, and with a further characterization of the distribution pattern, extend the direction and characteristics of nonhomogeneous in this low permeability oil field. Thus, the awareness of reservoir sedimentation, diagenesis features and the distribution of favorable oil area was raised, which is benefit to extralow permeability oil field to reach a high output. 