Research On The Characteristics And Genesis Of Ultra-low Permeability Sandstone Reservoir Of Chang 8 In Heshui Area Of Ordos Basin

Aiming at regional geologic settings, depositional conditionals and features of diagenetic evolution in the reservoir of Chang 8, following the guiding of modern petroleum geology, reservoir geology, reservoir physics, geophysical logging, with data from laboratory testing, the author has expounded both the geological characteristics of low permeability reservoir and the factors by studying microstructure , flowing characteristics and diagenesis of the reservoir of Chang 8. Firstly, based on the particular geological characteristics of low permeability reservoirs, the author establishes multi-well logging interpretation model constrained by geological conditions, and comprehensively interprets and evaluates more than 80 wells in study area. Then, establishing integrated evaluation standards with the comprehensive evaluation method of fuzzifying mathematics, quantitatively evaluate the storage of the reservoir of Chang 8 in study area and predict the range of favorable reservoir.The main results and cognition are as follows:1. The reservoir of Chang 8 in Heshui area can be classified into the kind of low porosity, low permeability, and ultra-low permeability reservoir, whose features are of low compositional maturity, fine gain diameter and complex pore structure. There are many types diagenesis and the diagenesis of the reservoir sandstone of Chang 8 is during the late diagenesis B. There are three kinds of influencial factors causing the reservoir with features of low, and ultra-low permeability: the internal factors are original composition and textual feature; the dominant factors are squeezing action and cementation; and the external factor is weak erosion and dissolution.2. The wettability of the reservoir of Chang 8 in Heshui area is mainly from slightly oil wet to neutrality. There is the important influence of wettability and pore structure on oil and water relative permeability and distribution of the irreducible oil. Displacement efficiency is lower when the pore structure is more complex and the separation factor of pore and throat is higher. As to the reservoir rock of slightly oil wet, the irreducible oil is mainly in the fine pore and the border or cant of the pore, while the water will be in the macropore and the center of the pore, the flow capacity of the water is stronger and the displacement efficiency is lower.3. The porosity and permeability of core samples in each well have good exponential positive correlation, but the correlations are various in different well segments in the result of shaliness and diagenesis. Therefore, multi-well logging interpretation model constrained by geologic conditions aims at evaluation of reservoir of Chang 8, and the computational results of all kinds of reservoir parameters meet the demand of reservoir description.4. Regarding ten factors affecting reservoir according to their affection, with the comprehensive evaluation method of fuzzifying mathematics, the reservoir of Chang 8 sandstone reservoir can be classified into 3 types: the most favorable reservoir, the more favorable, and the favorable.