Comprehensive Evaluation And Fluid Identification Of Fracture-Cavity Carbonate Reservoir

Carbonate formation in Tuofutai well area is a kind of close platformopen platform sedimentduring the Ordovician. The target formation in the paper, Yijianfang group;, belongs to interbank sea, bioclastic bank,grain beach sediment and local deposition sponge barrier reef plot.The upper Ordovician strata occurs twice uplift in early and late stage of Hercynian movement. Which made strata outcropping. After serious weathering and erosion reservoir space in Ordovician carbonate reservoir became very complex and formed several reservoir types such as dissolved pores, cracks and caves. Consequently, heterogeneity and anisotropy in the are are very strong. And reservoir and permeability varied complicatedly.The features increased difficults during comprehensive logging evaluation and fluid identification.The paper studied lithology identification method, reservoir parameter calculation method and fluid identification methods of carbonate reservoir of Ordovician Yijianfang Group by making full use of the geology, logging, core data, etc., and made synthetic logging evaluation for target layers in the study area according to above methods, summarized synthetic evaluation laws of fracture-cavity carbonate reservoir and built synthetic logging evaluation system being suitable for the study area. The evaluation system dealt with problems about logging interpretation and fluid identification of fracture-cavity carbonate reservoir, increased coincidence rate of predicting and identifying reservoir with logging technologies and reduced exploration and development risk.These methods are based on the target layer in the study area to evaluate and summarize fracture-cavity carbonate logging evaluation of the law, and the establishment of the study area for logging comprehensive evaluation system to solve vuggy carbonates log interpretation and fluid identification difficulties, improve the utilization logging and fluid reservoir prediction accuracy and reduce the risk of exploration and development.This study focus on the several problems about fracture-cavity carbonate evaluation as follows:1, Study on logging response characteristics of different lithology types based on core analysis and logging lithological description.2, Study on accurate calculating model of reservoir parameters adapted to fracture-cavity carbonate.3, Study on lithology identification method based on logging response by distinguishing logging response of different lithology types with a few method.4, Forming evaluation criterion of fracture-cavity carbonate of Yijianfang group of the Ordovician by use of logging data.5, Creating method system adapted to fluid identification of fracture-cavity carbonate based on field and testing data.The research forms some opinions as follows:1, The carbonate reservoir of Ordovician Yijianfang group in Tuofutai well area contains bioclastic limestone and calcarenite with multiple structures such as micritic, microcrystalline, sparite and so on. The kind of limestone has the feature of corrosion holes on logs due to the structures, ingredients and otherfactors. However uniform corrosion can not be seen from core data. These phenomena are easily misunderstood reservoir during logging evaluation because of factors of structures and ingredients of rocks containing bioclastic limestone and calcarenite. Therefore, we produce automatic lithology identification mode, summarize lithology response characteristics with PCA and geostatistical theory base on core analysis data,and by analyzing logging response characteristics. These aspectsbuild the basis of reservoir identification.2, The conventional logging interpretation model is difficult to be used for fracture-cavity carbonatereservoir because it has muiltiple types of reservoir space including dissolved pores, cracks and caves. So we establish the dual-porosity model to calculate cave porosity and fracture porosity after deeply analyzing the response characteristics of logs from various types of reservoir space.3, The dual laterolog response characteristics are obtained by making forward modeling using different fracture parameters with finite element method. and analyze how fractures influence on the dual laterolog response characteristics. The modeling results get verified by the flume experiment in Sichuan Petroleum Administration. Based on research on high-resolution FMI and correlation between crack parameters of calculating imaging logging and dual laterolog, the resulted correlation between dual laterolog and the width of crack and between fracture porosity and fracture hydrodynamic width are very well.,.Deep lateral resistivity decays exponentially with the increase of fracture parameter.4, The reservoir can be divided into three classes, I, II, III, based on lithology analysis, crack analysis and practical data analysis. And the standard template of comprehensive reservoir evaluation can be created. Besides, we evaluate the reservoir types and filling degree. Above research shows that natural gamma rays and deep lateral resistivity increase with the growth of filling degree. Consequently, it is very effective method using GR-RD crossplot to evaluate the filling degree of reservoir.5, Fluid feature of reservoir can be analyzed by synthetically applying conventional crossplot method,, normal probability distribution method and rock physical parameters crossplot method(the ratio of Vp and Vs)with practical testing data. Research shows that it is effective to identify the fluid types in poro, fracture-poro and fracture reservoirs using normal probability distribution not getting good results applied in caves. And it is effective to identify fluid feature using ratior of Vp and Vs and crossplot of acoustic time difference. At the same time, The BP neural network model based on particle swarm optimization is applied in predictting the fluid feature. PSO-BP algorithm improves the shortcomings of traditional BP algorithm such as slow calculation speed, poor memorabilityand easily falling into local optimum. It is an excellent fulid identification method.The study builds a series of logging evaluation criterion adapted to Ordovician fracture-cavity carbonate in Tuofutai well area of Tahe oilfield and obtains good effect in practical application. Which has favorable practical value.