Researches And Application Of Caprock Logging Evaluation Method

A good cap layer is necessary to keep oil/gas validly in a reservoir. And a comprehensive evaluation of cap layers from well-logging information is the key to the study of oil/gas migration law and to accurate interpretation of hydrocarbon zones. Related to researching projects of oilfields, some far studies on evaluating cap layers by using of well-logging information is presented in this dissertation.It is indicated that cap layers classifying and lithological distinguishing in single well profile can be reached through well-logging facies analysis. The mathematical statistics method and extrema variance clustering method can be used to visible automatic classifying and reading of logging curves. The lithofacies classifying program basing on multi-mineral model analysis presents a new method to analyze logging-facies and more accuracy and visualized logging facies section can be reached by using this method. In addition, it supplies reliable lithologic layering reference for search and evaluation of oil/gas caprock and it also made up for the high cost of core-drilling and the inaccuration between lithic fragment description and depth.Some important parameters which are used to seal capability evaluate of capping bed, such as capping bed thickness(H), porosity(φ), permeability(K), breakthrough pressure(PA) and surplus pressure (△P),etc. can be obtained from well-log information. It has been found that PA will decay exponentially along with the increasing of φt, φe, K and Vsd. Meanwhile, when compared with φt, the effectof to PA is more notable. By combining the macroscopic distributions and microscopic seal-mechanism of capping rocks and educating these parameters by using of Grey Correlation Method, a series of reasonable capping layer evaluation standards has been set up.Based on its well-logging response characteristics, the cap layers can be classified into mud-cap layer, physical-cap layer and calcic-cap layer. In the evaluation of mud cap layers, cross-plot and nuclear magnetic resonance log porosity curve overlap method was adopted to the comprehensive analysis of YN2 well tight sand reservoir and 3 sets of reservoir-seal combinations are found accurately.After evaluated the cap layers of this well field quantitatively by different kinds of logging parameters and evaluation methods, it is founded that by introducing the analyses viewpoint and technology of reservoir-seal combination into logging interpretation, oil/gas layers and water layers can be distinguished exactly. This approach is very useful in searching of exploitability hydrocarbon-bearing reservoir.Based on aforesaid series methodological analyses and well field situation, a set of cap layer logging evaluation application program compiled by Fortran and VB language was developed and connected on Forward platform. The program has been successfully applied to the interpretation of the reservoir-seal combination more than 10 wells' information in the study well field and got anticipate effect.