A Study On Identifying Oil And Gas Layers By Using Geochemical Method For Tight Low-permeable Reservoir In The Xihu Sag

The middle and deep reservoir(> 3000 m)in the Xihu Sag in the East China Sea Basin are characterized by poor physical properties and complex fluid properties and it has been found that the fluid properties interpretation from gas logging by using Pikesler chart,hydrocarbon composition triangle chart and “3H method” chart showed poor effect and low accuracy in identifying gas layer.In this paper,it mainly aims to explore a new method for the interpretation of complex gas layers and the interpretation of several wells was completed.Based on the new method,the identifying methods by geochemistry and three dimensional quantitative fluorescence methods were added.For the layers which are inconsistent in the results from interpretation and test,the quantitative grain fluorescence experiments were conducted to explore the comprehensive identification method by using gas logging-geochemistry and three dimensional logging-geochemical experiments.The results show that the new method for the interpretation of complex gas layers based on gas logging mainly includes two matching interpretation methods,gas anomaly ratio chart and chromatographic component panel.It is validated by practice that it can identify the fluid with an accuracy of more than 80%.The identification of geochemical logging is mainly based on the interpretation of panel of heavy total hydrocarbon ratio and the interpretation of highlight index,which has better effects in identifying fluids in the Kongqueting and Huangyan areas.Three-dimensional quantitative fluorescence is mainly based on the interactive interpretation method established by oil index and contrasting magnitude,exhibiting certain effects in the whole Xihu Sag.Quantitative grained fluorescence experiment was conducted by using specialized standardization sample processing method and setting the specific fluorescence spectrometer parameters.And the key parameters such as quantitative grained fluorescence index and quantitative fluorescence intensity of extracts were calculated by analyzing the characteristics of fluorescence spectra and the cutoff values were summarized by combining with the drilling strata test(DST),thereby establishing the fluid properties identification panel which can be further employed in the interpretation and evaluation of drilling well practically.By the comprehensive study on the abovementioned methods,a comprehensive interpretation method by using geochemistry-gas logging and three dimensional-geochemical experiments for the fluid property applicable to the low-permeability tight reservoir in the Xihu Sag has been summarized.