Research On The Identification Method Of Gas-water Logging In The XX Volcanic Gas Field In The West

Although petroleum exploration of volcanic rocks has lasted a long time,few volcanic gas reservoirs have been found and their scale is small.Volcanic rocks are characterized by complex lithology,diverse pore types and structures,and variable mineral compositions.This makes it difficult to study the identification method of gas and water in volcanic rocks.Therefore,it is of great significance to systematically study the identification methods of volcanic gas and water logging,which can not only improve the production of volcanic gas fields,but also have important practical significance for the exploration and development of volcanic rocks in China.Based on the oil testing data,logging data,core data and geological logging information provided by the study area,this paper mainly studies the identification method of gas and water logging for the volcanic gas field in the study area.XX volcanic gas field has a variety of reservoir types,complex lithology and complex gas-water relationship.Reservoir gas-water identification has always been the research difficulty of this volcanic gas field,and is also the research focus of many scholars at home and abroad.In this paper,gas-water identification methods are studied based on conventional logging data,dipole acoustic logging data and gas logging data.Based on the adaptability analysis of the three porosity logging series,the application and limitation analysis of the porosity overlap method are completed.The response characteristics of main volcanic lithology logging are analyzed in order to make gas-water identification chart for six rock types in the study of gas-water identification method based on conventional logging data.In addition,the relationship between P-wave and S-wave velocity ratios and water saturation and porosity is analyzed.The response characteristics of P-wave and S-wave velocity ratios and Poisson's ratios under different lithologies are analyzed in detail.The gas and water layers are identified by P-S wave and Poisson's ratio-resistivity diagrams of basic neutral rocks,acid lava and intrusive rocks,tuff and tuff-gravel.The recognition rate of P-S wave ratio and Poisson's ratio is 82%.The identification method of gas measurement curve,multiple ratio method,normalized conductivity curve method and normalized conductivity change rate method are also selected to synthetically discriminate fluid properties.It is found that the recognition effect of gas measurement curve is higher than that of water layer.The main reason is that the recognition accuracy of dissolved gas interference in water layer.Direct application of multiple ratios of gas logging data results in poor distinguishing effect between gas reservoir and water reservoir due to large differences in gas logging values between different wells or small differences in drilling fluids in target intervals of the same well.The automatic normalization processing of curves improves the comparability of cross-well gas logging data and the feasibility of gas logging data in identifying gas and water.The coincidence rate of identifying gas and water layers with the cross-plot of total hydrocarbon and methane after normalization processing can reach 96%.When we study the identification method of conductivity curve,we find that it is difficult to distinguish gas layer,gas-water layer and water layer accurately whether it is export conductivity curve or normalized export conductivity curve.The limitations of this method are as follows:most wells have not drilled gas-water layer and water layer,and the outlet conductivity curve is straight and has little change.Therefore,the normalized conductivity values corresponding to these gas test intervals are on the high side.Logging data are affected by many factors,including the nature of drilling fluid.The conductivity of the same fluid is different with different density and viscosity of drilling fluid,which can lead to the conductivity of water layer is lower than that of gas layer.Therefore,in wells where the properties of drilling fluid are relatively stable,i.e.density and viscosity change little,the normalized conductivity curve,the size of normalized conductivity value and the shape of the curve can be used to judge the fluid properties more accurately.In order to further quantitatively identify gas and water layers,the normalized conductivity change rate method is introduced and good recognition results are obtained.In practical application,when identifying the gas and water layers of the targets,it is suggested that the gas and water layers can be identified synthetically by various methods combined with logging and oil testing data in order to achieve the most accurate and reliable identification.