Theory and Practice of Detection of Natural Gas Reservoir Using Integrated Well-log and Seismic Parameters
|Keywords||Deep gas Total porosity Interface parameters Reflection coefficient Seismic exploration Well logs Poisson's ratio Logging parameters Gray relational grade Natural gas reservoirs|
In the structure of world energy, the oil and gas are proportionally close today, butthe gas energy as a clean energy will inevitably exceeds the oil energy. So the gasexploration is one of the most important projects in the West Development of China.In the gas exploration, the well logging is an important technique. The techniquewas used to successfully find oil in the past, which has developed its mature theory,method, technology and experience. The method used for the logging of gas, however,has its own features besides their common points.In addition to the logging method for the oil exploration, the reflection seismictechnique as one of the important geophysical methods also provides a large amountof gas information. The seismic exploration has been aimed to provide the structuralshape of the physical interface. According to the theory that the oil and gas is locatedat the top of the formation trap, the well location for the cat well is provided, which isusually called the conventional seismic exploration. The scores of years ofdevelopment in the seismic exploration have proved that the conventional seismictechnique is indispensable and takes the lead place in the oil exploration. The currenttrend for the oil exploration indicates that the single conventional seismic explorationcannot meet the requirements of the oil exploration.With reference to the reservoir conditions, the oil and gas can be trapped not onlyin the anticline and fault block of the reservoir, but also in the lithologies that canform a great scale of oil and gas field. The study of the lithological oil and gasreservoir enables the seismic lithological theory and especially the AVO technique totake great progress.As substantial lithological reservoirs for oil and especially gas have been found, itis greatly significant to make comprehensive research on the special reservoir usinglogging and seismic data.The different geophysical method can be used to evaluate both shallow and deepgas formations.The application study of the logging and seismic property detect of the gasreservoir is aimed to make full use of the integrated logging and seismic data to studythe geophysical responses of the gas reservoir, which is currently the key subject inthe oil and gas exploration.The attempt to discuss some points of the project is available in the paper. Theproject is mainly concerned with the focus issues and applicable method about thecombination between the logging and seismic approaches, rather than makingcomprehensive study of the logging and seismic theory and methodology in the gasexploration. Based on the previous study of other authors, the following innovative progresses have been made theoretically and practically:1. A proposed applicable method is "extraction of shear andcompressional wave velocities from sonic fullwave with the energyratio of the long and short time windows", which improves the successrate of the AVO applications and interpretation of the gas reservoir.The AVO technique has made many successful cases in theevaluation of the gas and shallow gas reservoir, but also has manyfailures. Currently, in the AVO Forward model, such elastic parametersas the inaccurate shear and compressional wave velocities and Poissonratio are largely used so as to make it hard for the anomalyinterpretation of the AVO inversion results. The above-mentionedmethod can obtain such elastic parameters as the shear andcompressional wave velocities and Poisson ratio in the originalformation to enhance the match rate of the interpretation of the gasreservoir.The AVO technique was first used in Sanhu depression inChaidamu to find the new evidence for the regional gas exploration.The depression is the major biogenic gas reservoir of quaternary.2. The paper focuses on the study of the inversion theory of thelogging parameters, which introduces the" logging interface parameters",suggests a calculation method of gray correlation between parameters,applies the logging inversion of parameters in evaluation of the deep gasreservoir in Tarim and makes the prediction of the new region.The reservoir prediction technique in the oil and gas exploration,on the one hand, is used to make the macro description of the spacedistribution and geometric shape; on the other hand, it can make thelateral prediction of the micro characteristics of the reservoir using thecomprehensive seismic and logging data under the guideline of thegeologic theory.A new parameter is introduced to the specified geologic interface(assuming the interface exists): the relative change of a given physicalproperty in the formation above and below the interface is called theinterface parameters of the physical property. The reflectivity is theinterface parameter of the acoustic impedance. As far as the discretelogging data are concerned, the relative change between the adjacentsampling points of the curve is the logging interface parameters of thesetwo discrete sampling points of the curve. When there is the goodcorrelation between the logging interface parameter and acousticimpedance interface parameter, the logging parameter inversion wouldbe available.