Research And Application Of Integrated Geophysical Interpretation Method

With the increasing complexity of prospecting geological environment and itsburied depth increases, We can’t obtain data of high quality via a single geophysicalprospecting method in most cases. However, every geophysical prospecting methodhas limitations: seismic exploration is easily affected by the shielding layer; withexploration depth increasing, the electrical prospecting method’s (especially theelectromagnetic prospecting’s) longitudinal resolution drops rapidly; gravityexploration and magnetic prospecting method’s inversion results are affected intenselyby the non-uniqueness problem; the detecting ability of well logging to theunderground strata’s spatial distribution characteristics is limited, and so on, therefore,we often using several exploration methods in a study area to carry out the geologicalresearch. Meanwhile, the pace of finding new exploration districts is getting slow on anational scale, and many old resources areas are cling for "secondary development",based on this background, after decades of geological exploration work, manyprospecting areas have been monolithic geophysical prospected for several times, theobtained enormous geophysical data brings convenience for the subsequent integratedinterpretation.The limitations of various geophysical methods, observation error and limiteddata bring about the multiple solutions of geophysical inversion problem, which affectthe reliability of the geophysical exploration results. Many scholars put forward toimprove the multi solution on geophysical inversion by utilizing comprehensivegeophysical data, studying different physical characteristics of a geological target, andall kinds of geophysical methods contradict each other. Therefore, with theaccumulation of geophysical data and the constant development of computernumerical calculation technology, it’s necessary to summarize and improve theintegrated geophysical interpretation technology.Synthesize all above, commence from the new thought of geological-geophysicalcomprehensive interpretation and the new integrated geophysical numericalcalculation technology, the author summarizes a geological-integrated geophysicaljoint interpretation technique which can organically utilize of gravity, magnetoelectric, seismic geophysical exploration measured data with geological results and generatethe geological-geophysical model.Studying the geological-integrated geophysical joint interpretation technology isthe core of this paper. This method comprehensively utilize geological achievementsand properties, physical characteristics approaches, drilling data and gravity,magnetic，electric, seismic geophysical measured data，through the analysis ofpetrophysical characteristics, set up constraint mechanism by geological constraints,physical constraints, drilling vertical constraints, and constraints betweencomprehensive geophysical prospecting method, on this basis, combine withcomprehensive geophysical forward modeling and joint inversion, we can get thegeological-geophysical model which matches the practical geological situation best,.Finally, via the geological-integrated geophysical quantitative interpretation, we canconfirm the geological target’s prosperities of occurrence, lithology and age.The further use of physical statistical characteristic in geology-integratedgeophysical joint interpretation technique is the first innovation point of this article. Inthe example of power station foundation survey, through analysis of the apparentresistivity and seismic p-wave velocity, we can find that they are functions of watersaturation and porosity, and the conversion between them can be summed up by thelinear corresponding(delete) relation in logarithmic coordinate, and apply thetransformation relationship of apparent resistivity and p-wave to the petrophysicalconstrained joint inversion, and achieved good results. In addition, different physicaltransformation relations can also be applied to the geophysical measured dataprocessing, and can also be used to supplement the limited measured data.The second innovation point of this article is the optionally use of different jointinversion method in geology-integrated geophysical joint interpretation technique.Integrated geophysical joint inversion has four numerical computation methods,which are integrated geophysical independent inversion, integrated geophysicalsequential inversion, petrophysical constrained joint inversion and tectonicconstrained joint inversion. Through the analysis of the practical application, we findthat the integrated geophysical independent inversion should be the basis of jointinversion work, according to the actual situation of the geophysical measured data,choose which joint inversion method is prefer in sequential inversion, petrophysicalconstrained joint inversion and tectonic constraint inversion method,.while, usuallythe tectonic constraint joint inversion method often has better effect thanpetrophysical constrained joint inversion. In simulation calculation of tectonic constrained joint inversion, through the analysis of different kind of tectonic functions,we use the cross gradient function as tectonic function to tectonic constraint inversion,and we effectively realized the different characteristics of geophysical anomalies formathematical description of the same type of geological structure, and the experimentprove that this calculation method is effective and feasible.