The Study Of Complex Reservoirs’ Characteristics Based On The Forward Modeling

With the increase of the difficulty of the oil and gas exploration, the simpletectonic hydrocarbon reservoirs become less and less. The lithologic hydrocarbonreservoirs have been the key targets of the oil and gas exploration and development.The main way to find the undiscovered oil and gas reservoirs is to find the complexreservoirs, such as thin layer, thin interbed which are not easy to find, which havesmall extensions, thin but have economic value. So the seismic data interpretation hasshifted from tectonic geology interpretation to construction interpretation andpetrophysical interpretation. However because this kind of reservoirs has somefeatures such as elusiveness, complexity together with the restriction of seismic dataresolution, the research of this kind reservoir has great difficulty.The petrophysics is a bridge which can connect the characteristics andparameters of oil and gas reservoirs to seismic data. Through the fluid replacement ofthe rock, the research of fluid composition and saturation will be helpful to summarizethe changing regularity of equivalent compressional velocity, shear velocity anddensity of the rock. Through forward modeling, the impact the thickness of layer andthe formation fluid would make on seismic response will be analyzed, and thecharacteristics of seismic response under different fluid saturations will besummarized, the relations between rock fluid properties and seismic responses will bebuilt. So the fluid properties can be analyzed from the characteristics of seismicresponse and provide some certain basis for seismic data interpretation.The forward modeling has played a key role in seismic prospecting and is animportant technique of seismic exploration methods. It can associate the geologicalmodel with seismic response and make seismic reflection characteristics have doublemeanings which both contain geophysical meaning and specific geological meaning.The seismic forward modeling is an effective way to get wave propagation law ingeological model. The results contain the wave travel time, propagation path, energy change. Seismic forward modeling is used to get clear congnition about thekinematics and dynamics characteristics while wave is propagating in complex mediaand analyze accurately reflection wave field characteristics which are generated bygeological structures. If the geologic model is built on the basis of real seismic data,then certain rules can be obtained and help people to know more about undergroundgeologic which can supply certain guidelines about solving the real geologicproblems.Because the underground geologic condition is complicated, it is not easy torecognize the complex reflection characteristics from the seismic data which havebeen processed. At this time, seismic forward modeling can play its role in this. Theseismic forward modeling is an effective method to recognize the wave propagationtheory、law and wave field characteristics in complex geologic media. The research ofthe seismic forward modeling can get comprehensive congnition about the wavepropagation law in complex geologic media, and is helpful to build the seismicresponse recognition mode about different geologic bodies. What is more, it is helpfulto foretell the favorable target body using reflection seismic characteristics which ishelpful to avoid generating multi-solution in the interpretation processing and enhancethe precision of the seismic data interpretation and increase the success rate of theexploration of subtle gas and oil reservoirs.This paper first reviews the development histories of the seismic forwardmodeling method and reviews the theories of ray-tracing techniques and waveequation methods in detail. According to a contrast and analysis, wave equationmethod is used to do seismic forward modeling. This paper also analyzes therelationship between petrophysical parameters and seismic responses and chooses theproper wavelet for seismic forward modeling. This paper begins with the simplemodel and goes from easy to the difficult and complicated, and gets seismic wavefield characteristics about various complex reservoirs. Through changing theparameters of reservoirs, seismic response characteristics of different porosities,different fluids can be gotten and support some guidelines for the recognition ofcomplex reservoirs. The development of the seismic wavefield forward modeling techniques can provide scientific basis for the comprehensive interpretation of seismicdata, delineating the gas and oil reservoirs and its boundary rightly.