Research On And Application Of Seismic Comprehensive Prediction Method For Reef Reservior

A reef is a bio-sedimentary formation formed in water,which can be classified according to sedimentary morphology,reef-forming species,and coastal relationships.Reef reservoirs are usually more developed.They are well known as “Underground tank” since the high porosity and large reserves abundance features.Nearly 400 biogenic reef oil fields are found in western Canada,accounting for more than half of reef reserves.Nearly 40 oilfields related to the Manila reef are in the United States.Majority of the oil and gas wells that produce more than 10,000 tons of gas in the world are reef oil and gas wells.Therefore,the reef oil and gas field exploration has huge exploitation benefits results and economic value.The heterogeneity of the reefs is strong,and the lithology changes laterally.The growth and development of the reefs are influenced by many factors,such as paleoclimate,tectonic position and so on.Due to the difference in velocity and density between reef and surrounding rock,different reflection characteristics will be formed in the seismic section.But the amplitude information is often affected by many factors,such as sand body,buried hill,igneous rock and other geological bodies will also form a similar seismic characteristics.In addition,the surface geological conditions of the eastern Sichuan are complex,the dip of the stratum is large,the original data of the earthquake is low in SNR,and the noise interference is very heavy,thus prediction accuracy of the reef is been greatly influenced.At the same time,the individual fractured reef reservoirs have low dolomitization degree and low matrix porosity,which need to be reconstructed by later reservoirs for fracture communication.However,none of the current inversion techniques consider the compressibility factor.In this paper,the definition,classification,formation and development of reefs are been discussed in detail,and the reef exploration of the Upper Permian Changxing Formation in the DMP area is taken as an example.Based on the forward modeling of viscoelastic wave equation,the seismic,logging,geological and sedimentary characteristics of DMP block reefs are been studied and analyzed,and the seismic response patterns of DMP block reefs are been summarized.In the data processing section,on the basis of the conventional processing,the independent component analysis method,which is mostly used in medical field,is applied to the random noise attenuation of seismic data to improve the signal-to-noise ratio.At the same time,the dynamic deconvolution method which is based on generalized S-transform is used to improve the resolution of seismic data.The aim of data quality improvement is been achieved through the targeted treatments mentioned above.Thus a solid foundation for the prediction of reef facies belt and reservoir of the target block is been placed.Based on the regional geological analysis,the K-means clustering method is been improved and been combined with the neural network-based waveform classification method in the reef facies prediction section.And the favorable facies belts of the reefs in the DMP block were obtained by the technique of paleogeomorphology restoration and attribute analysis.Compared with the original results,the new phase result is more refined and more reliable.In the reef reservoir prediction section,the fracture prediction method based on pre-stack P-wave azimuth anisotropy is improved,and the high-order term of Ruger formula is added to improve the prediction adaptability to steep dip stratum.Rather than using the conventional post-stack gather migration data,the pre-stack migration angle gather is been adopted to maximally preserve the velocity anisotropy.Finally,the least square method is used to solve the over-determined equation to improve the prediction accuracy.The method of prestack parameter inversion based on Bayesian theory is been studied.A series of inversion parameters are calculated based on the inversion parameters,which can be applied to the exploration of reef oil and gas reservoirs.Both of the reservoir thickness and the potential of reservoir fracturing area could be obtained through this method.Based on the reservoir prediction method,the reservoir prediction of the DMP block is completed with the constraints of the predicted reef facies belts.And the reservoir thickness distribution map is also been completed.The prediction results show that the accuracy of the reef facies and reservoirs is been remarkably improved compared with the previous results.In addition the prediction result is consistent with the actual drilling conditions.Based on the basic geological analysis,this paper starts with the characteristics of logging,drilling and seismic response of the reef reservoir.The study has been carried out specifically for the processing and interpretation stages.This study can effectively solve the problem of fine reef facies belt and reservoir prediction in the high steep tectonic region of the Sichuan Basin,which can provide important reference for reef exploration in similar areas.