Trend Analysis Based On Seismic Inversion For Identification And Prediction Of Carbonate Reservoirs

The Tarim Basin is one of the large closed inter-mountain basins in the northwestern part of China.The geological structure is a stable block surrounded by many deep faults.The basin is rich in oil and natural gas resources,accounting for about one-sixth and one-quarter of the national oil and gas resources.Shunbei Oilfield in the Midwest of Tarim Basin and is a new discovery of Sinopec in the exploration of carbonate marine oil.The carbonate reservoir in the Shunbei 1 well is deeply buried.It has been drilled to a depth of more than 7,500 meters.The reservoir is highly heterogeneous.The seismic information of the surface layer of the Yijianfang Formation（O₂yj）is covered by the“Red Trough”,and its internal seismic amplitude is weak.The seismic response characteristics of the reservoir are not obvious,so it is difficult to quantify and describe accurately.Based on this,the yijianfang formation（O₂yj）near the red trough area is taken as the research object.Firstly,the seismic data are preprocessed by reconstructing wavelets and enhancing faults,then the numerical simulation of the fractured-cavern reservoir is carried out.Finally,two different inversion prediction methods are applied,and on this basis,residual wave impedance is obtained by trend analysis of inversion data volume.The spatial distribution characteristics of the fracture-cavity reservoirs in the study area are obtained,and the following points are obtained:（1）Fracture control accumulation:In the vertical direction,the deep hydrothermal fluid moves upward along the fracture,transforms the periphery of the fault and forms pore.Oil and gas migrates upward from Cambrian source rocks and fills in the pore-developed Yijianfang Formation（O₂yj）,with the mudstone of Sangtamu Formation（O₃s）as the caprock above;In the lateral direction,the reservoir development is distributed along the trunk fault.（2）The reconstructed wavelet algorithm removes the red trough and enhances the resolution of seismic information,which satisfies the requirements of subsequent inversion.The fault enhancement significantly weakens the noise in the seismic data,making the seismic profile less noisy and the faults easier to identify;Forward numerical simulation shows that fractured-cavern reservoirs favorable for oil and gas development have"beads"reflection characteristics,and there are fracture fault zones between"beads"and"beads"as oil and gas transportation channels,which have certain identifiability.（3）Although the results of constrained sparse spike inversion and model broadband constrained inversion have their own merits,the coincidence rate between the two residual impedance after trend analysis and well is 100%,which is more credible than the absolute impedance inverted by single inversion.The model broadband constrained inversion residual impedance has better effect in depicting two NE-oriented fault zones in plane.（4）The residual impedance attributes calculated by the two inversion methods are superimposed,and the four favorable regions I,II,III and IV are determined based on the coincidence degree.The designed verification points A and B are validated effectively by drawing cross sections.The results show that the reservoir prediction method has certain reliability,which provides a reference for the next adjustment of reservoir development.