Research On Structural Uncertainties Analysis Based On Stochastic Simulation

Uncertainty is inherent in every stage of the oil and gas exploration and production(E&P) business. Structural uncertainties have a direct and large impact in exploration, development and production, and in drilling decisions. Comprehensive understanding of structural uncertainties enables mitigation of E&P risks. Therefore, it is necessary to quantify structural uncertainties.Structural uncertainties have many sources, typically migration, horizon picking, fault interpretation and time-to-depth conversion. In seismic exploration, seismic velocity is a pivotal parameter, velocity uncertainty is key to uncertainty of migration and time-to-depth conversion. Assessment of capacity of trap and decisions on well positioning should take into account the structural uncertainties related to the non-uniqueness of a velocity model. The primary objective of this thesis is to investigate efficient methods for analyzing and estimating structural uncertainties related to time-to-depth velocity.On the basis of the theory of geostatistics and methods of kriging, we have done research on Velocity Modeling method based on Kriging with an External Drift combined with Ordinary Kriging(VMKEDOK), which can take advantages of the high vertical accuracy of well data and the high horizontal accuracy of seismic data, to improve the dependability and accuracy of the velocity field. Finally, we verified the effectiveness and practicability of this method through practical application.On the basis of the theory and methods of stochastic simulation, we have done research on stochastic velocity modeling for variable-velocity mapping, analysised the practicability of error simulation, probability field simulation and sequential gaussian simulation method for velocity modeling in actual field, analysised the statistical characteristics of realizations obtained by three methods respectively and compared them with the outcome of the VMKEDOK method, then analysised the velocity uncertainty. Using the realizations of velocity, we obtained many realizations of structural map for formation of interest, and compared them with the outcome of the VMKEDOK method. Finally, we have done trap assessment and analysised the statistical characteristics of trap area for different structural maps and obtained three probabilistic reserves, while we analysised and assessed the target depth uncertainty. The applied results showed that error simulation method was ineffective for structure uncertainties analysis of the actural field, which was caused by the actual conditions doing not satisfy the limiting conditions, the probability field simulation and sequential gaussian simulation method were more efficient for the structural uncertainties analysis.