Exxonmobil Upstream Research Company

Dezhi Chu

Xinyou Lu

Brent D Wheelock

Ganglin Chen

David D McAdow

Xin Zhan

John E Bishop

A method for inversion of 4D seismic data, including: determining time shift between baseline and monitor geophysical datasets; determining time strain from the time shift; iteratively repeating until a stopping criteria is satisfied, performing an iterative elastic AVO inversion with a 4D difference providing an update, from an initial model including the time strain, to generate an updated time strain and an updated physical property model, wherein the stopping criteria is a misfit between synthetic data generated from the updated physical property model and the 4D difference being within a predetermined noise level generating final values for the physical property model; and converting, with a rock physics model or a reservoir simulation model, the final values to saturation and/or pressure changes for a subsurface region.

4D time shift and amplitude joint inversion for obtaining quantitative saturation and pressure separation

A method including analyzing seismic data relating to a producing hydrocarbon reservoir is disclosed. The seismic data includes first and second sets of seismic data obtained at different times. An interval composed substantially of hard rock is identified in the hydrocarbon reservoir. 4D seismic attributes for the region are calculated. Rock physics relationships are applied to seismic data related to the interval according to the permeability associated therewith. A fluid saturation change or a pressure change of the interval is inferred based on outputs of the first or second sets of rock physics relationships and the calculated 4D attributes for the interval. The inferred fluid saturation change or pressure change of the interval is outputted.

Method for determining the fluid/pressure distribution of hydrocarbon reservoirs from 4D seismic data

Method for deriving a reservoir property change data volume from time shifts used to time-align 4D seismic survey data (). The time alignment is performed on at least one angle stack of 4D data to determine a time-shift data volume (). When multiple angle stacks are used, the time shifts are corrected to zero offset. A running time window is defined, and within each window the time shifts are best fit to a straight-line function of time (depth), one angle stack at a time (). The slopes from the straight line fits from different angle stacks are averaged at each voxel in the data volume, which yields a reservoir properties (&#x394;&#x3bd;/&#x3bd;) data volume (). This data volume may be filtered with a low-pass filter to improve signal-to-noise (). The resulting data volume may be merged with the 4D data volume to expand its bandwidth (), or it may be converted into a reservoir saturation and pressure change data volume () using a rock-physics model ().

Estimating reservoir properties from 4D seismic data

A method for predicting differences in subsurface conditions useful in 4D applications. In an example embodiment of the method, at least one layer is defined in a data volume representing a first subsurface condition such as shale volume fraction (). An exhaustive search methodology is then performed over a second subsurface condition such as pressure or saturation for some or all of the first subsurface condition data points () based on a data fit of synthetic geophysical data to measured geophysical data. The exemplary method may additionally comprise performing a statistical analysis to determine whether the error in data fit is significantly reduced () if one of the layers is divided into two or more layers (). The layer is divided into multiple layers () if the error is significantly reduced (). In this manner, the measured survey data are inverted to predict values of the second subsurface condition.

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Houston, TX, United States of America

Dezhi Chu