Seismic imaging of sandbox models.

Abstract

Analogue sandbox models are important in the study of reservoir geology because they can offer insight into geological processes that we are rarely able to observe in nature. Seismic physical modelling is used to study the effects of seismic wave propagation in isotropic and anisotropic media and is particularly suited to isolating the effects of a single parameter independently from all others in an infinitely complex geological system. Seismic physical modelling has also been used for the testing of numerical processing algorithms, aid to evaluate interpretations of field seismic sections with scaled representations of geological formations. For this project, I set about developing methods to combine these two independent modelling techniques for the first time. However, previous attempts to use sand as a seismic modelling material failed due mainly to problems with understanding and controlling the distribution of the grain packing.This research has addressed a number of these problems through systematic laboratory experimentation that has provided new insight into the factors that affect unconsolidated sediment acoustics. An innovative technique of recording seismic physical modelling surveys has been developed so that it is now possible to successfully record ultrasonic reflections within analogue sandbox models in three-dimensions (3-D), providing benefits for both analogue sandbox and seismic modelling disciplines. For sandbox modelling, the recording of seismic images allows more detailed analyses of the structures than previously possible. For seismic modelling, more geologically realistic settings can be modelled at a fraction of the cost and construction time of conventional models. However, the greatest benefit of this new technology is that it is now possible to build seismic physical models from porous media, rather than solid, non-porous materials that are conventionally used. This scientific advance allows different fluids to be incorporated into physical models for the first time.Time-lapse 3-D seismic is becoming increasingly important in the management of hydrocarbon production, yet there is a lack of model data to support some of the conclusions being deduced. The controlled physical modelling laboratory environment combined with the ability to consistently repeat the 3-D seismic survey process now allows time-lapse seismic experiments to be performed without the need for the costly and time consuming data processing that is necessary to match legacy 3-D field data. This subsequently avoids any pitfalls that may be associated with the process, such as the masking of true fluid flow anomalies or the generation of false anomalies from data acquisition footprints.A series of time-lapse models are presented where the three-dimensional movement of fluids through the models is remotely monitored using time-lapse 3-D seismic data. These models demonstrate the true seismic response that comes from recording real data from models that undergo real changes representative of reservoir environments. Such models are inexpensive and allow rapid data turn around in a matter of days. The techniques developed here provide a new research tool that can be used to improve our understanding of the dynamics of fluid flow within porous sediments, or to study the seismic response of reservoirs as they change with time.