The primary focus of this paper is to emphasise the large volumes of information related to faults and fault systems that are present in, and extractable from, 3D seismic data. During most interpretations, this information is seldom included and transferred to the reservoir model so that their effects can be accounted for during reservoir simulation. Reasons why they are not included are generally related to the time constraints imposed on studies when commercial considerations are often given precedence above any scientific justification. The inadequacies of what are presently considered acceptable models are highlighted'and methodologies that could lead to improved reservoir models are proposed. These methodologies are derived from an investigation of how fault systems will manifest themselves in seismic data, based on both theoretical concepts and the use of synthetic models. From these information sources, principles are derived for the identification of faults and fault systems in 3D seismic volumes. These principles are then tested in two case studies selected to emphasize the limitations imposed on seismic resolution by both target depth and seismic frequency content. After highlighting the diversity of fault related information, which is accessible and currently under-utilized by current reservoir modelling techniques, potential methods for automatic mapping and digital extraction of fault information are proposed. When these automated methods are implemented into seismic interpretation software, commercial reasons for ignoring small seismic-scale faults will be significantly reduced and as a result, reservoir performance predictions will become more realistic.TOWNSEND, C., FIRTH, I. R., WESTERMAN, R. et al. 1998. Small seismic-scale fault identification and mapping.

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The common wisdom is that gravity methods have limited application in the oil industry although they have long been available. The main use of gravity has been for exploration purposes. 4D microgravity monitoring is another new promising gravity application to monitor changes of fluid contacts. Some successful 4D monitoring surveys have been conducted in the industry revealing that this technique is a proven technology in monitoring of gas-water contacts.This paper studies the ability of microgravity to capture movement of the injected water in a giant carbonate field. The oilwater case is more difficult due to the significantly lower density contrast as compared to the gas-water case. Monitoring water floodfront in the field is a key factor in applying successful reservoir management practices to maximize recovery and prolong the field life. The monitoring of inter-well fluids would characterize any pre-mature water breakthrough to allow planning and design of appropriate remedial well interventions. The current applied monitoring tools such as carbon-oxygen and resistivity logs can only detect fluids near to the wellbore due to their shallow radius of investigation. For the study field, 4D seismic cannot be used for fluid movement detection due to issues related to formation acoustics impedance and data quality.The study has shown that surface microgravity monitoring could successfully detect the inter-well fluid changes due to water injection with a high precision tool (0.01 microgal). It also shows that microgravity monitoring can capture water bodies located hundreds of meters away from the location of the 4D measurement.

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Abstract-Recent research into very large, regularly shaped, geological structures has shown that in the 100 kHz to 10 MHz frequency range electromagnetic waveguide behaviour is observed when the material forming the structure is not too lossy (conductivity σ < 0.0001). While mode formation and modal behaviour in electromagnetic waveguides is very well understood, much of the literature describes high frequency structures for which it can generally be assumed that the loss tangent of the wave guiding medium (tan δ) is very much less than unity. In this case, wave attenuation is small and can generally be considered to be insignificant. This is not true for large low frequency waveguides, such as those formed by geological strata, and little seems to have been reported in the literature on the nature of modes in waveguides of this description. The paper takes the form of a parametric study aimed at ascertaining the limitations to modal formation in waveguides, for which tan δ is greater than unity, by revisiting the basic equations describing electromagnetic wave propagation in lossy media. The theoretical predictions are supported by modelling studies on large waveguide strata formed from material layers with dimensions typical of a geological structure such as a coal seam or oil-wet, strata-bound, petroleum reservoir.