There are increasing numbers of published examples from around the world in which significant 4D time shifts have been observed in the overburden above producing reservoirs.Indeed, this topic prompted the TLE special section "Rocks under strain" in December 2005. The significance of these 4D observations is that, if we wish to fully understand the 4D signature of compacting reservoirs, we can no longer think of the reservoir in isolation. The seismic response outside the reservoir changes because the nonreservoir rocks deform in response to reservoir activity. While these nonreservoir 4D seismic changes can obscure or contribute to the reservoir-level signal, making the 4D interpretation uncertain, if utilized appropriately they may also be used to provide information on the actual reservoir pressure changes. This new pressure information can thus be used to complement well measurements or other 4D seismicbased methods (such as the multi-attribute pressure and saturation inversion outlined by Floricich et al., 2006), providing valuable data for reservoir monitoring and management. In this paper, we build on the work of several authors who have presented methods to invert surface deformation measurements for reservoir volume or pressure change. We show how 4D seismic can extend this approach by focusing on the inversion of 3D strain deformation estimates for the overburden derived directly from the repeated seismic data. The method is then applied to Genesis Field in the Gulf of Mexico, in which there are series of compacting unconsolidated stacked turbidite reservoirs. Time-lapse time strain.Rock velocities are sensitive to changes in stress and strain so that if a volume of rock strains, the change in traveltime through it will be made up of a contribution due to the change in distance traveled by the seismic wave and a contribution due to the change in velocity. A perturbation formula relating changes in vertical traveltime t, velocity v, and vertical layer thickness z, assuming small changes in thickness and velocity, is given by Landrø and Stammeijer (2004) (1)Hatchell and Bourne (2006) went on to make the assumption that changes in thickness and velocity can be linearly related by a constant of proportionality, R, which relates the fractional change in velocity and vertical strain so that ∆v/v = -Rε zz , resulting in the following relationship (2) where we have replaced ∆z/z by ε zz , signifying the vertical component of the strain tensor. The left side of Equation 2 is the derivative of the time-shift field, which we term time strain. A method to obtain time-lapse time strains from 4D seismic is described in the companion paper in this special section ("4D time strain and the seismic signature of geomechanical compaction at Genesis"). If we have knowledge of the magnitude of R, we can obtain estimates of vertical strain directly from 4D seismic observations. With estimates of vertical strain for the overburden, a linearized inversion can be employed to obtain reservoir pressure change. Segall (1992) shows ...

Three-dimensional pore network reconstructions of mudstone properties are made using dual focused ion beam-scanning electron microscopy (FIB-SEM). Samples of Jurassic Haynesville Formation mudstone are examined with FIB-SEM and image analysis to determine pore properties, topology, and tortuosity. Resolvable pore morphologies (>~10 nm) include large slit-like pores between clay aggregates and smaller pores in strain shadows surrounding larger clastic grains. Mercury injection capillary pressure (MICP) data suggest a dominant 1-10 nm or less size of pores barely resolvable by FIB-SEM imaging. Computational fluid dynamics modelling is used to calculate single phase permeability of the larger pore networks on the order of a few nanodarcys (which compare favourably with core-scale permeability tests). This suggests a pore hierarchy wherein permeability may be limited by connected networks of inter-aggregate pores larger than about 20 nm, while MICP results reflect smaller connected networks of pores residing in the clay matrix. [Received: May 12, 2011; Accepted: September 14, 2011] Keywords: shale gas; Haynesville formation; pore networks; focused ion beam; FIB.Reference to this paper should be made as follows: Dewers, T.A., Heath, J., Ewy, R. and Duranti, L. (2012) 'Three-dimensional pore networks and transport properties of a shale gas formation determined from focused ion beam serial imaging ', Int. J. Oil, Gas and Coal Technology, Vol. 5, Nos. 2/3, 230 T.A. Dewers et al.Biographical notes: Thomas A. Dewers is a principal member of the technical staff in the Geomechanics Department at Sandia National Laboratories in Albuquerque, New Mexico. He has over 21 years experience in industry, academia, and government relating to work in the geosciences, and holds a PhD in Geology. His current research interests include nano-to-reservoir scale inquiries into rock mechanics, multiphase flow and reactive transport.Jason Heath is a senior member of the technical staff of the Geophysics and Atmospheric Sciences Department, Sandia National Laboratories, Albuquerque, New Mexico. He has a PhD and MS in Hydrology and Geology, respectively. His research focuses on efficiently estimating well injectivity for large-scale CO 2 storage projects, CO 2 -water-rock interactions, and caprock sealing behaviour.

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