A volume-conserving representation of cell faces in corner point grids

Corner point grids is currently the standard grid representation for use in reservoir simulation. The cell faces in corner point grids are traditionally represented as bilinear surfaces where the edges between the corner points all are straight lines. This representation has the disadvantage that along faults with varying dip the cell faces on either side will not precisely match, giving overlapping cells or gaps between cells. We propose an alternative representation for the cell faces. The four vertical cell faces are still represented as bilinear surfaces, but instead of having linear edges between the cell corners along the top and bottom faces, we propose a representation of the vertical cell faces where any horizontal intersection will give a straight line, giving column faces whose shape is independent of the corner point locations of the individual grid cells. This ensures that the grid columns match up and that there are no gaps or overlapping volumes between grid cells. This representation gives a local parameterization for the whole grid column, and the top and bottom grid cell surfaces are modeled as bilinear using this parameterization. A set of local coordinates for the grid cell permits all the common grid operations like volume calculation, area calculation for cell faces, and blocking of well traces.     

Thermal, mechanical and chemical influences on the performance of optical fibres for distributed temperature sensing in a hot geothermal well

Structural well-bore integrity is an important issue for sustainable provision of geothermal energy. Raman scattering based fibre optic distributed temperature sensing (DTS) can help to monitor the status of a well and therefore help to optimize expensive work-over activities. This study reports on the installation of a fibre-optic cable in the cemented annulus behind the anchor casing in the high temperature geothermal well HE-53, Hellisheiði geothermal field, SW Iceland. Although the cable has been damaged during the installation, temperature data could be acquired during the entire length of installation down to 261.3 m. Temperature measurements were performed during the installation in spring 2009, during the onset of a flow test in summer 2009 and after a 8.5 month shut-in period in summer 2010. During the flow test, maximum temperatures of 230 °C were measured after 2 weeks fluid production. Using optical time domain reflectometry (OTDR), attenuation measurements at 850 and 1,300 nm enabled to identify mechanical, thermal, and chemical degradation along the optical fibre. The observed degradation led to erroneous temperature readings and limits, due to the optical budget of the DTS system, the accessible length of the fibre. The characteristics and the influence of the different degradation mechanisms on the accuracy of the DTS measurements are discussed and recommendations for an optimized installation are given.     

On tourmaline

The first part of this paper presents chemical analyses and physical properties for 12 tourmalines of varying color, 10 samples from Mozambique, one from Afghanistan and one from Madagascar. The data are summarized in Tables 1–3. The second part reviews the isomorphism in the tourmaline group on the basis of data gathered from the literature. Plots of c₀ against a₀ for 198 X-rayed tourmalines and of (Fe, Mn, Mg, Ti) against the unit cell volume of 57 analyzed and X-rayed tourmalines supplement Epprecht's review.     

Joint interpretation of the size and time distributions of seismic activity around the Hengill triple junction (SW Iceland) between 1993 and 1999

A newly developed clustering algorithm is described which uses the Unified Scaling Law for earthquakes to identify correlations between events that lead to clustering. This algorithm is applied to a dataset from the Hengill triple junction in south west Iceland to separate spatially and temporally overlapping earthquake sequences. We show that the algorithm successfully identifies spatio-temporally clustered events.A search for certain patterns in the identified clusters is performed. These patterns emerged in numerical simulations of seismicity performed by Hainzl (2003) when viscous coupling was introduced in order to reproduce features of swarm earthquakes. Namely we look for a combination of increased Gutenberg-Richter b-value and decreased exponent of the waiting-time distribution α. This pattern, indicating the strongest influence of viscous coupling on the characteristics of the seismicity, could be localized beneath an extinct volcano approximately 5 km north of an area of recent crustal uplift.     

A Stochastic Object Model Conditioned to High-Quality Seismic Data

We present an approach for modeling facies bodies in which a highly constrained stochastic object model is used to integrate detailed seismic interpretation of the reservoir’s sedimentological architecture directly in a three-dimensional reservoir model. The approach fills the gap between the use of seismic data in a true deterministic sense, in which the facies body top and base are resolved and mapped directly, and stochastic methods in which the relationship between seismic attributes and facies is defined by conditional probabilities. The lateral geometry of the facies bodies is controlled by seismic interpretations on horizon slices or by direct body extraction, whereas facies body thickness and cross-sectional shape are defined by a mixture of seismic data, well data, and user defined object shapes. The stochastic terms in the model are used to incorporate local geometric variability, which is used to increase the geological realism of the facies bodies and allow for correct, flexible well conditioning. The result is a set of three-dimensional facies bodies that are constrained to the seismic interpretations and well data. Each body is defined as a parametric object that includes information such as location of the body axis, depositional direction, axis-to-margin normals, and external body geometry. The parametric information is useful for defining geologically realistic intrabody petrophysical trends and for controlling connectivity between stacked facies bodies.