3-D Seismic Interpretation: Time-lapse seismic
We saw in chapter 5 how seismic data can be used in favourable cases to infer the nature of fluid fill (gas, oil or brine) in a reservoir. An application of this is to follow the way that fluids move through a reservoir during production, by carrying out a baseline seismic survey before production begins and then repeat surveys over the production lifetime. Where 3-D surveys are repeated in this way, they are often referred to as 4-D seismic , with the idea that time is the extra dimension over standard 3-D. Differences in seismic amplitudes or travel-times between the surveys can reveal the movement of fluid contacts (e.g. where produced oil has been replaced by brine) or the extent of pressure changes that affect reservoir properties. As sketched in figs. 8.1 and 8.2, it is not always straightforward to separate out the causes of the changes. At a producing well, the pressure drops, and if it drops far enough then gas will come out of solution. This will result in a decrease in both P velocity and in density, resulting in a drop in acoustic impedance. On the other hand, the drop in pore pressure causes an increase in P velocity and density. At a water injector (fig. 8.2), we replace oil by water, which in itself would increase P velocity and density; however, the injection also increases the pore pressure, which causes the reverse effect on P velocity and density.
Seismic Monitoring of "Hot" And "Cold" Heavy Oil Production
Time-lapse seismology has proven to be a valuable tool in the characterization of reservoir conditions in enhanced oil production. Our collective research experiences with Canadian Oil Sands at Athabasca, Cold Lake, and Lloydminster demonstrate the utility of seismic monitoring for mapping steam front zones. Due to seismic velocity decrease with temperature increase in oil sands, seismic monitoring can be achieved by time-lapse mapping of seismic reflectivity, impedance, and amplitude variation with offset (AVO). The application of seismic monitoring for “cold flow” mapping is even more challenging. In “cold flow” heavy oil production of oil sands, we see the development of high porosity zones known as “wormholes”. These high porosity zones are much smaller than a seismic wavelength so their detection will be extremely difficult. Nevertheless, it is interesting to speculate whether time-lapse seismology has a role to play in the reservoir characterization of “cold flow” as well as in steam injection.
Geological, mineralogical and chemical characterization of Devonian kaolinite-bearing sediments for further applications in the ceramic (tiles) industry in La Paz, Bolivia
Clay minerals are widely distributed in Bolivia; among them, illitic clays are most common in the Altiplano where they are mined for use in the ceramic industry that has been growing in the last few years. In addition to illitic sediments, kaolinitic sediments have been recently discovered in sedimentary units in the Bolivian Altiplano. Residual ball clay occurrences in Devonian sedimentary units were studied as part of this work. Geological mapping and geophysical studies (ERT and GPR) were done for better understanding the origin of the deposits and were part of a preliminary study of the mineral potential to define the relationship with the host rock. Chemical and mineralogical techniques such as X-Ray Diffraction, Scanning Electron Microscopy and Inductively Coupled Plasma analyses were performed in samples from the studied area to verify the presence of kaolinite. Atterberg limits and behaviour of the raw material in ceramic specimens supported by chemical analyses show that this material is suitable for manufacturing tile ceramics. This study provides fundamental knowledge for deposit exploitation and future generation of an alternative source of employment for the inhabitants of Micaya.