Interpretation of the Geophysical Data - Article Example

Interpretation of the Geophysical Data Discuss the relevance of seismic properties measured at the laboratory scale for the interpretation of the geophysical data at field scale. Compare the accuracy and precision of the field and laboratory techniques Geophysical data is collected at the field scale but its accurate interpretation is done on the laboratory scale. Seismic properties play a major role in such interpretation because they are helpful in removing the on-field constraints. However, they should be relevant to the geophysical data and peculiar characteristics of material collected. The measurement scale has significant impacts over the interpretation of geophysical data (Acosta-Colon, 2009). On the other hand the interface of geophysical data also affects the seismic properties and their subsequent interpretations. For instance, the granular and fractured materials are largely dependent upon the geometry and size of fluid-fluid interfaces. The seismic properties of both granular and fractured materials are impacted by cementing material and the stress effectiveness when the interfaces are solid (Knight, 2010). Although the difference in interfaces causes variations in seismic properties but they have greatly facilitated the development of new ways through which measurements of geophysical data can reveal more information about processes and properties of sub-surfaces. Here, it is important to notice that the composition and size of fluid-solid interface straightly influences the interpretations and different reaction in the laboratory setting. This is subsequently responsible to cause variations in composition and size of interface itself (Knight, 2010). Seismic data fundamentally includes necessary information about the medium properties and geometric structure about the collected geophysical data (Brevik, 2009). Research indicates that seismic properties are commonly determined in order to measure and interpret the geophysical data in laboratories. The calculation of seismic properties remains same irrespective of measurement setting either laboratory or field scale. Velocity Vp, Compressional wave (P wave), Velocity Vs, Shear wave (S wave), attenuation and the elastic waves amplitudes (Knight, 2010). Seismic properties are used to interpret geophysical data related to the exploration of minerals and petroleum. They are also found useful in depicting an increasing advantage for Critical Zone Studies (Knight, 2010) . Studies indicate that researchers have give prominent importance to seismic properties. Colon along with some other researchers conducted a study in order to reveal the relevance of seismic properties measured at two different scales i.e. field and laboratory. Since the experiment was conducted on a smaller scale therefore the conventional acoustic scans were utilized. The laboratory tests were applied to two samples of limestone. Each of them contained one fracture which was induced in to it (Acosta-Colon, 2009). This was compared with the controlled sample of acrylic. Subsequently analysis was made on the basis of the signals measurement. Hence average coherent sum was taken in to consideration at both laboratory and field settings. Observations indicate that the geophysical data collected at the field primarily impacts the interpretation of laboratory studies (Acosta-Colon, 2009). In order to comprehend the relevance of seismic properties measured at laboratory scales to interpret the geophysical data at the field it is important to first discuss the measurement techniques of seismic properties. Trippetta mentioned three basic seismic techniques in his research paper for interpreting the geophysical data including seismic anisotropy, seismic tomography and seismic sequence (Trippetta, 2010). Seismic anisotropy is typically defined as the reliance of seismic velocity on the angle (Thomsen, 2002). It can be divided in to two broad categories so as to interpret the geophysical data. Firstly it is used in situations where anisotropy is creating hindrances particularly for the analysis and therefore it is supposed to be removed for accurate interpretations. Secondly it is used when the researchers require enhance the analysis procedures through seismic anisotropy measurement (Wild, 2011). Seismic tomography has different types, for instance, cross-well seismic tomography which is basically used to build seismic slowness with comparatively high resolution. This estimates to have 1/velocity through aquifers along the planes (Hyndman, 2000). Seismic sequence stratigraphy is essentially used when researchers are needed to explore and predict the composition of rock. This measurement is conducted on the basis of seismic data as well as the sparse well and distant data (Neal, 1993). Seismic stratigraphy also facilitates in the source study of seals and rocks. Moreover, the experts’ opinion is that with the passage of time the seismic stratigraphy will become a substantial tool for exploitation while also playing a significant role in constraining the extent, shape and reservoirs continuity (Neal, 1993). Several problems arise when geophysical data is interpreted at the field scale. For instance, the three dimensional rebuilding of the geology sub surface is usually very time consuming procedure. On the other hand it also includes different constraints such as issues with depth geometries which most of the time becomes changeable for input automated up to a certain extent (Archibald, 1989). In addition to this measurements made at the field scale are based upon heterogeneous earth which reveals resistivity issues (Resistivity Methods, 2011). However, the issues identified at the field scale are generally unique as per the research area, for example, the environmental and engineering applications problems usually arise within the range of 1 to 10m of the exploration (Gravity Methods, 2011). Apart from this following is the list of issues with the interpretation of geophysical data at the field scale (Department of System Geological-Geophysical Research, 2010): There are significant issues concerning the compilation, enhancement and modification of geophysical data particularly collected from oceans and arctic. Mapping of the gravitational field (AGF) and the anomalous magnetic field i.e. AMF, transformation of different values and preparing information for further analysis is also a difficult task at the field level. Formation history and the geological structure especially at the bottom of oceans are significantly complex in nature which further makes the interpretation of collected geophysical information difficult at the field. Moreover, problems occur with the exploration of minerals particularly the hydrocarbons. The above discussion reveals that geophysical investigations primarily include different inferences which are quantitative in nature and relate to the sub-surface characteristics of geophysical measurements. There are number of unavoidable difficulties involved in on-field geophysical observations whereas the data collected is most of the time insufficient to make interpretations (Takahashi, 2000). Hence, geophysical data interpretations made at the field scale usually give uncertain results even after estimations. These uncertainties are usually caused by insufficient data availability and inconsistent data acquisitions, flawed dependence, resolution limitations and incomplete physical knowledge about the actual and observed properties of the field (Takahashi, 2000). Since these uncertainties have been recorded over a considerable time period therefore in order to reduce the impact of inconsistent geophysical data observed at the field scales seismic measurements are used. This is usually initiated by the use of presently available laboratory data and existing parameters for different models in physics. A general relationship is built between the properties of observed geophysical data at the field scale with the typical seismic features (Takahashi, 2000). Seismic features which are selected on the basis of optimization actually facilitate in differentiating between various properties of collected geophysical data. Moreover, they are combined with the statistical formulae, for instance, Bayes decision theory and information theory along with the models of rock physics (Takahashi, 2000). This subsequently helps in defining the relevancy of seismic features on various significant properties of observed data. Different sources of estimated but ambiguous rock properties are quantified through the use of newly developed formulae. In addition to this if the Bayes inversion and stochastic simulations are combined together for the uncertainty quantification about the relevance factor between targeted properties and seismic observations then the laboratory or field scale effects can be studied. Furthermore, when the geophysical data is quantified by the seismic measurements then it significantly helps in decision making at different stages of exploration (Takahashi, 2000). Field and laboratory techniques for the interpretation of geophysical data have different accuracy and precision levels. For instance, the above discussion indicates that field interpretations are usually weak and inconsistent due to observational issues and also because of the external experimental conditions which are significantly difficult to control. Researchers have identified that the accuracy of field measurement decline beyond the range of 12-15 kilometers. With the use of scintrex autograv gravimeter the gravity of observation field can be determined up to the absolute level (Geographical Data Aquisition, 2006). These can generate an average accuracy level more than 0.03 mgal in comparison to the gravity value in absolute conditions (Geographical Data Aquisition, 2006). However, when it comes to the seismic measurements conducted at the laboratory scale then the accuracy is relatively higher. It is also found to be affected by the observed data and the techniques used for making interpretations. Geophysical data is usually collected by shipborne, ground-based or different airborne platforms (Anderson-Mayes, 1998). Since all of these are field scales therefore there are significant chances of recording incorrect information. However, due to the inconsistent data there are certain precision issues faced by the researchers. Although the latest computer technology has increased the relevance of field scale interpretations but spatial resolution, accuracy and precision is still very weak as compared to the laboratory based seismic measurements (Anderson-Mayes, 1998). Hence researchers are making continuous efforts in order to increase the efficiency of interpretational and computational techniques used at different geophysical fields. References Acosta-Colon, A., Pyrak-Nolte, L.J. & Nolte, D.D. (2009). Laboratory-scale study of field of view and the seismic interpretation. Geophysical Prospecting , 209–224. Anderson-Mayes, A. (1998). Simple Spatial Analysis of Complex Multivariate Airborne Geophysical Data. University of Queensland . Archibald, N. Gow, P. & Boschetti, F. (1989). Multiscale edge analysis of potential field data. Retrieved April 21, 2014, from Virtual Explorer Australia. Brevik, I., StatoilHydro, P. T. Gabrielsen, Vestfonna & Morten, J.P. (2009). The role of EM rock physics and seismic data in integrated 3D CSEM data analysis. SEG Houston International Exposition and Annual Meeting , 835-839. Department of System Geological-Geophysical Research. (2010). Retrieved April 21 2014, from VNIIOkeangeologia. Geographical Data Aquisition. (2006). Retrieved April 21, 2014, from University of Pretoria. Gravity Methods. (2011). Retrieved April 21, 2014, from US Environmental Protection Agency. Hyndman, D. H. (2000). Inferring the relation between seismic slowness and hydraulic conductivity in heterogeneous aquifers. Water Resources Research , 2121–2132. Knight, R., Pyrak-Nolte, L.J., Slater, L., Atekwana, E., Endres, A., Geller, J., Lesmes, D., Nakagawa, S., Revil, A., Sharma, M.M. & Straley, C. (2010). Geophysics at the interface: Response of geophysical properties to solid-fluid, fluid-fluid and solid-solid interfaces. Physics Research Publications , 1-30. Neal, J., Risch, D. & Vail, P. (1993). Sequence Stratigraphy-A Global Theory for Local Success. Oilfield Review , 51-62. Resistivity Methods. (2011). Retrieved April 21, 2014, from US Environmental Protection Agency. Takahashi, I. (2000). Quantifying Information and Uncertainty of Rock Property Estimation from Seismic Data. Stanford University , 1-208. Thomsen, L. (2002). Understanding seismic anisotropy in exploration and exploitation. SEG -EAGE Distinguished Instructor Series . Trippetta, F., Collettini, C., Vinciguerra, S. & Meredith, P.G. (2010). Laboratory measurements of the physical properties of Triassic Evaporites from Central Italy and correlation with geophysical data. 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