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Quantitative information and interpretation can optimize your field development plan

Sound QI's Chief Geophysicist, Carl Reine, discusses quantitative interpretation of seismic data, a key component in optimal field development. 

The session explores the:

  • Added information quantitative interpretation gives.
  • Factors leading to effective quantitative information.
  • Process to convert to useful geological information.

Abstract:

Structural interpretation of seismic data has been the main contribution of geophysics since its early development. Mapping the subsurface elevation of potential reservoirs along with thickness changes and fault activity provides useful information for certain reservoir types. However, there is much more information contained in the seismic reflections and using this information to characterize the subsurface is increasingly important in more complex reservoirs. Quantitative interpretation (QI) provides information about the measured elastic properties of the rocks, which in turn can be directly related to geological parameters such as porosity, lithology, or fluid saturation. In this presentation, we will look at an overview of how the quantitative information is obtained, and more importantly, how it is turned into geologically useful information, providing more insight than conventional interpretation on its own.

Classic interpretation takes into account the structural changes of the reservoir in conjunction with analysis of the amplitude variations and integration of the well-log data. QI does not ignore these principles but rather considers them in a more analytical manner. AVO inversion is one of the backbones of QI, using the effects of the rock properties on the reflected amplitudes. By analyzing the amplitudes in prestack data, AVO inversion provides volume estimates of P-impedance, S-impedance, and density. These, in turn, can be transformed into a multitude of other elastic parameters as necessary.

Interpreting elastic properties is a crucial function of the geophysicist to explain the results in a geological context. The link between geological properties and elastic properties is found through well analysis and rock-physics modelling. In well analysis, the sonic, dipole sonic, and density logs are used to generate the equivalent elastic properties measured from AVO inversion. These log calculations can then be compared with additional petrophysical data, such as porosity, lithology, or saturation, providing a recipe for how to interpret the seismic results. Similarly, rock-physics modelling produces estimates of the same elastic properties based on theoretical models. These are calibrated to the known well data to ensure appropriate behaviour but can then be altered in a systematic way to discover the properties of rocks that may not have been encountered by wells.

The final output of QI is a geologically classified volume. Often created in the crossplot domain, seismic inversion attributes are compared to those from well analysis and rock-physics modelling and clusters or trends are identified. The resulting volume contains meaningful classes that can be used across disciplines for field development, geological modelling, and general planning purposes by geophysicists and non-geophysicists alike.