oa Reservoir Connectivity and Fluid Uncertainty Analysis Using Fast Geostatistical Seismic Inversion

Stochastic seismic inversion (Haas and Dubrule, 1994; Francis, 2006) enables the uncertainty in<br>seismic inversion to be explored. Additional information in the well logs is statistically exploited in<br>accordance with the variogram model. Each stochastic seismic inversion realisation has a spatial<br>constraint imposed by a variogram, is conditional to the well and stratigraphic horizon data and is<br>conditional to the seismic data within the bandwidth of the wavelet. Using a frequency domain fast<br>stochastic seismic inversion algorithm a sufficiently large number of stochastic realisations enables<br>probability and 3D connectivity volumes corresponding to lithology or fluid indicators to be generated.<br>Two applications of 3D Connectivity analysis of stochastic seismic inversion realisations are presented.<br>In the first example using post-stack seismic inversion impedance realisations, the acoustic impedance<br>is classified by sand and shale discriminators (Francis, 1997). The sand indicator is used to process<br>each realisation using 3D connectivity to identify geobodies. By selecting realisations containing<br>geobodies which are consistent with known connectivity criteria between wells, these realisations can<br>be used as candidates for constraining geostatistical modelling.<br>In the second example, pre-stack seismic inversion results and a rock physics analysis are used to<br>identify hydrocarbon fluid effects from the seismic response. Pre-stack inversion using Extended Elastic<br>Impedance (Whitcombe et al, 2002) is used to generate a large number of joint stochastic impedance<br>realisation pairs. Based on the rock physics analysis the EEI impedance realisation pairs are rotated to<br>obtain pairs of optimal fluid and lithology predictor realisations. The rotated realisation pairs are used<br>to evaluate the probability of new well targets being partially depleted by existing production, to<br>estimate sand volumetric uncertainty and to perform a risk analysis of a proposed horizontal well trajectory.