Vijay Khare

Correction for NMO stretch and differential attenuation in converted-wave data: A key enabling technology for prestack joint inversion of PP and PS data

In many parts of the world, P- or S-wave impedance (I P or I S or seismic velocities ( V P or V S ) are not good indicators of lithology. In these cases, estimation of density or V P / V S is essential for reservoir characterization. Conventional inversion of PP-mode data is known to yield I P and I S , but a reliable estimate of density requires prestack inversion of very large-angle PP data (Roy et al., 2008). Such large-angle PP data sets necessitate acquisition and true-amplitude processing of unusually large offsets.

Joint PP-PS angle-stack analysis and AVA inversion in Grane Field, offshore Norway

Eleven years ago, publication of the UK North Sea Alba Field OBC converted-wave (PS) image examples by MacLeod et al. caused quite a stir. The authors provided convincing evidence that “the Alba survey is the first 3D OBC survey in which successful converted-wave imaging of the reservoir has created significant economic benefit.” Most of us with an interest in multicomponent seismology know it well, as Alba has become one of the classic examples of a “stealth” reservoir (Rape et al., 2005), having low P- but high S-impedance contrast. The Alba reservoir and others like it are difficult to recognize on conventional P-wave images, but they stand out quite nicely when viewed on their PS equivalents.

Pre‐conditioning angle stack input for joint PP‐PS inversion

We present a workflow for pre-conditioning convertedwave (PS) and P-wave (PP) angle stacks prior to joint inversion. The process includes the following steps in order to improve the resolution of PS data and the registration of PP and PS reflections: 1) bandwidth enhancement of the far-angle data via Qand waveletstretch compensation, 2) native-domain (PP and PS) AVA inversions or attribute calculations, and 3) interval VP/VS derived from the initial inversion passes is used to further refine data alignment prior to final joint inversion. Examples using data from current project work are shown.

A Second Look At the Background Trend For AVO Interpretation

The intercept-slope crossplot technique is routinely used for seismic identification of reservoir fluid in the oil industry today. The underlying physical link between the intercept-slope crossplot and rock properties is given by Castagna et al. (1998). According to their theory, the slope of the background trend (the data cloud for water-wet sands and shales in the intercept-slope crossplot) is related to the average Vp/Vs of the rocks. They also predict that the slope becomes flatter as the average Vp/Vs increases.

Seismically Integrated Geologic Modeling: Guntong Field, Malay Basin

Exxon Production Research Company, Esso Production Malaysia Inc., and Petronas Research & Scientific Services participated in a joint research project on seismically integrated reservoir modeling involving the Guntong Field, Malay Basin. The goal of this effort was to develop and test a process for interpreting reservoir properties from 3-D seismic data and for integrating these data into the building of 3-D geologic models that would be suitable for use in flow simulation studies. The project produced a 3-D geologic model for three reservoir intervals (IR010, IR023, IR025) and three predominantly non-reservoir intervals. Each reservoir interval was subdivided into facies that were determined by integrating core; well log, and seismic interpretations. Predictions of porosity and lithology used in building the geologic model were made using seismic attributes calculated from acoustic impedance data. The strong DHI in the reservoir intervals assisted in interpreting lithofacies. The geologic model was built following a sequential process that produced a lithology model, a porosity model, and a permeability model. Each model was generated using geostatistical simulation techniques that integrated seismically interpreted facies, reservoir properties, and reservoir property continuity into the process of cell estimation. Two sets of geologic models were built to assess the contribution of seismically derived reservoir properties to the accuracy of the geologic models. Flow simulation results show a significant improvement in history match using the models that integrated all seismic information.