Use of Well Logs in Seismic Reservoir Characterization
This is a paper given by Dr. Joel Walls to the SIPES luncheon meeting 21 October, 2004.
Abstract
Seismic Reservoir Characterization, also known as reservoir geophysics, has evolved over the past several years into a multi-disciplinary, business-critical function in most ED&P organizations. Sheriff defines reservoir geophysics as "The use of geophysical methods to assist in delineating or describing a reservoir or monitoring the changes in a reservoir as it is produced." Reservoir geophysics is applied across a wide spectrum of the oilfield life cycle from discovery and early development to tertiary recovery. One critical part of this process is careful analysis and understanding of petrophysical properties from well logs and core data (seismic petrophysics).
This presentation will illustrate why seismic petrophysics is so important and to show how carefully constructed synthetic models can help the geoscientist interpret acoustic and elastic impedance inversion from seismic data.
Generalized Seismic Petrophysics Workflow
Seismic Petrophysics can be performed on single or multiple wells and consists of the following basic steps.
Geophysical Well Log Analysis (GWLA)
Collect and organize input data, reservoir conditions, and fluid propertiesPerform geophysical log interpretation for volume minerals, porosity, and fluids over entire wellEdit logs and perform mud filtrate invasion correction (as needed)Generate missing curves (for example Shear Wave Velocity)
Rock Physics Modeling and Perturbations
Perturb reservoir properties using rock physics effective medium models and compute new Vp, Vs, density curves.
Fluid SaturationPorosityLithologyNet/gross
Synthetics
Compute synthetic seismic traces for in-situ and modeled conditions.
May also include:
AVO responseAcoustic impedance (AI) and elastic impedance (EI)Other seismic attributes as needed
Examples show the effects of mud filtrate invasion effects, wellbore washouts, and bad Vshear log on seismic well tie. An example is also shown of how seismic petrophysics can be used to interpret acoustic and elastic impedance inversions for oil saturation and porosity in an on-shore US oil sand.
The primary benefits of seismic petrophysics are improved well-to-seismic ties, improved calibration of seismic attributes to reservoir properties, and more reliable models of seismic response due to reservoir changes (vertically laterally, and temporally). These models can improve interpretation of 3D seismic data, especially acoustic and elastic impedance inversion. This improved interpretation can reduce drilling risk, enhance field productivity, and ultimately increase asset value.
Note: This presentation is based on OTC paper 16921, May, 2004.
Stacked synthetics before and after corrections for mus filtrate invasion and wellbore washout
Biography
Joel Walls obtained his PhD in geophysics from Stanford University in 1983. He has been active in research and technical services related to core analysis, rock physics, and seismic reservoir characterization. Dr. Walls founded PetroSoft Inc. in 1992 to bring rock physics technology to the desktop. Rock Solid Images (RSI) was founded in 1998 from the merger of PetroSoft Inc., Seismic Research Corp., and Discovery Bay. RSI has 30 employees in Houston and Oslo Norway. Dr. Walls is Vice President of New Business Development.