Rock Physics Analysis

The Foundation for Comprehensive QI Studies

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PGS’ robust statistical rock physics workflow approach to rock physics and AVO studies. It is the foundation of all our more extensive quantitative interpretation studies.
  • Understand the range of elastic property trends for each study area in a depth-dependent manner
  • Understand the sensitivity of elastic properties to different reservoir properties in each study area
  • Guides and calibrates subsequent seismic inversion studies

We seek to understand the population behavior of key lithology and fluid combinations as a function of rock type, fluid content, reservoir quality and depth. Depth trend analysis is a standard part of our rock physics workflow. Indeed, the quantification of depth dependence is an important control on the range of expected rock properties. It can also be very important in lithology and fluid prediction pursuits.

We perform and use a petrophysical interpretation to evaluate lithology, reservoir properties and fluid content before any rock physics analyses. The interpretation will integrate all relevant information, including wireline and non-wireline logs, lithological descriptions, core analysis, petrographic studies and well test information.

Elastic rock property trends as a function of depth are defined using well information. The use of end-members and a depth-dependent model is critical to quantify the inherent scatter in resultant rock properties. It is also essential to understand the range of seismic responses (and associated inversion derivatives) that may be observed. Seismic amplitude and rock property forward modelling is performed stochastically, via a Monte Carlo sampling of all variables with uncertainty.

We use results from stochastic modeling as a qualitative guide to the interpretation of both seismic and inversion data. Capturing the population behavior enables the degree of discrimination to be assessed.  The sensitivity to depth, its effects, reservoir quality, fluid type and lithology can then be interpreted and subject to QC.

Interactive Regional Rock Physics Models | rockAVO 

Our interactive rock physics atlas browser, rockAVO is integrated into the PGS MultiClient data library. This makes it possible to access seismic with well data, including rock physics models, interactive seismic AVO modeling capabilities, and data atlases. Rock physics atlas coverage is offered for USA, west Africa, and Europe. We also offer RockAVO-based services for customer well data.

An Expert Rock Physicist’s Perspective on rockAVO by Per Avseth, CTO DIG Science

Per Avseth, CTO DIG Science says, “Data matters, and good data matters even more. In my daily work as a rock physicist, I depend on good-quality well-log data. I rely on good quality petrophysical (CPI) logs, in particular saturation, clay volume, and porosity, in order to test and calibrate my rock physics template models. Both during my time as an exploration geophysicist in Tullow Oil, and more recently as an independent geophysicist in Dig Science doing collaboration with PGS, I had the opportunity to use the rockAVO database. This has made my workday much more efficient. Not only are a lot of the log curves, that I often used to spend days and weeks generating, now available. The data are also standardized into a format that makes it convenient to pool lots of data together and perform big data analytics on these data, like extracting multilinear relationships between different elastic and geologic parameters, or to perform facies classification using machine learning."

"Traditionally, petrophysics has focused on the reservoir zone only, but in this database, all intervals, including reservoir, cap-rock and overburden, are considered equally important. The rockAVO database has therefore been proven to be very useful during the process of generating uplift maps, as it covers all intervals and wells over large areas of the Norwegian shelf. During AVO feasibility studies and QI work, rockAVO has been a nifty support, as synthetic seismograms for different fluid scenarios are already available. In an increasingly data-driven industry, I will therefore not hesitate to recommend the rockAVO as a ready-to-use seismic petrophysics database, and also a great toolbox for quick-look analysis that can be utilized by QI practitioners with varying degrees of experience in rock physics”.

rockAVO is an interactive rock physics modeling tool enabling perturbation modeling for lithology, fluid, and reservoir properties. Shown here is the Lille Prinsen well (16/1-29ST2 ) rockAVO result focusing on the Tertiary interval.

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