Generating a Litho-fluid Model

The QI Stochastic Model window incorporates a stochastic (Monte Carlo) forward modelling concept using a depth-dependent end member elastic rock physic model with the relevant degree of uncertainty. This results in depth-dependent multivariate rock property probability density functions, also known as PDFs, which quantify the inherent scatter observed in rock and fluid properties. These PDFs are generated from all the individual stochastic realisations. 

The Iterations input box within the Litho-fluid Model tab defines the number of realisations. Intuitively, the higher the number of iterations, which represent the number of random realisations taken from the depth-dependent elastic rock physics model, the better the estimate of the rock physics model.

  1. Rock Stochastic Model Parameters:
    • Depth: Insert depth range for the simulation run based on TVDBML (True Vertical Depth Below Mud Level); min-max [interval].
    • Limit Vp/Vs: Select and insert the min and max values to limit the Vp/Vs.
    • Error: Error probability percentage associated with each lithofluid.
    • Iterations: Enter the desired number of iterations.

Note: Each iteration is based on probability theory whereby Insight runs a probability session for each parameter. The higher the iteration is set, the better the estimate of the models is. The higher the number of iterations, the longer it takes for Insight to run them.

  1. Probability Density Function: Select the horizontal and vertical axes of the PDF crossplot charts. To remove any chart, click the Remove Row icon. To add, click the Add icon. 
  2. Lithologies: Make sure all the desired lithologies are included in the export. To remove any lithology, click the green Show/Hide button, and the button will turn amber.
  3. The lithofluid depth override validity range is displayed.
  4. Optionally set alternative minimum and maximum interface depths in the Override Depths boxes.

View in Crossplot: Click to view the crossplot in the Crossplot window.

Re-Run Simulations: Click to update the stochastic modelling output after changing any of the rock stochastic modelling parameters. 

View Log/Warnings: Click to view successful generation and warning logs. A warning icon indicates issues that the Stochastic Model window has run into and where the problem has arisen, normally relating to over-extrapolation of trends. This means that the stochastic modelling was performed at a much deeper or shallower depth than where the picks are available in the trending phase. 

Export PDF: Click to save the litho-fluid composite into .dustat format for further litho-fluid modelling purposes.