ROCKTRACE

Simultaneous AVA/AVO Inversion

Since its introduction in 2000, RockTrace® has significantly impacted the way the industry uses and incorporates pre-stack time migration (PSTM) seismic data. It is the only technology that quantitatively integrates well log elastic rock properties and AVA seismic to produce calibrated quantitative 3D volumes of rock properties.

RockTrace builds on InverTracePlus technology by extending it to the AVO domain. In InverTracePlus, the constraints applied are in terms of acoustic impedance (Zp). In RockTrace, the objective is to solve for shear impedance (Zs) and density in addition to acoustic impedance, so the constraints are set for all three parameters independently. The parameterization can be in terms of triplets of elastic parameters:

• Zp Zs and density
• Zp, Vp/Vs and density
• P-Sonic S-Sonic and density
• Vp, Vs and density

When applied in global mode, just like in InverTracePlus, a spatial control term is added to the objective function and large subsets of traces are inverted globally at the same time. The RockTrace seismic inversion algorithm takes multiple angle-stacked seismic data sets and generates three elastic parameter volumes as output. The algorithm is an extension to the global multi-trace seismic inversion algorithms in the InverTracePlus program, which takes a single seismic data volume as input and produces a single impedance volume as output. While the RockTrace algorithm is generalized for three elastic parameters, many of the principals and constraints of the other programs remain.

This is unique in the industry and brings the following significant advantages:

• The elastic parameters are real rock properties that can be directly related to reservoir properties.
• No approximations are made as the full Knott-Zoeppritz equations are used.
• Full allowance for amplitude and phase variations with offset. This is done by deriving unique wavelets for each input partial stack.
• The elastic parameters themselves can be directly constrained during the seismic inversion.
• Rock physics relationships can be applied constraining pairs of elastic parameters to each other.
• Enhanced robustness against noise as all input data must conform to a single output model.
• Final elastic parameter models optimally reproduce the input seismic, as this is part of the seismic inversion optimization.
• Analysis of QC issues easier and more precise because process is integrated with all data conforming to a single model.