By Dr. Clare Maher
iEnergy Editor in Chief, Halliburton Landmark
THERE IS NO RIGHT OR WRONG, JUST VARYING DEGREES OF UNCERTAINITY
Assessing the subsurface risks of a new venture is an integral part of any exploration program. Evaluating risk is even more challenging in frontier basins due to limited data control. When data is sparse, exploration geoscientists need to consider the bigger picture, using whatever information is available to build and calibrate a subsurface model that can be used to guide subsequent decision making.
But it’s important to always keep in mind that a model is never completely accurate — it is simply a synthesis of the available data with sensible and realistic extrapolation applied. And as more data becomes available, the model will evolve accordingly. Despite these inherent limitations, a properly constructed and calibrated model can help geoscientists qualitatively assess risk in their basin, providing valuable insights and shedding new light on subsurface risks.
YOU’VE GOT TO START SOMEWHERE
One of the best places to start any frontier exploration project is the interactive web portal by Exploration Insights, a product service line of Landmark. Featuring comprehensive regional geological data underpinned by a proprietary, global sequence stratigraphic model, Exploration Insights provides a geological framework for building a functional basin model, including depth surfaces, gross depositional environment maps, paleotopographic maps, and well and geochemical data.
This was recently demonstrated by Kate Evans, product specialist, Landmark, and Kathleen Gould, geoscientist, Landmark, using the Zambezi Delta Depression as an example. Employing Permedia® software, they constructed a detailed earth model using the Exploration Insights geological framework. They used the earth model, along with additional meta-information, to construct a full 3D basin model, with pressure and temperature calculated through time. This basin model was then used to understand the timing of source rock maturity and expulsion.
Where subsurface datasets are limited, regional understanding and analogues can be selected to produce a most likely case; however, sensitivity analysis is needed to understand the range of possible outcomes. Permedia software includes tools to quickly generate different scenarios to evaluate the impact of varying the most poorly understood parts of a basin’s petroleum system. In this case, it was the source rock. By running migration simulations on a variety of source rock scenarios, Evans and Gould were able to test the results using sensitivity analysis to better understand the qualitative risks associated with the petroleum systems in the Zambezi Delta depression.
Where basins are concerned, there are no right or wrong interpretations, just varying degrees of uncertainty. These uncertainties need to be minimized. The qualitative risking technique used in this example is a relatively rapid method that provides insights into how basin models respond to different conditions, and into the range of subsurface risks. The results can be high graded for further qualitative and quantitative risking.
To learn more about sensitivity analysis application techniques, watch Kate Evans and Kathleen Gould’s webinar “Capturing Uncertainty in Basin Modeling: Better Subsurface Risk Assessment in Frontier Basins.”