3D geologic subsurface modeling within the Mackenzie Plain, Northwest Territories, Canada

Abstract

Three-dimensional (3D) models are widely used within the geosciences to provide scientists with conceptual and quantitative models of the earth’s subsurface. As a result, 3D geologic modelling is a growing field, such that scientific research often cannot keep up with technical advancements. Literature often shows conflicting results with respect to which interpolation algorithms produce the best surfaces, and it is not always clear which methods are most appropriate for a particular geological setting.

This study looks at three commonly used interpolation techniques – Inverse Distance Weighting (IDW), kriging and triangulation – and assesses their effectiveness at capturing geologic structures in the subsurface. The study uses a modified Horizons method to create a solid 3D stratigraphic model of the subsurface of an area within the Mackenzie Plain, NWT, in Canada.

The Horizons method involves interpolating individual stratigraphic surfaces, or horizons, representing their depositional sequence. Surface intersections are corrected where necessary, and a solid model is built by extruding each surface down to the top of the surface below.

Triangulation produced the most geologically appropriate surfaces, whereas IDW produced surfaces with a stronger bullseye effect; although kriging produced some surfaces well, it did not result in acceptable surfaces where discontinuities were present. Structural features such as folds in the subsurface were captured only where the data density was sufficient. Large folds spanning the majority of the study area were visible in the modelled surfaces; however smaller folds and monoclines were not visible. It was possible to model a thrust fault in the subsurface by creating two separate stratigraphic models on either side of the fault, cutting them at the fault plane and merging them together after each side was converted to a solid model.

The model produced in this study showed promise as a basis for future modelling and further 3D model refinements. The modelling process was capable of highlighting areas where surface mapping did not match up with subsurface measurements, and conversely, highlighted areas where subsurface measurements did not match with observed surface features. However, comparing the modelled results with seismic survey images in the region showed that the specific locations of the subsurface structures (e.g. fold troughs) were not captured in the correct location. As well, the presence of discontinuous surfaces made it necessary for manual edits to be performed, in order to accurately represent the known subsurface geology – complicating the model and making replication more difficult.

The results presented in this thesis can be used to guide methods in other similar 3D modelling exercises. As well, it will help us apply the most appropriate methods for any given geologic setting, resulting in more accurate and efficient 3D models.

Popular Abstract

Three-dimensional (3D) models are widely used within the geosciences to provide scientists with a conceptual and measurable model of the earth’s subsurface. They can also allow non-specialists to more easily visualize the subsurface, which has traditionally been simplified into 2-dimensional maps. These models are also important in the management of natural resources. For example, within the oil and gas industry, they can be used as input to oil reservoir simulations. For these reasons, it is important for research to continue on improving modeling accuracy as well as streamlining methods required to create these models, to increase efficiency and to reduce risks associated with inaccurate models.

In this study, a methodology is developed for creating 3D geologic subsurface models for a region within the Northwest Territories, in Canada, called the Mackenzie Plain. From drilled well data, it models each individual geologic layer in the subsurface independently, and builds the model upwards from the bottom surface modelled, mimicking the natural deposition of these geologic layers. Three different methods for creating these surfaces and estimating values between points, were tested. Faults, which are abrupt displacements of the geologic surfaces, are difficult to model, and a methodology for incorporating them is presented.

The results of this study found the best interpolation algorithm to be used, a method for displaying faults in 3D, as well as highlighted points which should be considered in the model building process – to ensure the most geologically realistic model possible. The model had difficulty representing subsurface structures in their exact location, however it provided a reasonable first pass, and the whole process of building the model had merit. These findings will help other scientists determine if this methodology is appropriate for the type of geology they wish to model, and for the type of input data they have. This will allow them to make the most accurate model possible, without wasting resources.

• author: Raska, Nadine
• supervisor: David Tenenbaum; Karen Fallas
• organization: Dept of Physical Geography and Ecosystem Science
• course: GISM01 20171
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: geology, 3D modeling, geography, geographic information systems, horizons, stratigraphic modeling
• publication/series: Master Thesis in Geographical Information Science
• report number: 65
• funder: Geological Survey of Canada, GSC
• language: English
• additional info: External supervisor: Karen Fallas, Geological Survey of Canada, Canada
• id: 8902243
• date added to LUP: 2017-02-03 09:05:58
• date last changed: 2017-02-03 09:05:58