Data Analysis - Case Study 1

Tweed Lake, Northwest Territories. Canada

Field Summary

• 1985 Frontier Anticline Gas & Condensate Discovery in Cambrian Mt. Cap and Mt Clark formations at a depth of about 1300m.
• Discovery well, M-47; drill test tested 6.7 mmcf/d from the Mt. Clark
• Area of approximately of 83 km2
• Estimate reserves of about 120 BCF

Survey Design Summary

• Total of 48 Gore™ Modules installed.
• Discovery and dry wells were modeled.
• Single transect with 250m spacing through discovery well

Introduction

The Cambrian was deposited in a semi-closed epicontinental marine basin with multiple depocenters and ridges. Initial transgression resulted in the deposition of a variably thick basal wedge of marine sandstone (Mount Clark Formation) followed by lower energy deposition of clay and carbonate-muds (Mount Cap Formation). Subsequent deposition of the Saline River Formation resulted in a thick section of evaporates and salt up to 500m thick.

Gas and condensate has been recovered from sandstones reservoirs in the Mount Clack Formation and bitumen is a common component of the Cambrian sandstones and along fractures in the carbonates throughout the basin. In addition, surface oil seeps have been reported at Rond Lake, west of Colville Hills and in sands at Lac des Bois and the west flank of the Belot ridge (Cook & Aitkin, 1971).

A total of 26 wells have penetrated the Cambrian resulting in three fields (Tweed Lake, Tedji Lake & Nogha) with total initial marketable reserves of 619 Bcf gas. The Mount Clark reservoir occurs at a depth of 1000 to 1400m with net pays of 10 to 12m. It is estimated that the trend contains 84 structural prospects varying in area from 4 to 150 square kilometers. The undiscovered gas in place is estimate to be 5,791 Bcf contained in about 77 undiscovered fields. The two largest pools with mean gas in place of 1,595 Bcf and 782 Bcf are currently undiscovered. It is estimate that there is a 90% chance the undiscovered potential is greater than 4,620 Bcf and a 10% chance that the potential might exceed 7,224 Bcf. The Cambrian structural play of the Colville area, Northwest Territories is one of the largest potential and simplest play type left to exploration in western Canada (Natural Gas Potential in Canada 2001; Canadian Gas Potential Committee).

Survey Results
In the winter of 2007, Geochemical and Gore™ conducted a large surface amplified geochemical surface in the Great Bear Lake area of which the Tweed Lake model was a component. A total of 48 modules were installed in the Tweed Lake area. Two wells (M-47 and C-12) were modeled and one transect was conduct along a northeast-southwest seismic line.

Tweed Lake M47 Gas/Condensate Model
All samples from the Tweed Lake M-47 gas well were used to define the general character of gas/condensate reservoir emanation at the surface. Similarly, all samples from the Tweed Lake C- 12 dry well was used to define “background” emanation character.

The model was developed using the end-member sample sets to collectively define their respective “gas/condensate-like” and “background-like” emanationsignatures in two-way discriminant analysis. This process produces a statistical separation of the end members, defining which principal component factors best discriminate or separate the centroids of the defined classes.

The orientation (or vector) of maximum separation between the end-member centroids in the models can be related back to the original compound data axes by the factor loading values derived for each qualified organic compound in the target compound list. The correlation between this orientation and each compound was calculated for the samples of the two end-members and defines the geochemical model.

Tweed Lake C12 Background Model
The Tweed Lake C-12 dry well site was intended to be a calibrationmodel for background in the Colville Hills area. This well is located ten kilometers from the Tweed Lake M-47 gas discovery well. Linear Discriminant Analysis LDA was used to make a geochemical model of gas based on the Tweed Lake M47 well as the gas end-member versus the Tweed Lake C-12. The chart below shows the concentration relative to the compounds.

The results for the Tweed lake M47 gas-like model in Colville Hills identified a geochemical feature at least 3.5 kilometers long along the transect over the Tweed Lake field. The geochemical feature truncates along the transect 1.5 kilometers northeast of the Tweed Lake M47 gas well and appears to closely correlate to the fault that defines the eastern edge of the Tweed Lake pool.

Tweed Lake M47 appears to be geochemically stable and is a reasonable chemical expression for “gas/condensate”. The model is stable in the sense that the “gas/condensate character” is not a function of one compound only, or a small number of compounds isolated across the range of analysis. Such a condition is a sign of model instability, as isolated compounds or single compound occurrence is not thought to represent realistic geochemical source influence. The model consists of light and medium range aliphatic compounds (commonly associated with gas and condensate) in the C2 to C8 range; the C15 and C17 normal alkanes plus pristane and phytane.

Back to the top of the page