Application of High Resolution Aeromagnetic Survey to Structural Basin Delineation

Pavlo Cholach
BP Canada Energy Company, Calgary, AB, Canada

This paper discusses application of high resolution aeromagnetic (HRAM) survey for structural delineation of Crowsnest Coalfield in south-east British Columbia, Canada (Fig. 1). Survey was acquired by Fugro Airborne Survey in fall 2007 and has total length of 5961.6 km (including 1198 line-km of tie lines). Airborne magnetometer Fugro D1344 with Scintrex CS3 sensor (sensitivity of 0.01nT) was used. Survey covers in excess of 550 km² of Crowsnest Coalfield with traverse lines spacing of 200m and sampling interval of ~ 2.9 m along the lines which provides the dataset of excellent special resolution (Fig. 2) particularly suitable for detailed structural modelling.

Crowsnest Coalfield is one of the most prominent coal mining districts in British Columbia (BC), with historic references for mining dating back to 1899 (e.g. Smith, 1989). With more then a century of surface and subsurface mining activities coal distribution through out the filed is well studied and documented. Present day localized shallow coal of Crowsnest Coal field provides resource potential of over 25 billion tones of coal and CBM resource of over 6 TCF according to BC government estimates (e.g. Ryan, 2007).

Structurally Crowsnest Coalfield is located in south-east part of Front Ranges of Foreland Front and Thrust Belt (FFTB) of Canadian Rockies and also know as “Fernie basin”. Synclinal feature of Fernie basin with well preserved Cretaceous and Jurassic coal bearing sedimentary sequences surrounded by lower Paleozoic rocks (e.g. Hardebol et al., 2007) is the main object of HRAM investigation.

HRAM map of IGRF corrected total magnetic intensity with reduction to pole (RTP) was used to identify shallow and deep structural elements and magnetic lineaments and correlate results of interpretation with structural map. In order to forward model magnetic response of the Fernie basin and compare it to HRAM data 3D digital model of the basin was developed based on surface geology and mining data. Ten structural W-E profiles through the field were extracted from 3D model for forward magnetic modeling. In order to match magnetic response of HRAM stratigraphic layers of the model were populated with assumed magnetic susceptibility that reflects lithological description. Example of the comparison of observed and calculated total magnetic response is illustrated in Fig. 3.

High level of correlation between modeled and observed magnetic anomalies was achieved for all 2D profiles. This paper will discuss results of both structural interpretation of HRAM and magnetic modelling with implication to refinement and further delineation of existing subsurface 3D model of the basin.

References:

Hardebol et al., 2007, Kinematics of the SE Canadian Fold and Thrust Belt: Implications for the Thermal and Organic Maturation History in Thrust Belts and Foreland Basins: From Fold Kinematics to Hydrocarbon Systems by Lacombe et al., pp.172-202.

Ryan, B., 2007, A Summary of Coalbed Methane Potential in British Columbia, publications of Ministry of Energy And Mines, British Columbia.

Smith, G.G., 1989, Coal resources of Canada, Geological Survey of Canada, Paper 89-4.

Fig.1.Location of HRAM survey