Comparison of airborne and marine magnetic data in Donegal Basin, Ireland

Abstract

Exploration of Ireland's Donegal Basin in the last 10 years concentrated on structural plays within the Triassic Sherwood Sandstone and culminated in the Corrib gas discovery in 1998. Despite this economic success, the structural history (and hence petroleum geology) of the basin remained poorly understood, due in large measure to igneous intrusives and salt which degrade seismic data quality. These problems caused operators to consider alternative methods and, given the success of potential fields in adjacent areas (Faroes, Irish Sea), new gravity and magnetic surveys were undertaken in 1999. Before 1999, the only speculative magnetic data set over Donegal Basin was a 5-km grid of various vintages compiled by the Geological Survey of Canada. This was useful for identifying regional structural trends but little else. As exploration intensified in 1999, a 2D seismic survey was acquired along with marine gravity and magnetics data. The new data enabled better structural definition within the basin but still left many unanswered questions about the detailed character and extent of igneous intrusions. To address this, a high-resolution aeromagnetic (HRAM) survey was flown in late 1999. The dense data coverage and high sampling rate provided much greater detail than previous surveys (Table 1). View this table: Table 1. Comparison of acquisition parameters for various surveys acquired in the Donegal Basin This paper discusses the advantages and disadvantages of the various data types acquired in Donegal Basin. Each has an optimum application determined by technical objectives and budget, but to choose the most appropriate, it is important to understand the limitations that each has. The underlying aim of this paper is to help explorationists make better-informed decisions when planning acquisition of potential fields data. The 2D marine gravity and magnetics data acquired in conjunction with the 1999 seismic survey had line orientations that were north-south and east-west, respectively, and line spacing …