Identification of Basement Fracture Pattern from Aeromagnetic Data-Its Significance in Hydrocarbon Exploration

Paramjit Singh, Jitendra Kumar, and Durga Shankar Mitra
ONGC, KDMIPE, Dehradun, India

The highly fractured nature of basement on outcrop is obvious, but the sedimentary rocks in the basin hide this fracture pattern from view. The basement fractures are reactivated at later times during, or after, deposition of the sedimentary section and create structures and/or sedimentary facies that become oil and gas traps and reservoirs. Thus, the mapping of the basement fracture pattern under the sedimentary section is of great significance in hydrocarbon exploration. How can this best be accomplished? A part of it can be mapped with seismic or gravity methods. Magnetics can map the covered basement fault block patterns in detail; it is because of the rock type changes that occur across the basement faults. Each of the magnetic highs and lows represents a separate basement block and the faults (shear zones) occur on the intervening boundaries.

Assam Arakan Basin, in the northeastern part of India is widely regarded as a mature petroleum province. Although, truly giant discoveries are rare in mature basins, new plays are often successful when old paradigms are challenged and replaced by different out of the box ideas. Special processing of the aeromagnetic data over the basin is carried out and relationship of known hydrocarbon bearing structures over the basement fractured zones is established. The near basement horizon mapped from seismic is also conformable. It has been observed that the hydrocarbon bearing structural highs are located on the sheared basement zones. Relationship of known hydrocarbon bearing pools with magnetic basement patterns has also been reported from various basins in US, Canada and China. Prospective areas for future exploration in the Schhupen fold-thrust belt, Assam Arakan Basin have been identified with the analogy and correlation with oil and gas pool occurrences in the foredeep situated on fractured basement blocks.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery