Bright spot analysis within the Pannonian Basin using horizon velocity estimation and Hilbert and AVO attributes

For several years velocity analyses and Hilbert and AVO attributes have been utilized in hydrocarbon exploration in the Pannonian Basin. Herein we report on some of the experience gained on this topic. Objective of the analysis Reflections of higher energy than surrounding sediments have been observed in a seismic section within the Neogene sequence (Fig. 1). Phenomena of this nature may indicate gas-bearing sandstone, but they may also be associated with other geological features (e.g. hard rock, layers of shale) or unusual features of wave propagation (e.g. tuning effect, anisotropy). It is known from well data that one of the reflections (marked R) is generated by a brine sand. The question is whether the other reflection, marked BS as it is a bright spot, not penetrated by a well, indicates gas trapped in a porous layer. Geological setting The intra-Carpathian region can be divided into several sub-basins separated by pre-Tertiary basement highs and infilled by a great mass of Neogene source rocks and other sediment traps. This area is thought to contain a considerable amount of oil or natural gas in traps associated with the older Neogene layers and the fractured zones of the pre-Tertiary basement. In the survey area the pre-Senonian basement is a nappe overlain by Senonian formations of varying thickness. The Miocene rocks overlying the Senonian may well be very thick in deeper sub-basins. They are covered by Pannonian sedimentary sequences. The Neogene sedimentary complex contains the potential hydrocarbon traps. Within it can be found wedging-out Pannonian structures, roll-overs, and flower structures derived from significant strike-slip tectonics. Along these faults gas may have migrated from reservoirs to the surface or it may be trapped in sandy layers forming shallow gas pools. None of these intervals has been explored because of their small extent; moreover, the recovery of gas from poorly consolidated sands necessitates special technology. Recently, however, the importance of these shallow resources has increased, because upward-moving gas may pollute ground-water and may cause explosions in the water system. Fractured zones in the basement, and other targets outlined by direct hydrocarbon indicators within the Neogene or older, may all be promising targets. Also worthy of special attention are the nappe edges overlain by the Senonian sequence.