Application of high‐resolution seismics in studying reservoir characteristics of hydrocarbon deposits in Hungary

Abstract

In preparing for the production of hydrocarbons, there is an increasing demand for surface geophysics. We studied the potential of seismic reflection—and within this, how to increase resolution—when the reservoir is very inhomogeneous and is covered with a thick (∼2 km) young sedimentary sequence of high energy absorption. For high and nearly uniform resolution the lower frequency limit of sweep should be increased to at least 16–18 Hz, in addition to extending the frequency band upward. We carried out measurements over a gas‐capped reservoir made up of Badenian sandstone and a conglomerate of primary and Precambrian metamorphic rocks of secondary porosity, using a sweep from 18–92 Hz. Time sections contain high frequencies, with the upper frequency limit of trace spectra reaching 80 Hz. These time sections enabled us to extrapolate well data laterally. The structure of the reservoir can be mapped and zones barren because of geometric reasons delineated. Not only can rock units of primary and secondary porosity be distinguished but identifiable reflections could be obtained from the boundaries of sandstone and conglomerate beds about 25-m thick in the Badenian sequence. The dynamic features of reflections from the hydrocarbon‐water boundary observed in the region of secondary porosity indicate the grade of tectonization almost independently of pore fluid, and brecciated parts could be distinguished. Velocity anomalies in the Lower Pannonian sequence reveal a 10–18-m thick gas‐bearing sandstone layer. Wells drilled after our studies confirmed our conclusions.