SEISMIC MULTI-ATTRIBUTE ANALYSIS FORLITHOLOGY DISCRIMINATION IN THE GANSOFIELD, OFICINA FORMATION, EASTERNVENEZUELA

摘要

Even extensively drilled and supposedly well-understood fields have the capacity to surprise.Whilst drilling a fairly routine development well in the Ganso field, Oficina Basin, EasternVenezuela, ENI Dación discovered a new accumulation, reservoired in a high quality channelfacies sandstone 30ft thick and full of relatively light oil. The reservoir flowed at theexcellent rate of 950 bopd with 0% watercut on testing. The unexpected element of thisdiscovery was that the accumulation was found with the landing section of a horizontal welltargeting a deeper level, and the sand was completely absent in the pilot hole some 120maway.A seismic multi-attribute study was established with the objective of investigating whether theseismic data could be used for lithogy prediction and thus facilitate the mapping of this newreservoir. The study involved rock physics, seismic inversion and multi-attribute analysisusing a neural network technique.The results show that reliable maps of lithological discrimination can be obtained fromcombining two or more attributes such as the elastic impedance (P and S wave), the density,and Poisson's ratio. The final maps obtained of the target sand show consistent correlationbetween the wells and the predicted lithology. Finally, the reliability of the results wasvalidated by the drilling of a successful well showing a sand thickness as predicted by thestudy.