SEISMIC MULTI-ATTRIBUTE ANALYSIS FOR LITHOLOGY DISCRIMINATION IN THE GANSO FIELD, OFICINA FORMATION, EASTERN VENEZUELA

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, Eastern Venezuela, ENI Dación discovered a new accumulation, reservoired in a high quality channel facies sandstone 30ft thick and full of relatively light oil. The reservoir flowed at the excellent rate of 950 bopd with 0% watercut on testing. The unexpected element of this discovery was that the accumulation was found with the landing section of a horizontal well targeting a deeper level, and the sand was completely absent in the pilot hole some 120m away. A seismic multi-attribute study was established with the objective of investigating whether the seismic data could be used for lithogy prediction and thus facilitate the mapping of this new reservoir. The study involved rock physics, seismic inversion and multi-attribute analysis using a neural network technique. The results show that reliable maps of lithological discrimination can be obtained from combining 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 correlation between the wells and the predicted lithology. Finally, the reliability of the results was validated by the drilling of a successful well showing a sand thickness as predicted by the study.