Quantitative Interpretation of Seismic Facies - A case study, Oriente Basin Ecuador
Summary Interpretation of several 3D volumes from the Oriente basin suggests that faults define the extent of a given field. Additionally, the subtle stratigraphic boundaries characterised by the clay-filled zones of low porosity compartmentalise oil pools within a field. Identification of these zones is critical. In our experience, neural network based waveform classification has proven to be a successful tool to identify these zones. Qualitative analysis of seismic facies derived from the classification is a common practice. However, we demonstrate in this paper that the quantitative interpretation of seismic facies is possible provided a geological understanding of the seismic signatures is achieved. This paper discusses the extensive 1D-modeling carried out to comprehend the trace shape variations due to changing isopach of the sand/shale sequences, which was fundamental in assigning a realistic geological model to each facies. Also described in the paper is the workflow and a key methodology developed to derive “Net thickness” of reservoir sands from the seismic facies. Rigorous study of this technique on several 3D data sets from Ecuador’s Oriente Basin has produced results, which have established the foundation for understanding the depositional environments and the reservoir models, validated by subsequent drilling.
Aspects of the petroleum geology of the Oriente Basin, Ecuador
Abstract The Oriente Basin of Ecuador is one of the most productive of the South American Sub-Andean Basins. Cumulative production of oil to the end of 1986 was over one billion barrels, and current production stands at approximately 300 000 barrels per day. At least 20 oil fields have been discovered to date, including five giant fields, and exploration is currently in the early stages of a new and already successful phase in which ten new operators are scheduled to drill over 40 wells between 1985 and 1992. The Oriente Basin contains a sedimentary fill of Palaeozoic to Recent age. Major commercial interest is confined to the Cretaceous depositional cycle and all of the significant production comes from fluvio-deltaic and marine sandstones of the Hollin and Napo Formations. Most of the productive structures are low-relief, north-south orientated, anticlines of two distinct types: foot wall anticlines associated with normal faults, (Type 1) or hanging wall anticlines associated with reverse faults, (Type 2). Evidence points to the importance of pre-Miocene structural growth, comprising either early-mid Cretaceous rejuvenation of pre-Cretaceous ‘basement’ faults in the case of Type-1 structures and ‘Early Andean’ (latest Cretaceous to Oligocene) compression in the case of Type-2 structures. Few commercial discoveries have been made associated with ‘Late Andean’ (Miocene-Pliocene) compressional structures, essentially because these structures appear to post-date the main phase of primary oil generation and migration. The origin of the oils is problematical because the potential source rocks, the marine claystones and limestones of the Cretaceous Napo Formation, are generally immature or marginally mature within the confines of the present-day Oriente Basin. Oil analyses indicate a single family of oils. Available evidence, combined from structural and geochemical data, supports a major phase of Early Andean age oil generation and migration. There is a considerable variation of oil type from 37° API paraffinic oils with a GOR of 250–300 to altered 10° API oils. Marked variations exist not only between oilfields but also between reservoirs in the same well. The observed trends can in most cases be accounted for systematically in terms of: early primary oil generation, migration and entrapment; and subsequent structural evolution locally involving the processes of biodegration, water washing and/or flushing, and oil remigration.
Prevalence of Headache Within a College Student Population: A Preliminary Analysis
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