Reservoir Characteristics for South Caspian Oil Fields

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Abstract Original field data reports from the Azerbaijan sector of the South Caspian Basin have been used to compile statistical histograms of reservoir characteristics for both onshore and offshore oil fields. Two groups of statistics are presented here: the first group discusses reservoir thicknesses, areas, volumes and horizon depths for the onshore and offshore fields; the second group discusses permeability, porosity, oil viscosity, oil recovery factor, reserves and production for the onshore and offshore fields. These statistical distributions have been constructed so that one has available an historical data base for use in assessing the range of likely reservoir characteristics in exploration ventures in this Basin. Introduction The oil fields of Azerbaijan, both onshore and offshore, have been in production for over 130 years. During that period records of varying quality have been kept concerning the attributes of individual boreholes, oil and gas production, and reservoirs. Many of the very early records are either extremely incomplete or lost, while those records prior to the second World War are dominantly cumulative summaries of yearly oil/gas production. During and since the second World War, however, extremely detailed records have been kept of hydrocarbon production and of reservoir formation properties. Indeed, many of the original field record books are still available and, what is more, so are many of the individuals who either kept the field data or added to the field data. Some of those individuals are still working in the area. Thus the ability exists not only to obtain the original field data but also to question individuals about specific entries. In addition, there are often discrepancies between the actual Field data records, and the political formal reports sent to controlling authorities of the time. We have had the good fortune to have obtained access to the original field reports (some handwritten and, later, some typed) in which a wealth of data exists concerning production statistics, reservoir properties, structural and stratigraphic trap types, etc. These records have been translated, the data checked and then loaded onto a modern computer. In this way it is a relatively simple exercise to persuade spread-sheet computer codes to generate statistical distributions for all information loaded. We have done so. Each attribute that one chooses to investigate must first be referred back to the comments in the original field data notebooks to ensure its veracity. We have done this as well. Some attributes are of a statistically more robust character than others, of course. For instance, the number of producing horizons per field, for both onshore and offshore fields, is clearly an extremely robust statistic and has been used (Bagirov and Lerche, 1998) to predict the likely occurrence of future oil fields. Also for instance, the spatial locations of the producing oil fields are known and so the spatial distribution of producing horizons per field can be used to suggest likely regions for high finding probabilities for hydrocarbons and to tie-in the observed distributions to the tectonic evolution and sediment supply for the South Caspian Basin since Miocene time after Tethys closure (Bagirov and Lerche, 1999). This paper considers a different group of statistical properties, also of a robust nature, but more directly related to reservoir characterization for the Basin.