Technical Paper: Initial Characterization of an Extra Heavy Oil Carbonate Exploratory Field

Society: SPE
Paper Number: 153534
Presentation Date: 2012
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Reservoir discoveries are getting more difficult and complex. Currently in the Gulf of Mexico new Oil Fileds are being characterized. The presence of secondary porosity into dissolution cavities with extra heavy oil become in a complex challenge to characterize those exploratory reservoirs. Only 18 wells have been drilled in a total area of 1100 km2, with water depth between 100 and 680 meters. The API gravity varies between 6 and 13 ºAPI, which represent an adverse water-oil mobility ratio with a water-oil contact into fractures with high permeabilities. The main objective of this job is to show an advanced technique of Geosciences and Reservoir applied to an Extra Heavy Oil Carbonate Exploratory Field, to estimate the Original Oil in Place (OOIP) with probabilistic methods and define associated reserves to the field development.

The methodology applied starts with geophysics interpretation; Geo-statistics methods in the velocity model were used for depth conversion and a geo- mechanical model also was built for the development well design. The 3D Model includes: wells data, as well test, cores, electrical logs, horizons and faults in time and depth, geological tops, petrophysics, contacts and velocity model. Due to the high uncertainty, the 3D model integration was a challenge. The final result was a base case with a lithology and petrophysics properties distribution such as porosity, water saturation and net pay, used to calculate the OOIP.

Different workflows were used for the final result. Velocity variations were analyzed for the impact of each associated variable to the OOIP and understand area and thickness variability. Bayers Theorem was used for porosity, water saturation and net pay. Analogous wells by lithology were built, making more consistent the results and represent the reservoir in a best way possible into a numerical simulation model. Static and dynamic elements were integrated for reservoir and fluid behavior, including sensitivity analysis. The final result has uncertainty analysis, building of proxies and makes probabilistic forecasts to establish mitigation plans and define the more optimistic field development.

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