Integrating Petrophysical Data and Dynamic Modeling in Estimating Original Gas-Oil Contact in Post Production Reservoirs

Abstract

Clearly delineating contacts are usually aimed at before development, but what happens when later data indicates contacts different from what have been interpreted? How do we ‘work back in time’ to re-estimate the original contacts? Our case study documents a reservoir which due to the poor well coverage, paucity of log data, side wall sample and pressure data, was initially interpreted as an oil bearing reservoir, however, a new well drilled post production of over 20 years indicated the presence of a huge gas cap, the size of which could not have been due to the formation of a secondary gas cap. This necessitated the determination of the original contacts in order to properly define the reservoir volumes which will impact on its future development. This paper presents the use of an integrated thinking approach which makes use of all the available geological, petrophysical and dynamic data in determining the original fluid contacts in a post production scenario. Reservoir simulation using simple tools as material balance combined with petrophysical and geological concepts were applied in this paper. The results obtained shows that the use of static data alone such as petrophysical logs in determining the original contacts for post production reservoirs can be greatly misleading as the results obtained may conflict with dynamic data available for the reservoir and therefore not fully representative of the reservoir and its history.