Fluid Distribution Model for Structurally Complex Reservoirs in El Carito-Mulata and Santa Bárbara Fields, Venezuela

Carpio, Gelson (PDVSA Gas & Oil) | Rodriguez, Fernancelys Del Carmen (PDVSA Gas & Oil) | Khan Torres, Karem Alejandra (Petroleos de Venezuela S.A.) | Contreras, Anairt Lisseth (Petroleos de Venezuela S.A.) | Campos, Luis S. (Petroleos de Venezuela S.A.) | Idrogo, Crimilda (Petroleos de Venezuela S.A.) | Labastidas, Eduardo (Petroleos de Venezuela S.A.)


El Carito-Mulata and Santa Bárbara fields are located in Eastern Venezuela in the Maturín sub basin and cover almost 300 km2. The asymmetrical anticline of the reservoirs is the result of different tectonic regimes alternating compressive and extensive periods from the late Cretaceous to the Middle Miocene. The fields are producing 240,000 STB/D and their OOIP is estimated to be around 6.5 MMMSTB. The variation of the vertical fluid distribution is predominant. There is a light oil (condensate) at the top of the structure, black oil at the base and free water at different levels in the reservoirs. This vertical fluid distribution is not well represented in the
dynamic simulation model, which increases the uncertainty on any prediction or elaboration of the production plan.

The main objectives of this study are the determination of the original fluid contacts and the construction of a fluid model, which takes into account the free water presented in the reservoirs. This model can also define the vertical and lateral extension of the oil fields, indispensable for the reserves estimation.

The integration of the different kinds of static and dynamic information of 149 wells was necessary in order to obtain a well-supported fluid distribution model.

The analysis of the large number of data allowed defining the geometry of the Tar mat (asphaltene content > 20%), which is folded/faulted according to the structure and considered as a sealed layer in reservoir conditions, with thicknesses ranging between 300 and 500 feet. The irregular Tar mat surface limits the reservoirs and controls the free water levels in the fields. This new fluid distribution model was included at the numerical simulation model matching all the wells information about water or type of oil that has been produced or tested.