--> --> Abstract: Calcite Diagenesis, a Key Factor Controlling Petrophysical and Dynamical Behaviour of a Mature Field, by Frederic Brigaud and Frederic Pinçon; #90082 (2008)

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Calcite Diagenesis, a Key Factor Controlling Petrophysical and Dynamical Behaviour of a Mature Field

Frederic Brigaud1 and Frederic Pinçon2
1Geosciences, TOTAL EP Congo, Pointe Noire, Congo
2Geosciences, TOTAL, Pau, France

In field reservoir management, one of the main issues is to have a consistent view between geological understanding of the object and dynamic evidences of its behaviour. This becomes critical in mature fields, where enhancement of recovery is one of the main challenges. The question is “What are the critical geological heterogeneities controlling the dynamic split of the field?”
The case study is a mature field, located in the Gulf of Guinea, which has been producing since 4 decades with several tens of wells. It is a multilayered siliclastic reservoir divided laterally and vertically into seven main dynamic units. A new model was designed based on new seismic and well logs interpretations, and on new cores analyses (phi-K and mineralogy).

Heterogeneities due to lateral facies variations in the sedimentary model, and occurrence and magnitude of throws on the faults-pattern only partially explain the compartments. Intense calcite diagenesis occurring at basin scale affects the petrophysical characteristics of the reservoirs and has a direct imprint on their dynamic behaviour as evidenced on production logging tools and tests. Calcite will control the productivity of the reservoirs. At field scale, it will have no effect for volume <10%, it will reduce the reservoir productivity in the range of 10 to 30%. The reservoir will be completely tight for calcite >30%. Another interesting observation concerning the calcite coating in fault plans is that it is not necessary to have large throws to have the faults acting as dynamic barriers. This means that subseismic faults could play a role as dynamic boundaries of the field. This calcite property has been incorporated into the geological model and its impact has been quantified in the reservoir model, in terms of horizontal transmissivity. Reservoir simulations show a significant improvement provided with this model.

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