Improved Reservoir Fluid Estimation for Prospect Evaluation Using Mud Gas Data (Frode Ungar, Equinor ASA)


Frode Ungar from Equinor ASA


Maria Cecilia Bravo, Gulnar Yerkinkyzy, Tao Yang, Equinor ASA


Reservoir fluid estimation for exploration prospects can be rather random and of large uncertainties. Typically, the reservoir fluid estimation in a prospect can be derived from a geochemical basin model or seismic data interpretation with regional knowledge. An analog reservoir fluid sample will often be selected for reservoir fluid estimation. Such analog samples can come from a neighboring field at some distance. The best approach for accurate reservoir fluid estimation is based on the reservoir fluid data from nearby wells when available. This paper demonstrates that mud gas data from wells in or close to the exploration prospect provides a much-improved reservoir fluid estimation.

In our previous work, we developed novel methods to estimate reservoir fluid properties from advanced and standard mud gas data. This paper uses two field cases to illustrate how mud gas data can be translated into reliable reservoir fluid estimations for prospect evaluation for potential developments. We have standard mud gas data available for the two field cases. One example is a prospect evaluation with a single legacy well without reservoir fluid samples. Another example is a prospect evaluation of overburden for potential production.

For the first prospect, the geochemical basin model is available with guidance on reservoir fluid filled in the reservoirs. The analog reservoir fluid samples are from a nearby field with both reservoir oil and gas. The consistency of the existing methods is poor and leads to high uncertainty for prospect evaluation. The reservoir fluid estimation is crucial for the decision of an appraisal well and the potential development of the prospect. We utilized the mud gas data from the legacy well to improve the reservoir fluid estimation. The new reservoir fluid estimation is oil-prone and leads to a positive decision on drilling the prospect. The second prospect is the overburden of a different field. Due to the good experiences from near fields on production from overburden, the reservoir fluid estimation is required to distinguish if the reservoir fluids in the overburden are similar to those in reservoir zones or have an independent fluid system. We used mud gas data from a well close by sharing the same overburden formation. The results show the reservoir fluids in the overburden are close to those in reservoir zones.

The new method using mud gas data provides accurate reservoir fluid estimations for two prospect evaluations with significantly reduced uncertainty. The implementation of the new method for prospect evaluation has not been reported previously. Due to the wide availability of mud gas data, the new method can be broadly implemented for most prospect evaluations and generates large business impacts.


Education: Msc. Petroleum Engineering, Heriot-Watt University Experience: Reservoir Engineer, Production Engineer, Project Leader. all Equinor ASA Current role: Principal Engineer, PVT and Fluid phase behaviour, Equinor ASA