Tracer and Streamline Modelling for Pattern Validation and Improved Reservoir Modelling
Authors: Ahonsi Wilson , Lager Arnaud , Al Muhairi Layla Saleh , El Mahdi Ahmed 
Published: September 2016

Carbonate reservoirs are notoriously complex and difficult to characterize, due to their inherit homogeneity. The ability to understand and model such homogeneity accurately, leads to better reservoir management and improved field development strategy in terms of well placement and optimized well patterns. Dynamic reservoir model was built from the static geological model i.e. using MDT, pressure volume temperature (PVT), routine core analysis (RCA) and special core analysis (SCAL) etc. As part of the reservoir model validation process, history matching of the model was conducted to match the observed data. After history matching was completed, tracers injection analysis and streamlines modelling was conducted in other validate the reservoir model, the well patterns and improved the full field development strategy. The full field development scheme includes water alternating gas (WAG) miscible hydrocarbon gas injection, with 5 observers covering both the flank and crestal locations.

The tracer analysis included the injection of 11 different tracers in 11 different injectors, and the monthly monitoring of the producers within the well pattern. Streamline model was built simultaneously from the convention compositional model, in order to analysis and predict the different tracers break through times i.e. both observed from the field and simulated. In addition to this, streamline time of flight (TOF) analysis, the effect of tracking of different tracer components, geological and geophysical impact was evaluated, in order to improve the breakthrough time match between observed and simulated time.

As a result of this analysis reservoir management improved, as the source of increasing higher GOR in specific wells were discovered. Remedial actions were recommended to help reduced the increasing high GOR in the respective wells. Also the field development strategy improved, as injector's contribution per well pattern well was quantified. As a result injection could be redistributed. In producer wells with little or no support from their respective injectors, a plan was made to ensure that such patterns could be close appropriately. This improved and maintains the voidage replacement ratio (VRR) in the field, according to reservoir guidelines. This paper describes how by using gas tracer injection and streamline modelling reservoir management and field development can be improved.

In addition to the improvements in reservoir management and field development strategy, several lessons learnt and best practice were suggested from the tracer and streamline study conducted. They include but are not limited to; Different tracers can show different concentration level at breakthrough wells.Wells further away from injectors can show earlier breakthrough than well close to injectors, as it is dependent on reservoir connectivity.In analyzing model breakthrough times, the measurable tracer in the field needs to be used, as opposed to the actually first breakthrough seen in the simulator. As below such concentration cannot be measured.Operational changes in wells need to be captured properly in the simulator, in order ensure improve prediction of tracer breakthrough times.