Monitoring Double-Porosity Reservoir using Artificial Water Tracers : A Field Case Study

Juilla, Hugo
Total, Paris, France

This paper describes the improvement of our understanding of the complex flow dynamics in a double porosity water flooded dolomite field thanks to the valuable input provided by a water tracing campaign where new analytical methods were applied to detect extremely small tracer quantities and to interpret a non expected late tracer breakthrough.

Vert-le-Grand field, located in the French Paris Basin, produces medium oil from a double porosity reservoir (sandstones and dolomites alternations) of Chaunoy formation. Producers are completed in the dolomite layer whereas the only water injector is completed in the underlying sandstone. None laterally continuous vertical barriers are present between sandstones and dolomites limiting the effective water flooding but not the dynamic communication. The field pressure support is completed by an eastern lateral aquifer.

The main objective of the tracer injection was to confirm the existence of a preferential path between the injector and the producer wells. The well tests interpretation performed on two producers (VLG1 and VLG4) suggested the existence of a North/South fracture going through the injector. This hypothesis was accepted to explain the water breakthrough at the producer's wells although it was difficult to prove it only with the well test data.

Tracer injection was carried out in 2009 and monitoring is still on-going. Well known environmental friendly FBA tracers were used along with a thorough sampling program. Nevertheless, the tracer injection is an old technique in the oil industry. In this case, the tracer detection was not straightforward and classical analytical methods were useless. In fact, the limited vertical communication and the reservoir sweeping by an active aquifer delayed the tracer breakthroughs one year after the injection (quite after expectations) and in very small quantities due to a severe dilution. That is the main reason why the analysis procedure was improved to be able to detect the tracer breakthrough and to perform a satisfactory results interpretation. Water samples were analyzed twice using the new method in order to confirm the results.

This paper describes the improvement of our understanding of the complex flow dynamics in a double porosity water flooded dolomite field thanks to the valuable input provided by a water tracing campaign where new analytical methods were applied to detect extremely small tracer quantities and to interpret a non expected late tracer breakthrough.

Vert-le-Grand field, located in the French Paris Basin, produces medium oil from a double porosity reservoir (sandstones and dolomites alternations) of Chaunoy formation. Producers are completed in the dolomite layer whereas the only water injector is completed in the underlying sandstone. None laterally continuous vertical barriers are present between sandstones and dolomites limiting the effective water flooding but not the dynamic communication. The field pressure support is completed by an eastern lateral aquifer.

The main objective of the tracer injection was to confirm the existence of a preferential path between the injector and the producer wells. The well tests interpretation performed on two producers (VLG1 and VLG4) suggested the existence of a North/South fracture going through the injector. This hypothesis was accepted to explain the water breakthrough at the producer's wells although it was difficult to prove it only with the well test data.

Tracer injection was carried out in 2009 and monitoring is still on-going. Well known environmental friendly FBA tracers were used along with a thorough sampling program. Nevertheless, the tracer injection is an old technique in the oil industry. In this case, the tracer detection was not straightforward and classical analytical methods were useless. In fact, the limited vertical communication and the reservoir sweeping by an active aquifer delayed the tracer breakthroughs one year after the injection (quite after expectations) and in very small quantities due to a severe dilution. That is the main reason why the analysis procedure was improved to be able to detect the tracer breakthrough and to perform a satisfactory results interpretation. Water samples were analyzed twice using the new method in order to confirm the results.

Due to these methodology improvements, tracer campaign was considered successful as the obtained results help to identify the high-permeability paths where injection water goes through. Although the tracer injection is done at the south, the tracer broke through successively at producers from North to South (and first of all at the more distant producer well) proving definitely the existence of the fracture highlighted by the well tests.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012