Assessment of communication between water injectors and oil producers is a key issue to implement improved oil recovery programs. This paper presents an innovative use of isotope ratio water sample analysis to characterize injector-producer communication and intra-reservoir connectivity in a mature field.

Salt analysis is the standard approach to differentiate injection water from formation water, and assess water injection sweeping efficiency. This requires the brines to have different compositions. However, interactions from the mixing of the two waters or with the formation can prevent reliable information from being obtained from such analyses.

The isotope ratios of water samples are not sensitive to these interactions. This technique is often used in exploration to assess inter-reservoir connectivity at the delineation stage. This paper shows the successful application of isotope ratio analysis to the complex Mishrif carbonate reservoir of the mature Al Khalij field located offshore Qatar. The field has been in production since 1997 and water is injected from a shallow aquifer, while coning from a bottom aquifer is suspected.

In this field, Strontium, Oxygen and Deuterium isotope ratio measurements were carried out on samples collected from a number of wells across the field. This technique enabled us to assess the percentage of injection water produced at each well, and assist in optimizing water injection management.

Interwell tracing and water injection

Water injection is the most common secondary recovery process. Injection optimization requires a correct assessment of interwell communication. This is all the more valid in carbonate reservoirs which are commonly fractured; the dynamic impact is usually difficult to assess with static data such as wellbore images or seismic. Production logging or interwell tracing are among the most applied and valuable monitoring techniques to evaluate this impact.

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