Waterflooding involves injecting water into a reservoir, usually to increase pressure and thus stimulate production. However, when this action is being performed in a multi-layer reservoir it requires constant monitoring to identify the potential for water breakthroughs and target intervals not flowing, that may affect fluid production. The operator’s main goal was to gain a quantitative assessment of the flow contributions from each layer in the producer well, particularly in the undersaturated reservoir areas which hold free gas behind the tubing and casing.

The operator selected TGT’s Reservoir Flow product which is delivered by the True Flow diagnostic system, using Chorus (acoustic) and Cascade (thermal) technology. Reservoir Flow complements conventional Wellbore Flow (conventional production logging) diagnostics by evaluating flow profiles behind casing.

The diagnostic programme for data acquisition involved two passes for flowing and shut in surveys. The Chorus surveys revealed the flow contribution from each layer, which is a significant advantage over conventional production logging (PLT).

The producer under investigation was completed for separate production from two
sections of the multi-layer reservoir, with the upper section gathering production through the sliding sleeve door (SSD).

The diagnostics were performed across the target reservoir (Figure 1). Chorus (acoustic) platform captured multiple high-amplitude, broadband, depth-specific acoustic signals across the most permeable layers in both the flowing and shut-in regimes showing the fluid flow through the reservoir layers. The acoustic signals observed in the long shut-in regime indicated the presence of multiple wellbore crossflows, due to formation pressure differences between the layers and the heterogeneity of the oil displacement. Cascade platform made it possible to estimate the production profiles across both sections of the multi-layer reservoir, including the one behind the tubing, which was not possible by using PLT data alone.

The diagnostic results provided the answers the operator needed to plan an effective workover. Plan included the zonal isolation of water filled layers and a well recompletion that would improve waterflooding performance and increase recovery.