Seeing Beyond the Obscure Fluid: How an Enhanced Production Logging Approach Helped to Improve the Workover Design

Abstract

Abstract Typically, well workovers are performed based on production logging results. However, efforts to shut down water-producing layers may result in the opposite effect, such as increased water cut and decreased oil production. Hydrocarbon inflow behind the stagnant water at the bottom of the well that cannot be measured by typical production logging tool (PLT) sensors and may cause interpretation errors. As no alternative tools are available on the market, an enhanced evaluation approach is required to interpret the hydrocarbon inflow behind standing water column. Characterizing producing intervals in heterogeneous reservoirs with various saturation levels and low pay is difficult with only open-hole (OH) logs. A standard PLT approach based on spinners and density readings may not identify the oil and gas entry across stagnant water in vertical wells. Therefore, an enhanced procedure for PLT was developed. The flow behind the static or moving water column was first identified using a combination of pressure derivative (dP/dZ), temperature (dT/dZ), and density data. The zones with high dP/dZ fluctuations were used for potential hydrocarbon inflow. Secondly, the weighted average of the density trend was used to break down the potential hydrocarbon entry behind the water. The dT/dZ variation was input into the HC exact production. The OH results used for PLT correlation improved the final interpretation. Two cases with multiple historical PLT were evaluated for this study. In Case 1 (Well x02), PLT was carried out three times over a four-year period, and the water cut increased following production based on the standard interpretation. Different workovers were attempted to shut off water inflows, both successful workover that led to a 27% increase in oil production and a 68% decrease in water production was possible after the improved interpretation of three-phase flow from the enhanced PLT approach. In Case-2 (Well x06), the new technique confirmed a masking behavior of water to the wellbore fluid flow, and the interval above was selected to guarantee the evaluation from the lower part. The study shows that the new approach to interpretation successfully quantified zonal contributions, helping to enhance the workover strategy and mitigate the increase in water cut level of up to 30%. The improved PL interpretation workflow demonstrates that traditional PLT interpretation cannot be directly applied to reservoirs with three-phase flow and the objective of reducing water cut. The enhanced technique has good potential for successful interpretation and helped to reduce water production.