Maximizing the recovery factor achieved through water flooding depends on acquiring a detailed understanding of the vertical and areal sweep efficiency. DNA diagnostics can monitor changes in oil contributions from multiple zones and from injectors, becoming a leading indicator for the potential of water breakthrough, loss of injectivity, and the overall advancement of the water front when combined with subsurface information. This allows for proactive management of injection rates and timing to maximize recovery rates for green fields and brownfields alike.
DNA diagnostics use DNA markers acquired from microbes. DNA markers of produced fluids are compared to the DNA markers of injected fluids to establish relationships and shared fluid flow. This paper will cover the end to end workflow for long term waterflood monitoring:
Establishing end members, even for a mature field, with the use of new samples from offset wells, properly stored samples from existing wells, and the analysis of commingled samples in combination with the subsurface model.
Establishing the level of similarity between injectors and producers as an indication for the progression of the waterflood front using methods including Principal Coordinate Analysis (PCoA) of DNA marker profiles.
Performing time series analysis and establishing sampling periodicity for effective waterflood monitoring.
A pilot project, consisting of 12 producers and 3 injectors in a conventional California reservoir, was conducted to prove the concepts and further develop the required analysis for waterflood monitoring. Fluid samples were taken weekly on each well over 3 weeks to establish the difference in DNA markers between the fluids. The DNA markers were used to determine the probability that injection fluid was being produced from the surrounding wells. These results were overlaid to temporal changes in the Total Fluid Logs. Taken together, the results correlated and confirmed previous water breakthrough information and provided insights into arial and vertical conformance changes. Additionally, the project provided new insights into strength of producer and injector connection based on geological features and with that informing future infill drilling decisions.
Waterflood monitoring is a powerful application for DNA diagnostics that is deployable on new and existing waterfloods. The spatial and temporal monitoring limitations of modeling or tracer studies can be improved upon through this non-invasive diagnostic. Initial results demonstrate the insights that can be provided not just for monitoring the waterflood but also for further field development decisions.