Subsurface DNA Diagnostics™ is a low-risk, high-resolution evaluation tool offering oil and gas operators a measurement of fluid movement in the subsurface. DNA sequencing methodologies that use subsurface DNA markers acquired from well cuttings and produced fluids are currently used in all major US unconventional basins to elucidate drainage heights for new and existing wells. Dynamic drainage height estimations are especially important in field-wide development, when actionable turnaround time of drainage height estimates is a priority to improve subsurface understanding and maximize reservoir economics.
For this work, well cuttings were collected during drilling every 10’ MD from a 1000’ vertical section of interest in the Permian's highly stratified Wolfcamp formation. Subsurface DNA was extracted and sequenced from cuttings at the sub-formation level to create a robust DNA marker profile. Produced fluids were collected every 2 weeks through 140 days. DNA markers from each sub-formation were compared to every fluid time point using a Bayesian mixture modeling algorithm. This method produces an estimate of the relative contribution of DNA markers from each sub-formation for each fluid sample over time.
The result of Subsurface DNA Diagnostics is a novel subsurface log that characterizes DNA markers as a function of depth, and identifies the intervals with relative higher productivity compared to the other intervals over time. These drainage metrics are then overlaid with existing petrophysical properties to refine knowledge of oil and water behavior within different sub formations during a well's lifetime.
Subsurface DNA Diagnostic's use of well cuttings and produced fluids enables rapid scalability due to low-risk sampling (no downhole tools or lost production time) and minimal field personnel time. As such, an operator can relatively quickly characterize the drainage height of their field over time using several vertical baselines and a routine sampling protocol of producing wells in both exploratory, development, and producing phases of the asset.