Subsurface DNA is an emerging independent diagnostic offering oil and gas operators a high resolution and non-invasive measurement of fluid movement in the subsurface. DNA sequencing methodologies that use subsurface DNA markers acquired from well cuttings and produced fluids are being increasingly used in the Permian Basin to elucidate drainage heights for new and existing wells with increased temporal and spatial resolution. Drainage height estimates are applied across the asset lifecycle during appraisal, development, and production. We present a new exploratory application for DNA Diagnostics in the Midland Basin as a complementary data set for understanding reservoir characteristics when existing wells and data are not available.
In this work, Novo Oil and Gas and Biota Technology performed a study on an exploratory well in the Meramec formation of Ector County. Well cuttings were collected from a pilot hole to create a vertical DNA baseline through key Barnett and Meramec formations, and from a lateral section to estimate per stage oil and water contribution. Frac fluid was collected during completion and produced fluids were collected through the initial 189 days of production. A data science-based workflow was performed that tracked DNA markers within produced fluids and compared them to a well-cutting derived DNA baseline to estimate per-formation and per-stage contributions in the vertical and lateral sections, respectively. DNA Diagnostic results were integrated into a reservoir engineering workflow through comparisons with petrophysical logs, core data, geosteering reports, completions reports, production data, and oil tracers.
Results showed that initial drainage heights covered a large portion of the Barnett into Woodford formations and corresponded to the higher initial production values. Over time, the DNA drainage heights indicated a focused zone of contribution from the Barnett which corresponded to a steady, flat decline curve. Lateral DNA contributions estimates indicated the highest production contribution from a section of the lateral drilled within the intended landing zone towards the toe, which was corroborated with conventional oil-based chemical tracers. Additionally, the lateral DNA Stratigraphy plots allowed for the development of a hypothesis of a potential fault encountered in the lateral, which subsequent wells will investigate.
Overall, we demonstrate that Subsurface DNA Diagnostics provides an independent workflow to estimate drainage height and lateral production allocation by analyzing DNA markers acquired from cuttings and produced fluids. This work shows the complementary nature of incorporating DNA Diagnostics into traditional reservoir engineering workflows as a hypothesis generating tool and as a corroborative measurement. The scalability and non-invasive nature of the workflow has the potential to improve initial characterization and operations during field development, particularly exploratory areas with less operational history. DNA Diagnostics provided direct economic benefit to Novo's field development plan and informed subsequent capital allocation strategies.
Link to URTEC abstract and full publication: SPE Publication