Well Log Mud Densities as a Proxy for Reservoir Pressures in the Delaware Basin

Reservoir pressure is becoming increasingly important for optimizing field development, identifying potential drilling hazards, and mitigating induced seismicity in unconventional reservoirs in the Delaware and Midland sub-basins. Despite its value, robust pressure datasets are extremely difficult to obtain since bottomhole pressure (BHP) is either not measured, not reported to regulatory agencies, or both. Furthermore, most existing pressure data is derived from historical drill stem tests which are rarely measured in sub-millidarcy permeabilities and have inherently limited spatial and stratigraphic extent. As a result, reservoir pressure is routinely the least understood subsurface parameter for operators and generally relegated to rules-of-thumb.
 
To solve this problem, we will examine the pros and cons of utilizing drilling mud densities derived from well logs to map pressure trends. Unlike BHP measurements and drill stem tests, drilling mud densities are (1) commonly measured at casing points above and below unconventional targets; (2) widely reported on well log headers; and (3) are frequently submitted to regulatory agencies for public access. This combination of factors has yielded a massive untapped data source in the basin, including 107k+ well logs in New Mexico’s Lea and Eddy counties alone.
 
Ideally, the lower and upper limits of drilling mud density are constrained by reservoir pressure and formation breakdown pressure, respectively. Furthermore, we expect mud density to be biased towards the lower limit to save drilling mud costs (i.e., less additives). Through these assumptions, drilling mud density, and its corresponding hydraulic pressure, can be used to map pressure trends both spatially and stratigraphically. Impressively, these trends are readily observed even when data is limited to one or two measurements per square mile. Using this approach, we see most well logs report mud densities from 8.4 to 11 pounds per gallon (ppg) across the central and northern Delaware basin and yield little-to-no new insights; however, a highly overpressured zone can be found in southeastern Eddy and southwestern Lea counties. Mud densities commonly exceed 12 ppg in this area and routinely climb to 15+ ppg (equivalent to 10,000+ psi at depth). This pressure cell coincides with the Bone Spring and Wolfcamp petroleum systems and continues (as expected) into Loving County, Texas. In contrast, mud density tops out at 11 to 12 ppg in the University Lands tracts in Andrews County, Texas – another hotspot for deeper drilling activity for the Barnett Shale. Based on this proof-of-concept, we will visualize changes in drilling mud density in map view and cross sections across the northern Delaware and Midland basins as well as the Central Basin Platform.
 
Registration closes on October 1st at 8AM.