Abstract

Vertical to sub-vertical faults, interpreted from structural analysis of 2D seismic profiles, are rooted in the Precambrian basement in the northeastern Williston Basin near Parshall and Sanish Fields in Mountrail County, North Dakota, and are observed to be related to mapped surface lineaments with respect to directional trends and location delineating structural zones which may be acting as effective reservoir boundaries. Analysis of 3,485 lineaments reveal three dominant lineament orientations of N 55° W (1°), N 60° E (2°), and N 75° W (3°), from lineament line-length based orientation analysis, and three additional dominant lineament orientations of N 80° W (1°), N 55° E (2°), and N 5° E (3°), as revealed from lineament frequency based orientation analysis. Similar analyses of fault orientation trends revealed three similar trends consistent with mapped lineament orientations of N 55° E (1°), N 50° W (2°), and N 75° W (3°). An overall lineament density of 1.5 lineaments per mi² (0.58 km²) is observed to increase from the northeast to the southwest across the study area. Comparative analysis of the apparent structural relationship between interpreted basement faults and mapped surface lineaments in the 2,259 mi² (5,851 km²) study area, reveal structural relationships between 74 interpreted faults and 181 mapped surface lineaments, oriented along; similar trends — a coincident relationship, in 19 cases (26 percent), near and parallel to the fault trend — an adjacent relationship, in 44 cases (59 percent), tying together the ends of two lineaments along the same orientation of a fault — a bridging relationship, in 15 cases (20 percent), and extending the trend of a fault along lineament strike — an extending relationship, in 35 cases (47 percent), suggesting that basement rooted fault traces have migrated upward into the overlying Phanerozoic sedimentary rock column and are expressed as lineaments on the surface. Areas where lineaments and faults with similar orientations coincide define seven larger linear structural zones that define subsurface boundaries or structural discontinuities within Paleozoic reservoirs which may be acting as reservoir compartmentalization boundaries. Generally, higher overall rates of production are correlative to areas of greater lineament density, suggesting a relationship between potential production and cumulative structural development.