A petrographic study of the subsurface Gallup Sandstone of San Juan County, New Mexico

Recent exploration by petroleum companies has resulted in renewed interest in the subsurface Gallup Sandstone of the San Juan Basin, New Mexico. The present study provides detailed petrographic descriptions of samples from six wells and interpretation of the data obtained. Locations of the six wells are such that they follow the line of strike of the formation, and lithologies are similar at all locations. Quartz is the predominant mineral in all cases, with cacite being the most important cementing agent. The sporadic occurrence of siliceous cement is fre31quent enough to present a factor for consideration in any program of rock treatment for the purpose of increasing permeability. The most favorable area for additional exploration is believed to be to the south and southwest of the line of wells studied.