Paleostructural control of hydrocarbon production from the Cretaceous Niobrara in a part of the Denver-Julesburg Basin of Colorado and Wyoming

Abstract

Horizontal drilling and fracture stimulation of the Niobrara Formation chalks within the last decade have resulted in a widespread resource play in the Denver-Julesburg (DJ) Basin where over 50,000 vertical wells had already penetrated the Niobrara. The first fracture-stimulated horizontal Niobrara well in the DJ Basin was drilled in 2005. By the end of 2015, over 2000 horizontal wells had been drilled targeting the Niobrara and these new wells have made over 120 MMBO and nearly 500 BCF. Thickness changes correlate with the varying success of hydrocarbon production from the Niobrara in a part of the DJ Basin of Colorado. In the study area, the Niobrara comprises four chalks with interbedded marlstones; from top to bottom the A, B, and C chalks, and the Fort Hays Limestone. The Niobrara B chalk is the primary target for horizontal drilling; both the A and C chalk are secondary targets. The Niobrara Formation is self-sourcing and the hydrocarbons in the study area are not thought to have migrated. Within the study area, productivity in the Niobrara may be directly related to thermal maturity. Regionally thinner Niobrara trends are more likely to contain more productive wells than where thicker Niobrara is present. Thin intervals also coincide with higher resistivity values in the Niobrara B chalk and higher bottom hole temperatures. Temperatures were likely elevated in these locations in the past which led to increased organic maturity. Reservoir porosity and permeability may be enhanced along thin trends where shallow water currents winnowed sediments. Mapping the interplay of thickness, resistivity, and temperature of the Niobrara Formation can greatly improve the success rate of drilling in this play.