Horizontal Drilling in the Bakken Formation--The Hunt for an Elephant That Never Left the Source System

Abstract

New organic-geochemical studies show that bitumen extracted from the upper and lower shale members of the Mississippian Madison Group oils, and that the Bakken shales have contributed only a minor percentage of the conventionally produced oil in the Williston basin. Instead, organic-rich madison marls are an adequate source for the Madison oils. Also, few pathways exist for vertical migration of Bakken-generated oil to shallower Madison reservoirs. Vertical wells in older Bakken oil pools are perforated in one or all of the three units adjacent to the two Bakken shales but are not necessarily perforated in the Bakken shales. Rock-Eval analyses of 6- to 12-in. spaced core samples show that where Bakken shales are thermally mature, the three adjacent organic-poor units contain 10-20 times the hydrocarbons (HCs) they could have generated. Thus, Bakken-generated HCs appear to have moved into the three adjacent units, probably via fractures created by volume expansion of organic matter during HC generation in the Bakken shales. Bakken well histories reveal that unsuccessful Bakken wells appear due to questionable techniques during these operations and not a lack of fractures. If a large in-place resource base exists in the Bakken source system, its commercial recovery will depend on newmore » exploration, drilling, completion, and production technologies and on how much of the generated oil is in fractures rather than dispersed throughout the rocks.« less