--> ABSTRACT: Horizontal Drilling the the Bakken Formation, Williston Basin: A New Approach, by Julie A. Lefever; #91003 (1990).

Datapages, Inc.Print this page

ABSTRACT: Horizontal Drilling the the Bakken Formation, Williston Basin: A New Approach

Julie A. Lefever

Horizontal drilling is an attractive new approach to exploration and development of the Mississippian/Devonian Bakken Formation in the southwestern part of North Dakota. This drilling technique increases the probability of success, the profit potential, the effective drainage area maximizing recoverable reserves, and the productivity by encountering more natural occurring fractures.

The target formation, the Mississippian/Devonian Bakken, consists of three members in an overlapping relationship, a lower organic-rich black shale, a middle siltstone/limestone, and an upper organic-rich black shale. It attains a maximum thickness of 145 ft and thins to a feather edge along its depositional limit. Considered to be a major source rock for the Williston basin, the Bakken is usually overpressured where productive. Overpressuring is attributed to intense hydrocarbon generation.

Reservoir properties are poor with core fluid porosities being generally 5% or less and permeabilities ranging from 0.1 to 0.2 md. The presence of natural fractures in the shale are necessary for production. Two types of fractures are associated with Bakken reservoirs: large vertical fractures (of tectonic origin) and microfractures (probably related to hydrocarbon generation).

An economic comparison between horizontal and vertical wells show that well completion costs are approximately two times higher (average costs: $1,500,000 for a horizontal to $850,000 for a vertical) with average

payout for horizontal wells projected to occur in half the time (1.5 yr instead of 3.4 yr). Projected production and reserves are considered to be 2 to 4 times greater from a horizontal well.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990