Abstract

Over the past decade, shale oil becomes an important source of oil across the North America. Bakken Shale, one of the largest shale oil plays in the word, is producing about one million barrel oil per day. The main methods exploiting Bakken oil are drilling horizontal wells with multi-fracturing technology. Unfortunately, the oil rate declines rapidly from the initial high production. This decline is in part due to the deterioration of permeability resulting from the depletion of reservoir. Engineers and geoscientists cannot evaluate the relationship between permeability and pore pressure confidently without a permeability-pore pressure correlation developed from experimental data, although it is in general known that permeability declines as pore pressure is reduced. In this study, a large database was provided after the permeability were measured at different confining and pore pressure conditions for more than forty Bakken core samples. The significance of this study are: (1) measured data can be incorporated into reservoir model to simulate the reservoir performance to accurately forecast production from Bakken; (2) provided a correlation to calculate permeability as a function of pore pressure; (3) served as a guidance in analyzing other shale gas and oil plays whose reservoir characteristics are similar to Bakken formation.

1. INTRODUCTION

The Bakken Formation is a large unconventional reservoir in the Williston Basin, and covers parts of Montana, North Dakota, and Saskatchewan. The late Devonian to early Mississippian Bakken Formation consists of three members, the lower, middle, and upper. The upper and lower members are organic-rich shale, and the middle member contains sandstone, limestone, and dolostone [1].

Even though approximately 200 to 400 billion barrels of oil were generated [1] in Bakken Formation, the main method to exploit Bakken oil is drilling horizontal wells with multi-fracturing technology due to low permeability of Bakken Formation. However, the oil rate declines rapidly from the initial high production. This decline is in part due to the deterioration of permeability resulting from the depletion of reservoir [2]. Knowledge of the effect of pore pressure on the permeability of Bakken Formation is necessary in producing the hydrocarbon from Bakken shale.

This content is only available via PDF.
You can access this article if you purchase or spend a download.