ABSTRACT:
With the development of horizontal drilling and hydraulic fracturing in recent years, unconventional formations, such as the Bakken Formation have come into the foreground of the oil and gas industry. However, due to its heterogeneity and ultra-low permeability and porosity, the Bakken Recovery Factor remain low (5%-10%). Permeability is a key factor to predict the fluid flow in porous media. Therefore, the investigation of measurements accuracy is crucial to ensure successful assessment of future field development planning. Since various methods of permeability measurement can yield different results, a thorough understanding of these methods and their differences is essential. In this work, we compare the results of steady-state, Aspike and Multi-pulse permeability measurement methods. The steady-state method shows a low sensitivity to the confining pressure and the measurements can widely vary depending on the pore-fluid type (i.e. nitrogen or water). The range of permeability measured by the Aspike is 10 times higher than the Multi-pulse. The results of permeability tests on 37 Bakken core samples shows that the Multi-pulse values present a narrow distribution and high sensitivity to formation heterogeneity even when the permeability is within a nano-Darcy range. Also, we investigated the effect of anisotropy on permeability measurements using the Multi-pulse method. Overall the horizontal permeability is higher than 45°and vertical directions. At some location the Multi-pulse shows higher permeability in 45° direction which complies with the bedding direction at that specific location.
1. INTRODUCTION
Permeability is a property of rocks that characterizes the ease with which fluids can flow through it in response to an applied fluid pressure gradient, as defined by Darcy, 1856. Effective reservoir performance analysis, simulation, and field development planning requires an accurate evaluation of this property. Several methods are proposed to measure the permeability, which are all based on the interpretation of single-phase fluid flow and pressure transient (Brace et al, 1968; Fischer, 1992; Kranz et al, 1990; Boitnott, 1977).
