Abstract

The U.S. Department of Energy (DOE), National Energy Technology Laboratory has been conducting research on low permeability gas reservoirs for over 30 years. Major field experiments like the multiwell experiment and the multi-site experiment at Rifle, Colorado, have provided tremendous insight into the characterization of low permeability gas sands, the associated natural fracture network, and the implications of hydraulic fracturing. Since the early 1990's, the DOE has focused its research efforts on developing technologies and methodologies to detect and characterize natural fractures in the subsurface and on demonstrating methods for enhancing production.

Several successful technology advances are expected to have significant impact on the recovery of natural gas from low permeability formations. A horizontal well recently completed at 15,000 feet in the Frontier Formation in Wyoming, in conjunction with Union Pacific Resources (UPR), initially flowed 14 MMcfd and in the first 9 months recovered 2.75 Bcf of gas. UPR has two more wells underway and plans to drill additional wells based on the success of this project. Natural fracture detection techniques have been successfully demonstrated in existing fields in the Piceance and Wind River basins. An integrated 3-D seismic and geomechanical modeling approach was demonstrated in the Piceance basin and more recently in conjunction with the horizontal well drilled by UPR/DOE. The use of 3-D seismic attributes was demonstrated in the Wind River Basin.

DOE initiated several new projects to begin work in October 1999 that will

  1. demonstrate the use of natural fracture detection technologies as an exploration tool and

  2. advance the state-of-the-art in natural fracture detection by developing new techniques to quantify fracture properties that control the flow and transport of gas.

This paper will provide a detailed discussion for the projects that have recently been completed and for the new projects along with their implications for enhancing gas production from low permeability gas reservoirs.

Introduction

As new discoveries from conventional supplies decline, future supplies of natural gas will increasingly have to come from low permeability (tight) reservoirs. Basins containing significant resources and reserves include the Greater Green River, Piceance, Wind River, Uinta, and Anadarko. Other basins and plays also hold large resources of gas. The 1992 National Petroleum Council's (NPC) natural gas study1 concluded that 232 Tcf could be technically recoverable from low permeability sand formations. Assuming that technology improvements continued, the NPC estimated that 349 Tcf could be produced. In their most recent study2, the NPC states that "deeper wells, deeper water and nonconventional sources will be the key to future supply." Nonconventional production in the Rocky Mountain region is projected to increase by 1 Tcf per year by 2010 and as much as 1.5 Tcf per year by 2015. Significant technology hurdles must be addressed and overcome to assure a cost-competitive supply from these sources.

Gas production from low permeability formations is hindered by the formations' capability to allow gas to flow to the wellbore. Hence, economic production of natural gas can only occur where the flow path to the wellbore is enhanced. Geologic processes have created natural fractures in most formations that provide channels for gas to flow. In areas where the natural fracture network is extensive and dense, economic production can be achieved without wellbore enhancements. However, most low permeability formations require hydraulic fracturing to connect the wellbore to the formation to allow commercial production. The challenges facing industry are locating the areas of dense fracture networks and determining whether horizontal wells or vertically stimulated wells are more economical.

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