Study reveals how to improve natural gas production in shale

A new study on hydrocarbons contradicts conventional wisdom about how methane is trapped in rock, revealing a new strategy for easier access to the precious energy resource.

“The most difficult problem facing the shale energy industry is the very low recovery rate of hydrocarbons: less than 10% for oil and 20% for gas. Our study provided insight into the fundamental mechanisms governing the transport of hydrocarbons in shale nanopores, ”said Hongwu Xu, author of the Division of Earth and Environmental Sciences at Los Alamos National Laboratory. “The results will ultimately help develop better pressure management strategies to improve recovery of unconventional hydrocarbons.”

Most of America’s natural gas is hidden deep in shale reservoirs. The low porosity and permeability of shale make it difficult to recover natural gas from narrow reservoirs, especially at the end of well life. The pores are tiny – typically less than five nanometers – and poorly understood. Understanding the mechanisms of oil retention at depth is essential to increase the efficiency of methane recovery. Pressure management is a cheap and efficient tool available to control production efficiency that can be easily adjusted while the well is operating – but the study’s multi-agency research team found a trade-off.

This team, including lead author Chelsea Neil, also from Los Alamos, integrated molecular dynamics simulations with novel in situ small-angle neutron scattering (SANS) to examine the behavior of methane in Marcellus shales. in the Appalachian Basin, the largest in the country. natural gas field, to better understand the transport and recovery of gas when the pressure is changed to extract the gas. The investigation focused on the interactions between methane and organic content (kerogen) in the rock that stores the majority of hydrocarbons.

The results of the study indicate that while the high pressures are beneficial for the recovery of methane from larger pores, the dense gas is trapped in smaller and common shale nanopores due to kerogen deformation. For the first time, they present experimental evidence for the existence of this deformation and propose a range of methane release pressure that has a significant impact on methane recovery. This information helps to optimize strategies to stimulate natural gas production and to better understand fluid mechanics.

The behavior of methane was compared over two pressure cycles with peak pressures of 3000 psi and 6000 psi, as it was previously believed that increasing the pressure of fluids injected into fractures would increase gas recovery. The team found that an unexpected behavior of methane occurs in very small but widespread nanopores in kerogen: the interstitial absorption of methane was elastic to the lower maximum pressure, but became plastic and irreversible at 6,000 psi. , trapping the dense methane clusters that have developed in the submarine. -2 nanometers pore, which encompasses 90 percent of the measured porosity of shale.

Led by Los Alamos, the multi-institutional study was published in the new Earth and environment communications newspaper this week. Partners include the New Mexico Consortium, the University of Maryland, and the National Institute of Standards and Technology Center for Neutron Research.