Effect of liquid nitrogen cooling on the permeability and mechanical characteristics of anisotropic shale

Long Jiang,Zhongying Han,Lipei Fu,Yuanfang Cheng,Qi Gao,Chuanliang Yan,Huaidong Wang

doi:10.1007/s13202-018-0509-5

Abstract

Liquid nitrogen (LN2) fracturing is a promising new technology for unconventional reservoir simulation because it can effectively solve problems related to low permeability, low brittleness, and water shortage. The present work conducted a series of permeability and strength property-related experiments to evaluate the effect of LN2 cooling on the permeability and mechanical characteristics of anisotropic shale. The main findings of the study are as follows: (1) The influence of the bedding direction on the permeability of anisotropic shale cannot be eliminated by LN2 cooling. LN2 cooling could effectively increase the initial natural damage and the pore space of anisotropic shale, possibly increasing the volume of reservoir stimulation and provide more channels for the seepage and migration of oil and gas. (2) After LN2 cooling, the strength and brittleness of shale are obviously reduced, leading to the decrease in the ability of shale to resist deformation and failure, thereby helping to decrease the initiation pressure of reservoir stimulation. (3) The brittleness of shale will markedly increase during cryogenic fracturing, thus helping to form more complex fracture networks. Based on the present research, LN2 fracturing has obvious advantages compared with hydraulic fracturing in increasing the volume of reservoir stimulation. The results of this study are instructive for understanding the synergistic mechanism of LN2 fracturing and evaluating the effectiveness of reservoir simulation.

Highlights

Shale gas, which has become an important unconventional natural gas resource all over the world, has exploitable reserves of approximately 207 × 1012m3, accounting for 32% of the total natural gas resources of the world
The permeability parallel to the bedding direction is significantly greater than those in other directions for the three treatment methods. This result reveals that the influence of bedding directions on the permeability of anisotropic shale cannot be eliminated by LN2 cooling
These results indicate that cryogenic fracturing using LN2 can increase the volume of reservoir stimulation and provide more channels for the seepage and migration of oil and gas, which can greatly improve the production of shale gas in unconventional reservoirs

Summary

Introduction

Shale gas, which has become an important unconventional natural gas resource all over the world, has exploitable reserves of approximately 207 × 1012m3, accounting for 32% of the total natural gas resources of the world To meet the special requirements of shale gas exploration to reservoir according to the properties and geological environment, it is the focus of petroleum industry to improve the effect of volume fracturing and identify a substitute for the water-based fracturing fluid (Middleton et al 2015; Wang et al 2016). Many new waterless fracturing technologies, such as liquefied petroleum gas (LNG) fracturing (Lestz et al 2007), nitrogen foam fracturing (Gupta et al 1998), liquid/supercritical CO2 fracturing (Gupta et al 1998; Middleton et al 2015), and cryogenic fracturing using L N2 (Mcdaniel et al 1997; Grundmann et al 1998; Cheng et al 2017), have been considered by many scholars

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