Analysis of Nitrogen Stimulation Technique in Shallow CBM Formations

Abstract

Nitrogen (N2) stimulation has become the preferred technique for stimulation of coal seams in the Horseshoe Canyon play in Alberta. It consists of stimulating each seam by pumping at very high rates for short time (2-4 mins). Because the coal is producible at shallow depths, ERCB has been developing and updating regulatory guidelines that aim to protect the freshwater supply. This study was undertaken to improve the understanding of the process and provide recommendations on the regulatory guidelines for shallow depth (less than 200 m). The study was provided with extensive data from the industry (over 20,000 fractures in over 2000 wells) and has carried out several types of analyses in order to estimate fracture orientation and dimensions, and their dependence on N2 injection rate, duration and reservoir parameters. This included statistical analysis of large amounts of surface pressure data, pressure transient analysis of downhole pressure data, analysis of fracture mapping data, and conceptual simulations of the injection process using coupled reservoir and geomechanical models. Coupled geomechanical modeling provided realistic physical model of the process (in contrast to conventional models). Stress dependence of coal permeability and permeability anisotropy were shown to be the controlling mechanisms. This model was then used to investigate height growth mechanisms. After considering the results of the analysis, its limitations, uncertainties in geological description of the coal and shale sequences, available case histories, and other factors, recommendations were made for modifications of the ERCB Shallow fracturing Directive 27.

Efficient Use of Data Analytics in Optimization of Hydraulic Fracturing in Unconventional Reservoirs

“…In these reservoirs best working stimulation treatments are based on CO 2 and N 2 treatments (Cramer 2008). One of the examples for this kind of stimulation is Nitrogen stimulation for instance is Horseshoe Canyon in Alberta and has been stimulated effectively with coiled tubing (CT)-isolated N 2 fracturing (Settari et al 2010). The technique consists of isolating and sequentially treating individual coal seam with high rate nitrogen fracturing without proppant (Rieb and Leshchyshyn 2005).…”

A Study of the Effect of Freeze–Thawing by Liquid Nitrogen on the Mechanical and Seepage Characteristics of Coal with Different Moisture Content Values

“…In recent years, liquid carbon dioxide, liquid nitrogen, and other low-temperature fluids have been gradually applied to coalbed methane penetration mining [4]. Liquid nitrogen freeze-thaw penetration augmentation has the advantages of not polluting the reservoir, no hydration expansion, and high efficiency [5], and gasified nitrogen during penetration augmentation can reduce the partial pressure of methane gas in the coal seam, accelerate the resolution of coalbed methane, and improve the extraction rate of coalbed methane [6,7]. Therefore, it is necessary to further study the influence and laws of liquid nitrogen on the mechanical and percolation characteristics of coal samples with different water content values.…”