Liquid CO2 Fracturing: Advantages and Limitations
Authors: Sinal M.L. , Lancaster G. 
Published: March 2010

Abstract
The concept of fracturing with 100% CO2 as the sole carrying fluid was first introduced in 1981. Development of this process was an extension of comingling CO2with conventional treatments to aid in the recovery of load fluids. Well stimulation with CO2has since increased dramatically. Our knowledge about its advantages and limitations has been acquired from completing over 450 liquid CO2hydraulic fracturing treatments.
Technological advances and operational procedures have improved considerably over the past five years. This paper will discuss the advantages and limitations of liquid CO2 fracturing. Results from various fields will be assessed to demonstrate the success of the liquid CO2 fracturing process.

Introduction
The first introduction of 100% liquid CO2 as a sole proppant carrier for sand fracturing to the petroleum industry occurred in 1981. Initial application of liquid CO2 fracturing was based on an assumption that the process would succeed, rather than extensive research. Canadian Fracmaster had undertaken approximately one year of laboratory research, before liquid CO2hydraulic fracturing was implemented in the field. Laboratory research into CO2 properties and viscosifying systems has continued since development of the process. Numerical simulation research was introduced in 1984 to understand better the fracturing process using liquid CO2. Recent developments in liquid CO2, fracturing, along with its advantages and disadvantages will be discussed in this paper.

History
Carbon dioxide as a liquefied gas, has been used in oil and gas field stimulation since the early1960s, because of its unique phase behavior (Fig. 1). It can be transported as a liquid at −20 °C to −40 °C. Because these temperatures are non-cryogenic, the CO2 can be pumped with conventional frac equipment and injected directly into the well as a liquid. The CO2 then vaporizes as it approaches equilibrium with reservoir temperature and pressure. The lower viscosity of the gaseous CO2, allows it to flow back from the formation to the wellbore. The gaseous CO2 also aids in lifting formation fluids that are produced back during the clean-up operation.
The most recent development in CO2 fracturing has been accomplished by injecting the proppant directly into 100% liquid CO2. The obvious benefits are the elimination of any residual fluid or residue left in the formation from the frac fluid.
Carbon dioxide fracturing Technology, developed in Canada, has been patented (Canada Patent No. 1134258, U.S. Patent No. 4374545, British Patent No. 8225692). The initial field implementation of this process was conducted on the Glauconite Sandstone in 16-10-27–8W4M, completed on July 16, 1981.
To date over 450 fracture treatments have been performed using liquid CO2 as the sole frac fluid. Of these producing wells, 95% were performed on gas wells, whereas 5% were oil wells. Wells with depths greater than 3100 m have been fractured with the largest emplacement of sand being 44 tonnes. Ninety-five per cent of the wells treated have been less than 2500 m deep, with up to 22 tonnes of sand placed (see Tables 1 and 2 for distribution of treatment size and depth).