Abstract

Liquid carbon dioxide (CO2) fracturing technology is one of the waterless fracturing technologies. It has the advantages of avoiding the use of water, reducing damage, and increasing production by improving the reservoir pressure. However, the low viscosity of liquid CO2 and the difficulty to pump proppant are the main technical challenges. No conventional thickening agent can provide the required thickening used in 100% liquid CO2. In this paper, the problem of thickening gelled liquid CO2 has been solved by developing a new surfactant and thickening agent. Surface active agent can make the liquid CO2 gel by forming wormlike micelle or cylinder micelles structure. The cylinder micelles enhance the viscosity through entanglement inter-actions above a critical concentration.

Rheology and friction properties of liquid CO2 gel are evaluated through high pressure pipeline rheological experimental device. The viscosity of liquid CO2 gel fluid changes under different pressures (10 to 20MPa), temperatures (0 to 100 °C)and different shear rates. The experiment result shows that the effective viscosity of liquid CO2 gel fluid is between 7.654 ~ 20.012mPa.s. The liquid CO2 was thickening with viscosity increase at 86 to 498 times under the same conditions.

The field application of the new liquid CO2 based gel fracturing fluid in two wells of Jilin oil field in China shows that the production has been increased over 100%. 19.8 m3 of proppant has been successfully pumped to the reservoir in one well, and the mean proppant concentration is 6.8%.

Liquid CO2 based gel fracturing fluid provides a new fracturing system with less formation damage to fracturing operation. This paper will be beneficial to all engineers and technologists who are currently working at waterless fracturing applications.

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