Design, Optimization and Application of the Closed Blender for CO₂ Waterless Fracturing

The CO₂ waterless fracturing uses the liquid CO₂ to replace water as the fracturing fluid in reservoir stimulation. The continuity and reliability of the blender are key factors determining the performance of the waterless fracturing operation.

This paper proposed a novel closed blender, which introduces a vertical tanker for the operation, instead of a horizontal one. This modification can reduce the footprint and also effectively suppress the CO₂ gasification. The proppant supply is controlled collectively by the short auger rotation at the bottom of the blender, the opening adjustment of the proppant dosing butterfly damper and the liquid supplement rate of the blender tanker. Such proppant transportation combing the mechanical and non-mechanical approaches is able to ensure the proppant transportation stability and meanwhile greatly lower the maintenance cost.

The effective volume of the blender is 27 m³, and the maximum output flow rate is 8 m³/min, with a rated pressure of 3 MPa and a minimum operation temperature of −40°C. On the basis of the ground testing and field practice, the overall correlation among the liquid input, output, butterfly damper opening degree and the proppant transportation intensity has been well established, which facilitates the control of the system pressure and proppant supply. So far, the blender has been stably operated at the CO₂ waterless fracturing operation site for over 20 times. The pump rate can be up to 8 m³/min for a single operation, the sand transportation reaches 23 m³, and the liquid consumption amounts to 860m³. The proppant transportation is seen with good stability. The reservoir simulation performance is considerable, and the post-treatment production of the CO₂ waterless fracturing is 2.4 times that of the conventional hydraulic fracturing with an identical treatment scale.

The field practice suggests that the developed closed blender combines the advantages of both the vertical and horizontal blenders, and ensures the successful implementation of the CO₂ waterless fracturing operation.