Liquid CO2 fracturing is a novel stimulation technology, which helps realize multiple objectives such as conservation of water, sequestration of greenhouse gases and enhancement of single-well productivity and ultimate recovery. The blender used in PetroChina Jilin Oilfield is a huge vertical pressure vessel with a short auger conveyer at its bottom, which has poor sand controllability on sand feeding process. Making matters worse, the viscosity of liquid CO2 is very low, resulting poor sand-carrying capacity, which further enhances the difficulty on sand feeding.

Stability of sand feeding process is improved via coordination of multi-disciplinary systems. 1) Develop new additive system for liquid CO2, which can enhance the viscosity efficiently and has little damage to reservoir; 2)Adjust the auger conveyer structure to increase its control ability; 3)Ensure the pressure difference between in-tank and outlet of blender less than 0.05 MPa, by adjusting phase behavior of CO2 during treatment, liquid supplement rate to blender and opening degree of butterfly valve; 4) Apply casing fracturing instead of tubing fracturing, to enhance the pump rate.

Results are as follows. 1) Two new additive systems are developed, both can enhance the viscosity to 5cp with a dosage of 1wt%. 2) Tilted auger conveyer is applied, thus increases its controllability on sand feeding and accuracy on sand ratio measurement. 3) Small positive differential pressure between in-tank and outlet of blender forms easily in winter, but difficultly in summer. The reason is that the temperature is high and large amount of CO2 is gasified, resulting in the increase of in-tank pressure. In this case a heat exchanger is needed to sub-cooling CO2. 4) By apply casing fracturing technique, the pump rate can rise from 3m3/min to 8m3/min, make the sand feeding process much easier.

The sand feeding process of liquid CO2 fracturing is optimized via coordination of multi-disciplinary systems, which increases the sand ratio and total sand volume during fracturing, improves the construction stability, and eventually enhances the stimulation effect.

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