Novel CO₂ Foamed Fracturing Fluid for Acid Fracturing: From Lab to Field Deployment

Carbon dioxide (CO₂) foamed acid fracturing is gaining importance in maximizing flowback recovery. Under reservoir conditions, CO₂ is absorbed by water and transformed into carbonic acid. This paper presents a systematic approach to deploying in the field a novel CO₂ foamed fracturing fluid during acid fracturing.

For CO₂ foamed acid fracturing treatment, it is crucial to design pad stages using foamed fracturing fluids. The thermal stability of foam at high temperature is one of the main challenges. In this work, a CO₂ foaming acrylamide based terpolymer fracturing fluid was developed for temperatures up to 350°F. A circulating flow loop foam rheometer was used to measure the rheological behavior of foamed fluid. For successful field deployment, CO₂ foamed fracturing fluid was evaluated in the following sequence: chemical management, quality control, pre-job lab testing, compatibility testing, field mixing, on-site QA/QC, friction analysis and execution of main treatment.

In this study, a linear gel having 25 cp viscosity at 511 1/s share rate was prepared using a 35 ppt polymer loading. The foaming conditions were measured on site using a blender test. Static foam stability, which describes the change in foam height or liquid drainage with time known as foam half-life. Using the blender test, around 66.6% foam quality was achieved, which gave a 40-minute foam half-life. The compatibility of foamed frac fluid was also measured by mixing different ratios with acid blends and other diversion fluids. The rheological properties of CO₂ foamed linear gel were studied at 75% foam quality and two different temperatures. It gave 64 cp at 100 1/s at 300°F and slightly decreased to 54 cp at 350°F, measured at 2000 psi. The field performance of CO₂ foamed fracturing fluids was evaluated for two wells, one single stage vertical wells and another six staged horizonal well. Each stage utilized approximately 200 tons of CO₂. The stability of CO₂ foam depends upon the optimum hydrophilic-lipophilic balance (HLB) of surfactants, and it was achieved was achieved by optimizing various formulations using suitable surfactants with fracturing fluid as an external fluid.