Development of polyglycolic and polylactic acid fluid-loss control materials for fracturing fluids
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Fluid-loss is significant for the standard fracturing-fluids without adding solid materials. One method to reduce fluid-loss is to add silica flour, although it reduces fracture conductivity. Other methods are to use wall building polymers. However, the fluid-loss is still significant and complete removal of wall building materials are not possible even with breakers. We found that powder, granular and fibrous materials made of Polyglycolic Acid (PGA) or Polylactic Acid (PLA) are very suitable for fluid-loss agents since they are as strong as rock, while they dissolve as liquid acids after applications. Fluid-loss tests are conducted using the standard API slot tester and filtrate loss tester, mixing powders, grains and fiber, all made of PGA or PLA in frac polymer fluids. Ratio of grains, powder and fiber is optimized to minimize fluid-loss for porous media and fractured porous media. Then, the changes of particle size are measured under heated conditions. Fracture simulation studies are also conducted using a 3D fracture boundary element model to compare the fluid efficiency of the fracturing fluids with and without the PLA and PGA particles. The results show that the capability of preventing fluid-loss and plugging micro-cracks is maintained for the porous filters and small slots within reasonable time period. For short term applications less than 3 hours, both PGA and PLA fluid-loss agents are stable when the temperature is less than 212F. Mixing these materials often provides more efficient properties to reduce fluid-loss and to bridge micro-cracks. No residues are left after experiments if the fracturing fluid is kept being heated for 24 hours. The amount of the PGA and PLA fluid-loss agents required to reduce the fluid-loss is not significant. Hence, their field applications are feasible judging the cost and the benefit. The advantage in using these materials is that they turn from solid to liquid after applications so that no formation damage and no proppants conductivity damage occurs. The fluid-loss is also significantly reduced with the powder particles. In addition, because the PGA and PLA materials are degradable, solids with arbitrary sizes and shapes may be used as long as they control fluid-loss and plug fine fractures. Their applications are not only limited to reducing fluid-loss but they may be used for engineering fracture design to enhance the fracture conductivity. Copyright 2014, Society of Petroleum Engineers.
