Development of a new completion fluid using polyglycolic acid powder

Polyglycolic Acid (PGA) has been widely used as a string to stitch scars during medical operations. The string left in human body dissolves with time. It is harmless and biodegradable. Although these properties are attractive, the high cost prevents for oil field applications. However, a technology has been developed to produce tons of PGA with a low cost. Granular CaCO₃ has been used as a fluid loss control material for completion fluids. The mud cake has to be removed after completion instruments are installed, but tends to remain partially undissolved. The PGA powder turns to be a liquid acid with time if it is mixed in water. It is also environmentally harmless if it is disposed in ocean. It is judged that these properties may be suitable to replace the granular CaCO₃. The experiments consist of viscosity, fluid loss, and cake thickness measurements varying temperature and particle size distribution by using PGA powder as a fluid loss control material in a Xanthan Gum polymer completion fluid. Particle size distribution is optimized to minimize fluid loss. Then, the particle size change with time is measured. The mud cake consisting of PGA powder completely disappears after several days. The results show that the amount of fluid loss tends to decrease when the particle size is finer. Similarly, the thickness of the mud cake is significantly affected by the particle size distribution of PGA powder. It is proved that the PGA completion fluid has better mud properties compared with commercially available low solid polymer fluids. The advantage of the PGA powder as a fluid loss control material is (A) no permeability loss since it disappears with time in pores, (B) a low fluid loss since particle distribution is optimized to minimize fluid loss, (C) no acidizing is required after use since it dissolves itself due to hydrolysis, and (D) it is environmentally harmless.