The pay zone of Sulige gas field is the most typical tight sandstone rservior in China. In recent years, multi-stage completion practices of vertiacal and horizontal wells brought about significant enhancement of single well production rate and economic benefit and caused a sharp increase of water consumption as well. Currently guar-based polymers are largely used in fracturing operations in Sulige gas wells. The system exhibit good rheological properties on one hand, and it can not meet the requirement of water saving, environmental protection and factory fracturing mode on the other due to its tendency to degrade, complex disposal and high cost. As a response, a low-cost recyclable fracturing fluid is developed and tried for the gas field.
A polyacrylamide polymer with surface activity is synthesized based on the consideration of reservoir characteristics, requirements in fracturing and well pad situation. The polymer and alkyl sulfonate surfactant additive formed a reversible structure in water by the action between hydrogen bonds and molecular chains. The fluid provides a good viscoelastic behavior and can meet the needs of fracturing treatment. It can be broken upon contact with formation fluid and rock minerals without destroying the molecular structure of the polymer. The flowback fluid can regain the viscoelasticity and be reused after simple settling and adding in proper dosage of the polymer. Lab experiment shows that the novel fluid has good temperature/shear resistance and excellent proppant transport capability. It is also easy to be cleaned up without leaving residue. Moreover, the performance of the recycled fracturing fluid can reach the level of that of prepared with fresh water. From 2014 to 2015, the recyclable fluid has been applied successfully in 230 wells in Sulige with a total volume of approximate 1,000,000 m3. The recovered flowback fluid is 400,000 m3, of which 380,000 m3 was reused. The recycling rate is as high as 95%. The fluid can meet the needs for continuous-mixing and low friction during treatment. The flowback fluid is also easier and less costly to be recycled in comparasion to guar gel fracs. These advantages promise its wide adaptability.