DEVELOPMENT AND FIELD PILOT OF A NOVEL VISCOELASTIC ANIONIC SURFACTANT (VAS) FRACTURING FLUID

A novel fracturing fluid called VAS (anionic surfactant type) has been successfully developed and applied in both oil and gas wells in China oilfield. VAS can not only eliminate matrix damage induced by fracturing fluid absorbing onto the formation which is usually negatively charged, but it also can lower the water‑sensitive and water‑lock damage to the formation. This paper presents the rheology, leakoff and conductivity of this fluid system together with its case histories. The stimulation mechanisms of this novel VAS fracturing fluid are also analyzed. Results, Observations, Conclusions: This novel VAS fracturing fluid inherits all merits of traditional VES (surfactant type) hydraulic fluid, but gets rid of the wettability reversal induced by VES. The novel VAS fracturing fluid mainly consists of an anionic surfactant, EDTA, KCl, and KOH. Each major additive of the fracturing fluid system has the functions to initiate fracture, transport sand and enhance production. Field pilot tests demonstrate that the wells using VAS as a fracturing fluid had much higher production rate and longer stabilized effective life than those using Guar gum as a fracturing fluid. Applications: Until February 2009, this novel fracturing fluid had been successfully applied to 16 wells in Nanyang oilfield with a total increased oil production of 9,373 tons. It also had successfully applied to 4 wells in Changqing gasfield with an average AOF of 15.53C_‑104 m3/d after fracturing stimulation. Technical Contributions: The novel hydraulic fluid can significantly reduce hydraulic fluid damage on formation and proppant bed due to the involvement of anionic surfactant. This novel VAS fracturing fluid has been used successfully in fracturing operation of Nanyang oilfield and Changqing tight gas reservoirs. Lessons and experiences to develop and apply the novel fracturing fluid will be illustrated.