Novel Morphology Self-Degradable Fiber Enables Enhanced Stimulation Fluid Diversion in High-Temperature Carbonate Formations
Authors: Pooniwala Shahvir , Malik Ataur , Khan Abdul Muqtadir , Plyashkevich Vladimir , Yudin Alexey 
Published: February 2022

In stimulation application, currently available degradable fiber-laden viscoelastic self-diverting acids (FLVSDA) are limited to moderate reservoir temperatures due to the lack of fiber integrity and stability. The upper bound temperature for current fiber is limited by the rate of polymer hydrolysis, which results in inadequate stability and fast degradation in an aqueous environment. As reservoirs are being encountered with higher temperatures, there is an industry need to expand the technology application to higher temperature environment (up to 350°F) for enhanced diversion and leakoff control.

A novel high-temperature degradable fiber (HTF) was developed with two distinct features. First, the modified polymer is used with a highly ordered structure, resulting in higher melting point and enhanced thermal and hydrolytic stability compared to contemporary mid-temperature fiber (MTF). Second, the morphology is crimped, which enables better material dispersion and plugging efficiency when designed with higher concentration. Comprehensive laboratory tests were conducted for degradation and stability comparison in neutral and acidic media to replicate real acid treatment conditions. Also, bridging tests in slot geometry were conducted to characterize the diversion efficiency of the fiber-laden slurries. Finally, the material was tested in fields with temperatures ranging from 290 to 330°F.

Fiber integrity and stability differentiated the performance of HTF and MTF at temperatures higher than 275°F. The critical point of HTF performance was achieved after 6 hours of exposure at 290°F in 100% spent 15% HCl with a concentration of 175 lbm/1000 gal US, whereas MTF is stable for less than 2 hours under the same testing conditions. The HTF demonstrated similar enhanced diversion efficacy when tested in more antagonistic media such as 50% spent acid. Fiber mass loss is considered as a characteristic of fiber stability, and premature fiber degradation compromises diversion effectiveness. To confirm the correct fiber shape at the degradation point, scanning electron microscopy (SEM) was used, and HTF showed no change in original shape and diameter. Pressure response at bridging was used as an additional characteristic for relative comparison of bridging ability for different fibers in laboratory conditions. A total of eighteen-stage acid stimulation treatments were conducted in six HT horizontal and vertical wells in fracturing and matrix acidizing modes using 51 fiber-laden diverter pills where significantly boosted diversion was observed with novel morphology fiber. Consequently, up to 30% to 40% production enhancement was observed in the wells treated with HTF due to effective stimulation fluids diversion and stimulation across the entire net pay.

The broad-spectrum of fit-for-purpose diverters plays a critical role in optimal treatment fluid distribution during acid stimulation treatments. Innovation in the material and morphology of the existing fiber portfolio adds essential value by allowing the wells to deliver higher production rates through improved diversion and optimum reservoir stimulation.