Laboratory and Field Evaluation of a Combined Fluid-Loss-Control Additive and Gel Breaker for Fracturing Fluids

Abstract

More than 200% increase in fracture conductivity and permeability was obtained when a new degradable fluid-loss-control additive was used in place of silica flour (SF) in 40-lbm crosslinked hydroxypropyl-guar (HPG) fracturing-fluid systems. The new additive, an organic acid particulate (OAP), slowly degraded into water-soluble monomeric units at temperatures ~ 150°F after fracture stimulation experiments. The high-acid-content degradation product then acted as an excellent HPG gel breaker and effectively cleaned the proppant packs.As a fluid-loss-control additive, the measured wall-building coefficients were as good as, or better than, those of SF in crosslinkedgel, linear-gel, and N 2 -foam systems. This paper summarizes a 2-year study of the evaluation and application of this new product in fracturing-fluid systems. IntroductionRecent studies showed that HPG gels used in fracturing-fluid systems cause significant proppant-pack damage. 1-5 This study was aimed at finding a way to minimize fracture conductivity damage while HPG gel is used as a base fluid for fracturing stimulations.The new additive evaluated for a combined fluid-loss-control additive and gel breaker is an OAP-i.e., a polyester. The organic ester exposes increasing acid functional groups when degraded to soluble monomers. (The hydrolysis rates are a function of temperature and pH, as Table 1 shows.) Therefore, when the additive degrades after a fracture stimulation job, it imposes minimal formation damage. At the same time, when the degraded parts (acid) further break the linear and/or crosslinked gel used in fracturing fluids, the fracture conductivity is significantly increased. The HPG crosslinked polymer breakdown will occur because of the decrease in pH caused by the degraded parts of the OAP's and/or the crosslinking metal may be chelated by the organic acid monomer. Tyssee and Vetter 6 found that the HPG polymer degradation method may be backbone cleavage when the fluid-system pH is lowered.Because the OAP is a particulate, it will be retained in the gel filter cake when the fluid leaks off to the formation. As a result, the filter-cake cleanup should be much more efficient with a combined fluid-loss-control additive and gel breaker. The conventional water-soluble gel breakers leak off to the formation much more easily. To minimize the formation damage caused by unbroken gel during a spurt-loss stage, this volume could contain conventional soluble breakers. Our primary objective here, however, was to increase the fracture conductivity by minimizing the damage caused by the filter cake and residual gel in the fracture.Controlling fluid leakoff is also important in hydraulic fracturing. As Howard and Fast 7 show, fluid-loss characteristics of a fracturing fluid will influence fracture extension. To achieve an effective fracturing treatment, the fluids must have minimum leakoff while carrying the proppants. High fluid loss to the formation may cause ~remature termination of fracturing treatments by "sandouts." As a result, the OAP's have to b...

Research Advances of Microencapsulation and Its Prospects in the Petroleum Industry

“…Microcapsules used in this area probably require a much tighter coating to protect their active cores, while the outer membrane for the rupture mechanism is expected to have the characteristics of easy breakdown under the appropriate conditions [70]. As mentioned above, many types of natural and synthetic polymers are being explored, such as gelatin, chitosan, polyvinyl alcohol, and methylcellulose.…”

“…It is widely understood that additives, when applied in oil recovery, have to have excellent properties regarding salt tolerance, adequate mechanical stability, and temperature resistance [ 69 ], to allow for efficiency in the whole process. Microcapsules used in this area probably require a much tighter coating to protect their active cores, while the outer membrane for the rupture mechanism is expected to have the characteristics of easy breakdown under the appropriate conditions [ 70 ]. As mentioned above, many types of natural and synthetic polymers are being explored, such as gelatin, chitosan, polyvinyl alcohol, and methylcellulose.…”

Fracturing fluids

“…A condensation product of hydroxyacetic acid can be used as a fluid loss material in a fracturing fluid in which another hydrolyzable aqueous gel is used [117][118][119][120]. The hydroxyacetic acid condensation product degrades at formation conditions to set free hydroxyacetic acid, which breaks the aqueous gel.…”

Fracturing Fluids

“…A condensation product of hydroxyacetic acid can be used as a fluid loss material in a fracturing fluid where another hydrolyzable aqueous gel is used (Cantu and Boyd, 1989;Cantu et al, 1990aCantu et al, ,b, 1993. The hydroxyacetic acid condensation product degrades under formation conditions to release hydroxyacetic acid, which breaks the aqueous gel.…”