Encapsulated Breaker For Aqueous Polymeric Fluids

Abstract

MEETING. A13STRACT aused only a 2(r/a loss in viscosity in one hour. These kftratory tests Indicate that encapsulated breaker may Increase well Persulfates are commonly used as breakers for aqueous production by improving proppant pack clearkip. fluids viscosified with guar or cellulose derivatives. These breakers are necessary to minimize permeability damage to proppant or gravel packs at temperatures where there is little INTRODUCTION thermal degradation of the polymers. Unfortunately, dissolved persulfates are much too reactive even at moderate temperatures Recerd laboratory investigabons have shown that polynwrlc (60-93.30C) to be used at concentrations sufficient to thoroughly fracturing fluids can cause significant proppant pack permeablity degrade oonoontrated, Ngh mokmiar weight polymers. New technology described In this paper has been utilized to produce a 'delayed' breaker. The breaker is prepared bv encapsulating ammonium persultate with a water-resistaet coating. The coating shields the fluid from the breaker so that high concentrations of breaker can be added to the fluid v4thout causing premature loss of fluid properties such as viscosity or fluid loss control. Critical factors in the design of encapsulated breakers, such as coating harder properues, release mechanisms, and reactive-chemicals properties are discussed. The effects of encapsulated breaker on fluid dmlogy were compared for several encapsulated persulfates. Only one material had a coating adequate to protect the fluid from premature degradation. Additional rheology and conductvlty damage studies were done with this product. It was found that In a borate-crosslinked fluid at 71-0, 240 g/m3 of the encapsulated breaker caused an improvement in retained permeability from 15% to 490/., but References and illustrations at end of paper. impairment Major contributors to this problem are the stablifty of the polymers below 107.20-121.1 OC and the concentration of polymer which occurs dudng a fracturing treatment. Penny has suggested that the polymer is conoentmted 5-7 times due to fluid loss during pumping and closure. He reported 50% damage for conductivity tests using polymeric fluids when compared with tests run without fracturing fluids. Hawkins pointed out that under worst-case conditions, where all the polymer in the fluid is concentrated in the proppant pack, the concentration increase would be 25-told for fluid containing 240 kgtm3 sand. Higher sand concentrations in the fluid and a larger ratio of fractured area to ProPped fracture area would reduce the concentration factor in the proppant bed. Hawkins presented data shoimng the effect of final polymer concentration on fracture permeability. His tests showed that the permeability of a 850-425 ilm mesh sand pack decreased from about 138 lim2 to about 79 lim2 for 12 kg/m3 final concentration of polymer and to about 39 Jim for 36 kg/m3 polymer. This corresponds to retained permeabilities of 57 and 29%, respectively. Parker and McDaniel have emphasized the need to consider filtercake effect...

Fracturing Fluids

“…Interactions between enzyme breakers and fracturing fluid additives Gulbis et al (1990aGulbis et al ( ,b, 1992, and King et al (1990) Enzyme breaker b Gupta and Prasek (1995) Complexing agents c Boles et al (1996) a) Guar or cellulose derivatives b) Open cellular coating c) For titanium and zirconium; wood resin encapsulated including biocides, clay stabilizers, and certain types of resin-coated proppants have been reported (Prasek, 1996). Interactions between enzyme breakers and fracturing fluid additives Gulbis et al (1990aGulbis et al ( ,b, 1992, and King et al (1990) Enzyme breaker b Gupta and Prasek (1995) Complexing agents c Boles et al (1996) a) Guar or cellulose derivatives b) Open cellular coating c) For titanium and zirconium; wood resin encapsulated including biocides, clay stabilizers, and certain types of resin-coated proppants have been reported (Prasek, 1996).…”