Curable resin-coated proppants (RCP) have been used to minimize proppant flowback from propped hydraulic fractured oil and gas wells for years, yet proppant backproduction is still reported to be a major operational problem. The industry cannot currently explain why some hydraulic fractures propped with curable RCP produce proppant back while others containing only uncoated proppant do not produce any proppant back.
This paper presents results of a study done to help determine screening considerations for curable resin-coated proppants. The study involved curing and crushing proppant plugs under a variety of conditions ranging from frac-and-pack applications in shallow wells to fracturing applications in deep horizontal wells. These tests were conducted to identify suitable RCPs for given applications.
The unconfined compressive strength (UCS) of proppant plugs cured in the treatment fluid at reservoir temperature with closure stress applied, is currently used as the screening criterion for curable RCP. The UCS needs to be as high as possible while the same resin coating should not consolidate the proppant while left in the well after a treatment without closure stress applied. This study demonstrates that at least six data points are needed to obtain a representative value for the unconfined compressive strength (UCS) of proppant for any one set of conditions. Although several studies of factors affecting the performance of RCPs have been presented in the literature, the conclusions in these studies are generally based on limited data for one set of conditions and are, therefore, often questionable.
In addition, the effect of cooldown and subsequent heatup on RCPs after a treatment has not been considered previously as a factor in proppant backproduction. This paper demonstrates that this temperature effect is an important parameter to consider. Stress cycling has been identified as one of the failure mechanisms for RCP in experiments. These experiments were conducted at ambient temperature with proppant packs cured at temperatures between 160 and 200°F (71 and 93°C). We conducted similar experiments at simulated in-situ conditions to verify whether the mechanism was still effective for these conditions. We found that the addition of thermoplastic film material to RCP cured at 300°F (149°C) increased its resistance to stress cycling.