Laboratory investigation of the interactions between fracturing fluids andresin-coated proppants (RCP's) revealed (among other conclusions) that RCP'sare incompatible with oxidizing breakers. Areas covered included RCP effect onfluid rheology, fluid relationship to RCP strength, theoretical study ofrequired RCP strengths to prevent flowback, and experimental measurement toestablish minimum strength.
This paper describes the use of curable RCP's in fracturing treatments.Their primary purpose is to prevent proppant flow from the fracture duringcleanup and production. The use of such materials is increasing rapidly, yetmany concerns exist in design and application of fluid systems. These include(1) the effect of various crosslinked fluid systems on the strength of thecured, consolidated sandpack, (2) breaking of the gel system, (3) temperatureeffects on the resin system during curing, (4) the closure stress required tocause consolidation, and (5) the compressive strength required to preventproppant flow from the fracture. Laboratory experiments have been conducted todetermine the effect of various components in crosslinked fluid systems on theconsolidation of curable RCP'S. Available RCP products and field- applied resinsystems were investigated under several different curing conditions. Extendedcuring before stress was applied resulted severely reduced strengths. Flowexperiments (through consolidated packs) with oil and water were conducted tocorrelate velocity/viscosity packs) with oil and water were conducted tocorrelate velocity/viscosity relationships and proppant flow from a pack. Fluidsystems and techniques for optimized use of curable RCP's are identified, andgel breaker requirements are presented. Compressive strengths obtained underfield conditions generally were much lower than commonly reported.
The use of plastic materials for sand consolidation in producing wells datesback to 1945, when a phenolic resin was used. Since then, use of variousmaterials, including phenolic, furan, and epoxy resin systems, has beendescribed for various sand-control applications. In 1975, the application ofcurable RCP with a phenolic-based system was patented. Literature pertaining tothe use of plastic materials to control sand production has focused on gravelpacking and sand control. During the last decade, proppant production fromhydraulically fractured wells has increased. One reason is the use of higherproppant concentrations during the treatment. To control this proppantconcentrations during the treatment. To control this proppant productioneconomically, the use of curable RCP has grown proppant productioneconomically, the use of curable RCP has grown from novelty status to standardpractice. During the recent growth of RCP application, conductivity,compressive strengths, and general effectiveness have been considered, but someareas of their application remain relatively unexplored. These areas includethe RCP's effect on the fracturing fluid, the fracturing fluid's effect on theRCP, and the amount of bonding strength required to hold the cured RCP in aproducing fracture. The objective of this research was not to generate fractureconductivity data or proppant crushing, but to provide better understandingbetween the interactions of fluid and RCP. In addressing these issues, werealized that common fracturing fluids and conditions influence the resultingstrengths of cured, consolidated RCP. A better understanding of proppantconsolidation was desired because the fluid and curing conditions of RCP affectstrength. Therefore, this paper discusses the RCP's effect on fluid rheology,the relationship of fluid to RCP strengths, the theoretical study of requiredRCP strengths to prevent proppant flowback, and experimental measurements toestablish minimum required strengths. Two general methods are now used duringfracturing treatments to consolidate proppant. The most widespread method isthe use of curable phenolic resins precoated on the proppant. In this case,products are manufactured and delivered to location. Two curable phenolic RCPproducts were evaluated in this study: RCP-A normally contains 4% resin andRCP-B normally contains two layers of resin, 2 % precured followed by 2 %curable resin. A new approach is an on-site coating method where requiredmaterials are to the fluid and allowed to coat the proppant during pumping.This system, RCP-C, uses an epoxy-based resin system. The concentration resinused in this system can be varied to adjust the compressive strength of theconsolidated proppant. A precured similar to RCP-A was used and is calledRCP-D.
RCP Effect on Fluids
The influence of RCP on fluid rheology related to crosslink time andviscosity was examined. The effect of RCP on breakers used oil to obtain acontrolled reduction of the fluid's viscosity also was examined. The first testseries examined the influence of RCP-A on the ambient-temperature fluidcrosslinking rate. In these tests, aluminum-, titanium-, and boron-crosslinkedfluids were examined to evaluate acidic, neutral, and basic fluid systems.Table 1 gives the times to crosslink to a "strong" state. From thesefluids tested, we concluded that RCP-A did not significantly influence thecrosslink rate of these fluids. The RCP effect on fluid viscosity was examinedat 170F for a linear gel and a titanium-crosslinked fluid. For evaluating theinteraction of RCP and base gel viscosity, a 100-lbm/1,000-gal solution ofhydroxypropyl guar (HPG) was monitored for I hour at 170F. Because solidproppant usually is not used directly in the Fann Model 50 TM viscometer, theinfluence of RCP on viscosity was determined by mixing either RCP-A or RCP-B at6 lbm/gal in the water used for preparing the gel and then removing the solidsbefore gelation. Because the water-soluble gel most likely would be influencedby water-soluble components from RCP-A or RCP-B. we decided that this techniquewas a reasonable experimental approach. The gel mix water was exposed for 24hours to RCP-A or RCP-B at ambient and 170F temperatures. In anotherexperiment, RCP-A was allowed to cure in air at 170F and then was exposed towater for an additional 24 hours at 170F to determine whether the cured RCP-Awould affect the break properties. Table 2 shows the results of these tests.The procedures described above were repeated with a 50-lbm/ 1,000-gal solutionof HPG. In this case, the base gel was crosslinked with a titanate crosslinkerbefore the viscosity profile was run for 1 hour at 170F. Table 2 shows thesedata. profile was run for 1 hour at 170F. Table 2 shows these data. Included inthis data set is an experiment where dust collected from pneumatic transfer ofRCP-B during a south Texas fracturing treatment was added directly to thecrosslinked fluid. We concluded that the chemical effects on base gel fromRCP-A or RCP-B are minimal but that the titanate-crosslinked system viscositypotentially could be reduced by 50% under these test conditions. potentiallycould be reduced by 50% under these test conditions. SPEPE