Application of Surface Modification Agent in Wells with High Flow Rates

摘要

Proppant coated with conventional surface-modification agentsrn(SMA?s) enhances fracture conductivity by reducing flowback inrnwells with moderate flow conditions. However, SMA cannotrnwithstand the harsh flowback conditions associated with high fluidrnflow rates. An enhanced SMA (ESMA) increases the ability of thernproppant pack to withstand critical flow velocity by 10- to 20-fold.rnIn many areas, proppant flowback occurs after fracturestimulationrntreatments are performed. In some cases, fracturesrncan produce as much as half of the proppant placed during therntreatment. Produced proppant can abrade and foul equipment,rncausing service and disposal problems. It can also extend costlyrnwell-cleanup time. However, the most significant problem associatedrnwith proppant flowback is reduced fracture conductivity,rnwhich reduces potential well production.rnResearch has identified the following mechanisms that influencernproppant flowback:rn? Angle of Repose. When poured onto a flat surface, granularrnmaterial forms a conical pile. The sides of this pile form arnspecific angle with respect to the horizontal plane. Proppantrntends to produce from a packed fracture until this angle isrnestablished to the lowest perforation.rn? Erosion. Fluid flowing along the surface of the proppantrnpack can cause erosion. Theoretically, proppant will continuernto erode until it bridges against an obstruction.rn? Closure Stress. Proppant flowback cannot be entirely preventedrnwith formation closure on the proppant pack.rn? Embedment and Extrusion. When a fracture closes withrnsufficient force, and the formation surface is relatively soft,rnproppant grains can become embedded in the formation face.rnEmbedment tends to stabilize the proppant pack.rn? Proppant Size, Distribution, Angularity, and Roughness.rnAs proppant uniformity increases, pack stability decreases.rnHowever, flowback decreases when proppant angularityrnand roughness increase.rn? Mechanical Binders. Fibrous materials included withrnproppant can enhance bridging. However, this stabilizationrntechnique tends to reduce proppant-pack permeability.rn? Cohesive Forces. Increased cohesion between proppant grainsrnhelps reduce flowback by causing the grains to interlock.rnSMA, a liquid additive applied during the fracture treatment,rncan also be used to influence proppant flowback. This material isrnwater- and oil-insoluble, and it will not harden under reservoirrnconditions. It leaves proppant grains tacky, increasing their cohesiveness.rnSMA-coated proppant enhances fracture conductivityrnby increasing pack porosity and permeability up to 30%. The tackyrnsurfaces of the proppant stabilize fines generated during thernfracture treatment. They also stabilize the pack/formation-facerninterface, creating a flexible proppant bed that can withstandrnsurging flow conditions. However, sufficiently high flow rates willrncause SMA-coated proppant to flow.rnThe ESMA system consists of a slow-acting chemicalrncrosslinker added to conventional SMA. ESMA increases therncritical fluid velocity required to erode the proppant, but it leavesrnthe proppant grains tacky enough to retain cohesiveness.rnIn the Mesaverde field, proppant flowback is a commonrnproblem, and cleanup operations can take up to 1 week. However,rnwhen fractured with ESMA-coated proppant, these wellsrnexhibit no flowback, reduced cleanup times, and the best productionrnin the field.rnWhile SMA-coated proppant can significantly reducernflowback under moderate flow conditions, ESMA-coatedrnproppant can inhibit flowback under the harsh flow conditions ofrnlimited-entry wells. ESMA-coated proppant exhibits littlernflowback during cleanup and no flowback during well production.rnIn addition, production profiles indicate that ESMA-coatedrnproppant increases cumulative well production.