Application of Surface Modification Agent in Wells with High Flow Rates
Authors: Weaver Jim D. , Baker John D. , Parker Mark A. , Woolverton Sean 
Published: December 2007

Proppant coated with conventional surface-modification agents (SMA's) enhances fracture conductivity by reducing flowback in wells with moderate flow conditions. However, SMA cannot withstand the harsh flowback conditions associated with high fluid flow rates. An enhanced SMA (ESMA) increases the ability of the proppant pack to withstand critical flow velocity by 10- to 20-fold.

In many areas, proppant flowback occurs after fracture-stimulation treatments are performed. In some cases, fractures can produce as much as half of the proppant placed during the treatment. Produced proppant can abrade and foul equipment, causing service and disposal problems. It can also extend costly well-cleanup time. However, the most significant problem associated with proppant flowback is reduced fracture conductivity, which reduces potential well production.

Research has identified the following mechanisms that influence proppant flowback: Angle of Repose. When poured onto a flat surface, granular material forms a conical pile. The sides of this pile form a specific angle with respect to the horizontal plane. Proppant tends to produce from a packed fracture until this angle is established to the lowest perforation.Erosion. Fluid flowing along the surface of the proppant pack can cause erosion. Theoretically, proppant will continue to erode until it bridges against an obstruction.Closure Stress. Proppant flowback cannot be entirely prevented with formation closure on the proppant pack.Embedment and Extrusion. When a fracture closes with sufficient force, and the formation surface is relatively soft, proppant grains can become embedded in the formation face. Embedment tends to stabilize the proppant pack.Proppant Size, Distribution, Angularity, and Roughness. As proppant uniformity increases, pack stability decreases. However, flowback decreases when proppant angularity and roughness increase.Mechanical Binders. Fibrous materials included with proppant can enhance bridging. However, this stabilization technique tends to reduce proppant-pack permeability.Cohesive Forces. Increased cohesion between proppant grains helps reduce flowback by causing the grains to interlock.

SMA, a liquid additive applied during the fracture treatment, can also be used to influence proppant flowback. This material is water- and oil-insoluble, and it will not harden under reservoir conditions. It leaves proppant grains tacky, increasing their cohe-siveness. SMA-coated proppant enhances fracture conductivity by increasing pack porosity and permeability up to 30%. The tacky surfaces of the proppant stabilize fines generated during the fracture treatment. They also stabilize the pack/formation-face interface, creating a flexible proppant bed that can withstand surging flow conditions. However, sufficiently high flow rates will cause SMA-coated proppant to flow.

The ESMA system consists of a slow-acting chemical crosslinker added to conventional SMA. ESMA increases the critical fluid velocity required to erode the proppant, but it leaves the proppant grains tacky enough to retain cohesiveness.

In the Mesaverde field, proppant flowback is a common problem, and cleanup operations can take up to I week. However, when fractured with ESMA-coated proppant, these wells exhibit no flowback, reduced cleanup times, and the best production in the field.

While SMA-coated proppant can significantly reduce flowback under moderate flow conditions, ESMA-coated proppant can inhibit flowback under the harsh flow conditions of limited-entry wells. ESMA-coated proppant exhibits little flowback during cleanup and no flowback during well production. In addition, production profiles indicate that ESMA-coated proppant increases cumulative well production.