Successful Control of Fracture Height Growth by Placement of Artificial Barrier

Abstract

This paper presents a method to control fracture height growth through the selective placement of artificial barriers above and below the pay zone. These barriers are created prior to the actual treatment by pumping a mix of different size and density proppants with low viscosity carrying fluid, that allows fast settling of these proppants or, if desired, flotation to the top of the fracture channel or both. Typically a viscous pad is pumped to create a fracture channel. This pad is followed with 5-10 cp fluid slurry carrying a mix of heavier proppant that settles to the bottom of the fracture channel and a light proppant that rises to the top of the fracture channel. The proppant slurry is allowed to bridge at the top or the bottom tip of the fracture inhibiting further growth of these tips. The actual treatment following this barrier placement is thus focused through these barriers confining itself within the barriers and resulting in a longer extension within the pay zone. Such controlled fracture height allows further optimization of fracture length by reducing or increasing the amount of proppant as the design calls for. Two case studies are presented in this paper from two formations known to suffer from fracture height growth. This method is universally applicable to any formations where height growth at the cost of extension is suspected. Introduction For optimized well performance, adequate fracture half length and fracture conductivity are the two most important parameters. Generally, the importance of fracture half-lengths prevails over that of fracture conductivity in low permeability formations. it is quite well established that the lower the permeability, the longer is the fracture half length requirement. Although for low permeability formations if the reservoir pressure is high, the fracture conductivity may also need to be improved. This paper discusses the problems related to the fracture extension due to height growth and a very effective method of mitigation of this problem within some practical limitations. Warpinski, et al. (1980) showed the predominant influence of barrier in-situ stresses in the containment of height growth of induced hydraulic fractures. Recently with the emergence of three dimensional fracture models, other authors also confirmed Warpinski, et al.'s conclusions. It can be said that in the absence of adequate stress barriers, hydraulic fractures grow uncontained into the barriers at the cost of extension. Two dimensional fracture geometry models often undermine the effects of height growth resulting in an erroneous prediction of fracture length. Production performance or post fracture build-up tests often indicate this severe curtailment of fracture half lengths from designed. The problem is quite prevalent in some of the prolific hydrocarbon-producing formations in the Rocky Mountain region such as Codell, Frontier, Dakota, Mancos, etc. to name a few. Thus, an effective method of mitigation of unwanted height growth problem can be very useful in the optimization of fracture half length for maximum return on the stimulation investment. Fracture height containment has been studied for more than two decades by different authors.

Experimental Study on the Transport Law of Different Fracturing Granular Materials in Fracture

“…This method has been applied in the Mancos Shale formation of the Rangely Field. The actual production is increased after fracturing, which shows that this height control method can increase the effective fracture permeability and improve the productivity of these wells . The floating agent whose density is less than that of the fracturing fluid is used to form a dune in the upper part of the fracture.…”

Experimental Study on Vertical Propagation Behavior of Hydraulic Fracture Affected by Artificial Interlayer for Thick Oil Reservoirs

“…Research on how to generate the artificial interlayer and the mechanism of artificial interlayer restricting fracture height have been investigated. Mukherjee [2] recommended the use of low viscosity fracturing fluids with lighter proppant to seal the top fracture ends and successfully restricted hydraulic fracture height. Talbot et al [3] proposed a hydraulic fracturing method to limit fracture height propagation by adding front fluid with sand for bottom-water and energy-depleted reservoirs.…”