Hydraulic fracturing is a stimulation technique used to create high-conductivity flow paths in low-permeability reservoirs(shale, tight sandstone, tight carbonate). High-pressure fluid is pumped down the wellbore to crack the rock and place proppant to keep the fractures open.
1, Why fracturing is needed?
Unconventional reservoirs typically have:
-Very low permeability(0.0001-0.1mD)
-Natural fractures that are insufficient to sustain flow.
-High capillary pressure preventing hydrocarbons from flowing to the well.
Fracturing artificially increases permeability by 10x-10000x through:
-Creating new fractures
-Extending existing ones
-Placing stable proppant channels
2, Core components of a Frac job
Surface equipment
-Frac pumps(diesel or electric e-frac)-generate 5000-15000psi
-Blender-mixes sand and chemicals into fluid
-Hydration unit-prepares gel/FR fluid
-Sand kings/silos-proppant storage
-Data van-real-time monitoring
-Fracturing manifold/zipper manifold-routing high-pressure lines
-Chemical additive units
Downhole components
-Frac string/plug-and-perf guns/CT string
-Bridge plugs or ball-drop sleeves
-Packer assembly
-Frac ports & perforations
3, Fluids systems
Slickwater(shale frac)
-Water+friction reducer
-Low viscosity
-High pump rate(60-100bpm)
-Advantages: low cost, long fractures, good for shale
Crosslinked gel(conventional tight sandstone)
-Guar gel+borate/crosslinker
-High viscosity
-Carries large proppant volumes
-Used in conventional tight gas, deep high-pressure reservoirs
Hybrid systems
-Start with slickwater for fracture initiation
-Switch to gel for proppant transport
4, Proppant types
White sand(cheap, shallow wells)
Brown sand
Resin-coated sand
Ceramic proppant(high strength, deep＞8000-12000psi closure)
5, Frac job workflow(stage by stage)
-Rig up equipment
-Pressure test iron
-Perforate (plug and perf) or open sleeve(ball-drop)
-Breakdown
-Pad stage(no proppant)-create initial fracture volume
-Proppant stages-increasing concentration
-Flush stage-clear tubing
-shut-in
-Move to next stage(zipper frac for multi-well pads)
