Dickins, Mark Ian (2008-08). The impact of gravity segregation on multiphase non-Darcy flow in hydraulically fractured gas wells. Master's Thesis. Thesis uri icon


  • Multiphase and non-Darcy flow effects in hydraulically fractured gas wells reduce

    effective fracture conductivity. Typical proppant pack laboratory experiments are

    oriented in such a way such that phase segregation is not possible, which results in

    mixed flow. Tidwell and Parker (1996), however, showed that in proppant packs, gravity

    segregation occurs for simultaneous gas and liquid injection at laboratory scale (1500

    cm2). Although the impact of gravity on flow in natural fractures has been described,

    previous work has not fully described the effect of gravity on multiphase non-Darcy

    flow in hydraulic fractures. In this work, reservoir simulation modeling was used to

    determine the extent and impact of gravity segregation in a hydraulic fracture at field

    scale. I found that by ignoring segregation, effective fracture conductivity can be

    underestimated by up to a factor of two.

    An analytical solution was developed for uniform flux of water and gas into the fracture.

    The solution for pressures and saturations in the fracture agrees well with reservoir

    simulation. Gravity segregation occurs in moderate-to-high conductivity fractures. Gravity segregation impacts effective fracture conductivity when gas and liquid are

    being produced at all water-gas ratios modeled above 2 Bbls per MMscf. More realistic,

    non-uniform-flux models were also run with the hydraulic fracture connected to a gas

    reservoir producing water. For constant-gas-rate production, differences in pressure

    drop between segregated cases and mixed flow cases range up to a factor of two. As the

    pressure gradient in the fracture increases above 1 to 2 psi/ft, the amount of segregation

    decreases. Segregation is also less for fracture half-length-to-height ratios less than or

    close to two. When there is less segregation, the difference in effective conductivity

    between the segregated and mixed flow cases is reduced. I also modeled the water

    injection and cleanup phases for a typical slickwater fracture treatment both with and

    without gravity effects and found that for cases with segregation, effective fracture

    conductivity is significantly higher than the conductivity when mixed flow occurs.

    Gravity segregation is commonly ignored in design and analysis of hydraulically

    fractured gas wells. This work shows that segregation is an important physical process

    and it affects effective fracture conductivity significantly. Hydraulic fracture treatments

    can be designed more effectively if effective fracture conductivity is known more


ETD Chair

publication date

  • August 2008