Weakly consolidated sandstone reservoirs generally feature poor cementation, low strength, relatively high porosity and high permeability. Due to the significant effect of poroelasticity, stress redistribution resulting from the pore pressure perturbation around the injection well should be accounted for when determining the fracture pressure. During the long-term water injection, a flow barrier may form due to large particles plugging on the wellbore wall, likewise, the formation permeability around the well may suffer damage due to fine particles plugging the pore channels. Additionally, tensile failure and shear failure may occur in the weakly consolidated sandstone reservoirs since the pore pressure increases around the injection well. In this paper, we provide an analytical method for fracture pressure calculation of directional injection wells in weakly consolidated sandstone incorporating the effects of wellbore plugging and near-wellbore damage. Wellbore plugging and near-wellbore damage are exacerbated as the water injection, which leads to an increase in the fracture pressure. This paper provides a theoretical reference for the prediction of injection pressure in weakly consolidated sandstone.
The calculation of the water injection pressure in the oilfield should consider the tubing friction resistance, the pressure loss of the water distribution nozzle, the liquid column pressure and the fracture pressure (Li, 2005). The pressure loss along the wellbore and the bore-hole hydrostatic pressure are available when the amount of water injection is determined. Consequently, calculating the reservoir fracture pressure is the premise for ascertaining the water injection pressure. For the fracture pressure, the actual measured value obtained by the mini-fracturing test or drilling pressure test is preferred, and the empirical formula is used to calculate the fracture pressure when the measured value cannot be obtained (Yang et al., 2021). However, weakly consolidated sandstone reservoirs generally feature poor cementation, low strength, relatively high porosity and high permeability. During the long-term water injection, a flow barrier may form due to large particles plugging on the wellbore wall, likewise, the formation permeability around the well may suffer damage due to fine particles plugging the pore channels, which can easily cause wellbore plugging and near-wellbore damage, resulting in a change in the near-wellbore formation pressure (Zhang et al., 2019). Meanwhile, most of the injection wells in offshore oilfields are mainly directional wells. Existing models for fracture pressure prediction have not covered the above-mentioned factors for directional injection wells in weakly consolidated sandstone.
