The fracture pressure in the reservoir is a function of reservoir pressure. Reservoir depletion will reduce the magnitude of reservoir pressure and consequently the reservoir fracture pressure. The fracture pressure changes because of reservoir depletion can lead to challenges like closure of mud weight window. Hence, the ability of predicting the fracture pressure changes due to reservoir depletion is a key for field development including infill drilling campaign.
A reasonable amount of field data has been published across the oil and gas industry to understand fracture pressure reduction as a function of reservoir depletion. The data show approximately a linear relationship between the reduction of fracture pressure with reducing reservoir pressure. Several studies and laboratory measurements have also been made to assess the impact of the reservoir depletion on the fracture pressure. Almost all the studies and laboratory measurements show reduction of fracture pressure as a function of reservoir depletion.
In this study, we present several field examples showing that severe reservoir depletion has little to no impact on the fracture pressure and consequently on the mud weight window. The examples show that heavily depleted reservoirs were drilled with high over balanced mud weight without seeing any sign of loss events. These observations are not fully aligned with what has been observed in the published field data.