Correcting Underestimation of Optimal Fracture Length by Modeling ProppantConductivity Variations in Hydraulically Fractured Gas/Condensate Reservoirs

摘要

A study was carried out to forecast the productivity of ahydraulically fractured well in a retrograde gas-condensatesandstone reservoir using a numerical model. The fracture wasexplicitly modeled as a set of high-conductivity cells.At the gas velocities normally encountered in hydraulicfracture proppant packs, non-Darcy pressure drops dominate,and the apparent proppant permeability is one or two orders ofmagnitude lower than the Darcy permeability measured atsingle phase low-rate conditions. This is particularly true if aliquid phase is also flowing. The apparent permeability of theproppant is a function of:? Gas velocity (hence: rate and flowing pressure)? Ratio of free liquid rate to gas rate? Stress on the proppant? Type of proppantThus, apparent proppant permeability will vary withdistance from the wellbore, increasing towards the tip of thefracture where liquid ratio and velocity are lower.This variation of permeability was explicitly modeled inthe proppant pack by dividing it into segments and calculatingthe permeability in each segment. As a result of this modeling,the impact of increased fracture length on productivity wasfound to be more significant than in simpler modeling whereone permeability value is used for the entire proppant pack.The variation of apparent proppant permeability along thelength of the fracture and its impact on well productivity arediscussed in this paper. A comparison of predicted wellproductivity is also made with the use of a constantpermeability value for the proppant in numerical and analyticsimulators. We will show that using a constant proppant permeability value results in an estimate of optimal fracturelength that is too short.