Pressure Transient Analysis for Minifracs/DFIT and Waterflood Induced Fractures

Abstract

To date no efforts were published to (numerically) compute the pressure transients following shut-in for a fracture that during pumping was propagating at an arbitrary, not necessarily constant velocity; and to use these computations to systematically understand the physics (type curves) of pressure decline after shut-in for both very rapidly growing and very slowly growing fractures during pumping; and to compare this with (existing or new) PTA analysis methods incorporating fracture closure. Paul van den Hoek came up with a new methodology to address the problem. The method enabled to handle the otherwise unaddressed problem of ‘fractured’ injector wells for both end of the fluid leak off spectrum and associated pressure transient analysis – i.e. for DFIT tests done for very low permeability reservoirs to Minifrac (MF) tests for medium to high permeability reservoirs, up until Injection Fall-off (IFO) tests done as part of waterfloods in low to high permeability reservoirs. An easy to use analytical model was formulated by generalization of IFO model developed for fractured waterflood injectors (high leak-off case). This work compares Van den Hoek method against ‘standard method’ which in our report is industry wide used well test program FEKETE for a number of hydraulic frac field cases. To identify each methods short comings and advantages. The identified advantages and disadvantages are highlighted and used as ready made reference for future work on the subject. To serve as easy-to-use overview of commonly used existing approaches of artificial/hydraulically fractured wells for both end of spectrum – (low leak off) Minifrac /DFIT and (high leak-off) Injection Fall Off tests, highlighting the physics involved, fundamental assumptions, and how they differ from each other subtly is covered.
Brief summary of Paul's unified method was done. Fracture Compliance Method was shortly discussed for each data set. Lastly, a basic model was developed to identify permeability based on Lamei and Soliman's BCA model.