Page 211 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

180 Reservoir Engineering

Figure 5-106. EPT quicklook chart comparing curve response of induction
resistivity, neutron porosity, density porosity and EPT porosity in water
bearing and hydrocarbon-bearing zones [214].

Repeat Formation Tester. The repeat formation tester measures downhole forma-
tion pressures. The tool is operated by an electrically driven hydraulic system
so that several zones may be pressure tested on one trip into the hole. Once
the drawdown pressure and the pressure buildup have been recorded, they can
be processed by a computer at the well-site to provide Horner plots from which
permeabilities are calculated. Permeabilities from the drawdown test often vary
considerably from measured permeabilities and should be considered an order-
of-magnitude estimate. This is usually due to a.very shallow depth of investiga-
tion associated with drawdown tests [212]. The pressure buildup has a better
depth of investigation than the drawdown pressure test. Accuracy depends on
what type of pressure-wave propagation model is chosen [212,215,216] as well
as the compressibility and viscosity of the formation fluids.