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Volumetric Determination and Development Status of Jonah Field

DuBois, Dean P., Thomas M Smagala, and Julia C Gwaltney
EnCana Oil & Gas (USA) Inc, Denver, CO

Determination of hydrocarbon pore-thickness (SgPhiH) for Jonah Field is performed by using standard open-hole wireline petrophysical measurements. Input data include porosity determined from bulk density, neutron porosity, deep induction resistivity and natural gamma radiation. These data are normalized or checked against standards established in the field. Effective porosity (Phie) and water saturation (Sw) curves are calculated utilizing a dual water model that has been tied to core data from the Lance Formation within the field. “Net pay” (H) is the sum of feet which exhibit bulk volume water(BVW)<0.04, Sw<0.65 and Phie>0.04. BVW is the product of Sw and Phie. SgPhiH is summed over the “net pay” intervals using (1-Sw) * Phie.

A model of original pore pressure is used to construct an estimated original pressure curve for every well in the field. Averaging that curve over the “net pay” intervals yields a pay-weighted average pressure. Original gas-in-place (OGIP) is determined using temperatures from cased-hole logs, SgPhiH and pay-weighted average pressure data. OGIP for Jonah Field exceeds 10.4 TCFG. 

Full development of Jonah Field at 1 well per 40-acre spacing would yield an estimated ultimate recovery of 3.4 TCFG or less than 33% recovery factor. Several operators at Jonah Field have undertaken infill-drilling projects. Pressure data acquired from these infill wells compared to cumulative production from offsetting wells validates the OGIP estimates. Drilling increased-density wells at Jonah will allow operators to recover up to 85% of OGIP.