This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 207933, “The Integration of Analytical P/Z Material-Balance Method With Static Modeling and Integrated Asset Model To Generate Reliable Forecasting for a Giant Onshore Gas Field in Abu Dhabi,” by Bondan Bernadi, Yuni Budi Pramudyo, and Fatima Omar Alawadhi, ADNOC, et al. The paper has not been peer reviewed.
Reliable field gas initially in place (FGIIP) estimation is achieved by performing multiple reservoir-pressure/gas-compressibility (P/Z) calculations. Several scenarios are developed in the complete paper by defining key areas based on permeability variation, areal distribution, and pressure/volume/temperature (PVT) behavior. The best FGIIP estimation is then fed back into the static model to generate numerous realizations considering the static uncertainties to produce the same FGIIP. A giant onshore gas field is highly heterogeneous, with permeability, lateral composition variation, and dynamic interaction between wells. Incorporating the correct estimation of FGIIP into the integrated asset model (IAM) has helped yield reliable forecasting and has enabled more-efficient field development.
Reservoir A produces onshore from a limestone formation in the lower cretaceous horizon. The structure is a simple dome that is somewhat steeper on the eastern flank, with two extended noses in the south and southeast directions. The total thickness of this zone decreases down the flanks but more rapidly in the northeast direction. Formation porosity is in the range of 10 to 25%, with a permeability range of 0.5 to 88 md. The original reservoir pressure is approximately 4,300 psia, with a reservoir temperature of 260°F.
The field has been producing in depletion mode for more than 30 years, flowing into one common surface network with other depletion reservoirs. More than 100 wells had been drilled in the gas-cap zone, with an average gas-production rate of 15–20 MMscf/D per well. Because of the depletion scheme applied since the beginning of field life, gas-production decline is inevitable. The focus of the complete paper mainly relates to the gas-cap zone.