The Wamsutter field is located in south-central Wyoming within the eastern part of the Greater Green River basin. The field covers 1,620 square miles and includes more than 8,500 wells; it produces approximately 450 million cubic ft of gas a day. The Almond formation, which accounts for approximately 85% of the produced gas, was deposited in shallow marine parasequences characterized by strandplain, deltaic, or barrier island complexes and their non-marine counterparts. The upper interval, which was produced extensively, contains the thickest, most laterally continuous and best rock quality. Most of the remaining field development potential remains in sections characterized by thinner and discontinuous facies. In addition to the larger stratigraphic uncertainty, poorer rock quality makes permeability interpretation in uncored wells quite challenging.

We tackle reservoir uncertainty by taking gross depositional interpretation and superimposing gas effective permeability models that honor dynamic measurements. This paper describes our efforts to produce core-calibrated, log-derived, effective permeability models that match zonal contribution from production logging and initial production indices.

The critical steps in the petrophysical workflow are related to the interpretation of the log-derived absolute permeability and core-derived gas relative permeability. Log-derived absolute permeability was addressed by evaluating alternative stochastic (neural network-based) and deterministic models on wireline logs. Core-derived gas relative permeability was tackled by modeling unsteady, pulse decay-type measurements along with capillary pressure tests by rock type.

Alternative gas effective permeability models are integrated over perforated intervals (KegH) and compared to actual reservoir performance. The model exhibiting the best correlation with dynamic data is superimposed on gross depositional maps.

We discuss the assumptions and limitations of the various measurements that make up petrophysical workflows in tight-gas sands as well as their contribution to the location of infill and step-out opportunities.

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