How Pore-Scale Attributes May Be Used to Derive Robust Drainage and Imbibition Water-Saturation Models in Complex Tight-Gas Reservoirs
- G. Merletti (BP) | P. Gramin (BP) | S. Salunke (BP) | J. Hamman (BP) | D. Spain (BP) | V. Shabro (BP) | P. Armitage (BP) | C. Torres-Verdin (The University of Texas at Austin) | G. Salter (Core Laboratories) | J. Dacy (Core Laboratories)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- October 2016
- Document Type
- Journal Paper
- 447 - 464
- 2016. Society of Petrophysicists & Well Log Analysts
- 2 in the last 30 days
- 208 since 2007
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Tight-gas reservoirs undergo unique and often complex burial, diagenetic, structural, fluid pressure and saturation histories. Porosity alteration from compaction, cementation and grain leaching can continue after hydrocarbon charge, further complicating saturation modeling. Many reservoirs have gone through multiple cycles of drainage and imbibition, often at different stages on the diagenetic pathway to current pore-scale morphologies. The understanding of saturation distribution and state is not only desired but required for predicting reservoir performance, estimating realistic recoverable volumes, and optimizing costs for development and production.
The Almond Formation is characterized by three depositional facies associations: shoreface, deltaic and fluvial-coastal plain. These groups are commonly fine grained and well sorted. The differences in pore architecture arise from differences in primary depositional fabric and rock-frame mineralogy and their subsequent diagenetic alteration; yielding predictive trends in porosity-permeability space.
Drainage and imbibition saturation-height models have been developed from core studies and integrated with logs to verify that reservoirs are at primary drainage and to highlight any potential imbibition due to trap tilting or leaking. Centrifuge and multicycle mercury injection data were integrated to produce composite drainage capillary pressure curves. Stressed mercury extrusion tests are commonly used for modeling water saturation through the imbibition process. These tests display no correlation with rock quality at low capillary pressures. To circumvent these problems, mercury extrusion was integrated with maximum-trapped-gas measurements obtained by countercurrent imbibition experiments.
Using the resistivity-derived water saturation model as reference, the free-water level for drainage and imbibition models was optimized by matching saturation-height models in reservoirs free of resistivity shoulder-bed effects. The accuracy of the match in different rock qualities provided insights on the likely saturation state of reservoirs. Such observations were used to develop successful interpretations of the special distribution of free-water level, reservoir architecture, and hydrocarbon charge.
|File Size||29 MB||Number of Pages||18|