Perched Water Contacts: Understanding Fundamental Controls
- Iulian N. Hulea (Shell Global Solutions International BV)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- June 2019
- Document Type
- Journal Paper
- 438 - 449
- 2019. Society of Petrophysicists & Well Log Analysts
- 40 in the last 30 days
- 103 since 2007
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Building realistic and reliable subsurface models requires detailed knowledge of both the rock and fluids involved. While the hydrocarbon volume estimation has a profound impact on the viability of a development, next to the permeability, saturation-height models, free-fluid levels (FWLs) and the hydraulic communication have a significant role in determining the recoverable reserves.
When in different parts of the same field different free-fluid levels (leading to different fluid contacts for the same rock quality) are identified, the lateral hydraulic communication at the field level can be challenged. This aspect is of importance since the hydrocarbon volume distribution impacts the recovery factor. At the same time building and initializing a model based on different FWL positions (zero capillary pressure) is challenging.
Perched water contacts are the result of water entrapment (behind barriers for lateral flow) during hydrocarbon migration in the reservoir, as a result leading to locally elevated FWL or hydrocarbon-water contact position (for comparable rock quality). A signature of perching is that between two sampled wells, the hydrocarbon (HC) column is in hydraulic communication while two mobile water pools seem to be disconnected. The fundamental controls that lead to the formation of perched contacts are studied and shown to be the rock quality and relative permeability. The perching effect is not going to feature in poor quality rocks (submillidarcy permeability)—the effects would be visible only for a considerable barrier height. Regarding transition zones, the results showing no significant difference are expected above the perched zone when compared to the unconstrained parts of the field. Field observations and dynamic simulations are used to identify the perching controls. A clear distinction is shown between capillary pressure and buoyancy. The fundamental assumption that the capillary pressure can be calculated by using the height above FWL is shown to be deficient when water becomes immobile.
|File Size||10 MB||Number of Pages||12|