Fault Block Migrations Inferred from Asphaltene Gradients
- Chengli Dong (Shell International Exploration and Production Inc.) | Melton P. Hows (Shell International Exploration and Production Inc.) | Peter M.W. Cornelisse (Shell International Exploration and Production Inc.) | Hani Elshahawi (Shell International Exploration and Production Inc.)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2014
- Document Type
- Journal Paper
- 113 - 123
- 2014. Society of Petrophysicists & Well Log Analysts
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- 155 since 2007
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Characterization of complex reservoirs with multiple fault blocks is critical, especially in deepwater fields where an accurate description of sand continuity and fluid connectivity across fault blocks significantly impacts reserve assessment and production planning.
In this paper, a new methodology based on the distribution of reservoir fluid properties, especially asphaltene gradients, is developed to reveal details of reservoir structure and geological history. To our knowledge, this is the first study using asphaltene gradients to track fault-block migration and thereby represents an important new capability of fluid analysis for reservoir characterization. Depending on the reservoir charging history (sequence of heavy/light oils and gases), the asphaltene content of reservoir fluids is typically not in equilibrium at the initial charging stage. After charging, asphaltenes tend to equilibrate by mass flux through permeable connected sands so that the asphaltenes exhibit a smooth and equilibrated gradient. In isolated sand packages, or those with barriers or tortuous connectivity, asphaltenes remain in disequilibrium, often exhibiting abrupt changes.
Furthermore, during or after fluid equilibration, subsequent geological events such as faulting and folding may occur, resulting in displacement of fault blocks with their fluids. After faulting, originally equilibrated asphaltenes may exhibit a disequilibrium gradient across isolated fault blocks. On the other hand, fluid and asphaltene can re-equilibrate over juxtaposed sands that became newly connected after faulting.
Therefore, fluid distributions are impacted by sand connectivity in current reservoir architecture as well as geological dynamic history. The method applied in this paper uses an Equation of State (EoS) to assess asphaltene equilibrium, which is measured with a downhole fluid analysis (DFA) technique with high resolution and accuracy. An illustrative field study demonstrates how this method can provide insight into detailed reservoir structure, which improves accuracy of cross-section plot with reliable sand connectivity for improved production planning and field management.
|File Size||6 MB||Number of Pages||11|