Sand production risk prediction in weakly consolidated formations using an integrated geomechanical approach: A case study from Cuu Long basin, offshore Vietnam
Abstract
Sand production during hydrocarbon extraction represents a critical operational challenge, particularly in weakly consolidated formations such as the Miocene sandstones of the Cuu Long basin, offshore Vietnam, leading to production losses, equipment damage, and potential well abandonment. Accurate prediction is essential for optimizing completion design and selecting suitable sand control.
This study presents a multi-index geomechanical approach for predicting sand production risk using five indicators: (1) sonic transit time (DTCO), (2) sand production index - BI, (3) Schlumberger sand production ratio - SR, (4) combined elastic modulus - Ec, and (5) unconfined compressive strength - UCS. These indices are derived from basic well logs (gamma-ray, sonic, and density) and calculated geomechanical parameters.
The methodology was applied to a well in Blocks 01&02 of the Cuu Long basin, where five major sand bodies were subdivided into 15 distinct sub-intervals subject to log response variations. Results reveal substantial intra-sand-body heterogeneity: Sands 1 - 4 consistently exhibit high risk with measured values below critical thresholds, while Sand 5 overall appears low-medium risk. A detailed analysis of Sand 5 indentifies three distinct sub-intervals with dramatically different characteristics. Field validation confirmed prediction accuracy, with 600 psi depletion triggering sand production in the predicted intervals.
Based on these findings, active sand control measures are recommended for all high-risk intervals to ensure safe and sustainable production. The integrated multi-index approach provides enhanced reliability compared to single-criterion methods and can be readily applied to analogous geological settings with similar formation characteristics, offering a cost-effective alternative to extensive core testing programs.
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