Casing restriction was encountered during workovers in 10 wells in a field onshore Central Sumatra, Indonesia. The field is operated by BOB PT Bumi Siak Pusako – Pertamina Hulu. The problem was encountered in a shallow thin sand in the depleted mature field.
A geomechanical study was conducted to determine whether the casing restriction/deformation was from excessive loading, which may have been caused by reservoir deformation and/or shearing because of fault slippages. Geomechanical factors that can contribute to casing loading and shearing include sand failure leading to cavity formation and the loss of casing support in the production interval, reservoir deformation/compaction, faulting from pore pressure changes (depletion or injection) and the corresponding stress changes.
A field-specific geomechanical model was constructed using data acquired in four offset wells drilled in the field to quantify the stresses on the reservoir rock and the existing fault(s) under depletion and subsequent water injection. The model was used in failure analyses to determine whether the stresses were sufficient to cause rock failures and fault slippage that could potentially have deformed the casings.
The study highlights the value of geomechanics as a tool in the petroleum industry for solving production issues in mature fields. Understanding the risk of rock failure because of pore pressure and stress changes enables optimization of well placement, completion design, production parameters and reservoir management to maximize recovery of mature fields.