Long-term oil production can lead to pressure depletion in mature fields, which can cause noticeable wellbore impairments, particularly in soft formations. This paper presents a case study that was conducted with the application of mature field data from Latin America to identify stress field and casing load alteration caused by long-term production.
A stochastic reservoir model was built integrating field geological, geophysical, and petrophysical analyses. The model displayed facies-controlled petrophysical properties distribution. A simulation model was then developed to provide reservoir pressure profiles. The overburden displacements induced by pressure depletion were calculated using Geertsma’s analytical method based on the poroelasticity theory. Then, the strain and stress fields in the formation were determined following a finite difference scheme. Following, casing integrity and wellbore stability analyses were performed.
Reservoir simulation results show an average pressure drop of approximately 800 psi from initial field pressure. Pressure profiles were used to calculate displacements and stresses in overburden rocks, and displacements were incorporated in casing design software. Results show increased compressional stress along the casing string, which can lead to casing and cement failure. Moreover, the induced stresses caused by pressure drop alter the in-situ stress fields in the formation. The result is stress-cloud movement along the wellbore toward the failure envelope. Corresponding precaution is necessary to help mitigate risks associated with long-term oil production in this field.
This paper provides a methodology for predicting production-induced wellbore integrity problems and suggestions for helping improve safety management and reducing environmental risks associated with mature field development.