The Reasons and Mitigations Behind the Casing Deformation After Hydraulic Fracturing: Cases Studies from Oman Deep Tight Gas Wells
Authors: Al Hinai Adnan Saif , Al Jahdhami Ahmed Rashid , Al Farsi Shaima Abdulaziz , Chavez Juan Carlos 
Published: October 2022

Casing deformation has been detected in Oman's deep gas wells after hydraulic fracturing, particularly in Saih Rawl (SR) and Burhaan (BRNW) fields across Miqrat and Barik units. Hydraulic fracturing is a key enabler for the development of these reservoirs, understanding the conditions that lead to casing deformation after fracturing, is fundamental to define strategies to operate, reduce or eliminate its associated impact over well integrity and final hydrocarbon deliverability.

The casing deformation was observed following fracture operations across the target intervals. The deformations were localized in the pipe body and not in the connections, and they were identified as week points. The deformations were characterized by the ovalization of the casing, covering approximately 1 to 2 meters length along the pipe. These deformations could lead in some cases to the complete burst of the tubular or further damage as a result of plug milling operations.

A holistic approach was developed, following the QA/QC of gathered key data, combining the review of multi-arm caliper data, detailed geomechanical properties profiles, mini-frac analysis, camera imaging and casing integrity analysis under the anticipated fracture loads; this covering 3 vertical wells and 1 horizontal well, where deformation after fracturing was clearly detected. Following this combined review and the detailed evaluation of the operational events in each of these wells, it was possible for the first time to identify a correlation between variability of geomechanical properties, fracture propagating pressures and the observed casing deformations.

It will be presented how a strong correlation between high contrast in Young's modulus, with high net pressures observed during fracturing, was identified. It will be also discussed how this deformation occurs in 2 to 5 meters thickness zones, correlating to sharp changes in Young's modulus and high instantaneous shutting pressure gradient, observed during the mini-frac stage. All the prior conditions need to be present to create the circumstances that could lead to casing deformation. It is also clear the need to study in more detail the dynamic interaction between the fracture propagation, rock displacement and casing deformation, in order to enhance the completion, perforation and fracture strategies to prevent or manage this deformation. However, as our understanding has improved, we can now define strategies to reduce the risk and prevent further deformations; these strategies will be shared and discussed.

It is necessary to have a holistic approach to go beyond the analysis performed by using casing strength analysis, to assess the loads imposed during fracturing. It is required to incorporate the interaction of the fracture loads induced -during its propagation- into the formation and the ones generated by the pressure and temperature profile in the completion during fracturing. With the understanding on the conditions that lead to casing deformation in these fields, it was possible to define strategies that can reduce the risk and prevent deformations. Lessons learned can provide knowledge to reduce the impact over well integrity and hydrocarbon deliverability, obtaining improvements in production gains in such tight formations.