Casings can deform over the life of the well due to various reasons such as changing stress regimes, geological fault and fractures causing pinching, pressure differential created due to production, increased pressure due to injection, squeezing formations such as shale and salt, etc. A detailed casing deformation evaluation can provide insights to the operators in correlating the deformation to suitable reasons in their field.
There are various methods to evaluate the innermost casing or tubing using ultrasonic and mechanical caliper measurements but there is no technology available to evaluate outer or second casing deformation without first retrieving the inner casing or tubing. This work introduces and encapsulates the novel methodology of transforming the outer or second casing third interface echo (TIE) response, obtained by advanced ultrasonic and flexural measurement inside innermost casing or tubing, into a 3D wellbore view to suitably visualize and analyze the outer or second string deformations.
The work involves measuring the azimuthal radius and thickness of the innermost casing with the ultrasonic evaluation technique and computing the azimuthal annular distance between the two casings using the flexural wave TIE arrival time and its velocity in the annular fluid. The computed values are then combined to generate an array of azimuthal internal radius values of the outer or second casing and is finally converted into a 3D wellbore image for better and straight-forward visualization.
To validate the methodology, a shop inspection test (SIT) was carried out where the dimensions of the inner and the outer casing were precisely measured with a mechanical caliper tool. Following that, ultrasonic and flexural measurement tool was run inside the innermost casing to obtain the response of both casings.
The comparison showed a close match between the actual values and the measurements. Also, the 3D wellbore shape clearly showed the geometry of the outer string validating the methodology used in the creation of the 3D shape. The work can enable the operators to carry out time lapse outer string analysis on a periodic basis to give them early indications of any deformation in the outer or second string.
This novel technique or methodology also has valuable application in plug and abandonment (P&A) where the inner tubing and casing retrieval can be hindered due to outer casing deformation. This technique can also help in designing the right drilling BHA for sidetracking based on the minimum ID of the outer pipe through which slot recovery or side-track has to be performed.