A New Innovative Cement Evaluation Method for Highly Deviated or Horizontal Wells

Abstract

Evaluation of cement integrity to prevent fluid migration in the annular space behind casing may become challenging under certain well conditions. Conventional cement evaluation tools are useful in most scenarios, but in highly challenging operations (deviated or horizontal wells), there is a pressing need for more advanced cement evaluation and processing techniques to increase the confidence of the measurements for the evaluation of wellbore integrity. Pulse-Echo and/or Flexural wave measurement, along with sonic measurements, are generally run in tandem for improved cement evaluation. The method relies on knowing the wellbore fluid properties (acoustic velocity and acoustic impedance), which may change in deviated or horizontal sections of a well due to mud settling or mud segregation with lighter components on the high side and heavier components on the lower side of the well. This segregation phenomenon, if not accounted for, results in erroneous cement interpretation answers with uncertainty, such as low-acoustic impedance stripe in the direction of heavier mud components. A new advanced ultrasonic technology and its embedded unique inversion processing known as R+, based on 3-parameter inversion approach is developed, which first computes the wellbore mud impedance 360 deg and then uses it as an input to compute the annular material acoustic impedance accurately. This method can also reveal wellbore conditions such as mud settling and segregation. This paper demonstrates the application of new advanced ultrasonic tool and the R+ inversion processing through multiple case studies. In all the cases explained in the paper, we see that due to mud segregation in the borehole, it was difficult to identify true annular conditions. The R+ inversion method was used to confirm the wellbore fluid heterogeneity. All the case studies compare cement evaluation performed using the classic T3 method with R+ inversion method. The uncertainties faced due to mud segregation inside the wellbore were properly addressed with the new R+ inversion method, and the final cement interpretation helps the operators in taking operational decisions in time. The advanced ultrasonic technology and R+ inversion method will ensure accurate cement evaluation in challenging wellbore environments where mud segregation is expected irrespective of casing sizes and cement types. With accurate cement evaluation, the operators can avoid unnecessary costly cement remedial operations at any point (new well, intervention, plug and abandonment), thus impacting the rig activities.