Abstract
In North America the primary drilling and completion activities are for horizontal wells. Inclined wellbores make it more difficult to get high quality cement log data and, hence, additional information is necessary for proper execution and evaluation. These guidelines intend to describe which information is required and other critical aspects that need to be considered for obtaining good quality data. Examples of both good and poor quality logs are shown.
The additional information that is needed for proper log execution and evaluation are drilling records such as a gamma ray log for depth control, casing/centralizer record, borehole size, deviation / dog leg severity data and geological data for formation tops and / or ground water identification. Cement slurry densities, maximum expected compressive strength plus pressure/rates used during cementing are also required. Log quality is reviewed with the following aspects in mind:
Common interpretation mistakes
Tool selection
Tool calibration
Procedures during logging
Log presentation formats
Lightweight cement logging considerations
Using pertinent examples and evolving industry procedures, this paper provides necessary information for obtaining quality logs and performing a more effective cement evaluation for highly deviated or horizontal wells. Procedures and guidelines developed primarily for straight hole drilling have, unfortunately and too often, become the acceptable “norm”. Potential interpretation pitfalls have been included. These guidelines provided for will be useful for operators, service companies, and regulators alike to improve overall data and resulting interpretation quality.
Too many times relevant information is not provided and proper procedures are not followed resulting in a misleading or inaccurate interpretation of cement integrity. Therefore, incorrect decisions are being made. By adopting the guidelines presented in this paper better log quality data will result. This will then lead to better business decisions such as changing cementing/drilling procedures or determining if remedial repairs are needed. Better cement isolation could result in more effective stimulations and increased production or prevent fresh water contamination concerns or prevent some surface casing vent flow issues all of which could be very costly.
