Abstract

This paper discusses the importance of obtaining a good cement job in well completions, and the three areas vital to obtaining this effective wellbore cement seal. These three areas are (1) formation cement interface (2) casing cement interface, and (3) the cement sheath itself.

An operator is interested in getting best cement job possible for several reasons:

  1. shut off and/or protect fresh and salt-water zones,

  2. segregate producing zones,

  3. eliminate communication between gas-oil, oil-water, or gas-water contacts,

  4. stabilize the casing string, and

  5. seal well fluids in wellbore to prevent surface or subsurface pollution. prevent surface or subsurface pollution.

The steps involved in obtaining a good wellbore seal are (1) good borehole conditions, (2) good wellbore cleanup prior to cementing, (3) removal of excess filter cake from permeable formations, (4) selection of correct cement composition for given well conditions, (5) proper centralization of the well casing, and proper centralization of the well casing, and (6) preparation of the external casing surface for maximum cement bonding.

Several field case histories are presented to show the effectiveness of proper cementing practices, particularly the effectiveness of practices, particularly the effectiveness of resin-sand coating of the casing in producing an extremely strong bond between cement and casing. The application of the Cement Bond Log for evaluation of the final cement job is also presented. The paper concludes that potential presented. The paper concludes that potential problems of fluid leakage and their consequences problems of fluid leakage and their consequences can be minimized by the proper use of known technology.

Introduction

The cementing of oil, gas, gas storage, injection, and disposal wells throughout the industry has received a great amount of attention over the past 50 years in both research and field development areas. This attention and research is continuing. Probably no other aspect of the completion operation has been as widely studied and discussed. Yet, cementing problems continue. Partially, this is due to problems continue. Partially, this is due to the complexity of the problem, but unfortunately, it is also partly due to failure to properly apply known technology.

The cementing operation is designed to (1) shut off and/or protect fresh and saltwater zones, (2) segregate producing zones, (3) eliminate communication between gas-oil, oil-water, or gas-water contacts, (4) stabilize the casing string, and (5) seal well fluids in the wellbore to prevent environmental contamination.

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