Well Cementing

• Title : Well Cementing [ pdf ] by Erik B. Nelson
• Publish : Schlumberger Educational Services 300 Schlumberger Drive SugarLand, Texas 77478
• Type Document : pdf 
• Release : December 1990
• Total Page : 487 Page
• Size : 40.15 Mb

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Decrypted Contents

Testing Equipment

One of the most outstanding developments of mechanical testing devices for cement slurry design was the hightemperature, high-pressure thickening time tester developed in 1939 by R. F. Farris (retired, Amoco Production Company) (Smith, 1987). This device allowed a more accurate determination of the thickening time of cement slurries under a simulated downhole environment of
temperature and pressure. This device continues to be the standard for the industry 50 years later, and is part of the API Specification 10 for well cements.

Flow After Cementing
Perhaps the most important development for deeper high-pressure gas wells has been the control of flow after cementing. Without proper slurry design, natural gas can invade and flow through the cement matrix during the WOC time. This gas must be prevented from invading the cement. Failure to prevent gas migration can cause such problems as high annular pressures at the surface, blowouts, poor zonal isolation, loss of gas to nonproductive zones, poor stimuation, low producing rates, etc. All of these are costly to correct. It is generally acknowledged in the industry that the mechanism that allows gas invasion into the cement matrix is the gel-strength development
of the slurry as it changes from a liquid to a solid. In this condition, the cement loses its ability to transmit hydrostatic pressure, and gas invasion may occur. Other mechanisms include excessive fluid loss, bridging, and
the formation of microannuli. There are several successful methods (Cheung and Beirute, 1985; Garcia and Clark, 1976; Webster and Eikerts, 1979; Bannister et al., 1983; Tinsley et al.; 1980; Griffin et al., 1979) to control gas migration as shown in Fig. 4, each with its advantages. Usually a combination of methods works best. In selecting optimum methods for controlling gas migration, many well conditions must be considered: formation pressure, permeability, gas flow rate, bottomhole temperature; wellbore geometry, well deviation, height of the cement column, and formation fracture pressure.

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