Cementing over 3000 feet of production casing in an air-drilled hole, where a primary productive gas interval is a naturally fractured shale with a fracture gradient as low as 0.3 – 0.4 psi/ft. at the bottom of the well, presents quite a challenge. Historically this challenge had been met with a 12 ppg lightweight silicate cement, but not without limitations. The compressive strength of the completion slurry in 72 hours measures only 500 – 700 psi, not nearly enough to be seen with the cement bond logging tools most commonly employed. In fact, it is necessary to wait seven (7) days before running a variable density log because that is about the time needed for the cement to develop enough compressive strength and acoustical impedance to be “seen.” Although this slurry solved one problem, it caused another problem - lost production days due to "waiting on cement" time. Using knowledge of available Portland cements and compressive strength enhancing agents, a new cement blend was developed that could get higher compressive strengths and better acoustical impedance in a shorter time frame while maintaining the cement density at 12 ppg and slurry and process economics. Examples of pre and post-solution cement bond logs and economics related to lost days of production over a large drilling program will be presented.
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