Paper: The Cement-Scan Log Total Cement Evaluation For West Texas Wells

Schlumberger's Cement-Scan * log was offered to west Texas clients in June 1985. Since then, the product has greatly enhanced interpretation of cement conditions where standard cement evaluation techniques left unanswered questions. Specifically, the Cement-Scan log has provided superior answers in light (or foam) cements and in cements degraded by gas intrusion. The Cement-Scan log is a single presentation that combines information from both the CET* cement evaluation log and the CBL cement bond log. Through the use of a statistical gas logic system, Cement-Scan measurements can be used to discriminate between water channels and gas-cut cement behind the casing. Also, a new light-weight cement compressive strength algorithm is available for use when a known light or foam cement has been used in cementing operations. A cement map (from CET data) with shadings corresponding to acceptable cement, water channels, gas-cut cement, and free gas is presented. Additionally, a radial profile presents the four materials in terms of percent circumferential coverage of each. The above information is further enhanced by presenting a bond index curve and a Variable Density display from the CBL. The utility of the Cement-Scan log is illustrated by citing several examples from actual west Texas wells. Interpretation techniques, as well as gas logic verification, are described.