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The properties of low density foamed cement slurries have been advantageously employed to overcome cementing problems in North and South Dakota, Wyoming, and Montana. For over 30 years, operators in the Williston Basin have encountered completion problems associated with several salt and lost circulation zones. Poor mud displacement in washed out salt sections left long string production casing vulnerable to casing collapse. Weak zones prone to lost circulation necessitated use of multiple stage cementing techniques to perform long string casing cementing jobs. To solve these problems, foam cement has been used with exceptional success. The use of this lightweight cementing system has helped eliminate the problem of collapsed pipe, as well as allowing for the circulation of long intervals of cement, even back to surface, in a single stage.

A problem that has existed in oil well drilling operations is the successful placement of competent cement plugs at desired well depths.Repetitive attempts and failures in obtaining good cement plugs have cost many oil companies a considerable amount of capital both in extra rig time and service company expenses. This problem has recently been investigated with a unique 1/3 scale test model that allows visual observation of cement flow path and behavior of various well fluids during an actual job simulation.Test procedures and results are presented and discussed. Included in the results is a newly developed method which provides for successful plug jobs in severe well conditions. Field results of this method, which are also presented, confirm the results and demonstrate its value in field operations.

Gas migration has been a significant problem in cementing wells drilled in the Praire du Chien formation. Several types of gas-migration cementing systems have been used successfully during the past several years, but only recently has an analytical method been developed to help quantify the nature of gas-migration potential on an individual well basis. Once the probable limits of the gas flow have been established, it is possible to match an appropriate gas-migration-control cementing system for a specific set of well parameters. An important aspect of this process is computer analysis that establishes the probability of gas migration for a given set of well conditions and then selects an effective strategy for designing the cementing program for that particular set of conditions. This paper presents case histories illustrating applications of gas-migration-control cement systems with particular emphasis on the job design process.

Drilling activities in diverse areas can pose significant challenges for conventional cement systems and circulation methods. To overcome these challenges, a unique cementing system and circulation method has been tested in the field with great success. This paper details how these technologies and techniques were successfully used in the cementation process of one casing string in a relatively shallow geothermal well in central California and a relatively deep string in central Wyoming. Globally, a great many wells experience lost-circulation problems that require the reduction of circulation pressures to allow proper placement of cement to provide annular coverage. To help minimize these circulation pressures, cement was pumped into the annulus directly, significantly reducing placement pressures and allowing placement of the cement with no apparent losses - a process referred to as the reverse circulation placement technique (RCPT). In each of the deep and shallow applications discussed, the placement technique and the individual slurry designs address temperature issues. Introduction Drilling and completion of geothermal and deep, hot wells pose a number of challenges, including very high temperatures at great depths and at relatively shallow depths. The high temperatures pose challenges while the well is being drilled and completed, and after construction has been completed. In a geothermal well, CO2 may be encountered in some of the formations, which can be a serious corrosive threat to both the cement and the casing in the well. The most common problem faced when drilling wells in geothermal fields is lost circulation. Because of the typically fractured nature of formations in a geothermal field, lost circulation can cause serious problems during drilling and while casing is cemented across lost-circulation zones. Lost circulation that occurs during a cement job can lead to incomplete sealing of the annulus, which may require remedial cementing in an attempt to fill the annulus. Traditionally, when lost circulation is a problem, operators rely on conventional lost-circulation treatments before cementing. Additionally, various lightweight cement systems are employed to help minimize the pressure while cement is circulated into an annulus, which can help minimize the potential for lost circulation and associated problems. In central Wyoming, a 15,932-ft string of 10 3/4-in. pipe was successfully cemented using the RCPT. The positive results have led to additional applications of the technology in other parts of the U.S.A. A central California geothermal well was cemented using the technology as well. The reverse circulation technique was employed to cement a 13 3/8-in. casing string at a total depth of 3,720 ft. Reverse Circulation Placement Technique In the cementing technique known as RCPT, spacers and cement are pumped directly down the annulus. Using RCPT has a number of potential advantages, along with some challenges.