A new method of combining nitrogen with an intermediate-weight cement slurry (13 to 15 1 b/gal) to generate a stable foam has solved many of the problems associated with the use of conventional lightweight cements in oil-field operations. Foaming permits placing relatively high-strength, lightweight (6 to 11 lb/gal) cement slurries into the casing-formation annulus economically. Lightweight filler cement is often needed to provide a complete cement sheath along the length of the casing, where lost circulation is encountered or long lifts of cements are required. Various methods have been used in the past to obtain this lightweight slurry. These include the use of natural and chemical extenders, glass bubbles, ceramic bubbles and the combination of intermediate-weight cement slurries with gases. While the process of foaming cement to make lightweight slurries is not new, the technology for applying this process to oil and gas well cementing has been lacking. The new method requires special treatment and slurry design to obtain a hydrostatically balanced slurry along the entire length of the casing, but can be performed with current equipment and field personnel. Laboratory data and case histories have been used to describe these designs. The added safety requirements which must be in effect to successfully complete this type of cementing operation are discussed.
The process of foaming cement to make lightweight slurries is well known and documented in the literature.However, the technology for applying this process to oil and gas-well cementing has been lacking. New techniques and treatment designs have now been developed which show that the use of lightweight foamed cements in oil field operations can solve many problems.Treatments can be performed with the current equipment and personnel operating in the field.When compared to other processes for making ultra-lightweight slurries, foamed cements are very economical.
Results of a three-year study concerni ng the cementing of geothermal wells are reported. The U.S. Department of Energy (DOE) funded research included some specific tasks: (1) determination of properties an adequate geothermal well must possess; (2) thorough evaluation of current high-temperature oi 1 we 11 cement i ng technology ina geothermal context; and (3) recommendation of specific cement systems suitable for use in a geothermal well.
Regulated fill-up cement (RFC) slurries are thixotropic systems designed to aid in cement placement and obtain adequate fill-up in areas or situations where more conventional slurries are unsuccessful. RFC slurries are thin when mixed initially, but develop a high gel strength almost immediately after placement. The purpose of the high gel strength is to make the cement column support its own weight and, thus, relieve hydrostatic pressure at the bottom of the column. Originally developed to prevent fall-back of the cement column in areas of low fracture gradients, the RFC systems have proved capable of solving many difficult proved capable of solving many difficult cementing problems. They have application in shutting off lost circulation during drilling, patching holes in casing, and in reducing gas-cutting of the cement column during primary cementing operation. The RFC systems compare favorably to conventional slurries insofar as chemical and physical properties are concerned and investigation of the hydraulics show they can be placed with less bottom-hole pressure than the conventional slurries. pressure than the conventional slurries Introduction There are areas where the formation fracture gradients are of such low magnitudes that obtaining good cement jobs is difficult. These formations are normally highly-fractured zones, shale zones, granite washes, glacial deposits, etc. When using conventional cement systems, the combination of the hydrostatic pressure and frictional pressure is of such magnitude that these zones will break down and receive most of the cement slurry. The result will be a cement fall-back, leaving long sections of the pipe with no cement to support it. The usual approach to the fill-up problem under conditions encountered in problem under conditions encountered in such formations is a reduction of cement slurry density. This approach has several disadvantages due to the limits of cement weight variance. If a slurry is reduced to its lower limits of density, its set strength and permanence are greatly reduced. Further, with the slurry density at its lowest obtainable value, hydrostatic pressure of a column of the desired height pressure of a column of the desired height may still exceed the critical pressure of the formation. In this case, several stages of cementing will be called for. Each stage of cement has to wait until the previous stage has reached set strength previous stage has reached set strength before it can be placed.
This paper was prepared for the Rocky Mountain Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Denver, Colo., April 10–12, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Specially designed thixotropic cement systems often aid in cement placement and obtain adequate fill-up in areas or situations where more conventional slurries are unsuccessful. These slurries are thin when mixed initially but develop a high gel strength almost immediately after placement. The purpose of the high gel strength is to make the cement column support its own weight and thus relieve hydrostatic pressure at the bottom of the column. Originally developed to prevent fall-back of the cement column in areas of low fracture gradients, the thixotropic systems have proved capable of solving many difficult cementing problems. They have application in shutting off problems. They have application in shutting off lost circulation during drilling patching holes in casing, and reducing gas-cutting of the cement column during cementing operations. The thixotropic, or Regulated Fill-Up Cement, slurries have been used successfully on many wells to date. Since their use permits casing to be set through the pay sections without excessive loss of slurry to the formation, more selective and efficient stimulation treatments can be used. Thus, production increases from stimulation treatments have been two to three folds greater than in wells where conventional slurries were used. This paper describes the thixotropic slurries and compares their physical properties with conventional slurries. Information related to the hydraulics of cementing with thixotropic and conventional slurries is included. Introduction There are areas where the formation fracture gradients are of such low magnitudes that obtaining good cement jobs is difficult. These formations are normally highly-fractured zones, shale zones, granite washes, glacial deposits, etc. When using conventional cement systems, the combination of the hydrostatic pressure and frictional pressure is of such magnitude that these zones will break down and receive most of the cement slurry. Even in cases where a substantial quantity of cement is not lost to the formation during placement, the cement column will recede or fall back after the well is shut in. This leaves long sections of the pipe with no cement to support it. The usual approach to the fill-up problem under such conditions is a reduction of cement slurry density. This approach has several disadvantages due to the limits of cement weight variance.
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