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Bentonite is not typically used as the primary fluid-loss agent in normal-density slurries. In low-density slurries, where higher concentrations can be used, it may provide sufficient fluid-loss control (400 to 700 cm 3 /30 min) for safe placement in noncritical well applications. Fluid-loss control, obtained through the use of bentonite, is achieved by the reduction of filter-cake permeability by pore-throat bridging. Microsilica imparts a degree of fluid-loss control to cement slurries because of its small particle size of less than 5 microns. The small particles reduce the pore-throat volume within the cement matrix through a tighter packing arrangement, resulting in a reduction of filter-cake permeability.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.33)
- Information Technology > Knowledge Management (0.40)
- Information Technology > Communications > Collaboration (0.40)
Remedial cementing requires as much technical, engineering, and operational experience, as primary cementing but is often done when wellbore conditions are unknown or out of control, and when wasted rig time and escalating costs force poor decisions and high risk. Squeeze cementing is a "correction" process that is usually only necessary to correct a problem in the wellbore. Before using a squeeze application, a series of decisions must be made to determine (1) if a problem exists, (2) the magnitude of the problem, (3) if squeeze cementing will correct it, (4) the risk factors present, and (5) if economics will support it. Most squeeze applications are unnecessary because they result from poor primary-cement-job evaluations or job diagnostics. Squeeze cementing is a dehydration process. A cement slurry is prepared and pumped down a wellbore to the problem area or squeeze target. The area is isolated, and pressure is applied from the surface to effectively force the slurry into all voids. The slurry is designed specifically to fill the type of void in the wellbore, whether it is a small crack or micro-annuli, casing split or large vug, formation rock or another kind of cavity. Thus, the slurry design and rate of dehydration or fluid loss designed into the slurry is critical, and a poor design may not provide a complete fill and seal of the voids.
- North America > United States > Texas (0.93)
- Europe (0.67)
- Geology > Mineral > Sulfate (0.69)
- Geology > Geological Subdiscipline (0.67)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.46)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.45)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Information Technology > Knowledge Management (0.40)
- Information Technology > Communications > Collaboration (0.40)
In-situ gas generation * 7 Miscellaneous additives * 8 Antifoam additives * 8.1 Effects of foaming * 8.2 Use and characteristics of antifoam additives * 8.3 Types of antifoam additives * 9 Mud-decontaminant additives * 10 Radioactive tracers * 11 Dyes * 12 Fibers * 13 References * 14 See also * 15 Noteworthy papers in OnePetro * 16 External links Two forms of derivatized cellulose have been found useful in well-cementing applications. The usefulness of the two materials depends on their retardational character and thermal stability limits. This is commonly used at temperatures up to approximately 82 C (180 F) for fluid-loss control, and may be used at temperatures up to approximately 110 C (230 F) BHCT, depending on the co-additives used and slurry viscosity limitations. Above 110 C (230 F), HEC is not thermally stable. HEC is typically used at a concentration of 0.4 to 3.0% by weight of cement (BWOC), densities ranging from 16.0 to 11.0 lbm/gal, and temperatures ranging from 27 to 66 C (80 to 150 F) BHCT to achieve a fluid loss of less than 100 cm3 /30 min.
- Information Technology > Knowledge Management (0.40)
- Information Technology > Communications > Collaboration (0.40)
Summary Polymeric viscosifiers are added to cement slurries for a variety of reasons, including prevention of particle settling and control of fluid loss, gas migration, and free water. Many of these functions are critically important after the cement slurry has been placed behind the casing but before the setting of the cement. Some functions, such as particle-settling prevention, are also important during the pumping phase. Unfortunately, most of the viscosifying polymers suffer from thermal thinning at bottomhole temperatures, especially under shear. The amount of polymer required to maintain the required level of viscosity at elevated bottomhole temperatures causes excessive surface-slurry viscosification at ambient temperature. Pumping such slurries can require higher pump pressures, which, in some cases, might exceed formation breakdown pressures causing unintended fractures.This becomes a serious challenge when the window between the fracture pressure and the pore pressure of the formation is narrow. It would be a significant improvement to oilfield cementing technology to develop polymers that do not cause excessive slurry viscosification on the surface but gradually increase the slurry viscosity as it reaches downhole temperatures, with the maximum viscosity reached at the time the slurry becomes static behind the casing. This paper describes a chemical method, not based on encapsulation, for modifying biopolymers and their derivativesโfor example, hydroxyethylcellulose (HEC) and xanthanโthat renders them insoluble in cement slurries at room temperature (RT). When the cement slurries containing modified HEC are heated, the slurries develop viscosity upon heating, as reflected by changes to slurry rheology with temperature. The method also provides for increased viscosification efficiency of the modified polymers because of the increased molecular weights of the modified biopolymer products. Synthesis details, slurry rheologies at different temperatures, and job-placement simulation details are presented. A possible reaction mechanism that is operative in the chemical-modification step is also discussed.
- North America > United States (0.70)
- Europe > Norway > Norwegian Sea (0.25)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.49)
Abstract Extensive results from field tests in the Rocky Mountain area show how cement bonding may be improved through the use of a spacer, wash, and thixotropic cement. These results are the culmination of nearly three years field work undertaken to determine what factors affect bonding and what methods or materials could be used to consistently improve the cement -to-pipe and cement-to-formation bond. This paper discusses the recognized conditions associated with poor cement bonding and the materials that were used alone and in combination to improve cement bonding. Bond logs and other data are presented to show the results obtained through the use presented to show the results obtained through the use of a spacer, wash, and thixotropic cement. Other techniques used to improve cement jobs are briefly discussed. Introduction Field experience and laboratory studies have contributed to a better understanding of conditions which cause poor cement jobs. Some of the recognized problems in cementing are: problems in cementing are:Improper pipe centralization. Improper mud conditioning prior to cementing. Improper removal of mud during cementing. Cement contamination by mud. Cement-mud imcompatability (excess viscosity at interface). Loss of fluid from cement slurry. Gas cutting of cement prior to set. Lost circulation before or during cementing. Breakdown of zones after cementing(fallback). Salt and coal sections Washouts. Poor pipe centralization can be corrected by the Poor pipe centralization can be corrected by the proper number and placement of centralizers. proper number and placement of centralizers. Centralization aids in the removal of circulatable mud from the annulus during cementing. Proper mud conditioning through chemistry and sufficient circulation can be accomplished prior to cementing. Solving the problems associated with any one of the remaining listed items is important. However, where two or more of the conditions that cause poor cement jobs we present, the solution to obtaining a good cement job becomes more difficult. Most of the formations (Fig. 1) discussed in this paper, have several conditions which attribute to paper, have several conditions which attribute to poor cement jobs. Also, many of the bond logs poor cement jobs. Also, many of the bond logs presented in this paper indicate the presence of presented in this paper indicate the presence of these conditions. It has been difficult to correct all of these conditions in a single cementing operation. These correction efforts have either destroyed the system or resulted in the cost of the system becoming too expensive. The discussion of the bond logs and pressure data will show how the use of a spacer, wash, and thixotropic cement can improve cement jobs under a variety of conditions. SPACER A recently developed water-base spacer fluid that precedes the cement will solve many problems which precedes the cement will solve many problems which cause poor cement jobs. This spacer meets the following criteria:Compatible with most drilling fluids. Compatible with cement systems. Establishes fluid loss control ahead of the cement slurry. Viscosity control to provide a piston effect for efficient mud removal. Can be weighted to match or exceed the density of most drilling fluids. Can be salt saturated. Easily handled and mixed with conventional cementing equipment. The material for preparing the spacer is packaged in 50-lb sacks. One sack mixed with 39.2 gal of water will yield one bbl of 9 lb/gal spacer. This spacer is also compatible with lost circulation materials. WASH A wash system used ahead of cement slurries needs to meet as army of the criteria listed for the spacer system as possible.
- North America > United States > Colorado (0.97)
- North America > United States > Wyoming (0.96)
- North America > Canada > Alberta (0.71)
- North America > Canada > British Columbia (0.61)
- North America > United States > Wyoming > Uinta Basin (0.99)
- North America > United States > Wyoming > Powder River Basin > Shannon Formation (0.99)
- North America > United States > Wyoming > Bighorn Basin > Phosphoria Formation (0.99)
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