Field Performance of Ultralightweight Cement Slurry Compositions Used in the UAE
- B.N. Murali (Halliburton Services) | C.H. Tanner (Halliburton Services)
- Document ID
- Society of Petroleum Engineers
- SPE Production Engineering
- Publication Date
- August 1987
- Document Type
- Journal Paper
- 150 - 156
- 1987. Society of Petroleum Engineers
- 5.6.1 Open hole/cased hole log analysis, 1.10 Drilling Equipment, 1.14.3 Cement Formulation (Chemistry, Properties), 1.14 Casing and Cementing, 3 Production and Well Operations, 1.6 Drilling Operations
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Summary. Operators in the UAE have achieved a high degree of success with a high-strength microsphere (HSMS) cement additive to deal with lost circulation during drilling and/or cementing. Slurries made with the additive maintain good strength properties at low weights.
Of the various drilling conditions encountered in the UAE, loss of circulation during drilling or cementing is a severe and costly problem. One UAE operator, even when using conventional lightweight slurries, could not depend on returning cement to the surface when cementing surface casings. Some wells required one to five top-out jobs and/or other remedial work. When ultralightweight slurries prepared by adding an admixture of HSMS were used, cement could be returned to the surface without difficulty.
On the basis of the success of the surface casing jobs, the operator tried HSMS slurries to combat the lost- circulation problem during cementing of intermediate casings. The results (cement returns to surface and well log analyses) were good enough to prompt the operator to install a standardized cementing program that includes exclusive use of ultralightweight cements for all casings. Other UAE operators have successfully applied ultralightweight HSMS slurries. This paper presents an overview of their operations.
Theory and Definition
In the past, final density of a cement slurry was reduced by the addition of water, silicate extenders, or fillers, and the lowest practical density of cement slurries was about 11 lbm/gal [1318 kg/m3]. The limiting factors were predominantly physical; i.e., as water and fillers were predominantly physical; i.e., as water and fillers were added to a cement, the amount of cementitious materials was reduced. Diluted slurries have reduced compressive strengths and higher permeabilities. When HSMS's are used in a cement slurry, the same trends are evident; however, they are not noted until significantly lower weights have been achieved, compared with conventional light-weight slurries, because water is no longer the maim diluent used to reduce the slurry density when HSMS is used. The additive contains a gas encapsulated inside the HSMS. The encapsulated gas in the HSMS admixture is the principal factor in reducing the slurry density; slurry weights as low as 8.5 lbm/gal [1019 kg/m ] can be mixed with HSMS admixtures. This material has been successfully used in the Middle East for the past 5 years.
A cement composition with HSMS was initially used to enhance a cement slurry to combat lost circulation because the HSMS greatly reduced density and provided bridging capability. This composition was advantageous for cementing fragile permafrost formations and subsea conductor pipes and offshore casing set in unconsolidated mudstone and silt, as well as for weak, incompetent zones in general. HSMS has been successfully applied in these demanding situations and in the Middle East.
HSMS consists of hollow, inorganic, fused spheres similar in size to the coarse silica flour that is commonly used in oilwell cementing. Because of its size and particle distribution, HSMS offers several advantages.
1. It is easy to wet.
2. It can be readily mixed with conventional cement-mixing equipment.
3. It has a specific gravity less than the weight of water at most pressures.
4. It acts as a lost-circulation bridging material.
5. It is compatible with oilwell cements and their additives.
6. It can create slurries that have densities less than the weight-of water.
7. It aids in promoting acceptable early compressive-strength development.
8. It increases slurry yield compared with the yield of conventional cement slurries.
9. It aids in achieving relatively low permeability values.
Operator Background Information
A typical casing program used by one offshore operator is given in Table 1 (see Fig. 1). Many years of drilling have shown that even though circulation may not be lost during drilling of a 26-in. [66-cm] hole, losses during cementing of the 20-in. [51-cm] casing were a certainty. Numerous additives and procedures have been tried with little or no success. Top-out jobs on the 20-in. [51-cm] casing were an accepted practice in this area of the Arabian Gulf.
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