Cement slurries

Collapse load originates from the hydrostatic pressure of drilling fluid, cement slurry outside the casing and later on by moving formations e.g. salt... 

The chemistry of cement slurries is complex. Additives will be used to ensure the slurry remains pumpable long enough at the prevailing downhole pressures and temperatures but sets (hardens) quickly enough to avoid unnecessary delays in the drilling of the next hole section. The cement also has to attain sufficient compressive strength to withstand the forces exerted by the formation over time. A spacer fluid is often pumped ahead of the slurry to clean the borehole of mudcake and thereby achieve a better cement bond between formation and cement. 

The KDF Filter. The KDP filter (Pig. 23) (Amafilter, Holland) is based on the same principle as disk filters. It was developed for the treatment of mineral raw materials, like coal flotation concentrates or cement slurries, and can produce a filter cake of low moisture content at very high capacities, up... 

Zement-beton, m, cement concrete, -brei, m-cement slurry, -breanofen, m. cement kiln. 

Cementing Principles 1179. Properties of Cement Slurry 1183. Cement Additives 1193. 

Specific weight is one of the most important properties of a cement slurry. A neat cement slurry is a combination of only cement and water. The specific weight of a neat cement slurry is defined by the amount of water used with the dry cement. The specific weight range for a particular class of cement is, therefore, limited by the minimum and maximum water-to-cement ratios permissible by API standards. 

For dealing with other powdered materials that are additives to cement slurries, the absolute volume must be used. The absolute volume (gal) is... 

Properties of Neat Cement Slurries for Various Classes of API Cements... 

It is often necessary to decrease the specific weight of a cement slurry to avoid fracturing weak formations during cementing operations. There are basically two methods for accomplishing lower specific weights. These are... 

The cementing operation time (hr) is the time required for the cement slurry to be placed in the well ... 

The cement slurry chosen must have a thickening time that is greater than the estimated time obtained for the actual cementing operation using Equation 4-327. Thus, T > T. ... 

Thus the minimum thickening time for the cement slurry to be used this cementing operation is... 

A properly designed cement slurry will set after it has been placed in its appropriate location within the well. Cement strength is the strength the set cement has obtained. This usually refers to compressive strength, but can also refer to tensile strength. Cement having a compressive strength of 500 psi is considered adequate for most well operations. 

In the shear bond strength test, the cement slurry is allowed to cure in the annulus of two concentric steel cylinders. After curing the force to break the bond between the set cement and one of the cylinders (usually the inner one)... 

For Example 2, determine the total weight that can be supported by the set cement bonded to the 9 -in. casing. As.sume the cement slurry yield is 1.05 fC/sack... 

There are many chemicai additives that can be used to alter the basic properties of the neat cement slurry and its resulting set cement. These additives are to alter the cement so that it is more appropriate to the surface cementing equipment and the subsurface environment. 

The most common low-specific-gravity solids used to reduce cement slurry specific weight are bentonite, diatomaceous earth, solid hydrocarbons, expanded perlite and pozzolan. It may not be possible to reduce the cement slurry specific weight enough with the above low-specific-weight materials when very weak formations are exposed. In such cases nitrogen is used to aerate the mud column above the cement slurry to assist in further decreasing the hydrostatic pressure. 

Nearly all materials that are added to a cement slurry require the addition of additional water to the slurry. Table 4-160 gives the additional requirements for the various cement additives [167]. 

Hematite. This additive can be used to increase the specific weight of a cement slurry to as high as 19 Ib/gal. This is an iron oxide ore with a specific gravity of about 5.02. Hematite requires the addition of some water when it is used as an additive. Hematite has minimal effect on thickening time and compressive strength of the cement. 

A specific weight of 12.8 Ib/gal is required for a Class A cement slurry. It is decided that the cement be mixed with bentonite to reduce the specific weight of the slurry. Determine the weight of bentonite that should be dry blended with each sack of cement. Determine the yield of the cement slurry. Determine the volume (gal) of water needed for each sack of cement. 

It is often necessary to either accelerate, or retard the thickening and setting time of a cement slurry. 

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