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PETE 411Well Drilling

Lesson 32

Cementing - Salt Solutions

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Cementing - Salt Solutions

◆ Use of salt in Cement Slurries

◆ Unsaturated Salt Solutions

◆ Saturated Salt Solutions

◆ Types Cements

◆ Cement Additives

◆ Examples

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Read:Applied Drilling Engineering, Ch. 3

HW #17Cementing of Liner

due November 27, 2002

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Salt in Cement Slurries

Salt Zones

� Salt-saturated cements were originally used for cementing casing strings through salt zones.

� Fresh or unsaturated salt cement slurries will not bond satisfactorily to salt formations because the slurry tends to dissolve or leach away the salt at the wall of the hole.

� Salt-saturated cements will not dissolve any more salt so a good bond can be achieved

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Salt in Cement Slurries

Shale Zones

� Many shales are sensitive to fresh water.

� Salt helps to protect these shales in that they tend to prevent excessive sloughing or heavingof the shales.

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Salt in Cement Slurries

Accelerator

� In low concentrations salt tends to accelerate the setting of cement.

Retarder

� In high concentrations ( >5% by wt. of water) the salt will tend to retard the setting of the cement.

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Salt in Cement Slurries

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Salt in Cement Slurries

Expansion

� Salt results in a more expansive cement.

Freezing

� Salt reduces the freezing temperature of cement slurries.

9of solution

EXAMPLE:200,000 mg of NaCl800,000 mg of H2O1,000,000 mg of solution< 1 litre of solution

ppm

or m

g /L

mg/L

ppm

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Volume of Sodium Chloride Solution

EXAMPLE:Adding 30 lbs of NaClto 100 lbs of H2Oincreases the volume of solution by ~10.7%

30% by weight = 13.8% by volume(SG = 2.17)

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Density of Sodium Chloride Solution

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Example: Salt Solutions

30% NaCl (by weight of water) is added to one gallon of fresh water.

Calculate the density of the mixture:

(i) Before the salt goes into solution(ii) Using the solubility charts shown above.

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Problem : Salt Solutions

(i) Assuming that

lb/gal 9.51 mix ====ρρρρ

8.33) * (2.17 / 8.33) * (0.3011 x 8.33 * 0.301 * 8.33

++++++++====

mixmixSSWWmixmix2211 VρVρVρVρ...VρVρ ====++++====++++++++

mix

SSwwmix V

VρVρρ ++++====

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Problem : Salt Solutions

(ii) From the chart,

{ 9.51 lb/gal vs. 9.8 lb/gal !! }

{ what if we had 60% salt? }

lb/gal 8.9mix =ρ

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Problem

Calculate the density and yield of a cement slurry consisting of:

65% Class “A” cement

35% Pozmix cement,

6% bentonite BWOC and

10.9 gal/sk of water.

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Problem

(i) Initial tabulations and calculations:

Weight Specific Density Component lbs/sk Gravity lbs/galClass “A” 94 3.14 8.33*3.14 = 26.16Pozmix 74 2.46 8.33*2.46 = 20.49Bentonite 2.65 8.33*2.65 = 22.07Water 1.00 8.33*1.00 = 8.33

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Problem

(ii) Determine the properties of one sack of dry cement mixture; 65% Class “A” and 35% Pozmix:

(gal) Vol. (lbs) ht Weig Cement

3362.26.1661.1 61.194*0.65 sk 0.65 A,Class ==

2641.20.4925.9 25.974*0.35 sk 0.35 ,Pozmix ==

3.600 87.0

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Problem

(iii) Determine density and yield of final slurry:

14.7365 183.02

10.9 90.808.33*10.9 gal 10.9 Water,

2365.022.075.22 5.2287*0.06 6% Bentonite,

3.600 87.0 sk 1 mix, Cmt.

(gal)Vol. (lbs) Weight Component

=

==

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Problem

←←←←========ρρρρ lb/gal 42.1274.1402.183

mix

←←←←==== sk/ft 97.1 3

3gal/ft 48.7gal/sk 14.74Yield ====