Cement Testing - QA/QC

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All slurry and spacers are designed and tested at the Cementing Contractors Laboratory. Samples of cement (10kg), additives and mixwater must be sent from the well site to the laboratory for this purpose. Testing is carried out according to API Spec 10.

General Guidelines

  • Bulk cement shall be sampled for testing purposes.
  • After retaining a portion for bench testing, the remainder shall be despatched to the Contractor, Mud and Cement Laboratory.
  • The Laboratory test results shall be reported to the Operations Engineer/Drilling Superintendent in the form of a Lab Test Sheet.
  • Samples of all products used during the cementing operation shall be retained in case further testing by the Mud and Cement Laboratory is required.

Note: If necessary, the key cement properties may be reported by telephone or fax.

Despatch of Cement, Additives and Water Samples

Sampling Guidelines

Proper sampling of cement, additives and mixwater is essential to obtain accurate and representative test results. All sampling shall be carried out by the Drilling Supervisor.  

The following guidelines should be applied:

  • During unloading, the Drilling Supervisor shall take a sample directly from the supply line at a point half way along its length, or from the silos. It is essential that the cement sampled is representative of the cement to be used in the forthcoming cementing operation.
  • When powdered additives samples are requested by the laboratory, they must be taken from a sack of the same batch number to be used in the forthcoming cementing operation.
  • When liquid additives samples are requested by the laboratory, they must be taken from the batch to be used in the forthcoming cementing operation. The liquid additive must be well agitated before sampling.
  • Cement, additives and water must be sampled properly and stored/despatched in the appropriate containers. Containers must be clean.
  • Excess air must be removed from the containers since exposure to humid air may affect the results of the test, making the exercise useless, potentially leading to problems during cementation.
  • Samples of all products, including a 1 gal sample of the actual mixwater, must also be taken during the course of the cementing operations and kept on the rig until a few days after the cement job in case the laboratory required them for post mortem analysis of the cementation.

Samples Quantities

The sample quantities required are listed in the following table:

Material

Quantity

Cement

10 kg

Mixwater

1 gal (2 sample bottles)

Powdered additives

one full plastic bag (to be kept in laboratory)

Liquid additives

500 ml (to be kept in laboratory)

Bentonite

10 kg (to be kept in laboratory)

Sample Labelling

Cement Samples

All cement samples should be labelled with:

  • rig name
  • silo number
  • well number
  • the type of cementation forthcoming
  • date received
  • date despatched by flight
  • expected date of first cementation.

Additive and Mixwater Samples

All additive and mixwater samples should be labelled with:

  • rig name
  • well number
  • date despatched (to whom)
  • contents
  • expected date of first cementation

Cement Testing

Consistometer Test Conditions

The Pan Am(erican) Consistometer test is used. It is performed under dynamic conditions with the cement being sheared continuously. The test conditions used are defined the following table:

Parameter

Unit

Definition

Depth

ft

True vertical depth of the cementation

Test pressure

psi

Expected maximum pressure during the cementation (according to API recommendation)

Test temperature

oF

Expected circulating bottom hole temperature (according to API recommendations and related to average temperature gradient)

Slurry Composition

In general, additives for cement slurries are added to the mixwater with the exception of weighting material or silica, which are added to the initial cement slurry or may be dry blended into the cement if batch mixing is not feasible. Dead volume, if present to be taken into consideration when batch mixing.

The amount of dry powder additives to be used is given on the form in % weight by weight of dry cement (% BWOC w/w) and the amount of liquid additives in % gallons per sack (GPS). In addition the amount of water and chemicals required to prepare 1 m3 of mixwater is also given.

The base for mixwater will be specified on the form as industrial (fresh) or sea water. The salinity of industrial water should be less that 300 ppm chlorides.

The water/cement ratio (mixwater requirement) and slurry yield are given in cu.ft/sk.

Slurry Properties

The following key slurry properties are given on the cement test form:

Parameter

Unit

Test Details

Slurry gradient

ppg

 

Pumpability time

minutes

Pan Am consistometer test measured at Bottom Hole Circulating Temperature (API tables)

Thickening time

 

 

Compressive strength

psi

Strength of the cement at cementation depth, after the time shown, as determined according to API recommended practices

HTHP fluid loss

cc/30 min

Determined at 1 000 psi pressure differential and bottom hole circulating temperature

Fann VG Meter Readings

 

Dial readings obtained at 600, 200, 100, 6 and 3 RPM measured at BHCT to a maximum of 200 oF.

Rheology

600 rpm reading
300 rpm reading
200 rpm reading
100 rpm reading
6 rpm reading
3 rpm reading

Tested at standard temperatures 80o F and 457oF

Notes:

* The pumpable time of the slurry must exceed the planned job time, including mixing, by a contingency time to allow for any problems which may be experienced. As a general guide, one hour contingency should be used for casing cementations and half an hour for plug-back cementations.

* The final strength of cement typically used for primary cementations must be greater than 3 000 psi with higher strength around the shoe.

Tests at the Well Site

General Guidelines

The following general guidelines should be applied during bench tests:

Bench testing shall be carried out at the rig site since it is the main mechanism for quality control on the mixwater and provides a comparison with the results of the Mud and Cement Laboratory to confirm that the mixwater of the rig is properly prepared and not contaminated.

Testing must be carried out according to the procedure detailed in this section using representative samples of the cement and mixwater.

Testing should be completed well in advance of the job, so that time is left to make new mixwater and to repeat bench tests if necessary.

Bench tests must be carried out with samples of the mixed slurry to give an indication of when the cement downhole has hardened sufficiently to proceed with operations. It is important to note that the downhole pressure will accelerate the setting of the cement slurry.

Procedure for Testing Mixwater

1. MIX 500 grams of properly sampled cement with enough mixwater to achieve the planned water/cement ratio for five minutes, using the mud mixer (Hamilton Beach) at high speed.

2. PLACE the slurry in a plastic bag in a water bath controlled at expected static bottom hole temperature (SBHT) or at 82o C, whichever is lower.

CALCULATE the expected SBHT.

3. CHECK every 15 minutes for thickening time and hardening time.

 

Notes:

Make sure that the mixwater/additive mixture is homogeneous before sampling.

If the cement job is delayed by a substantial amount of time, with the mixwater having been prepared earlier, extreme care must be taken to ensure that additives have neither settled out nor deteriorated. The bench test should be repeated shortly before the job, leaving enough time to prepare new mixwater if required.

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