AIM
a. To provide a practical or laboratory means of evaluating hydraulic cement for a particular type of oil well cementing operation.
b. To prove a practical field or laboratory means for a direct comparison of two different cements under identical conditions of temperature and agitation.
Apparatus
The apparatus used is the Halliburton Atmospheric consistometer.
INTRODUCTION
The knowledge of the behavior of cement slurries under elevated temperature is necessary to understand properly cement rheology in moderate deep well cementing operations. The design of optimum cement slurry for oil well is highly challengeable for high temperature wells because slurry stability is a major requirement for successful oil well cementing. The main objective of cementing include, control of abnormal pressure, zonal isolation, prevent hole from washout and caving.
THEORY
Cement slurries are complex multicomponent dispersion systems based on water and plugging material with different additives that are designed for plugging of different channels in a well (space between the casing string and formation wall) and in a formation (formation fractures). They are also used for well casing and cementing, stabilization of producing formation, and isolation of formation water inflow.
Many chemical compounds have proved to be effective in modifying the properties of Portland-cement slurries. These compounds, when used alone, will have a primary effect upon the cement slurry that is considered to be beneficial. They will also exhibit at least one secondary characteristic that may be either beneficial or detrimental to the cement-slurry performance properties. The effects of the additives are reduced or enhanced by modifying the additive or by using additional additives. For most downhole requirements, more than one additive is needed. This give-and-take relationship between additives is the basis of cement-slurry design.
The reaction of these additives with the cement and the interaction between them is not well defined chemically. What is actually known are the physical effects of these additives on the slurry performance properties? The slurry performance properties that are measured include: thickening time, compressive strength, rheology, fluid loss, free fluid, and slurry stability.
Cement manufactured to API depth and temperature requirements can be purchased in most oil-producing areas of the world. Any properly made Portland cement (consistent from batch to batch) can be used at temperatures up to 570°F. For example, Class H cement with the proper additives has routinely been used at depths up to 20,000 ft.
The Halliburton Atmospheric Consistometer provides a simple method for conditioning the cement slurries in preparation for performing these tests.
The slurry is poured into a container and placed into the consistometer. Next, the temperature and pressure are brought to the desired levels. The slurry container is rotated at a constant speed to impart circulation to the cement in the slurry container.
The temperature control loop controls the rate of rise of temperature in the slurry. When it reaches the set level the control loop automatically holds the temperature at that level until the cement sets. Control of pressure is maintained by adjusting the air pressure to a pump and by operating a pressure relief valve. The consistency (viscosity) of the cement is determined by measuring the torsion generated by the slurry pressing against a standard paddle as the slurry container is rotated.
Test Procedure
Remove the two slurry containers and fill them with freshly prepared slurries to mix inside the containers. The volume of slurry to these marks is 500cc. Replace the containers and inserts the paddle and lid. Being careful that the slotted shaft engages the pin on the lid. Switch on the instrument. The fluid level gauge should indicate a half-full position.
Select a suitable temperature using one of the positions (LOW, MEDIUM 0R HIGH) of the thermo regulator knob. One of the neon lights should go on at each position.
Select a suitable rotary speed using the Rotary shaft control.
When the instrument is on. the viscosity of the slurry is read directly on the consistency dials for any selected temperature and rotary speed.
CONCLUSION
Rheological behavior of cement slurry is essential for proper displacement at high temperature condition.
Temperature has effect on the performance of cement slurry as it increase as plastic viscosity and yield point decrease
PRECAUTION
It was ensured that the slurry were properly mixed inside the container.
It was ensured that the slotted shaft was carefully engaged with the pin on the lid.
It was ensured that the viscosity of the slurry was properly read on the consistency dial to avoid error.
REFERENCE
- Allan, M.L. and L.E Kukacka, 1994. Lost circulation control.
- PEE 401 Laboratory manual
- Wikipedia.com
