5 Effect of High Temp on Muds

8/12/2019 5 Effect of High Temp on Muds

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1Agip KCOWell Area Operations

Drilling Supervisors Training Course Drilling Muds RPW2021A

EFFECT OF HIGH TEMPERATUREON MUDS





EFFECT OF HIGH TEMPERATURE ON MUDS

When exposed to high temperatures, all muds become thinner then stabilize before

reaching their thermal limit.

When static downhole temperatures become excessive, both gelation and excessive

viscosity become major concerns. Rheological properties affect many downhole

parameters, including Equivalent Circulating Density (ECD), hole cleaning, barite sag,

surge/swab pressures during tripping, pump pressures and bit hydraulics.

A preventive study has to be conducted when a well has to be drilled in HT-HP

condition. It concerns measurement of rheology and it is run using a VIRTUAL

hydraulics programme to estimate and if necessary, modify the behaviour of the fluids






Rheology takes on an even greater importance in deep HTHP wells where the

typically smaller hole diameter increases ECD pressures.

Thermal thinning of water-base mud compared to water





Abnormal pressure in HTHP wells require high mud density.

The risk of becoming differentially stuck increases in an HTHP well because the mud

weight needed to control pressures may be much higher than the pressure in other

exposed formations.

Excessive viscosity and gelation increases the possibility of lost circulation.

Contamination also will have a destabilizing affect on filtration control and will reduce

the thermal stability.






The lubricity of the filter cake is an important factor in avoiding stuck pipe, especially

in extended-reach, high- angle wells.


Effect of bentonite concentration on thermal stability





In water based mud system

Conventional WBM are sensitive to temperature, but are not very compressible.

Active clays can promote gelation and other rheological problems at high

temperatures for HT-HP applications. When a WBM system is designed, bentonite

concentration must be kept low (5 lb/bbl for 18 lbs/gal MUD)

Conventional treatment to WBM in HT ambient:

• Addition of thermal rheological stabilizers (anionics).

• Addition of thermally stable fluid loss additives.

• Maintaining Ph as much stable as possible.

• Prevent contamination of CO2 (from degradation of lignite/lignosulfonate) by addition

of lime.











EFFECT OF THE TEMPERATURE ON MUDS

IN OBM SYSTEM

Oil-based systems are sensitive to both temperature and pressure. Oil-based fluids thin

with increasing of temperature and expand, so downhole viscosity and density will be

different from that measured on the surface. Fortunately, this situation is compensatedby the compression due to high pressure and high density.

Conventional treatment from OBM in HT situation:

• Use of special high temperature organophilic clay.

• Addition of high-temperature asphaltic fluid loss (5 to 15 lb/bbl).

• Maintain an excess lime content higher than usual (>10 lb/bbl).

In HTHP well there are some limitations while using OBM:• If lost circulation occurs, it is more difficult (and more expensive) to control the problem.

• Barite settling in case of decrease in viscosity (for gas influx).

• Kick detection. It Is more problematic because of the solubility of the gas in the OBM

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5 Effect of High Temp on Muds