BAKER HUGHES - Drilling Fluids Reference Manual

TABLE OF CONTENTS
Cementing
• Cementing across in-situ hydrates offers a challenge not yet solved by the industry (i.e., API):
• Cement has an exothermic reaction during transition.
• Hydrates are endothermic during dissociation
• Dissociation of in-situ hydrates by cement can lead to a gas filled void behind casing and
negatively impact the cement bond.
• Foam cement should be used due to:
• The accelerated right-angle set and reduced transition time.
• Lower exothermic temperature when setting over conventional cement
• Past success in shallow gas environments
• The foam cement should be specifically designed to meet these well criteria. All foam
cements are not created equally (stability, quality control, insulating maximization, and
stiffness).
• Cement should be designed to expand.
• Weight of cement should be maximized for hydrate stability.
Weighted mud should be employed to drill the hole section below structure pipe.
• The increase in annular pressure will be advantageous to the stability of the in-situ hydrates
• Free gas, below the in-situ hydrates, will need to be controlled.
• A Dynamic Kill Drilling device should be utilized to supply weighted fluid
HYDRATE FORMATION IN DRILLING FLUID
Hydrate formation in drilling fluids is a relative new experience off shore. Temperature, pressure and
gas composition determines the conditions for hydrate formation. Solidification occurs as the
temperature decreases and/or the pressure increases.
Figure 13 - 5
Idealized Gas Hydrate Pressure/Temperature Plot
Pressure (psi) ---->
Catastrophic
Nucleation
C o o lin g
C yc le
H eating C ycle
Point of
Dissociation
Tem perature (F) ---->
As the temperature of the fluid decreases and/or pressure is increased, seed crystals or hydrate nuclei
are formed. At a critical pressure / temperature / gas combination, catastrophic nucleation and
encapsulation of gas into the hydrate structure occurs. At elevated pressures and low temperatures in
deep water drilling ( > 500m and below 10°C) hydrate formation is promoted. This process is
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 13-14