12b. hydrates

8/9/2019 12B. Hydrates

1/42

1

TAMU - Pemex

Offshore DrillingOffshore Drilling

Lesson 12B

Hydrates


2/42

2

Lesson 21 - Hydrates What are they?

Why are they important?

Where are they found?

Conditions for existence

Drilling-related problems

Remedies -

Procedures


3/42

3

Hydrates - What are they?

Gas Hydrates are solids formed

from hydrocarbon gas and liquid

water They resemble wet snow and can

exist at temperatures above the

freezing point of water

They belong to a form of

complexes known as clathrates


4/42

4

The Burning

Snowball

Methane hydrate

supporting its

own combustion


5/42

5

Clathrates - What are they?

Clathrates are substances having a lattice-

like structure or appearance in which

molecules of one substance are completely

enclosed within the crystal structure of

another

Hydrates consist of host molecules (water)

forming a lattice structure acting like a

cage, to entrap guest molecules (gas)

LATIN: clathratus means to encage


6/42

6

Types of Hydrates

The following gases when combined with

water under the right conditions are known

to produce hydrates:

Natural gas molecules ranging from

methane to isobutane Hydrogen sulfide

Carbon dioxide


7/42

7

Hydrates - Why are they

important?

A very large potential source

of natural gas

A hindrance to the natural gas industry

Often cause plugging of lines and

equipment (like an ice plug)

In drilling, under well control situations,

hydrates may plug lines and chokes


8/42

8

A Natural Gas Resource?

Conditions for hydrate formation are

satisfied in more than 90% of the ocean

floors, but hydrates will only be present if

there is a source of natural gas and a

structure suitable for gas accumulation

It has been estimated that total worldwide

hydrate resources are as much as 1016 m3,or twice as large the combined fossil fuel

resource.


9/42

9


Possibly as much as 98% of the hydrate

resource is below the worlds oceans

The remaining 2% that is found on land,

below permafrost, is estimated to be twice

the size of the conventional natural gas

resourse

Natural gas has been produced from

hydrates for decades in Russia


10/42

10


It is estimated that gas contained in

naturally occurring gas hydrates mayexceed 16 trillion tons of oil equivalent

One cubic foot of hydrate can hold 170

standard cubic feet of gas


11/42

11

A Problem in the Natural

Gas Industry?

In the 1930s it was discovered that

natural gas hydrates were blocking gas

transmission lines, frequently at

temperatures well above the freezing

point of water

This discovery led to the regulation of the

water content in natural gas pipelines


12/42

12

A Problem in the Natural

Gas Industry?

It has since been determined that gas

hydrates may exist at temperatures ashigh as 20-30

oC.

As the pressure increases, hydrates can

exist at higher temperatures


13/42

13

A Problem in Drilling?

Where hydrates are present in-situ in

petroleum reservoirs, they can cause

blowouts if drilled into inadvertently Extreme conditions of temperature and

pressure mean that hydrates may form

during the drilling process if fluids

containing water come into contact with

the reservoir fluids


14/42

14


Formation of solid hydrates can plug up

subsea risers, choke and kill lines, and

BO

Ps Conditions during well shut-in are

particularly favorable for hydrate formation

if high pressures are combined with falling

temperatures and there is sufficient time

for equilibrium to be reached


15/42

15


Water depths near the West Shetlands

and Hebrides rapidly reach 1,000 meters

or more, with seabed temperatures down

to -2o

C In the deepwater regions of the Gulf of

Mexico the seabed temperature is

typically around 4o

C or even lower Such extreme conditions present risks of

hydrate formation


16/42

16

Where are Hydrates found?

Hydrates are found in situ in the deep

oceans of the world, on the ocean

floor or in the sediments below the

seafloor

Hydrates are found in situ in

permafrost regions

Hydrates are also found in

extraterrestrial environments


17/42

17


18/42

18


19/42

19

Hydrate-

forming

conditions

for natural

gases


20/42

20

Temperatures Profile in the Gulf of Mexico

0

2,000

4,000

6,000

8,000

0,000

2,000

4,000

6,000

30 35 40 45 50 55 60 65 70 75 80

T , F

D

h, S Fl


21/42

21

Temperatures Profile in the North Sea


22/42

22

Pressures @ 8.6 lb/gal

2

2

2

P u p

p


23/42

23

(not the GOM)


24/42

24

Results of a

typical hydratethermodynamic

test


25/42

25

The probability of hydrate formation increases as

you move towards the supercooled temperature

Schematic ofconstant-volume

temperature

ramping

experiment


26/42


27/42

27

Hydrate-Related Drilling Problems

There are two basic types of hydrate-

related drilling problems:

Drilling through formations already

containing natural hydrates, and

Experiencing drilling conditions that maybe conducive to formation of hydrates


28/42

28

Techniques for drilling through

Zones containing Hydrates Reduce the temperature of the drilling

mud

Drill at controlled drilling rates (not too

fast - to reduce heat generation rates)

Increase mud weight - if possible

Increase mud circulation rate to ensure

turbulent flow to achieve better cooling

and to remove any gas


29/42

29

Techniques to avoid Hydrate

Formation while Drilling

Keeping the temperature above, or the

pressure below hydrate formation

conditions

Using chemicals to depress the hydrate

formation point, i.e., use thermodynamic

inhibitors such as methanol, glycols and

salts (methanol is very toxic)


30/42

30

Techniques for avoiding Hydrate

Formation while Drilling - contdAdding chemicals that reduce the rate of

nucleation of hydrate crystals

Adding chemicals to reduce the rate ofgrowth of hydrate crystals which have

nucleated

Adding chemicals that tend to preventagglomeration of crystals, so that solid

plugs do not form (kinetic inhibitors)


31/42

31

Thermodynamic Inhibitors

Basically, thermodynamic inhibitors

reduce the temperature at which

hydrates will form

The inhibitor dissolves in the water

phase, increasing the stability of the

liquid water with respect to the hydrate

An inhibitor like methanol will also enter

the gas and liquid hydrocarbons


32/42

32

Thermodynamic Inhibitors - contd

Salts are the most commonly usedinhibitors: NaCl, KCl and CaCl2

Saturated NaCl (26%) provides a ~21oK

margin relative to pure water

Glycols and glycerols can also be used

Mixed inhibitors can be used and their

effect is approximately additive

20-23% NaCl polymer muds are the most

commonly used for deepwater drilling


33/42

33

Kinetic Inhibitors

Kinetic inhibitors work by reducing therate of nucleation of hydrates, the growth

rate of the crystals, or the agglomeration

of the crystals They cannot prevent hydrate formation,

but they may increase the delay between

the time when a fluid enters the hydratezone and the formation of a blockage

These have not been tested in drilling


34/42

34

Remedies

Depression

of hydrate-

formationtemperatures

with

methanol and

diethylene

glycol


35/42

35

Remedies

Inhibition ofhydrate

formation

temperatures

caused by glycol

Glycols may

experiencesevere viscosity

increases at

cooler

temperatures

0%

20%40%


36/42

36

Oil-based and synthetic-based muds also require

inhibition since they contain a water phase

Remedies

?


37/42

37

Note that

below ~3,000 ft

water depth,

inhibition with

salt alone cannot guarantee

a hydrate-free

environment

Remedies

Effect of gas gravity, mud weight and

salt content on hydrate stability

Seawatertemperature

profile


38/42

38

Well Control Remediation Methods

Prevent hydrocarbons from entering the

wellbore

(adequate mud weight, rapid shut-in)

If hydrocarbons enter the wellbore,prevent them from reaching the wellhead

(monitoring, bullheading)

If hydrocarbons reach the wellhead andBOP, prevent formation of hydrates

(high salinity mud; glycol mud standby)


39/42

39

Well Control Remediation Methods - contd

If hydrates do form, eliminate them

(methanol on standby for pumping

down kill line, heated seawater ready

to be pumped up riser)

Methods for removing hydrate blockages:

Depressurization to dissociate the hydrate

Addition of chemical inhibitors to melt the

hydrate

External heating to dissociate the hydrate

Mechanical (drilling)


40/42

40

References

Clathrate Hydrates of Natural Gases, by E.Dendy Sloan, Jr., Marcel Dekker, Inc., New

York,1998.

The Properties of Petroleum Fluids, by William

D. McCain, Jr. PennWell Books, Pennwell

Publishing Company, Tulsa, Oklahoma, 1990.

Controlling, Remediation of fluid hydrates in

deepwater drilling operations, by B.Edmonds,R.A.S. Moorwood and R. Szczepanski,

Ultradeep Engineering, March 2001.


41/42

41

References - contd

IADC Deepwater Well Control Guidelines.International Association of Drilling

Contractors. Houston, Texas, 1998.

Lab work clarifies gas hydrate formation,

dissociation, by Yuri F. Makogon and Stephen

A. Holditch. Oil & Gas Journal, Feb.5, 2001.

Experiments illustrate hydrate morphology,

kinetics, by Yuri F. Makogon and Stephen A.Holditch.Oil & Gas Journal, Feb.12, 2001.

SPE, OTC...


42/42

42

THE ENDTHE END

12b. hydrates

Documents