Assignment 1

1) What is SAGD?2) Briefly explain the screening Criteria for SAGD:

i. kv/khii. k

iii. viscosityiv. thickness of HC

3) What is steam quality?4) What are other existing thermal method?5) What is steam trap in SAGD? – shallow depth : drill 2 horizontal well6) Summarise SAGD process – include technical term (T,u,k)

Assignment 2

1) What is CSS-Cycling Steam Stimulation2) Describe screening criteria for CSS- energy-inject use gravity, viscous oil3) What is incubation time/ soaking period? What is average soaking period over size? 4) What is steam quality?5) Impress me, Explain about CSS the best.

1) SAGD

Steam Assisted Gravity Drainage (SAGD) is visualized as the

technology with the greatest potential to increase the recovery factor

in heavy and extra-heavy oil reservoirs. This technology is based on

the steam continuous injection process using two horizontal wells, one

injector and one producer, which allows the maximum sweep

efficiency due to the predominant effect of the gravity drainage

production mechanism. With the application of hot steam and

pressure, the tar melts and flows by gravity to the lower well, where it

is pumped to the surface.

Figure 1: Essential feature of the SAGD process

2) Screening Criteria

a. Gravity: >8 to 13.5

b. Viscosity: <200000cp – 4700cp

c. Composition: Not Critical

d. Oil Saturation: >40%-66%

e. Formation Type: High porosity sand/sandstone

f. Net Thickness: >20ft

g. Average Permeability: 200-2540md

h. Depth: <4500-1500ft

i. Temperature: Not Critical

3) Steam Quality:

Figure 2: Phase Envelope

a. What is Steam Quality?

i. Steam quality is the proportion of saturated steam (vapor) in a saturated

condensate (liquid)/ steam (vapor) mixture. A steam quality of 0 indicates 100 %

liquid, (condensate) while a steam quality of 100 indicates 100 % steam. One (1)

lb of steam with 95 % steam and 5 % percent of liquid entrainment has a steam

quality of 0.95. The measurements needed to obtain a steam quality

measurement are temperature, pressure, and entrained liquid content.

ii. A high percentage (88 % or more) of industrial steam systems use saturated

steam for process applications. Saturated steam (meaning steam that is

saturated with energy) is completely gaseous and contains no liquid. The boiler

operation uses chemical energy from a fuel source to deliver energy to the

boiler water. Inside the boiler, liquid gains energy from the combustion process

and changes state into saturated steam. Water enters the boiler at point A and

the water gains sensible energy (hf) to point B.

iii. The change of state is referenced as point B on the chart. As the saturated

steam acquires more energy from the boiler combustion process, the steam

achieves a high quality, (moving left to right) as represented on the chart, points

B to C. The increase in energy gained by the steam from points C to D goes

toward the superheat of the vapor. There exists a directly proportional

relationship between temperature and pressure in saturated steam.

iv. That is, as the temperature increases so does the pressure. Illustrated by the

“Lines of constant pressure” on the graph, more sensible energy (hf) is needed

to for water to transition from point A to point B and become a vapor. When

steam enters the process, the energy level goes from right to left as the process

absorbs the energy from the steam.

b. How is Steam Quality measured?

i. A true measurement of steam quality can be obtained from the use of a

throttling calorimeter and Ganapathy’s steam plant calculations. Unfortunately,

most industrial plants do not have the luxury or capability of doing the testing.

Another way to measure steam quality is relying on the basics of steam.

Saturated steam is a dry invisible gas and only becomes visible with the

entrained air or liquid. Therefore, opening a steam valve and allowing steam to

be released into the atmosphere provides an estimate of the steam quality in

the system.

c. What are the effects of Steam Quality?

i. Reduced heat transfer efficiency: The major problem with low steam quality is

the effect on the heat transfer equipment and process. In some cases, low

steam quality can reduce heat transfer efficiency by more than 65 %. The liquid

entrained in the steam has sensible energy (16 % estimated – varies with

pressure) which has a significantly lower amount of energy than the steam

vapor’s latent energy (94 %). Therefore, less usable energy is being delivered to

the steam process equipment. Also, the additional liquid (low steam quality)

collects on the wetted surface of the heat exchanger causing an additional

buildup of a liquid which reduces the ability of the steam’s latent energy to be

transfer to the product.

ii. Premature Valve Failure: Liquid passing through steam control valves will erode

the internals of the valves causing premature failure.

iii. Internal Turbine Component Failures: Liquid introduced with the steam in a

saturated turbine operation will reduce the life expectancy of the internal

components.

iv. Waterhammer Steam systems are usually not designed to accommodate the

additional liquid in steam. Additional liquid creates the chance for

waterhammer to occur. Waterhammer is a safety issue, and may cause

premature failure in the steam system.

4) Other existing thermal method

a. In-situ combustion

b. Standard forward combustion

c. Wet Combustion

d. Oxygen enriched combustion

e. Reverse combustion

f. Steam and hot water injection

g. Hot-waterflooding

h. Steam stimulation

i. Steamflooding

j. Surface mining and extraction

- Steam Flooding

- Steam flooding methods include cyclic steam injection, steam drive and combustion to

introduce heat to the reservoir. These methods improve the sweep efficiency and the

displacement efficiency. Steam injection has been used commercially since the 1960s in

California fields. In 2011, solar thermal enhanced oil recovery projects were started in California

and Oman. This method is similar to thermal EOR, but uses a solar array to produce the steam.

Steam flooding introduces heat to the reservoir by pumping steam into the well in a pattern

similar to that of water injection. Eventually the steam condenses to hot water. In the steam

zone the oil evaporates and in the hot water zone the oil expands. As a result, the oil expands,

the viscosity drops and the permeability increases. To ensure success, the process has to be

cyclical. This is the principal enhanced oil recovery program in use today. In situ combustion of

oil on site or fire flood, works best when the oil saturation and porosity are high. Combustion

generates the heat within the reservoir itself. Continuous injection of air, or other gas mixture

with high oxygen content, will maintain the flame front. As the fire burns, it moves through the

reservoir towards the production wells. Heat from the fire reduces oil viscosity and helps to

vaporise reservoir water to steam. The steam, hot water, combustion gas and a bank of distilled

solvent all act to drive oil in front of the fire toward production wells.

- There are three methods of combustion: Dry forward, reverse and wet combustion. The dry

forward method uses an igniter to set fire to the oil. As the fire progresses, the oil is pushed

away from the fire toward the producing well. In the reverse method, the air injection and the

ignition occur from opposite directions. In the wet combustion method, water is injected just

behind the front and turned into steam by the hot rock. This quenches the fire and spreads the

heat more evenly. The conditions of use for this kind of technology are very strict. Underground

ignition is extremely difficult, so this technology is rarely applied.

- Gas Drive Oil

- Gas injection or miscible flooding is a general term for injection processes that introduce

miscible gases into the reservoir. A miscible displacement process maintains reservoir pressure

and improves oil displacement because the interfacial tension between oil and water is reduced.

This refers to removing the interface between the two interacting fluids. This allows for total

displacement efficiency. Gases used in this process include CO2, natural gas or nitrogen. The

fluid most commonly used for miscible displacement is carbon dioxide because it reduces the oil

viscosity and is less expensive than liquefied petroleum gas. Oil displacement by carbon dioxide

injection relies on the phase behaviour of the mixtures of that gas and the crude – these

behaviours are strongly dependent on reservoir temperature, pressure and crude oil

composition. As oil and gas have a cognate symbiosis in the same structural trap, their physical

and chemical properties are similar. As such, the Gas Drive Oil method has the potential to

deliver better displacement process efficiency and higher recovery rates than other techniques.

However, this theory is relevant only under specific reservoir conditions. If these specific

conditions are present, then the volume expansion of the injected gas which acts to move the

oil, takes precedent over the smaller chemical reactions from the gas drive process at the oil and

gas interface.

Thermal EOR Thermal EOR methods are generally applicable to heavy, viscous crudes, and involve the

introduction of thermal energy or heat into the reservoir to raise the temperature of the oil and reduce

its viscosity. Steam (or hot water) injection and in-situ combustion are the popular thermal recovery

methods. Three common methods involving steam injection are cyclic steam stimulation (huff and puff),

steam flooding and steam assisted gravity drainage (SAGD). In-situ combustion involves the injection of

air, where the oil is ignited, generates heat internally and also produces combustion gases, which

enhance recovery. Steam injection has been most popular in heavy oil sand reservoirs with ongoing

projects in Alberta (Canada), Venezuela, California, Indonesia, the former Soviet Union, and Oman3.

Lesser (small commercial or field trials) have been reported in Brazil, China, Trinidad and Tobago, and

other countries. SAGD has been mostly popular in the oil sands and extra-heavy crudes of Alberta, and

tested in Venezuela with limited success. Several hybrid versions of SAGD have been reported but

remain at field-trial levels only6. In-situ combustion projects, not as popular as steam flooding, have

been reported in Canada, India, Romania, and the US. It has been applied mostly to heavy oil sandstone

reservoirs. A new version, HPAI, for light crudes has been gaining in popularity over the past 10 years

and shows potential, especially in light oils and low permeability carbonate reservoirs. Several projects

have been concentrated in the north-western US and Mexico is also considering HPAI for one of its

fields. The future of thermal methods is perhaps the brightest for the more difficult heavy oil and tar

sands resources. Currently, SAGD is primarily being applied in Alberta and several hybrid technologies

(e.g. injection of solvent with steam) are being tested. This technology is ripe for being applied in other

parts of the world. Air injection, if tamed and understood, may also have applications in light oil

reservoirs as the injectant supply is plentiful. Steam flooding too has been tested successfully in light oil

reservoirs that satisfy certain criteria (depth < 3,000 ft, oil saturation-porosity product > 0.1).

5) What is steam trap in SAGD?

Figure 3: Heat transfer mechanisms in the producer vicinity

a.

6) Summarise SAGD process – include technical term (T,u,k)