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Question:

 

What is the average pressure, viscosity and specific gravity of crude oil found in the Bakken?

 

Derek W.

 

Answer:

 

Results below are based on a survey of test samples done at a crude oil testing facility in Williston, North Dakota. Crude oil derived from the Bakken, on average, exhibits a vapor pressure of 16.72 psia at 50°C. Majority of the oil samples tested had a viscosity ranging from 36 API to 45 API, with the highest rating being 49 API. Specific gravity of these samples tested ranged from 0.7 to 0.8.

 

Other notable qualities of Bakken oil in all samples tested showed a very low sulfur content. Results showed on average 0.14 sulfur weight and a very low corrosity.  Flashpoint on average varied from 50 to 59°C. Samples also showed a significant chemical variability — depending largely to the location where crude oil samples were taken from.

 

Jeri

 

Question:

 

What are the similarities and differences between acidization, acid squeeze, acid fracturing and hydraulic fracturing and what are their specific uses?

 

J. R.

 

Answer:

 

The term ‘acid squeeze’ and ‘acid fracturing’ refers to the same technology. This technology is employed to stimulate the performance of an oil or natural gas well in a carbonate based formation.

 

Acidization is mainly used specifically to remedy a damaged well bore in the process of being drilled. In such instances, acid is dropped down the hole without requiring to move the rig from the wellsite. Quantities are usually small, as low as 100 liters, or an amount sufficient to restore porosity in the well bore.

 

There are some similarities between acid and hydraulic fracturing; both use pumps to push the solution to open up reservoir or stimulate well into viable production. Hydraulic fracturing employs water as the main substance, along with sand, walnut shells or aluminum pellets as a proponent. Some acid may be part of the chemicals in the mixture.

 

Acid fracturing is used for low permeability formations which are composed of carbonate, limestone, or dolomite. Significant quantities of an acid solution are pumped down a well which has been perforated.

 

Quantity and strength of the acid is tailored to the specific requirement. In most cases acid required is ten thousand liters or more to open up naturally occurred fractures or cracks in the reservoir.

 

Hydraulic pressure in acid fracturing does not play a significant role in creating new cracks for oil or gas to flow into the well. It merely pushes the acid solution to open naturally formed cracks which previously remained closed or were impermeable.

 

Hydraulic fracturing is mainly used to release oil or natural gas out of very tight shale, tight sandstone or clay formations. A liquid solution based mainly of water, chemical inhibitors, proponents such as sand, aluminum pellets, sintered bauxite and walnut shells may be used in combination as a fracturing fluid.

 

This fracturing fluid is pumped under very high hydraulic pressure down a well that has been cased and perforated.  A number of stages are determined from drilling data and each stage fractured individually. Quantities of water in the fracturing fluid may run into millions of liters; small quantities of the solution returns to the surface and is trucked to designated pits or treatment plants.

 

High hydraulic pressure pushing the mixture causes cracks or fissures to develop in the tight and impermeable formation. The proponents retain the new structure to remain porous and allow gases or oil to flow into the well.

 

Jeri

 

Question:

 

I talked with a rigger friend of mine about directional and horizontal drilling. I was surprised to hear that there are limitations to this drilling technology in depths of less than 300 meters. He stated even if a directional hole can be drilled, it would be impossible to install a pipe or casing as it would jam up and buckle in such situations. What’s the minimum depth of changing from a vertical to a horizontal direction in drilling an oil well?

 

Miss My Hockey

 

Answer:

Its been proven that shallow directional or horizontal drilling is possible. It has been achieved with success in reservoirs at 60 meters below ground level and hole diversion from 0° to 90° was attained in a radius of only 25 meters. A much simpler and less problematic way is to have the drilling rig positioned at a slant instead of at a vertical.

 

Inserting a casing can be challenging in sharp directional well bores as the one described without the proper tools. There is new technology which makes it easy. A pipe slider is used; it employs a hydraulic ram which positions and drives a pipe or casing without buckling or jamming it in the well bore. A submersible electric pump is used to push the oil up to the surface.

 

Jeri

 

Question:

 

Could you please explain well logging, its value and how it works.

M.B.

Answer:

‘E’ logging or electric wireline logging has been used for over 80 years. It provides a variety of useful data for the rig and service operator and the company which is seeking commercial supplies of oil and gas. If done properly, it can spell the difference between success and failure.

 

The simple electric logging device was invented in France by Conrad and Marcel Schlunberger in 1927. It consists of a wireline and a cylindrical electrode device sent down the well or the bore hole.

 

At present, there are many variations of well logging devices. These down hole tools can be categorized into three basic types. One measures the voltage or ohm variation between the electrode and the side wall. The second tool uses a source of excitation and a sensor to detect resonance or acoustic vibrations. The third type of tool retrieves actual core or sidewall samples    

 

Information gathered from well logging details the type of formation, the oil or gas bearing zone, the wells possible production viability and the future of the prospective property .

 

If properly analyzed, logging data reveals the upcoming necessary procedures for the rig and service rig operators. A well depth may have to be increased or where the casing should be perforated. The well may need to be acidized, or fractured or other action taken pending the evaluation.

 

Electric well logging surveys show the physical properties of the actual formation and give inexpensive and very valuable information.

 

Jeri

 

Question:

 

Why is Brent more expensive than WTI crude oil ? I understand that Brent is a heavy and cheap grade of oil with loads of sulfur in it, as well as lower API numbers. I am puzzled why buyers are paying a premium for this cheaper quality of oil.  Do you have an explanation?

 

Craig

 

Answer:

 

The premium for Brent crude is a temporary situation caused mainly by the Mid-east riots, demonstrations and political changes in Egypt and Libya and speculation of oil shortage in Europe. Under normal circumstances Brent prices fluctuate within several dollars of WTI. Historically, Brent prices have been slightly less than WTI but in 2007 and now in 2011 are significantly higher.

 

For your clarification, Brent is not ‘a heavy grade of cheap crude oil’ as you stated. Its characteristics are within close limits of West Texas Intermediate (WTI) crude. Brent crude is associated with oil coming from the North Sea. It has a sulfur content of approximately .37%,  whereas, WTI contains  less sulfur content, and averages at  about .24%. Brent crude is blended to an API gravity of 38.06 whereas WTI has a gravity blend of 39.6 API. West Texas Intermediate crude does set a standard of quality and is mainly used for premium quality fuel and petroleum products.

 

Jeri

 

Question:

 

Is the API rating of oil the same as viscosity? The recent announcement of the Kerrobert heavy oil project  makes me wonder how heavy is the oil in the Lloydminster area compared to the oil from the Canadian tar sands, oil from the Orinoco Basin in Venezuela, and conventional oil. What’s the best grade of oil and how is it rated?

 

Saskco Kid

 

Answer:

 

API gravity is a method for calculating the specific gravity of oil only. There is no relation between specific gravity and viscosity. If you take two different crude samples they may have the same density, but the properties of the 2 samples will most likely vary and so will their viscosity. Viscosity varies with composition, density and temperature. The API gravity index of crude oil is constant (unless subjected to high pressures and very long duration of time).

 

The API index is not the only property of crude oil that determines its quality. High sulfur and other minerals may lower crude quality.  Crude oil is classified as paraffin based, asphalt based and mixed paraffin-asphalt base.

 

Crude oil density falls into four categories: Oil with a density of more than 45° is classified as near critical oil. Some of the Bakken oil falls into this type of top quality crude. Light crude is the classification given to crude oil with an API gravity of 31.1 to 45°. Medium crude falls in between 22.3 and 31.1°. Heavy crude has a gravity index of 10 to 22.3°. Bitumen, or extra heavy crude oil has an index of less than 10°. Oil from the Canadian oil sands and Orinoco Basin falls into this category.

 

Crude oil with a density of more than 10° will float on water. Bitumen, or extra heavy crude is heavier than water. Most of the crude oil from Lloydminster area has an API gravity index of 9 to 18°. There have been some reported samples with an API of 6° but that is rare for that area.

 

Jeri

 

Question: Is there any definitions on oil reserves as per Canadian governing stipulations? I find this information to be difficult to find and possibly not relevant to our Canadian standards.

 

Thanks in advance,

Susan H.

 

Answer:

 

Proved reserves are those quantities of petroleum, which by analysis of geosciences and engineering data, can be estimated with reasonable certainty to be commercially recoverable, from a given date forward, from known reservoirs and under defined economic conditions, operating methods, and government regulations.

 

Probable reserves are those additional Reserves which analysis of geosciences and engineering data indicate are less likely to be recovered than Proved Reserves but more certain to be recovered than Possible Reserves.

 

Possible reserves are those additional reserves which analysis of geoscience and engineering data indicate are less likely to be recovered than probable reserves.

 

Contingent resources are defined as those quantities of oil and gas estimated on a given date to be potentially recoverable from known accumulations but are not currently economic. The contingencies that result in the classification of the Gething CBM as a contingent resource include, but are not limited to: permeability to gas, gas saturation and/or content, an appropriate and successful field development plan, corporate commitment, and economic factors.

 

Discovered resources are those quantities of oil and gas estimated on a given date to be remaining in, plus those quantities already produced from, known accumulations. Discovered resources are divided into economic and uneconomic categories, with the estimated future recoverable portion classified as reserves and contingent resources, respectively. The reported Discovered Resource cannot be classified into one of the sub-categories of reserve, contingent resource, or unrecoverable resource at this time because it is not possible to estimate the portion of the discovered resource that could be recoverable and/or unrecoverable due to the lack of commercial tests or production testing in the vicinity of Company interest lands. There is no certainty that it will be technically or economically viable to produce any portion of the reported Discovered Resources.

 

Hoping this clarifies it for you Susan,

Jeri

 

 

Question:

 

Why do we hear so many contradictions as to how much oil is in the Bakken Formation? Why can’t journalist get their facts straight? What is the real potential of this oil field?

 

B.J.

 

Answer:

 

There are some journalists that may be confused about the potential and actual recoverable oil.

 

The US Energy Information (EIA) Report as presented in 2006 states, “Estimates ranging up to 503 billion barrels of potential resource is in place.”

 

In most conventional oil fields it is easy to extract a possible 20% of the oil in place. The Bakken Formation should not be confused to be a truly conventional oil field.

 

To simplify, the cross sectional view looks somewhat like an Oreo cookie. The crude oil is trapped in a very thin layer, 5 to 12 meters, sandwiched between two non-porous rock formations and approximately 300 meters below the Mississippian Formation. The Bakken formation is very difficult to drill. Best success is by employment of horizontal drilling.

 

With present technology it is estimated that a very small portion of the trapped oil is recoverable. Thus, if you hear that Saskatchewan has about 100 billion barrels of crude hidden in the Bakken Formation, it may be true but not all oil can be recovered. With today's technology it may be possible to recover 1 to 2%.  Thus, Saskatchewan has about 1.5 billion barrels of recoverable light sweet crude.

 

Recoverable reserves of 1% to 2 % are similar to Saskatchewan in Manitoba, Montana, and North Dakota. This will change as new technology comes on stream.

 

Jeri

 

 

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Question:

I was doing some research work last year and came across a proposal to use captured carbon dioxide to replace steam (from water) to extract the heavy oil from the tar sands. Have you heard or do you know anything about this?

Susan D.

Answer:

I am not aware of any studies using CO² alone to liquefying the heavy oil in the tar sands, or to use CO² as a substitute for steam. I believe that it may have possibilities but in companion with heat from a source. 

Texaco Inc. of US was awarded a patent for such an intriguing process some 23 years ago. The patented process uses a combination of in situ combustion along with bursts of injected carbon dioxide to lower the viscosity of the heated heavy oil. This would increase the mobility of the heavy oil in tar sands and heavy crude oil.

Carbon dioxide may be used in crude with a density of 25◦ API , or more. In general, any heavy crude with a lower than 22◦ API, is not suitable for CO² injection.

There have been several studies commissioned in Canada to study how to alleviate the problem of very high CO2 emissions as a result of developing oilsands. These studies mainly dealt with sequestering CO2 and moving it via a pipeline into an area where there are slow producing heavy oilfields; in particular the heavy oilfields bordering central Saskatchewan and Alberta.

Last November there was yet another announcement in Edmonton of such study. It would further evaluate the potential for sequestering and establishing a pipeline from Fort Saskatchewan into areas where CO² may be used to enhance slow producing oil fields.

Jeri

Question:

I understand that there are considerable reserves of oil shale in Canada. Why is it not being developed? I was told that a process invented in Alberta is being used in Australia successfully. Why isn't this process in use here on our continent?

 Kurt

Answer:

We don't have large deposits of oil shale in Canada like those in the US. Their estimated reserves are well over two trillion barrels of equivalent crude oil. More than half is estimated to be recovered. Our shale reserves are a token in comparison and are close to 16 billion barrels.  Oilsands Quest is developing deposits in northeastern Saskatchewan. Reserves in that area are estimated to be 7 billion barrels.

The ATP, Alberta Taciuk Process that you mention was developed in Alberta and was used in Australia in the Stuart Development Project near Gladstone, in northeastern Australia. It was originally developed for use in the Canadian Tar Sands.

It's a very simple processor. Raw product is strip mined and hauled to the processing unit. It is shaped in a form of a long extended rotating drum oven that consumes the raw fuel product on one side to heat and extract oil or kerogen on the opposing side. Operating temperatures of +500 degrees Celsius must be attained to extract kerogen. This works well in sandy shale or oilsands. Problems may arise when processing carbonate shale.

This process was not designed for this era where greenhouse gases are of a major concern. The single problem in its use was that high amounts of carbon dioxide and noxious gas are expelled in this process. The project failed in Australia due to environmental concerns. Another project resumes processing oil shale in Australia but uses a more advanced technology and is more environmental friendly.

Jeri

Question:

"Extracting oil in Alaska's North Slope is a bigger problem than you may imagine. While some may think this field is old and depleted, this is not the problem. The oil is deep below the permafrost. The oil is heavy and in some cases so thick it cannot flow. Why is SAGD technology not being used? Curious to know if Petrostar's newly developing technology may work?"

JD

Answer:

We must look and understand where the unique field is and it's problems. The North Slope is situated in Beaufort Sea, approximately 250 miles north of the Arctic Circle, and 1,300 miles south of the North Pole. Alaska's North Slope is the 18th largest field in the world. It is the largest field in North America. The Prudhoe Bay discovery well was drilled by Atlantic Richfield Company and Humble Oil and Refining Company way back in 1967.

Unilateral wells in that area are now drilled. The main vertical wells reach 5000 feet and may have as many as five horizontal legs in symmetrical configuration. Each leg may be an additional 5000 feet with a possible total of 25000 feet into sand containing heavy oil. Some of the oil is extremely heavy and will not flow. The situation in this field is far different from any field that I know.

I believe that the biggest problem with steam-assisted gravity drainage (SAGD) is environmental concern. In some cases there is perma frost to depths greater than 2000 feet. While these wells are drilled at depths well below the perma frost precautions must be made to prevent thawing and environment damage.

I understand that one of the operating companies in the North Slope are looking at very similar technology that Petrostar is developing for it's heavy oil wells in southern Saskatchewan. This device is lowered down into a well. Steam is generated at levels far below the surface up to a maximum of 5000 feet from the surface to liquefy the very heavy oil. Petrostar representative felt that their device is suitable for the North Slope. The technology is now in final stages of development and testing. I understand that their device is patent pending.

Jeri

Question:

"A friend told me that by forcing sand into the well it is possible to pump more heavy oil. Is this true?"

Thanx.

Answer:

The technology is CHOPS: Cold heavy oil production with sand. CHOPS is a newly developed economical technology for heavy crude production. This technique is used on conventional heavy oil that can be pumped. Using conventional means production levels may be unprofitable due to very low production.

This technique is used on heavy crude with a minimum of 12° API gravity. Specific intent is for the carbonate heavy oil reservoirs straddling along the Alberta and Saskatchewan border.  Sand is deliberately forced into a perforated oil well. After oil seeps into the mixture of air and sand, it is pumped to the surface with screw pumps and oil is extracted. Fresh sand and air is continuously forced back into the well. In effect the forced sand acts as a carrying agent.

This newly developed technique requires careful field management and skilled coordination. While it requires more attention than a regular oil well, production rates can be dramatically increased with good economic returns.

Jeri

Question:

You spoke of Genoil and their GHU heavy oil upgrader. One of their competitors is Chevron-Lummus, who seem to be getting the contracts in Canada. Does Chevron-Lummus have a technological advantage or are they simply bigger and provide less risk? Thanks.

SCP

Answer:

The CLG technology developed by Chevron-Lummus was developed specifically for refining heavy oils. Heavy oils from the tar sands contain vanadium, nickel, and other metals in significant quantities. This poses a variety of problems and proper technology must be used. CLG technology is successful in this area and is well recognized throughout the heavy oil refining industry.

The Genoil GHU technology on the other hand is not a refining technology. The GNU technology simply upgrades heavy crude from non-fluid heavy oil to regular viscose crude oil. It upgrades heavy crude and makes it pipeline ready. The real economic gain is where heavy crude must be transported long distances to a refinery which was not designed for heavy crude. It is meant to work in addition to, not as a replacement for a regular refinery.

Jeri

Question:

I've noticed that crude oil statistics are mostly in metric. How many barrels of oil are there in one metric tonne?

Shane

Answer:

In your question you didn't state the grade of oil. To give you an approximate answer we will assume that 0.88 is the correct specific gravity.

If oil has a specific gravity of 0.88 that means 1 litre weighs 0.88 kilograms.1 barrel [US, oil] = 158.9872972 liters. Therefore, 1 barrel weighs: 158.9872972 x 0.88 = 139.908821536 kilograms

1 metric tonnne is 1000 kilograms:

139.908821536 / 1000 = 7.1475121

So there are a little over 7 barrels of oil in a metric tonne.

To be more exact you must know the grade, or specific gravity of the oil.

Jeri

Question:

What purpose does mud serve in drilling? Wouldn't it be much easier, simpler and more economical to use water alone?

Bud

Answer:

Use of mud serves a variety of purposes. As the mud flows down to the bottom of the well and through the drill bit, it cleans the drill bit teeth and cools the drill bit. Drill bits generate a lot of heat simply because there is a great amount of friction, especially in soft sedimentary formations. It has been proven that mud as well enhances the cutting action of rotary drill bits. As drilling proceeds through layers of rock formation, the mud acts as a bonding and filling agent in pockets of empty spaces. This stabilizes the sides from falling into the well and subsurface fluids are prevented from entering the well.

Common drilling mud is made up of bentonite clay and water mixture. Adding barite makes heavier mud. There are a variety of chemicals, which may be added to mud as required under extreme drilling conditions.

Perhaps the most important aspect of mud is that it prevents accidental explosions with subsurface gases and prevents dangerous blowouts.

Jeri

Question:

I've heard oil workers talk about Christmas trees at well sites. What does that refer to? Could you explain?

John

Answer:

The term 'Christmas tree' refers to the top of the wellhead where there is a collection of valves and fittings. Once made up at the well site they now are made as one integral unit. Their function is to direct the flow of gas or oil from the well to the pipeline or the holding reservoir. The may also have a pressure control valve if high pressures or oil or gas are experienced at the wellhead. In the event of an oil or gas leak in the pipeline, or should there be some other emergency, supplies can be shut off.

Jeri

Question:

Is acidizing and fracing the same? I often hear these terms but I am not sure whether they have the same meaning. Could you please give me an explanation?

 

Just learning the ropes

Answer:

The term "fracing" is derived from the word fracturing. Fracing involves pumping a fluid into the well at very high pressure to create cracks in the reservoir rock. Sand or other material may be used to prop open the gaps created by fracing. Acidizing is a technique for increasing the flow of oil, or gas into a well. Hydrochloric acid is pumped into the oil-bearing rock. The acid dissolves limestone in the producing zone enlarging pores and flow into the well bore with less restrictions.

 Jeri

Question:

What information can be learned from oil seeps? Does it necessarily mean that there is oil down below?

Howard H.

Answer:

Oil seeps along with emitted gases offer much information. Microbial activity in an oil reservoir results in formation of methane, ethane, propane, and butane. Butane is the heaviest of these gases. Significant amounts of microbial activity may degrade the quality of oil in the reservoir.

High methane values without ethane are usually associated with dry gas reservoirs. High propane and butane values, especially the latter, are indicative of a heavy oil reservoir. The relative concentrations of these light hydrocarbons (methane, ethane, propane, and butane) are directly related to maturity, quality and yield of the reservoir.

Subsurface hydrocarbons that are emitted and deposited as surface seeps provide a footprint as to what the hidden reservoir may be like.

Jeri 

 

Question: It seems that we are far less advanced than our American neighbors in shale gas exploration. I understand that we should be looking more at horizontal drilling. Why the hold back?

 

Greg Z.

 

Answer:

 

One of the reasons gas exploration companies have shied away from horizontal drilling is the added costs over conventional vertical drilling. A horizontal well costs at least three times as much as for vertical well. At times cost may exceed more than four times.

 

Natural gas prices have remained relatively low in comparison to crude oil prices. Thus, there is the reason for lack of activity in gas exploration. I believe that a price of $15 to $20/MMBtu would stimulate shale gas exploration. To take added costs such as employment of horizontal drilling, gas companies need better returns.

 

Jeri

 

Question:

 

Could you explain what LNG is and what is the excitement about it?

Ann B.

 

Answer:

 

LNG use will help reduce the global carbon emissions and decrease supplies of surplus natural gas. It is an economic fuel. Some have already proclaimed it as the future fuel.

 

The only drawback is the necessity of using energy and special pumps to compress it into a liquid. It must be stored in insulated containers which can withstand high pressures

 

LNG is purified and compressed form of natural gas which is composed almost entirely of methane. When subjected to great pressures and chilled to 162°C, pure natural gas turns into a very safe liquid. It is non-combustible and safe to transport. LNG occupies 1/600 the space of natural gas.

 

Surplus supplies of natural gas make it cost wise to convert into LNG. Present delivery and receiving ports make it convenient and economical to deliver over long distances across the ocean or land.

 

Jeri