Unconventional Plays Revealing New Stories of the Earth

Convection vs Conduction in Thermal Maturation of Organic Matter for the Generation of Hydrocarbons

By Waqas Haider*

Surprise...!!! Hot Spots (Hydro-thermal Fluids Generation Points) Can be Useful in Unconventional Plays

I was caught by a surprise while coming across this study, it looked strange to me because we've been studying so far that radioactive elements in the Earth's crust emit enormous heat, and that heat reaches the Rock Columns gradually (not simultaneously) and cause organic matter in the rocks thereby to get thermally mature which is necessary for the generation of hydrocarbons. But here is a different story, the evidences has been collected by a member of AAPG in First Shot Field (Eagle Ford -USA) as well as Stanley and Parshall Fields in Williston Basin (USA-Canada). The whole new story is as follows:

In the beginning while evaluating the unconventional plays (new phenomenal shale play bonanza), general perception was that the rocks were homogeneous throughout area of interest. But then in Oil & Gas industry the E & P (Exploration and Production) players realize via drilling bit that heterogeneity rules, and homogeneity and isotropy are not even bit players in the big picture. In reality these dense rocks can considerably vary from one well to an adjacent well adding a considerable curiosity and associated risk in leasing and drilling. 

Better Handling of Potential Area (Before we go for Seismic Technique):

Seismic data techniques are utilized to analyze and to evaluate the production potential of a prospective area. But Seismic Method is an expensive method so it is recommended to go for applying small cost techniques to grasp on with which to proceed. These methods include remote sensing, integration of inorganic and organic petrography (well data), gravity and magnetic methods and other various types of thermal maturity data (basin studies) to recognize the areas having the potential to give us commercial production. 

Once the Geoscientists get better understanding of a certain potential area, they can then opt more comprehensive and expensive technologies like seismic for further "better handling of the prospective area". 

Fig. 1: Conduction and Convection (with Faults and Fractures
acting as Conduits for Hydrothermal Fluids). (Credits: AAPG).

Heat Source:

You're thinking it would be conduction ... Umm No..!! It's Convection Actually..

According to Miss Edman (a member of AAPG): "experts have independently come together on the concept of using a combination of less expensive screening technologies to identify areas of localized high heat flow where recurrent movement of basement faults in areas already known to contain rich source rocks results in the maturation of hydrocarbons by Hydrothermal Fluids". 

"The published findings that at both a mega- and a micro-scale, an internally consistent genetic model can be developed, showing in multiple diverse locations that unconventional play sweet spots are often related to hot spots".

The "General Model of Generating Hydrocarbons" has been compared with "New Model of Generating Hydrocarbons (in which convection plays the key role)". In general model of generating hydrocarbons where we have organic matter in the source rocks and conductive heat coming up from the basement into the sedimentary section . That heat matures the organic matter causing hydrocarbon generation. 

In Earth's crust there are radioactive elements emitting heat that comes up by the conduction into the sedimentary section, and that's the source of heat for most hydrocarbon models, or basin models based on burial history.

But in the work by Miss. Edman, she said: "we actually have fluid movement, and heat from the hot fluids is causing maturation of organic matter, so it's a different heat source".

Convective Heat from the Fluids is causing the Generation."

DEM (Digital Elevation Model) of North Dakota.
(Credits: AAPG)

Convection vs Conduction:

The two types of heat transfer are quite different:

Conduction:

With conduction, the transfer of heat occurs quite slowly from the bottom to top of successive rock units that are in direct physical contact, according to Edman. 

Convection:

With convection, there is a rapid elevation of temperatures in multiple rock units simultaneously due to the relatively unconstrained movement of hot fluids (hydrothermal fluids). 

Experts emphasize that convective heat flow via hydrothermal fluids is much more efficient than the transfer of heat by the conductive heat flow. Also igneous activity in the shallow crust is more common than people realize, it;s this igneous driver that's the ultimate origin of the hydrothermal fluids. 

Faults Acting as Conduits for Hydrothermal Fluids:

The flow of hydrothermal fluids into the sedimentary section can be attributed to conduits provided by recurrent movement on faults and lineaments that extent to the basement.

Two Major Indicators of Sweet Spots in Unconventional Plays:

Two main elements needed to find the hot spots leading to the prediction of potential sweet spots are:

1. An igneous driver (igneous activity) for the hydrothermal fluids' generation 
2. A system of naturally occurring faults and fractures acting as conduits for hydrothermal fluids. 

Evidences from the Fields:

Besides serving as conduits for hot fluid flow, natural fractures are important to create areas of increased permeability. Application of combination of techniques are of key importance and they work best in a particular area of interest. 

For example in area of dense vegetation GPR (Ground Penetrating Radar) and Remote Sensing are not the ways to go. Also a well or more than one wells can help us in the integration of organic and inorganic petrography. 

A micro-photograph (Edman showed) that shows carbonate cement that came in with hydrothermal fluids. Then you have these trails of oil, fluid inclusions included in that carbonate cement showing that you had generation of that oil at the time the hydrothermal fluids moved in.

Oil inclusion trails in carbonate micro-veins of the upper Bakken
Member in the Long 1-01 H Well - microscal evidence that hydro-
-carbons were generate in situ at Parshall Field.  

It has been noted that AAPG member Dan Jarvie and his colleagues demonstrated in 2011 that oil at Parshall Field (Williston Basin) in North Dakota was generated in situ. 

That's what this story tells: "A lot of people think the hydrocarbons migrated in from the west where the Bakken is more thermally mature, but looking at the biomarkers from Parshall Field, they're not all that mature. 

Edman and her colleagues have some convincing examples from the Eagle Ford at First Shot Field in Texas and the Parshall and Stanley fields in the Williston Basin showing that better production is related to areas of localized convective heat flow. 

This is a great inexpensive way to search for sweet spots in these Unconventional Plays. 

References:

       American Association of Petroleum Geologists. 

Louise S. Durham 

Janell Edman (Principal at Edman Geochemical Consulting in Denver). 

*
Waqas Haider
Student of M.Phil. Geophysics
Department of Earth Sciences
Quaid-I-Azam University Islamabad (45320) | Pakistan. 

email: geomindx@gmail.com

cell: +923215140154

   

U.S. Seen as Biggest Oil Producer After Overtaking Saudi Arabia

The U.S. will remain the world’s biggest oil producer this year after overtaking Saudi Arabia  and Russia as extraction of energy from shale rock spurs the nation’s economic recovery, Bank of America Corp. said.
U.S. production of crude oil, along with liquids separated from natural gas, surpassed all other countries this year with daily output exceeding 11 million barrels in the first quarter, the bank said in a report today. The country became the world’s largest natural gas producer in 2010. The International Energy Agency (IEA) said in June that the U.S. was the biggest producer of oil and natural gas liquids.
“The U.S. increase in supply is a very meaningful chunk of oil,” Francisco Blanch, the bank’s head of commodities research, said by phone from New York. “The shale boom is playing a key role in the U.S. recovery. If the U.S. didn’t have this energy supply, prices at the pump would be completely unaffordable.”
Oil extraction is soaring at shale formations in Texas and North Dakota as companies split rocks using high-pressure liquid, a process known as hydraulic fracturing, or fracking. The surge in supply combined with restrictions on exporting crude is curbing the price of West Texas Intermediate, America’s oil benchmark. The U.S., the world’s largest oil consumer, still imported an average of 7.5 million barrels a day of crude in April, according to the Department of Energy’s statistical arm.

Fig. 1 Oil Pumps stand at the Chevron Corporation. Kern River Oilfield in Bakersfield, California
(Photo Credits: Ken James/Bloomberg)

Surpassing Saudi:

U.S. oil output will surge to 13.1 million barrels a day in 2019 and plateau thereafter, according to the IEA, a Paris-based adviser to 29 nations. The country will lose its top-producer ranking at the start of the 2030s, the agency said in its World Energy Outlook in November.

“It’s very likely the U.S. stays as No. 1 producer for the rest of the year” as output is set to increase in the second half, Blanch said. Production growth outside the U.S. has been lower than the bank anticipated, keeping global Oil Prices high, he said.

Partly as a result of the shale boom, WTI futures on the New York Mercantile Exchange remain at a discount of about $7 a barrel to their European counterpart, the Brent contract on ICE Futures Europe's London-based exchange. WTI was at $103.74 a barrel as of 4:13 p.m. London time.

Islamist Insurgency:

“The shale production story is bigger than Iraqi production, but it hasn’t made the impact on prices you would expect,” said Blanch. “Typically such a large energy supply growth should bring prices lower, but in fact we’re not seeing that because the whole geopolitical situation outside the U.S. is dreadful.”

Territorial gains in northern Iraq by a group calling itself the Islamic State has spurred concerns that oil flows could be disrupted in the second-largest producer in the Organization of Petroleum Exporting Countries after Saudi Arabia. Exports from Libya have been reduced by protests, while Nigeria's production is crimped by oil theft and sabotage.

Libya will resume exports as soon as possible from two oil ports in the country’s east after taking back control from rebels who blocked crude shipments for the past year, Mohamed Elharari, spokesman for the state-run National Oil Corp., said by phone yesterday from Tripoli.

The U.S. will consolidate its position as the world’s biggest producer in the coming months if returning Libyan supply limits the need for Saudi barrels, said Julian Lee, an oil strategist who writes for Bloomberg News First Word. The observations he makes are his own.

Record Investment:

“There’s a very strong linkage between oil production growth, economic growth and wage growth across a range of U.S. states,” Blanch said. Annual investment in oil and gas in the country is at a record $200 billion, reaching 20 percent of the country’s total private fixed-structure spending for the first time, he said.

A U.S. Commerce Department decision to allow the overseas shipment of processed ultra-light oil called condensate has fanned speculation the nation may ease its four-decade ban on most crude exports. Pioneer Natural Resources Co. and Enterprise Products Partners LP will be allowed to export condensate, provided it is first subject to preliminary distillation, the companies said June 25.

The decision was “a positive first step” to dispersing the build-up of crude supply in North America, Bank of America said in a report on June 27. The U.S. could potentially have daily exports of 1 million barrels of crude, including 300,000 of condensate, by the end of the year, according to a June 25 report from Citigroup Inc.

References:

Mr. Grant Smith (Bloomberg.net)
Mr. Alaric Nightingale  (Bloomberg.net)
Mr. James Herron
Mr. Randall Hackley 

By:
Waqas Haider
Student of M.Phil. Geophysics
Department of Earth Sciences
Quaid-I-Azam University|Islamabad (45320)|Pakistan.

Contact Info:
 Email: geomindx@gmail.com

 Mobile: +923215140154

GROUND

PENETRATING 

RADAR (GPR)

Ground Penetrating Radar (GPR):

Ground Penetrating Radar (GPR) is a geophysical method that uses radar pulses to image the subsurface. GPR is a non-destructive geophysical method that uses electromagnetic radiation in the microwave band (wavelength: 1mm to 1 meter and Frequencies: 300 MHz to 300 GHz) (UHF/VHF Frequencies; where UHF = Ultra High Frequency designates the ITU radio frequency range of electromagnetic waves between 300 MHz and 300 GHz, also known as decimeter band or decimeter wave; VHF = Very High Frequency is the ITU designated of radio frequency electromagnetic waves from 30 MHz to 300 MHz) of radio spectrum and detect the reflected signals from the subsurface structures. GPR can be used in a variety of media including soil, rock, ground water (fresh), ice, structures and pavements. This technology can detect voids and cracks, changes in material and objects.

  

GPR uses high frequency (usually polarized: "polarization is the property of waves that can move with more than one orientation such that electromagnetic waves and light waves etc, but this is not the case with sound waves that only travel only in the direction they're propagating to) radio waves and transmits into the ground. When the waves hit a buried object, boundary, interface or horizon with different dielectric constants (a dielectric material (dielectric in short) is an electrical insulator that can be polarized by an applied electric field) , the receiving antenna records variations in the reflected return signal. The principles (as shown in Fig.1) involved are similar to reflection seismology except that electromagnetic energy is used instead of acoustic energy and reflections appear at boundaries with different dielectric constants instead of different acoustic impedances.

Fig.1: A GPR in Operation

Depth Range of GPR:

The depth range of GPR is limited by the electrical conductivity of the ground, the transmitted center frequency and the radiated power. As conductivity increases, the penetration depth decreases. This is because the electromagnetic energy is more quickly dissipated into heat, causing a loss in signal strength at depth. Higher frequencies do not penetrate as far as lower frequencies, but give better resolution. Optimal depth penetration is achieved in ice where depth of penetration can achieve several hundred meters. Good penetration is also achieved in dry sandy soils or massive dry materials such as granite, limestone and concrete where the depth of penetration could be up to 15 meter (49 feet). In moist clay laden soils and soils with high electrical conductivity, penetration is sometimes only a few centimeters. Ground Penetrating Radar (GPR) antennas are generally in contact with the ground for the strongest signal strength, however GPR air-launched antennas can be used above the ground.

Applications of Ground Penetrating Radar (GPR)

Like other Geophysical Methods, Ground Penetrating Radar (GPR) has many applications in a number of fields. In the Earth Sciences (Geophysics/Geosciences) it is used to study bedrock (first hard rock under soilar-regolith), soils, ground-water and ice. In alluvial gravel beds (the sediments brought up via rivers especially when floods come and surrounding flooded areas are then covered via soft sediments (alluvium) on the retrieval of the water to its original channel (normalcy), also alluvium gravel beds occur in deltas of rivers) GPR is of some utility in finding gold nuggets and diamonds by searching natural traps in buried stream beds that have the potential for the accumulation of heavier particles (gold and diamond particles). That is why GPRs can also been used on the surfaces of other planets and moons(such as Moon and Mars etc). Similarly other applications of GPR include Non-Destructive Testing (NDT) of structures and pavements. locating buried structures and utility lines, and studying soils and bed rock.

Although GPR has many applications in environment, archaeology and military as well. But here I'm restricted to discuss its applications only in Geophysics. Geologists and Geophysicists rely on GPR (Ground Penetrating Radar) to gather high resolution subsurface information rapidly. Compared to other geophysical methods nothing comes close in terms of the amount of ground coverage that is obtained with GPR surveying. GPR is the most versatile geophysical technique, used in wide variety of near surface application areas. Even though physical properties of the subsurface will limit resolution with depth, GPR remains as the unmatched champion of high resolution subsurface profiling, object detection and mapping. GPR is generally used for investigations of the subsurface down to roughly 30 meters depth, but in favorable media the technique may penetrate several hundreds of meters. Major business benefits include reduction in the survey's cost are achievable because of GPR's inherent advantages over other geophysical methods; versatility; high speed data acquisition; portability and ease of use; and possibly the most important- the optimization of the resources i.e., one man replacing a large field crew. GPR also offers indirect project benefits by limiting opportunity cost for the system operator and third parties resulting from e.g., limited surveying ability in rough terrain areas. Top applications of GPR are as follows:

• Borehole Profiling
• Sinkhole Investigation
• Fracture Detection and ore delineation
• Environmental Investigations
• Mapping of Ground-water resources
• Landfill Delineation
• Contaminant Plume Profiling
• Site Assessment
• Hazardous Material Delineation
• Bedrock Profiling
• River and Lake Bottom Profiling
• Karst Environmental Evaluation
• Sinkhole Investigation
• Stratigraphic Assessment
• Soil Conductivity Mapping
• Rock Fracture Detection and Mapping
• Cavity Detection
• Peat (accumulation of partially decayed vegetation) Investigations
• Ore Delineation
• Archaeological Investigations
• Cemetery Mapping
• Anthropological Remains Location
• Ancient Building and Foundation Location
• Ice and Snow Measurements
• Avalanche Investigations
• Snow Thickness Measurement
• Ice Thickness Measurement 
• Crevasse Detection
• Tree Trunk and Root Assessment
  Following Diagrams are for Environmental Investigations, Mapping Groundwater Resources, Landfill Delineation, Contaminant Plume Profiling, Site Assessment, Hazardous Material Delineation, Bedrock Profiling, River and Lake Bottom Profiling, Karst Environmental Evaluation, Sinkhole Investigation, Stratigraphic Assessment, Soil Conductivity Mapping, Rock Fracture and Detection Mapping, Cavity Detection, Mapping Ground-water Resources, Peat Investigations and Ore Delineation, Archaeological Investigations, Cemetery Mapping, Anthropological Remains Location, Ancient Building and Foundation Location, Ice and Snow Measurements, Avalanche Investigations, Snow Thickness Measurements, Ice Thickness Measurement, Crevasse Detection and Tree Trunk & Root Assessment respectively.

 The latest techniques which have been developed in GPR (Ground Penetrating Radar) are discussed as follows: 

Helicopter Borne GPR Surveys include GPRTEM- Time Domain EM and GPR (towed with the helicopter)  as shown in figure below. 

 

GPR-equipped fixed wing aircraft are used mainly for surveying large areas or inaccessible regions, for example desert areas, permafrost areas and high mountain ranges. A GPR system installed in a helicopter is an effective way to survey large areas with high data density. Large areas even in inaccessible regions can be surveyed within a short time and even limited logistic demands. The high agility of a helicopter allow to increase the data density in areas of special interest. Using Ground Penetrating Radar (GPR) for geological applications a high resolution of near surface structures is necessary. Stepped frequency radar technology offers an attractive alternative to the classical pulse radar systems. For example a newly developed Helicopter Borne GPR system includes following components: transmitter-receiver unit, antenna, data acquisition and a GPS navigation unit. The antenna is a corner reflector with two dipoles in a distance of λ/4. The dipoles are installed in such a way that an optimum bundling is achieved. The antenna is towed to the helicopter via 15 m towing rope and a coaxial cable. The system can be operated mono-statically as well as bi-statically. The normal operating frequency is 150 MHz, but it can vary between 70 MHz and 150 MHz. The above discussed system was modified for near surface application in 1999-2000. These modifications were firstly tested during a survey at the Careser glacier in the Italian Alps in October 2000. The results clearly show the base of this glacier in a depth range of 10 to 80 m. Afterwards a stepped frequency GPR was developed that was also able to be operated from a helicopter. Frequency of the stepped frequency GPR can be varied between 20 MHz and 2 GHz. The system-antenna is mounted on a non-conductive frame connected to the helicopter as a sling load. All electronic parts are installed in the helicopter. This alternative GPR system was flown about along the same flight tracks at the Careser glacier to compare the performance of the SF-Radar and Pulse Radar systems. In the following figures a comparison between PRS (Pulse Radar System) and SFRS (Stepped Frequency Radar System) is given:

    

Limitations of GPR:

Similar to other geophysical techniques GPR technology also has some limitations which are as follows:

• GPR can only perform significantly in high conductive materials such as clay soils and the soils that are salt contaminated.
• Application of GPR is also limited by scattering in heterogeneous materials such as extensive variation in the lithologies of the subsurface rocks.
• Considerable expertise are the most important preference in designing, constructing and acquiring data from GPR surveying. 

However, the GPR technology is still developing day by day because of its convenience in getting high density data over large ares especially acquiring data in inaccessible and rough terrains as discussed above. Although the present GPR technology offers a limited scope to delineate the subsurface structures only at shallow depths. Because high resolution electromagnetic waves are used in GPR applications so they limit spontaneously the power of penetration to deeper horizons of the subsurface.

Moreover, from Oil & Gas exploration's point of view; the borehole GPR is an indispensable tool for fracture and ground-water flow analysis. It will provide us high resolution data regarding the rock formations surrounding the borehole. 

In writing this material, I'm indebted to the following references:

In Association With:

Wilson, M. G. C.; Henry, G.; Marshall, T. R. (2006). South African Journal of Geology (Geological Society of South Africa).

Penguin Dictionary of Civil Engineering (Page # 347; Radar).

Conyers, L.B. (2004).

Walnut Creek, CA., United States: AltaMira Press Limited.

Gaffney, Chris; John Gater (2003).

Stroud, United Kingdom: Tempus.

All Rights Reserved ©2014 

geophyx.blogspot.com

Author:

Waqas Haider

M.Sc. Geophysics (2011-2013)

Department of Earth Sciences

Quaid-I-Azam University (45320)

Islamabad (ICT), Pakistan.

Contact Information:

Email: geomindx@gmail.com

Mobile: +923215140154