An Emerging Hydrocarbon Province – Lebanon (Part 2 of 6)

Lebanon-Anticlines
Constrained, multi-measurement (Grav, Mag, EM) 2-D structural and stratigraphic cross-section running E-W in onshore Lebanon showing basement-driven structural highs in the Triassic and Paleozoic intervals.

We continue our Lebanon neoBASIN project series, this time, taking a look at some large, basement-driven  structural highs that have been identified in the Triassic and Paleozoic intervals in the survey area.

Our highly constrained, multi-measurement methodology for developing these types of 2-D cross-sectional models is covered elsewhere (you might review our MMI 101 narrated slideshow (click here) or read our 2014 Marcellus case study from URTeC (click here) if you want a richer refresher.

In a nutshell, we develop these models by evaluating the response of actual acquired multi-physics geo-data (in this case, gravity, magnetic and EM resistivity measurements), making certain assumptions about the thickness and physical properties (density, magnetic susceptibility, and resistivity) of key intervals, and iterating until the model converges with all acquired data and with any other constraints we might have, such as outcrop, well or seismic (which we didn’t have in this case) information.

In the image above, you’ll note that we determined that there were some topographic highs in the basement (the red interval) and that these basement-involved features affected the younger intervals deposited above them – in particular, the Paleozoic (green) and Triassic (purple) horizons.  Faults were mapped with other datasets, in particular magnetic but also EM.  To learn more about the importance of basement topography, faulting and composition in hydrocarbon exploration, read our article in E&P.

These fault-bounded structural highs were seen in other parts of the survey area as well.  In many cases, interpretations of the acquired Grav-Mag and EM datasets suggest that these features continue ‘into and out of the page’, thereby creating elongated anticlinal structures that could be intriguing exploration targets.

Now if only NEOS had some seismic imaging capabilities to further delineate the vertical and lateral extent of these anticlinal structures (???), but I digress…

In Part 1 of this series, we described the presence of oil seeps on the surface, in many cases, concentrated along faults and juxtaposed stratigraphic intervals outcropping on the surface.  If the seeps were generated from Paleozoic or Triassic source rocks, what are the odds  that some of the hydrocarbons became trapped in structures like these as they migrated towards the surface?

In an upcoming post, we’ll share some intra-horizon resistivity anomalies that indicate an increase in interval resistivity in structures similar to the ones highlighted here as one moves up the geologic column.

A View From Space: Gravity & Magnetic Data

A new way to look at the Earth began with the launch of the first satellite in 1957.  Today more than 2,200 satellites orbit the Earth, many providing a steady stream of scientific data. Accurate satellite imagery may be the most cost-effective source of data collection in oil and gas exploration.  And it often has the ability to reach parts of the Earth that are otherwise too difficult to access.

The most common and valuable types of satellite data used in the energy industry include multi-spectral, hyperspectral, gravity, magnetic and remote sensing (the use of aerial photography [often satellites], combined with other methods to view that which cannot be seen by the unaided eye).

NEOS geoscientists generate valuable interpretive products using satellite or public data, including:

  • Assessments of basin-scale geologic trends
  • Maps of basin architecture and regional structure
  • Maps of key lineaments, regional fault systems, and intrusions
  • 2-D and 3-D structural and stratigraphic models
  • Maps of basement topography, faulting and composition
  • Assessments of relative acreage prospectivity derived using predictive analytics.

In this blog series, we look closely at the data provided by satellites that reside in the public domain, to see what value can be gleaned, as well as encountered limitations that result from partial spatial samples or true global coverage.

GRACE Satellite – Data available via Center for Space Research

The above images are provided by University of Texas Center for Space Research and NASA.
The above images are provided by University of Texas Center for Space Research and NASA.

What is it:  The GRACE (Gravity Recovery And Climate Experiment) mission is dedicated to making detailed measurements of the Earth’s gravity field anomalies.  Its twin satellites fly about 220 kilometers apart in a polar orbit 500 kilometers above Earth.  They map the Earth’s gravity field by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. GRACE is on an extended mission, which is expected to continue through 2015.

The GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite is also used to measure gravity.  Orbiting at the lowest altitude of any observation satellite, its instrumentation was a highly sensitive gravity gradiometer, mapping the Earth’s gravity field at unprecedented resolution.

Bouguer gravity anomaly, distinguishing thick from thin crust by more negative and positive values. Image provide by ESA/IRENA.
Bouguer gravity anomaly, distinguishing thick from thin crust by more negative and positive values. Image provide by ESA/IRENA.

Value:  Gravity data is used to define areas of varying density within the Earth for insights into subsurface structure and composition.  Satellite gravity data has improved greatly in the last five years and is ideal for imaging basin and tectonic elements, and regional reconnaissance.  The data is available for most parts of the world, including both onshore and offshore environments.  Also, since the gravity satellite data is available now, there is no lag time for acquiring new data.

Limitations:  Like most satellite data, the limitation of the satellite data is resolution.  It cannot detect subtle variations in the subsurface.

Swarm Satellite – Data available via ESA

‘Snapshot’ of the main magnetic field at Earth’s surface as of June 2014 based on Swarm data.  Red represents areas where the magnetic field is stronger, while blues show areas where it is weaker. Image provide by ESA.
‘Snapshot’ of the main magnetic field at Earth’s surface as of June 2014 based on Swarm data. Red represents areas where the magnetic field is stronger, while blues show areas where it is weaker. Image provide by ESA.

What is it:  As for magnetic data, there have been several satellites since the late 1970s that have collected the Earth’s magnetic field.  The most recent is the SWARM mission, which is comprised of three identical satellites.  These satellites have new generation instruments to deliver extremely accurate satellite magnetic data.  It joins the Orsted and CHAMP satellites, both still in operation.

Value:  Magnetic data deduces subsurface lithology and structure, including the presence of ore deposits, intrusive and extrusive bodies, and faults.  In hydrocarbon exploration, magnetic techniques help geoscientists infer both total sediment thickness and the thermal maturation history of a basin by imaging the basement structure.

Limitations:  Again, the limitations of the magnetic satellite data is resolution.  It is ideally used for regional reconnaissance or basin imaging, where preliminary insights can help guide more detailed programs aimed at highgrading acreage or sweet spot mapping.

NEOS Tech Series: Multi-Physics Reveals Basement Secrets

The NEOS MMI methodology, specifically with the use of potential methods, is greatly suited to provide understanding of the structural complexity of a basin, at the basement level.

While gravity and magnetic methods use different rock properties (density vs. susceptibility), these methods are diagnostic and when taken together can eliminate many geologic alternative scenarios therefore putting constraints on geologic models.

In oil and gas exploration, the understanding of depth and structural configuration of basement plays a significant role. The depth-to-basement estimates from gravity and magnetic data lead to an estimate of thickness, depth of burial and thermal maturity of a horizon of interest. These parameters are very important in modeling and determination of hydrocarbon generation.  In addition, the understanding of basement structure leads to the understanding of global plate tectonics. Many of the world’s rift basins and spreading centers are recognized based on the magnetic data, two examples are the Red Sea Rift basin and Mid-Atlantic Ridge.

mag data along mid atlantic ridge
Magnetic data along the Mid-Atlantic Ridge

Magnetic data also typically highlights the changes in composition of the basement rock that would lead to differential thermal conductivity and thermal maturity of the source rock. In some recently surveyed areas, NEOS Geoscientists were able to relate enhanced production in shales based on its thermal maturity due to differential basement lithology in the area.

Click here to learn more on NEOS’ Basement Applications of Multi-Measurement Interpretation. For a better understanding of MMI methods throughout the entire geologic column watch the narrated slideshow.

NEOS Tech Series: Gravity & Magnetics

A multi-physics approach to geoscience allows NEOS to simultaneously interpret several possible geophysical measurements in order to uncover deeper insights into regional prospectivity and well productivity. While there may be potential for the inclusion of a number of measurements within an interpretation, each is equally unique and beneficial on its own accord.

GRAVITY & MAGNETICS – A PART OF MMI

NEOS incorporates gravity and magnetics in all neoBASIN programs, as these measurements are fundamental to the company’s multi-measurement interpretation (MMI) methodology. Gravity and magnetic data is acquired, along with other MMI measurements, using airborne systems simultaneously in a fast, efficient and non-invasive way, which reduces the turnaround time for the data acquisition, integration and interpretation. The data collected gives NEOS insight into the subsurface over large regional, basin-scale areas or at the more detailed, prospect level.

Gravity and magnetic methods are commonly referred to as potential field methods because the measurements involve a function of the potential of the observed field of force (gravity or magnetic). The data is used to help delineate geologic features in the Earth’s upper crust related to lithologic changes caused by natural hazards (faults, volcanoes), natural resources (gas, minerals) and tectonic events such as the formation of mountain belts.

These measurements take advantage of the variation in different lithologic characteristics of subsurface rock in a given area and can quickly and easily map location, extent, depth and structure of sedimentary basins. In addition, these methods can quickly identify faults, mineral deposits, igneous intrusive and extrusive, and depth-to-crystalline basement.

While typically grouped together, it’s still important to understand how each functions, so let’s look at gravity and magnetics individually.

Left image is Gravity Map and right image is Magnetic Map of the Gulf of Mexico.
[Left] gravity image and [right] magnetic image of the Gulf of Mexico.
GRAVITY

Gravity measures very small variations (anomalies) of the Earth’s gravitational field that are caused by lateral variations in the density of Earth material.

Specifically, gravity data is useful whenever the formation(s) of interest have densities that are different from surrounding formations. There is a wide range of densities within the Earth’s crust, from essentially zero density of air-filled voids in near-surface formations to the highest densities related to iron/magnesium-rich basement rocks and metallic ores. Because of the wide range of densities within all rock types, geoscientists interpret measurements and draw conclusions regarding the distribution of underground rock types that may be commonly favorable to trapping oil or gas. A typical gravity survey will map sedimentary basin configuration, structure and thickness, and faults. It will also map basement configuration where basement rocks are of higher density than sedimentary section, and salt bodies and distribution.

For example, salt has a very low density of 2.15. The identification of a salt dome would help to locate possible oil and gas reservoirs as many oil and gas deposits are located along the structures caused by salt movement within the sedimentary basin. A typical example of this is the large oil and gas reservoirs along the Gulf of Mexico.

MAGNETICS

The magnetic field of the Earth is generated by electrical currents in the liquid outer core. Rocks that have high magnetite content typically have the property ideal for magnetization, also known as susceptibility. Magnetic data measures the minute changes in a rock’s magnetic response caused by contrast in the susceptibility after an external magnetic field is removed. Field data responds to tectonic fabric, due to the redistribution of magnetite rich rocks and is typically used in mapping basement structure or the thickness of sedimentary section.

Faults and fractures are easily detected by magnetic method due to mineralization along fault planes. This method is widely used in the exploration and distribution of mineral deposits containing magnetite.   In oil and gas exploration, magnetic method is used in determination of depth-to-basement, fault detection and distribution, basement rock type leading to recognition of differential thermal conductivity or the thermal maturity of a basin.  

In the field of regional exploration, magnetic data is useful in delineating crystalline basement structures and tectonic elements as rift basins and basement involved tectonic elements. It also can delineate the distribution of volcanic material, both intrusive and extrusive. Recently, NEOS has used magnetic data to look for changes in basement lithology and successfully related it to enhanced production in overlying shales.

Click here for more detail on gravity and magnetic measurements.

Unlock the Potential: Neuquen

Neuquen Header

Argentina’s Neuquén Basin is one of the world’s most dynamic and underexplored hydrocarbon systems. Its two principal shale targets – Los Molles and Vaca Muerta – have been rich source rocks for the conventional reservoirs that have been produced in the basin for more than 50 years. With new technologies available for unconventional asset exploration and development, producers are taking a second look at these extremely thick oil- and gas-charged shales. While several seismic and non-seismic datasets have been acquired the coverage lacks uniformity, and no one has been able to integrate the data into a single, actionable interpretation — until now.

NEOS GeoSolutions has acquired high-resolution, airborne geophysical data over 30,000 square kilometers of the Neuquén Basin. Using innovative, multi-measurement methodology, the company has integrated these new measurements with existing well, geological, geochemical, and seismic data available in the public domain, from third parties, and from the project’s underwriters. NEOS designed the Neuquén survey to provide the project’s underwriters with an enhanced basement-to-surface understanding of the basin and its potential.

Initially, high-resolution hyperspectral imaging was acquired to map the regional lithology, the total organic carbon (TOC) of the target shales, and oil seeps and indirect hydrocarbon indicators on the surface. A second work stream generated 3D models constrained by the structural aspects of existing seismic lines, available well data, and newly acquired gravity and magnetic measurements. These models provided useful exploration insights by depicting isopachs, burial depth, depth-to-basement, and proximity-to-intrusives for all target shale horizons…

To continue reading the rest of this case study (or to view more case studies from the Unlock the Potential series), click here.