Analyzing the organic carbon content and distribution of sediments is a key challenge in exploring for and producing conventional and unconventional oil and gas. A new geochemical tool to analyze rock samples, or cores, the Laser Induced Pyrolysis System (LIPS), offers a solution. It identifies centimeters-thick organic-rich intervals in carbonate reservoirs likely to contain tar mats — oil shale and shale gas deposits — using an innovative, automated quantitative measurement system with high vertical resolution.

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Stéphane Teinturier

Reservoir

Obtaining a detailed quantitative measurement and the precise location of total organic carbon (TOC) in deposits is vital to rigorously estimate and map an unconventional prospect’s reserves. Rock-Eval pyrolysis and LECO combustion analysis are the most widely used geochemical analysis methods in the industry. They have limitations. Slow to carry out, both techniques require manual, destructive preparation of a limited number of crushed rock samples.

The resulting TOC measurements have poor vertical resolution, usually greater than a meter, which means that rock characteristics in the intercalated intervals are lost. This fuzzy picture of the vertical distribution of organic material content isn’t good enough. The succession of strata contains many thin shale intervals, some just a millimeter thick, that could be individual micro-reservoirs.

Devising a System Featuring High-Resolution Logging

Hence our R&D push since the early 2000s to develop a more accurate measurement method. The idea is to use laser technology to continuously measure TOC content in core samples. This disruptive concept developed by Daniel Dessort, an organic geochemistry specialist, produced our unparalleled Laser Induced Pyrolysis System or LIPS.

 

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A world-class innovation in use since 2010 at the CSTJF engineering and research center in Pau, France, our system is based on:

  • Micro sampling using a high-energy, class-IV, infrared laser source with 20 megawatts per square meter of power. The organic carbon’s virtually instantaneous pyrolysis lets technicians take a huge number of micro samples and measure organic carbon in centimeters-thick areas using continuous high-resolution logging. During data acquisition (several thousand measurement points spaced a centimeter apart), the laser impact creates minuscule craters measuring around 1 to 3 millimeters in diameter on the surface of the core. This affects only a tiny sample volume. A first, low-power laser pulse cleans volatile contaminants off the sample’s surface. A second, high-energy pulse on the same area dislodges the solid organic matter and vaporizes it to volatile organic compounds (VOC), nanoparticles and fullerenes.
  • Detecting the products formed and collected. Electrostatic filters remove the inorganic dust, which is analyzed by a photo-ionization detector (PID) that instantly identifies their composition. The PID is not sensitive to the CO and CO2 formed by the thermal decomposition of the carbonates. So it only detects the organic carbon.
  • Quantitatively analyzing TOC content. After calibrating the raw LIPS signal obtained, conventional methods (Rock-Eval) or LECO analysis) are used to quantify the organic carbon.

A Hundred Times More Precise, Much Faster & Fully Automated

LIPS offers a number of advantages:

  • It can collect 100 TOC values on a one-meter-long core. The frequency of online measurements can be increased to up to three measurement data points per centimeter.
  • Acquisition time for a data point is around one minute. So the analysis of a one-meter-long core takes just 90 minutes for 100 data points.
  • LIPS is fully automated: cores advance centimeter by centimeter and the analysis unit acquires data continuously.

 

LIPS is compact and can be shipped to and used on site in countries that restrict the export of cores. A second system is now up and running in our Qatar affiliate. That next-generation LIPS includes an automated core loader and flame ionization detector (FID), ten times more sensitive than PID. Other detectors are being tested. They will enable LIPS to automatically measure more organic compounds and parameters, such as hydrocarbon liquids saturation and the quality and type of kerogen.

Identifying Stratigraphic Intervals at the Centimeter Scale

For the first time, we have continuous, high-resolution well logs with very dense TOC values obtained using LIPS that can:

  • Refine the calculation of average organic material content for the entire target formation or for specific stratigraphic intervals.
  • Identify very thin, organic-rich intervals at the centimeter scale.
  • Better pinpoint the most appropriate target locations for horizontal drilling.
  • Improve the calibration of other conventional well logging data, such as gamma ray logs.

 

Originally designed to more accurately identify tar mats, the thin layers of tar that act as permeability barriers, in the Middle East’s conventional carbonate reservoirs, LIPS is now a vital tool in the unconventional oil and gas field. An example is Argentina, where LIPS helps engineers better understand the vertical distribution of the organic material ratio in the giant Vaca Muerta shale gas and oil sand formation. That ultimately helps them identify the sweet spots for optimal location of future development areas in the Total-operated Aguada Pichana license.

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