(White Paper - April, 2011) 

SUMMARY

     For over 50 years, explorationists have evaluated prospect areas using various near surface measurement techniques to assess the vertical migration of volatile compounds from subsurface reservoirs and thereby identify subsurface reservoirs.  Why the interest in this technology?  Near surface measurement technologies not old identify charged subsurface areas, but cost approximately 90% less than seismic studies.

     While many advances in this technology have occurred over the years, one method, Gore's Amplified Geochemical Imaging™, has moved to the forefront. The Amplified Geochemical Imaging™ is the only near surface technique that allows the identification and quantitation of C2-C20 hydrocarbons that move to the surface through vertical microseepage. 

Figure 1. Microseepage Diagram

     However, Amplified Geochemical Imaging™ results can be enhanced when combined with other complimentary technologies such as near surface extractions. While Amplified Geochemical Imaging™ can indicate charged or uncharged subsurface areas, near surface soil extractions can indicate the depositional environment, organofacies, age, as well as the maturity of detected hydrocarbons.   

     Amplified Geochemical Imaging™ is also now being used in  conjunction with basin modeling to define reservoir structures, their potential charge, timing of charge with relation to structure formation, migration pathways, hydrocarbon types (e.g. gas, condensate, or oil), and burial history. Consequently, when explorationists combine Amplified Geochemical Imaging™ with near-surface extractions, and/or basin modeling, they experience extremely high rates of success for accurately identifying hydrocarbon charged reservoirs and obtain a wealth of valuable information that aids them in characterizing the associated petroleum system.

INTRODUCTION

     The Amplified Geochemical Imaging™ technique uses a passive hydrophobic adsorbent material to collect C2-C20 hydrocarbons that move to the surface through vertical microseepage. Sampling modules are deployed at a depth of approximately 0.5 meters at predetermined locations in a grid pattern across an area of interest. The modules are kept in-place for 17 days. During this time volatile compounds that rise to the surface through microseepage, are passively adsorbed from the soil (Figure 1). In Figure 1 blue arrows indicate vertical migration of background hydrocarbon seepage, while red arrows indicate the microseepage of hydrocarbon gases arising from a charged reservoir (indicated by the green area).

     After the 17 day collection period, each module is retrieved and shipped to the laboratory for analysis. Each sorbent tube is thermally desorbed to release the captured volatile compounds. The 85 organic compounds are then separated and quantified by gas chromatography/mass spectrometry (GC/MS) down to a level of approximately 1 part per billion (1 ppb). This low level of sensitivity is unmatched in the industry and is one of the key components that allow Amplified Geochemical Imaging™ to be successful when other techniques are not.

     Traditional near-surface methods typically use GC analysis to identify and measure light-end components up to C5, thus limiting their ability to identify hydrocarbons restricted to the gas range. Amplified Geochemical Imaging™ can detect 85 organic compounds thus identifying not only dry gas and wet gas charges, but also condensates, oils, normal paraffins, iso-paraffins, cyclo-paraffins, aromatics, and naphtheno-aromatics. This extensive target compound list not only enables the user to identify hydrocarbon types with precision, but it also allows differentiation between naturally occurring background hydrocarbons and hydrocarbons found over charged reservoirs. This unique ability is one of the important technical aspects that distinguishes Amplified Geochemical Imaging™ from other techniques and identifies charged areas and predicts dry holes with extreme accuracy.

MULTIVARIATE STATISTICAL ANALYSIS

     The extended compound list and the large grid pattern enables the user to perform sophisticated statistical processing and modeling of complex geochemical signatures (up through phytane).  Some of the processes used include hierarchical cluster analysis, canonical variates analysis and discriminate analysis.

     One of the statistical techniques used to interrogate the data is hierarchical cluster analysis (HCA).  HCA groups samples of like composition according to the values of all input variables.  The result is that samples are separated into subsets or "clusters" according to their similarities.  In other words, the HCA evaluation clusters the data into hydrocarbon types such as background, gas, condensate, or oil. This classification is made possible by an extended compound list.

     Canonical variates analysis (CVA) is an important part of the quality control process within Amplified Geochemical Imaging's™. CVA provides the ability to distinguish between field samples and control blank samples. As seen in Figure 2, CVA clearly separates field samples, indicated in yellow, from the various quality control samples.

Figure 2. Canonical-Variates Scores for QC 

CONTOUR MAPS OF GEOCHEMICAL PROBABILITIES

     The results of the Amplified Geochemical Imaging™ are expressed in terms of maps that are plotted at a scale appropriate to the size of the survey and spatial distribution of the samples.  When possible, geographical information system (GIS) layer files containing relevant geological and geophysical (G&G) information (seismic line locations, structural interpretation contours, mapped fault polygons, etc) should be provided by the client for appropriate integration into the geochemical result. An example of a finished survey map is seen in Figure 3. As seen on the map legend, the shading transitions from gray to dark blue indicating the presence of background hydrocarbons or a dry hole area. The purple and deep red areas indicate a strong probability of hydrocarbons resulting from a reservoir charge.

 Figure 3.  Map contouring of reservoir hydrocarbon probabilities.

CASE STUDY - RUSSIA

     NOVATEK OJSC drilled in the Western Siberian Basin for many years and had determined that this was an active gas and/or gas condensate field. To date, no oil had been discovered in this field despite fairly extensive drilling. The area of interest for the client was the middle and lower Jurassic formations at 2,500 - 3,000 meters. Sampling took place in frigid Western Siberian winter conditions of frozen ground and temperatures at -40OC (see Figure 4).

Figure 4.  Western Siberian field

     Data supplied by the client showed a gas condensate well 30 km south of the survey site. Upon completion of the project, the survey data indicated not only a gas condensate signature on the site, but also an oil accumulation. As seen in Figure 5, hierarchical cluster analysis (HCA) indicated three distinct groups of samples, gas condensate, background, and oil. Each horizontal line is a single sample from the site. Each red mark indicates a carbon compound at that carbon number.

Figure 5.  HCA Results for W. Siberian Basin

     The lower group shows hydrocarbons detected in the C4 to approximately C12 carbon range. The middle group of samples depicted little or no hydrocarbons present while the uppermost cluster indicated hydrocarbons in the C10 to C20 range (i.e. oil range). Figure 6 provides an alternate representation of the data for clarification.

Figure 6.  Alternate HCA data view for W. Siberian Basin

     The colored lines to the right of each cluster represent the samples associated with each cluster type (i.e. gas condensate, background or oil). As oil had never been found in this field previously, the client was skeptical of the survey results. Drawing on these survey results the client was able to pinpoint the location of optimal well placement, resulting in a major oil discovery. Based on this success, the client decided to use Amplified Geochemical Imaging™ for all future projects and wrote the following letter of recommendation, 

"Performing the geochemical survey on the area allows us to rank those local uplifts 

which were earlier identified by the seismic work 

depending upon the degree of their prospectivity.

The geochemical anomalies identified at the Yarudey and Shuginskaya areas 

were 100% proven by drilling and the discoveries of oil and gas condensate deposits."

Victor E. Ponomarev

Head of Resources Base Development and Reserves Balance".

COLLABORATIVE CASE STUDY - OFFSHORE

     GORE and StratoChem Services conducted an offshore survey collecting piston core samples. Part of each piston core sample was sent to GORE for Amplified Geochemical Imaging™ analysis. The data confirmed what the client suspected in that they had an offshore petroleum system. The GORE survey clearly delineated the extent or the petroleum system. 

     Additionally, part of each piston core was also sent to StratoChem Services for extraction and analysis. Each extract was analyzed for oil fingerprint analysis by GC and then later analyzed for biomarkers by GC/MS. The resulting biomarker data indicated that the offshore oil system was similar in make-up to an onshore petroleum system. Thus, the StratoChem Services analyses not only confirmed the presence of an offshore system, as detected by the Amplified Geochemical Imaging™ survey, but indicated that instead of having two separate petroleum systems the client had one large system that started onshore and extended offshore.

CASE STUDY - EGYPT

     GORE Amplified Geochemical Imaging™ can also be used in conjunction with basin modeling. One client in Egypt wanted to release potential property within a lease and performed an Amplified Geochemical Imaging™ survey to validate that the section did not contain significant hydrocarbon quantities.

     The client subsequently commissioned StratoChem Services to perform a basin model of the area to confirm the GORE survey and to direct future drilling efforts for the retained property. Figure 7 shows an overlay of the GORE survey and the basin modeling results. The blue shaded areas indicate potential positive anomalies for hydrocarbon reservoirs based on the StratoChem Services basin modeling while the red shaded areas indicate potential positive anomalies for hydrocarbon reservoirs based on the StratoChem Services basin modeling. The heavy black line indicates the area being evaluated for relinquishment by the client.

Figure 7.  An overlay of a GORE survey map and a basin modeling map.

     Both the Amplified Geochemical Imaging™ survey and the basin modeling results indicated little presence of hydrocarbons within the area of interest. This confirmatory information provided the client with a great comfort level when deciding to relinquish the area. Additionally, the basin survey identified large high prospect areas to the northwest of the survey area. Thus, the use of both Amplified Geochemical Imaging™ and StratoChem Services basin modeling allowed the client to rank their prospects and identify hot prospect areas for future drilling. The client later drilled to the area in the northwest resulting in an oil discovery.

CONCLUSION

     Amplified Geochemical Imaging™ is an innovative technology, which provides for the direct detection of surface geochemical microseeps caused by subsurface oil & gas accumulations. While the Amplified Geochemical Imaging™ surveys have demonstrated a 93% accuracy rate of predicting hydrocarbon accumulations, this accuracy and information can be enhanced when combined with near surface soil extraction technologies and basin modeling.

Near surface extraction can not only confirm the presence of subsurface accumulations, but can also indicate:

·  depositional environment,

·  organofacies,

·  age, as well as

·  maturity of detected hydrocarbons. 

Basin modeling can be used to define:

·  reservoir structures,

·  their potential charge,

·  timing of charge with relation to structure formation,

·  migration pathways, and

·  hydrocarbon types (e.g. gas, condensate, or oil), and burial history.

Resultantly, these collaborative technologies can now be used together to enhance exploration success and help clients rank prospects with greater certainty.

For additional information contact Rick Schrynemeeckers with StratoChem Services at:

Rick.S@StratoChemLabs.com

                                                         

   State-owned energy giant Sonatrach will launch a pilot project for developing unconventional gas resources in 2012 in Algeria and has spoken to international oil companies, an executive said on Wednesday. 'We are ready to go it alone if we cannot find a partner,' the head of Sonatrach E&P Exploration Djamel Bekkouche told Reuters on the sidelines of an energy conference.

     The North African OPEC member supplies about 20 percent of Europe's natural gas but some analysts say it has under-invested in new oil and gas projects.  Bekkouche, who described the shale gas prospects as very interesting, said there had been an exchange of views with international oil companies about shale gas development. 'Italian oil and gas group Eni is looking,' he said.  

     Eni has entered shale gas development projects in Poland and the United States. It has agreed to develop shale gas opportunities with China's PetroChina. It has said it is looking into non-conventional resource development in North Africa.

     Bekkouche said it normally took between five and eight years for shale gas projects to come on line. come on tap, said Sonatrach is planning to invest $46 billion in upstream activity in the medium term.

     With images ripped from the roadway, API argues that the administration "has taken specific steps to stop or delay the development of domestic oil and natural gas resources." According to the trade group, those include:

• The Interior Department's decision not to proceed with a Bush-era plan for leasing the outer continental shelf that would have opened broad swaths of coastal waters for oil and gas development. The Bush plan would have run from 2010 through 2015 and replaced an existing leasing blueprint that runs through the middle of 2012.