How to Properly Plan and Execute a Geological Field Program
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Overlook of Machu Picchu, southeastern Peruvian Andes.
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A geological field program is not the same as a geological field trip. Geological field trips are designed to familiarize geoscientists and non-geoscientists with general geological concepts by visiting classic or specific outcrops where the record of such processes is clear and unambiguous. For the most part these trips are less physically and logistically challenging and usually involve less personal risk to the participants. They are frequently of shorter duration and do not involve follow-up work in the laboratory or office.
As opposed to a geological field trip, a geological field program, with few exceptions, is designed to address specific geoscience problems through field observations, measurements, sampling, and laboratory analyses that cannot be resolved otherwise. A geological field program can be logistically simple, short, and safe, or logistically challenging, last for weeks, and involve recognizable personal risks. The staff at Cayo Energy has led and participated in both types of programs and can say with conviction that every program has its own set of unique challenges, risks, and logistical hurdles. These challenges, risks, and hurdles can be anticipated and managed through proper planning and preparation on the part of those leading and participating in the work.
The basic foundation of geology has at its core the art and science of observation. As an observation-based science, geology requires its practitioners to have some experience working in field situations, such that all geologists may understand and appreciate the links between the field, the office, and the laboratory. Even geological field trips are a necessary part of this foundation, as those unable to participate in field programs can still understand and appreciate these links.
Nevertheless, the need for true field work must still be justified, as the costs and risks to Company staff are real and significant. If all other avenues for resolving key problems or questions have been addressed and those issues are still unresolved, then a field program might be the best or only way to obtain the required information and data. If this work can be done by consultants then every effort should be made to have consultants do the work. Risks to Company staff have risen beyond the physical aspects of a strenuous or logistically difficult work program, and management must now consider other unpleasant possibilities and risks such as street crime and terrorism before approving such work.
Justifying your field program to management is only the first step towards delivering a successful venture. Some advance planning will in most cases save time and money, and can save you and your Team from unfortunate or dangerous situations. Understanding and planning for problems that might occur before you leave might mean the difference between being unprepared to deal with an emergency situation and handling an emergency with minimal risk to the participants and the program.
A sample of the information contained in our comprehensive Guide to Planning and Executing Geological Field Programs can be found below. Please check out our free High-Level Summary for Planning and Executing a Geological Field Programs here.
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Building the Right Field Team
Field Team in the Amazon jungle, foothills of the eastern Peru Andes.
Assembling the right Field Team is about more than choosing Team Members based on skill sets. The best Teams combine the critical skills, attitude, and endurance necessary to safely and successfully execute the program.
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Field Transportation Safety Protocols
Helicopter approaching a pre-arranged LZ (Landing Zone), Rio Mimbos, western Venezuelan Andes.
Regardless of the type and technical sophistication of the available modes of transportation, always be sure to follow the safety protocols established by your Company when planning field transportation logistics. Whether traveling via air, land, or water, know the risks and limitations of each and be prepared!
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4-wheel drive vehicles are a must, regardless of the terrane. In some countries, rental agencies supply qualified drivers as to handle the vehicles, especially in difficult conditions.
4-wheel drive field vehicles, Tarapoto to Yurimaguas road, eastern Peruvian Andes.
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Combination vehicle and passenger ferry across the Rio Huallaga, eastern Peruvian Andes.
River travel can be very dangerous in remote areas. Your Company may require life jackets or other measures as safety precautions.
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Typical Peruvian small river boat, western Amazon foothills. Note the crew member is wearing a life jacket.
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Outcrop Conditions - Shorelines and Rivers
Manzanilla Formation upper middle to upper shoreface sandstones and siltstones cropping out on Manzanilla Beach, eastern Trinidad.
Outcrop work along shorelines and rivers can present special challenges and risks, including tides, sudden storms, and flooding. Be prepared by knowing the local conditions in your field area and planning and practicing for safe field operations!
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The best places to encounter outcrops in mountainous jungles and forested terranes very often occur along fast-flowing rivers. River crossings under such conditions may require ropes and other safety gear, and may also require special training. The best way to minimize risks is to work within the dry season if at all possible.
River traverse in San Antonio Formation sandstones, Rio Querecual, Serrania del Interior, Eastern Venezuela.
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Structure, Stratigraphy, and Sedimentology
Chambara Formation carbonates overlain by the Aramachay Formation carbonates, tuffs, and black shales, valley of the Rio Utcubamba, north-central Peruvian Andes (photo adapted from Erlich et al., 2017a, in press).
Critical technical skills to have within the Team include structural geology, stratigraphy, and sedimentology. The work includes macro- and micro-scale observations, descriptions, and analyses, so be prepared!
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Lower Goyllarisquizga Group upper shoreface sandstones, Chachapoyas road, north-central Peruvian Andes (photo adapted from Erlich et al, 2018b). Can you find the channel?
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Los Cuervos Formation upper shoreface sandstones and siltstones, Rio Lobaterita, western Venezuelan Andes.
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Contact between Navay Formation limestones and cherts (left) and the Guayacan Limestone, Rio Sto. Domingo, east flank of the western Venezuelan Andes (photo from Erlich et al., 1999a). Can you see the unconformity surface?
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Montage of the Upper Cretaceous section, eastern Peruvian Andes (photo from Erlich et al., 2018b). Can you find the omission surfaces?
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Measuring Sections and Collecting Field Samples
Measuring and describing lower slope and basin floor limestones, siltstones, sandstones, and black shales, Punta de Las Animas, Fuerteventura, Canary Islands.
Measuring outcrop sections requires teamwork and focus. Establish a process that everyone can agree on to achieve accurate, efficient, and effective results.
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Hand-held gamma-ray logging of outcrop sections is now a common practice in field geological programs, especially during the initial measuring and sampling of the outcrop. Such logs can help locate units of specific interest for detailed sampling and subsequent analysis, and can help calibrate outcrop geology and stratigraphy to subsurface gamma-ray and lithology logs (gamma-ray and lithology log from the Cretaceous section along the Rio Sto. Domingo, eastern flank of the Merida Andes, western Venezuela. From Erlich et al., 1999b).
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Systematic sampling is often critically important and requires experience and skill. Such work should be done in teams so that while one Team Member takes samples and makes observations and measurements the other records data and notes while being vigilant of physical risks (photo: Sampling cherts and black shales, Fuerteventura, Canary Islands).
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When collecting samples for geochemical and biostratigraphic analyses always try and excavate the outcrop at least 1 meter to help minimize the impact of weathering (photo: Excavating Aramachay Formation black shales and siltstones, north-central Peruvian Andes).
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Oil seeps can be critically important and any sampling must be done with sealed glass containers. Strive to minimize the amount of water and other contaminants collected while sampling seeps (photo: Sampling an active oil seep along the Rio Chazutayacu, Amazon jungle, foothills of the eastern Peruvian Andes; from Erlich et al., 2018a).
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Large bivalves, Chambara Formation, valley of the Rio Utcubamba, north-central Peruvian Andes (photo adapted from Erlich et al., 2018a).
When collecting outcrop samples for specific analytical work take care to collect samples for macro- and microfossil biostratigraphy. In addition to providing classical age control on your stratigraphic sections these samples can also offer valuable insights into the paleo-environmental conditions that existed during their times of deposition.
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Ammonites are important age and paleo-environmental fossils in Mesozoic sections. Do not overlook them! (photo: Aramachay Formation black shales and tuffs, north-central Peruvian Andes).
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Microfossil assemblages have revealed much about key hydrocarbon source rock units within Mesozoic sections throughout the Subandean Basins of South America.
Planktonic and benthonic foraminifera within the upper part of the La Luna Formation, Sierra Perija, western Venezuela (adapted from Erlich et al., 2000).
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Field Sample Documentation
Describing an outcrop sample section, including sample information, Condorsinga Formation limestones, north-central Peruvian Andes.
Proper documentation of key outcrops and samples is critical to the successful outcome of any geological field program. Confusion and mislabeling of samples for various types of analyses is quite common and can lead to ambiguous or incorrect conclusions regarding the age, geochemistry, and depositional environment of key stratigraphic sections. Avoid these mistakes! Make sure your sample bags are annotated with the correct sample number, physical location, GPS location, date, program, and analytical work to be done. Note this information and any additional outcrop and sample descriptions in your waterproof field notebook and add photo numbers and locations that reference sample numbers and GPS/physical locations.
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The first and one of the most important forms of documentation to be done when arriving at the outcrop location is photography. You must insure that every outcrop and sample are properly documented with a photo, with photo numbers and descriptions of each photo taken logged in your waterproof field notebook. Besides the overall outcrop structural and stratigraphic setting, include photos of key fossils and sedimentologic features.
Documenting key sedimentologic features of the Los Cuervos Formation along the Rio Lora, western Venezuelan Andes.
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Proper Field Sample and Core Description
Describing core in a core warehouse, Republic of Trinidad and Tobago.
Now that you have your outcrop samples or cores available in a laboratory facility or core warehouse you can describe the samples in more detail. Slabbed samples and cores can provide insights not initially evident in the field, and represent the second level of data gathering commonly used in successful geological field programs. Whether they be hand-held outcrop gamma-ray logs or more sophisticated subsurface well logs, be sure to calibrate your samples and cores as precisely as possible to the logs. Note the types of analytical work to be done for each sample on the core and catalog that information with the analytical plan for each sample that was developed prior to the start of your program.
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Whenever possible, outcrop samples should include pieces that are large enough to slab. Such samples often reveal important details and information not immediately obvious in the field (photo: Miocene branching coral Stylophora imperatoris Vaughan, Republic of Trinidad and Tobago; from Erlich et al., 1993).
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Slabbed sample of the Tres Esquinas Member of the La Luna Formation, western Venezuelan Andes. We had observed large fish bones while collecting the outcrop samples, however, once slabbed (and subsequently thin sectioned) we also observed large marine reptile teeth, likely from a Mosasaur (adapted from Erlich et al., 2000). Can you spot them (hint: they don't look like teeth in this orientation)?
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Slabbed cores from the Morne Diablo-34 well, Republic of Trinidad and Tobago. Slabbing the cores was instrumental in understanding the depositional setting of each facies within this submarine slope fan system (from Erlich et al., 2003).
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Thin Section Petrography, Petrology, and SEM Description
Thin section photomicrograph of the basal part of the Tres Esquinas Member of the La Luna Formation, western Venezuelan Andes (adapted from Erlich et al., 1999a).
Although geochemical analyses can be started on field samples prior to laboratory description, it is strongly recommended that specific analyses follow laboratory, thin section, and SEM description. This may not be the fastest way of processing field samples but it is the most efficient in terms of cost and precision. Thin section and SEM observations and descriptions will reveal the constituents of the samples and allow for targeted analyses that are more likely to be successful then just using random analytical techniques. Justifying the cost of analytical work is a key pre-program activity and in an era of declining budgets, making the most of your analytical budget is a critical component in deriving the most and best data from your field samples.
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Understanding the depositional setting and composition of organic carbon-rich rocks is of paramount importance in unconventional reservoir plays. The nature of organic matter, constituent grains, and micro-porosity as revealed by thin section petrography and petrology contribute valuable data, enable high-grading of specific play areas or parts of the target section, and help guide drilling and completion techniques.
Organic carbon-rich shale from the La Luna Formation, Quebrada La Luna, Sierra Perija, western Venezuela.
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SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), and EPMA (Electron Microprobe Analysis) are frequently combined with Kevex (x-ray fluorescence) and EDAX (Energy Dispersive X-ray) analyses to help reveal diagenetic and poroperm-related problems within unconventional reservoirs (Left: SEM image of authigenic framboidal pyrite within a carbonate microfossil. Right: Kevex elemental composition of the sample, confirming the petrographic and mineralogical interpretation of pyrite cements in the sample; from the Tamana Formation, Republic of Trinidad and Tobago. From Erlich et al., 1993).
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Organic and Inorganic Geochemical Analyses and Radiometric Dating
Biomarker cross-plots of key extract and oil samples (from Erlich et al., 2017a, in press).
Careful planning and proper field sampling techniques should yield important and diagnostic data from your field program. Four types of analyses are frequently performed on field sample sets:
- Organic geochemistry
- Inorganic Geochemistry
- Biostratigraphy (discussed above)
- Radiometric Dating
Organic geochemistry most often involves standard RockEval and TOC screening of the samples in order to determine which (if any) samples may require additional, more detailed analyses. Standard stable isotope (carbon, oxygen, sulfur, etc.) and Major and Rare Earth Element (REE) analyses are also frequently performed on rocks and hydrocarbon fluids. Detailed biomarker analyses using Gas Chromatography-Mass Spectrometry (GC-MS and GC-MS-MS) are performed in order to help identify and correlate hydrocarbon source rocks to oils, define various families of oils, and help understand the age and depositional environments of hydrocarbon source rocks and oils.
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Inorganic geochemical analyses are varied and targeted to address specific geologic problems. Standard analyses include X-ray Diffraction (XRD), which is primarily used to identify specific minerals and clays, and X-ray Fluorescence (XRF), which targets individual elements. Rare Earth Element (REE) analyses are also frequently part of a basic inorganic geochemical analysis suite. Cross-plots of commonly co-occurring elements and minerals can show clear statistical correlations, while vertical plots of occurrence within the stratigraphic section, calibrated by biostratigraphic and/or radiometric age control, can reveal key details of the depositional history of area (adapted from Erlich et al., 1999b).
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Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb radiometric dating of detrital zircons is one of many radiometric dating techniques currently in use for field and subsurface geologic samples. The results are often used to describe the provenance and origins of sediments. Many other techniques with specific applications to geologic problems are also in use; please contact us for additional information provided in our Guide to Planning and Executing a Successful Geological Field Program (figure from Erlich et al., 2018b).
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