You’re conducting a geophysical survey. What are the most reliable tools to use?

In my 40 years of experience (starting in the early ‘80) I don’t recall drilling a well without some type of seismic data. That goes for onshore (conventional) and offshore wells. Seismic can help with QI and structural understanding. I’m sure there were a few exceptions such as twins or maybe updip to a producer with good offset data like dipmeters and fault control via well cuts. I’m also sure there basins where you can drill without seismic but I don’t think the US gulf coast and the Gulf of Mexico (shelf and deep water) fit that bill.

Seismic data remains the main source for any investment into subsurface oil and gas accumulations. As a Petrophysicist, I count myself lucky to have worked my fellow geoscientists, in providing support for seismic interpretations, through; Well synthetic seismograms Well-to-seismic matches Seismic velocity models Seismic attribute analysis Seismic ray-trace modelling VSP Processing Pore pressures predictions And so on. Seismic data carries a significant amount of uncertainty. Many of the big fields of today, were found on the basis of 2-D seismic. For many of these fields, the structures may have changed over time, with the acquisition of higher vintage 3-D and 4-D seismic over time, all in an effort to narrow structural uncertainty.

Tenho 46 anos de experiência na indústria de Petróleo, 30 dos quais na Petrobras, onde gerenciei grandes projetos e ativos de produ??o na Bacia de Campos em Macaé, Ativo de Urucu em Manaus e Ativo Mar no RN. Ent?o para ter sucesso na produ??o, manuten??o da produ??o, adensamento de malhas e novos projetos com novos po?os em novas zonas produtoras por exemplo, sempre tive a sísmica como aliada fundamental.

In my opinion seismic survey is the most important tool to identify the potential reservoirs by providing detailed images of the subsurface. It is used in conjunction with the other surveys mentioned in this article to provide a better and detailed understanding of the subsurface. On this basis, the prospects are determined and it finally leads to drilling of wildcat well which can finally ascertain the presence of hydrocarbon.

the very primary and reliable source of collecting geophysical data is seismic wave, which includes reflection and refraction methods

EM survey uses electromagnetic waves to map subsurface conductivity variations. It is useful for mapping groundwater resources, detecting buried objects, and identifying potential mineral deposits

A key advantage lies in their cost-effectiveness, speed, and minimal environmental footprint, making them ideal for large-scale surveys. Yet, the effectiveness of these methods hinges on meticulous correction and interpretation, as they are susceptible to interference from external factors such as noise, terrain, and human activities. Navigating through these challenges, however, unveils a wealth of information, enabling stakeholders to identify potential reservoirs, structural traps, and geological anomalies. By harnessing the power of gravity and magnetic methods, industries can make informed decisions, optimize exploration strategies, and sustainably manage Earth's resources.

Magnetic and gravimetric methods are some of the most useful tools a geologist or petroleum engineer can have. Although they lack precision, they are some of the least expensive and most versatile methods you can find, and sometimes that can be worthwhile.

The gravity and magnetic methods offer insights into subsurface structures, depths, and potential traps, vital for exploration. Despite being cost-effective and non-invasive, they require meticulous correction and interpretation due to susceptibility to noise and surface features. Overall, they're valuable for regional assessments, though careful consideration of environmental and cultural factors is necessary for accurate results.

Electrical Resistivity Tomography (ERT): ERT measures the electrical resistivity of the subsurface to map changes in subsurface materials. It is useful for identifying groundwater resources, mapping geological structures, and detecting buried objects.

The most reliable tools for a geophysical survey depend on the specific goals and conditions of the survey. However, some of the most common and versatile tools include: Ground Penetrating Radar (GPR) for locating buried objects and features. Magnetometers for detecting metal objects and geological anomalies. Electromagnetic (EM) conductivity meters for mapping soil types, groundwater, and contamination. Seismic surveys for imaging subsurface layers and structures. Gravity meters for identifying density variations underground.

While often associated with oil and gas exploration, electrical and electromagnetic methods find applications in various other fields. These include groundwater exploration, environmental studies, engineering investigations (such as assessing the integrity of dams and foundations), and archaeological surveys. The depth of investigation achievable with electrical and electromagnetic methods varies depending on factors such as the instrumentation used, the conductivity of subsurface materials, and the survey parameters. While some methods can penetrate to significant depths, others are more suitable for shallow investigations.

Once during a Geophysics course, we did an electrical resistivity evaluation in a well-known area with the objective of comparing the method with the historical data. The conclusion was really positive. We used very few equipment, we spent only a few hours, and we ended up validating with reasonable precision the location of the groundwater resources. There is no doubt that these methods can be very effective when working near the earth surface.

There is only a handful of logs that measure directly the presence of hydrocarbons. Thermal decay is one of them, but it requires radioactive material handling which becomes challenging in frontier areas. Image logging provides input on stratification, natural fractures and wellbore stability and can be run while drilling. With horizontal drilling LWD is more practical and cost efficient. Advanced hydrocarbon analysis from cuttings offers reliable qualitative input to corroborate logs. These methods are fast and can provide on time input for completion adjustments.

Well logging is the primary means to know about the petrophysical properties (porosity, permeability). It is done After the hydrocarbon has been affirmed by the wildcat well (as mentioned in the previous points). In layman terms it has a sonde which is lowered in the wellbore which gives real time information at the surface about the petrophysical properties. The different types are Gamma ray log, SP log, Resistivity log, Density log, Neutron log, etc. It is vital for making informed decision about the field development strategies leading to efficient extraction of hydrocarbon.

To the specific question of geophysical surveys - borehole seismic surveys and Sonic logs can provide the critical link between time and depth. By lowering sensors into the well you can directly measure the transit time to a particular depth and also measure the sonic velocity of the rock at a specific depth. Both these measurements help turn the surface seismic survey from a time domain to depth so you can better decide how to reach your targets

Each method's reliability increases with well-logged data, leading to a higher level of certainty in geophysics. Logging moves our perspective from uncertainty to confidence, similar to how drilling eliminates doubts about the presence of hydrocarbons. With a variety of tools available, we can validate numerous aspects, enhancing our confidence in the field. Some logs goes as far as identifying the presence of gas, oil or water and even the kind of formation or zone it is located.

Interpreting well logs is often a game of exclusion about what it cannot be. Usually, the combination of 3,4, or even 5 different types of logs will give you an indication about what type of rock and fluid content you could be dealing with. Common logs include: Resistivity Logs, Gamma Ray Logs, Neutron Logs, Density Logs, Sonic or Acoustic Logs, Nuclear Magnetic Resonance (NMR) Logs, Caliper Logs, Dipmeter Logs, Formation Pressure Tester, Temperature Logs, Spectral Gamma Ray Logs, Imaging Logs

The competence of the team doing the data collection, analysis and interpretation. "A tool is as good as the user". The choice of the geophysical tool largely depend on the target type but when you have a competent team, the choice will be largely appropriate. This will also minimise the expenditures on ground truthing.

Uma curiosidade somente, muitos pensam que a sísmica no mar é ambientalmente invasiva, de difícil ou complexa execu??o, mas a verdade é que no "Mar" verde de uma floresta virgem, a sísmica é muito mais complicada, quem sabe um dia posso contar esta história de sucesso da Petrobras.

Some surveys could be, seismic, electrical resistivity, magnetic or gravitational. Each fits specific and certain applications more than others. I worked with all in the past from looking for shallow water using electrical surveying to mapping under asphalt bed rocks using magnetic and gravitational to seismic for hydrocarbon structural traps mapping.

Remote satellite sensing offers spectral analysis for methane, ethane, other hydrocarbons that point to seeps, or migration paths which should be consistent with hydrocarbon accumulations. This method is assisted with heavy computational analytics to improve reliability.

LiDAR: LiDAR uses laser pulses to create high-resolution images of the Earth's surface. It is useful for mapping topography, land cover, and identifying potential geological hazards.