The Use of Direct Hydrocarbon Indicators (DHIs) is Growing in Oil & Gas Exploration Due to Successes: Seismic Attributes Help Find Hydrocarbons (But Not All Reservoirs Are Amenable to Discovery Through DHIs)

     According to the Society of Exploration Geophysicists (SEG) Wiki page, direct hydrocarbon indicators (DHIs) are:

“…an anomalous type of seismic amplitude that may occur due to the presence of hydrocarbons. They occur due to a change in pore fluids, which cause a change in the bulk rock’s elastic properties.”

     According to the National Science Foundation:

“Seismic direct hydrocarbon indicators (DHIs) are anomalous seismic responses caused by the presence of hydrocarbons. DHIs occur when a change in pore fluids causes a change in the elastic properties of the bulk rock which is seismically detectable (i.e. there is a “fluid effect”). DHIs display one or more types of characteristics that are consistent with hydrocarbons filling pores in a rock matrix.”

     DHIs are often based on the different acoustic properties of different reservoir fluids of different densities and bulk moduli, as shown below.

     Note that DHIs are basically seismic amplitude anomalies. Some anomalies are amplitude increases (bright spots), and others are decreases (dim spots). 

     DHIs are common in relatively young, unconsolidated siliciclastic sediments with large impedance across lithologic boundaries. They are used in exploration wells to help mitigate risk. To the untrained eye, seismic sections are just a bunch of squiggly lines, but to a trained interpreter, they can reveal a lot about the rocks in the subsurface and the fluids in those rocks.

     Citing an AAPG article on an Introduction to Seismic Interpretation, ExxonMobil, and other sources, SEG Wiki notes:

“The acoustic impedance is determined by the P-wave velocity and density of a rock; also related to the mineralogy, porosity, pore fluids, temperature, and pressure. Impedance will change based on the fluids in the pores, which can be filled with water, oil, or gas. As the pore space is filled with gas, the Vp lowers while Vs remains unaffected; therefore, it affects the reflection coefficient at the top and bottom of a reservoir, which are known as DHIs. In general, sands tend to compact faster than shales, as they have a higher impedance; yet, water sands have about the same impedance as shale, meaning the amplitude of reflections are weaker. Oil sands have a lower impedance than water sands and shales; while gas sands have a lower impedance than oil sands. If encased by shales, especially the gas sands, they would have a higher reflection amplitude due to the opposite polarities. These are differentiable based on their amplitude response. Gas is compressible, whereas water is not. Therefore, the presence of either will lower the P-wave velocity. The difference in impedance tends to lower as we go deeper, as the amplitude response will become less diagnostic. The greater the impedance between the sand and the shale, the greater the anomaly.

     Time-to-depth conversion is very important in seismic interpretation. Velocity measures the relationship between time and depth, with the formula shown below. 

     Velocity is controlled by geology, specifically age, depth, and lithology. Time-to-depth conversion can reduce data noise, validate structural interpretations, and aid economic evaluations. Before, during, and after conversion, the following steps are routinely performed: 1) Check available data and its quality. 2) Consider velocity structure. 3) Determine best method of conversion. 4) Perform conversion. 5) Check calculated depths and make corrections.

Amplitude Variation with Offset (AVO)

     Amplitude variation with offset, or AVO, is a method of analysis that can lead to DHIs. The goal is to determine the velocity, density, porosity, lithology, thickness, and fluid contents of a rock. For AVO to be successful, the fluid type in the rock must be known. AVO is prone to misinterpretation since it relies heavily on just P-wave analysis. In AVO analysis, different amplitude responses may be interpreted as DHIs. These include bright spots, dim spots, flat spots, phase change, gas chimneys, and shadow effects. It is important to remember that AVO in itself is not the same as a DHI, but something that can lead to one if other knowledge supports it.

Bright Spots

     Bright spots refer to an increase in amplitude, which may be associated with a hydrocarbon accumulation. They can indicate gas in the pore space and are usually greater in unconsolidated clastic rocks. Bright spots have higher amplitude than background values. They are a common DHI.

 

Dim Spots

     Dim spots are used to indicate sandstones and may be caused by highly consolidated sands with a much greater acoustic impedance than the overlying shale. The velocity and density of the sandstone will decrease if hydrocarbons are present in these cases. Dim spots have lower amplitude than background values.

 

Flat Spots

     Flat spots usually suggest fluid contacts (gas-oil, oil-water, or gas-water). Flat spots are notoriously difficult to find and may be misinterpreted. Low saturated gas could cause them as well. They show up as flat spots that cross existing stratigraphy, contrasting with the surrounding dips.

 

Phase Change

     A phase change, phase or polarity reversal, occurs “when the overlying reservoir has a lower velocity of the reservoir rock.” These are also notoriously difficult to find but often occur at boundaries where seal or caprock meets reservoir rock. The seismic sections below show interpreted bright spots, dim spots, flat spots, and phase changes.

Gas Chimneys (an Indirect Hydrocarbon Indicator)

     Gas chimneys occur where gas has leaked up from a lower formation, usually along faults, and result in lower velocity of the rocks above, usually shale. Aside from identifying leaked gas, they generally don’t have economic value as DHIs but may be considered indirect hydrocarbon indicators. See the slide above for an example.

 

Shadow Effects

     Shadow effects may be caused by hydrocarbons lowering the velocity. They often occur above and below a bright spot due to the high-amplitude processing.

 

Pitfalls of DHIs

     SEG Wiki lists the following pitfalls of exploring with DHIs. These underscore the importance of not relying on DHIs alone since there are situations where DHIs are vulnerable to misinterpretation.

·        Problem in differentiating the wells with gas buildups and wells with low-saturation gas (fizz gas), which are considered dry holes. These are principally costly due to their locations and lack of infrastructure.

·        Dry holes are often interpreted as false positives; which are often found in tight reservoirs and thick wet sands.

·        Low-saturation gas phenomenon is often related to a break in a reservoir seal and is due to residual gas that assemble a high amplitude effect similar to a commercial saturation.

·        Flat reflections may be caused by unusual lithologic variations rather than fluid contacts.

·        Rocks with low impedance could be mistaken for hydrocarbons, such as coal beds, low density shale, ash, mud volcano, etc.

·        Polarity of the data could be incorrect, causing a bright amplitude in a high impedance zone.

·        Superposition of seismic reflections and tuning effects.

·        Signal contamination due to noise.

 

     As a geologist involved in oil & gas exploration and development, I have looked at many seismic lines, both uninterpreted and interpreted. I am not very competent in interpreting seismic lines. I often relied on interpreted sections. Earlier in my career, I looked at a lot of 2D seismic lines with very small bumps, known as “eyebrows,” that indicated prospective erosional remnant traps in an unconformity play. Later, I utilized lots of interpreted seismic lines for geosteering wells. Most were fairly accurate at predicting geology, even when it was quite complex. However, the resolution was sometimes not good enough to see smaller faults or folds, so there are some limitations when a higher resolution is preferable.  

 

The Growing Use and Growing Success of DHIs

     A May 2025 article in AAPG Bulletin by authors from ExxonMobil notes that exploring for more challenging geological traps with subtle geophysical responses, such as the now prolific play offshore Guyana and Suriname, has benefited from DHIs. Ecopetrol’s Sirius discovery in Colombia is another example. It is projected to potentially triple the country’s reserves, which had dropped in recent years due to depletion. ExxonMobil developed a statistical approach guided by machine learning that has led to significant improvements in predicting the presence of economic hydrocarbons.

“More recently, the DHI evaluation process adopted expectation-based metrics and now leverages machine learning for scoring, which leads to improved accuracy, while mitigating human bias. These adaptations allow the process to be more broadly applicable across a global portfolio of prospects. Discernibility, an innovative metric, describes the expectations and confidence in geophysical observations and helps guide both risking and resource estimation. A significant challenge to predictability involves reconciling contradictory information between geological and geophysical observations. Applying the new integrated workflow, geoscientists integrate geological and geophysical observations through a Bayesian framework guided by discernibility. This framework allows for integration of all observations into a single COS {chance of success} value in a simple, repeatable manner.”

     ExxonMobil’s prospect maturation process is shown below. DHIs come early in the process in the geologic risking phase. Below the process chart are the three risk groups and six geologic elements of its nine-element geologic risk evaluation process.

     The map below shows ExxonMobil’s wildcat drilling since 1994, predominantly in offshore plays, and the heavy correlation with the presence of DHIs.

     ExxonMobil revised its prospect maturation flow and its DHI attribute classification system in 2021, with the historical and revised DHI attributes shown in the charts below.

     Below are ExxonMobil’s revised quality attributes and data examples of its revised DHI attributes.

     ExxonMobil’s system involves integrating geological chance of success (GCOS) and DHIs to derive DHI discernibility and integrated chance of success (iCOS).

“In the iCOS framework, discernibility becomes the key metric for informing how much modification of the GCOS prior by DHI observations is warranted.”

     ExxonMobil’s DHI discernibility matrix and iCOS integration graph are shown below.

     Volumetric parameters and the weighting of the column height of the fluid contact are shown below.

     Below is shown a fluid contact followed by a DHI interpretation of the Liza prospect area in the Guyana Basin, followed by four individual well prospects (A, B, C, and D) evaluated according to the iCOS system.

     The following graphs compare the historical and revised systems of determining COS in the Guyana Basin prospects via DHI scoring before and after drilling and accuracy analysis.

     In July 2025, Barry Friedman wrote in an article for AAPG, ‘How DHIs Are Driving Giant Discoveries,’ that the use of AI algorithms combined with DHIs is increasing accuracy and leading to big hydrocarbon discoveries.

“When coupled with artificial intelligence algorithms, which automate and speed up identification of DHI characteristics, scientists can more efficiently and accurately predict potential oil and gas reserves in four specific areas:

·        Identifying the presence of potential reserves

·        Improved drilling decisions

·        Assessing specific insights of the prospect in terms of trap area, pay thickness and sometimes porosity

·        Reducing overall geological risk

     According to Henry S. Pettingill, chairman of the Rose and Associates’ DHI Interpretation and Risking Consortium:

“Approximately two-thirds of the reserves from all deepwater giant discoveries were found using DHIs.”

     He also notes that DHI gas discoveries have outnumbered DHI oil discoveries because gas is easier to detect than oil, since oil and water are more difficult to distinguish seismically. However, in reservoirs with high gas-to-oil ratios (GORs), oil detection is nearly as good as gas detection. He cites reservoirs in the Gulf of Mexico, the Kutai Basin in Indonesia, and Guyana as good examples. However, he also notes that many economic hydrocarbon accumulations are not amenable to discovery through DHIs if:

“…seismic data quality (imaging) was not good enough to resolve DHIs or because the rock properties of the sands and shales show insufficient contrast in acoustic impedance, hence no amplitude anomaly.”

     Pettingill notes that DHIs have significantly improved success rates in frontier basins, but also notes that they are not in themselves a shortcut to success. They must be used along with geological interpretation.

“Typical frontier wildcat success rates are 25 percent without DHIs, and 50 percent and upward with DHIs. In some plays it can be 80 percent.”

    DHIs are also being explored for carbonate reservoirs. Pettingill’s colleague, Rocky Rosen, noted that there are three areas where DHIs are showing future promise:

·        Ocean bottom node seismic: “It’s very expensive but for imaging-challenged plays like sub salt, there is nothing better, and the results keep getting better,” said Roden.

·        Full waveform inversion seismic processing, including elastic FWI (eFWI): “Again, it’s all about better imaging, and the advancements have been incredible,” he said.

·        Computing power: “This follows Moore’s Law of integrated circuits, which states that the semiconductor compute power doubles every two years,” Roden added.

     Geologist Teresa Martins of Galp, who utilized DHIs in its Mopane discovery in the Orange Basin Offshore Basin offshore Namibia, which I wrote about just last week – see link.

“Right now, the role of DHIs is shifting from being a ‘cherry on top’ to a quantitative, probabilistic input in full-cycle risk analysis. Instead of being used as isolated ‘bright spots,’ DHIs are increasingly embedded in workflows that combine geology, petrophysics, and seismic attributes to generate predictive, statistically backed models of reservoir presence and quality.”

     Basically, improved imaging, processing, AI integration, and overall exploration modeling is leading to the ability to see DHIs in prospects where they could not be seen before, which suggests that more prospects will be amenable to DHI analysis as time goes on. The ability to better image sub-salt plays, in particular, is a breakthrough.

“Future breakthroughs, {Pettingill} believes, will include continued resurgence of onshore DHIs, subsalt DHIs, dim spots and other subtle DHIs, electromagnetic surveying in appropriate setting, advances in seismic acquisition and processing and, that elephant in the room – AI/ machine learning.”

     

References:

 

How DHIs Are Driving Giant Discoveries. Barry Friedman. AAPG Explorer. July 2025. How DHIs Are Driving Giant Discoveries

Direct hydrocarbon indicators. Society of Exploration Geophysicists (SEG) Wiki. Direct hydrocarbon indicators - SEG Wiki

Direct Hydrocarbon Indicators. Sage. Earthscope. National Science Foundation. Direct Hydrocarbon Indicators- Incorporated Research Institutions for Seismology

Integrated and improved direct hydrocarbon indicators: A step forward in petroleum risk discrimination. P. W. Monigle, T. S. Hedayati, and F. J. Goulding. AAPG Bulletin, v. 109, no. 5 (May 2025), pp. 617–636. BLTN24030_proof.pdf

Direct hydrocarbon indicators (DHI). Hatem Radwan. Slide Share. Direct hydrocarbon indicators (DHI) | PDF

 

Scaling Hybrid Building Tech from Defense to Commercial Use: GTI Energy Webinar - September 9, 2025: Summary & Review

         This webinar explores hybrid technology for buildings, especially chiller plants and hybrid rooftop unit (RTU) systems that combine natural gas and electric heating technologies with adaptive, AI-enabled controls. Susan Stover, GTI’s Director, Defense, Energy, and Collaborative Programs, talks with Jason LaFleur, GTI’s Senior Program Manager of Building Technologies.

     Chillers, boilers, and heat pumps are being used in the defense industry for practical energy efficiency reasons. Resilient, reliable, and efficient building energy is important for military buildings. In these hybrid systems, there is also redundancy, which may be more expensive upfront but which also provides superior reliability, resiliency, and efficiency.

     Two large Illinois National Guard buildings that are over 100 years old were outfitted with natural gas heat pumps. This is an outdoor system that provides year-round heating and cooling. These were integrated with hybrid boiler and chiller plants. The gas heat pumps provided significant savings for cooling, reducing electricity costs.  

     Hybrid rooftop units (RTUs) can provide heating, cooling, and ventilation with a gas-fired furnace for backup. These are drop-in replacements for electricity access. The gas system comes on when temperatures hit 0 degrees F. 

      These units also switched over to lower-impact refrigerants, including R-32 and R-454B. The switch to gas can be done based on temperature, energy costs, or emissions. Electric to gas price ratios vary significantly in different parts of the country. One goal is to avoid peak demand periods. Sometimes the electric heat pumps and gas furnaces were used simultaneously. Emissions concerns depend on local sources of power generation. Electricity rates are an important factor. As shown below, these systems can provide about 26% total cost savings.

     They modeled costs in different states and regions based on heating degree days and cooling needs. They utilize smart fuel-switching controls. At what temperature the system switches to gas depends on energy costs and desired emissions. These hybrid RTU systems are mostly DOD demonstration projects that can be applicable to the commercial market. Commercial applications of gas heat pumps for buildings can be developed from the military demos and inform utility incentives.

     Q: Can extreme temperatures affect hybrid RTUs? A: They can reduce efficiency, but the system can be programmed to adapt and kick in when needed to keep environmental conditions the same in the building.

     These systems can also take advantage of dynamic power pricing to optimize costs. Power and natural gas reliability are factors as well. If one goes out, the other is available. Each project and each area will be different and unique based on power availability, costs, and climate. Smart controls can optimize.

 References:

Scaling Hybrid Building Tech from Defense to Commercial Use - September 9, 2025GTI Energy Tech Talk Data Driven Energy Systems - July 23, 2025 on Vimeo

 

Plastic Recycling Via Pyrolysis: Significant Environmental, Health, and Safety Concerns and Limited Economic and Environmental Benefits

   Plastic is notoriously difficult to recycle. There are many different grades of plastic with many different components. Plastic is generally a complex mixture of polymers and chemicals. In the U.S., less than 5% of plastic is recycled. Plastic can only be recycled a few times, unlike aluminum and glass, which can be recycled many times. Recycled plastic often is mixed with virgin plastic, so at best it is really only partially recycled. Mechanical plastic recycling involves washing, shredding, grinding, pelletizing, and other steps. These processes also release VOCs, particulate matter, and microplastic particles into the environment. They are also quite flammable and present very real fire risks at these facilities. Even plant-based “biodegradable," or "compostable” plastics are only partially recyclable. These only make up about 1% of plastics, and only about 1% of that 1% are considered environmentally benign. These bioplastics may also release more microplastics than regular plastic.

     Chemical recycling of plastic is occurring at some facilities, but there are very significant air quality and other environmental concerns with these facilities. One method used is incineration under low oxygen conditions to melt the plastic in a process known as pyrolysis. Other methods of chemical recycling include gasification, solvolysis, and solvent-based purification. According to the Natural Resources Defense Council (NRDC), pyrolysis makes up the bulk of operating and planned plastic chemical recycling facilities, about 80% of them. The NRDC notes that pyrolysis, as well as gasification, are forms of incineration with major toxic impacts. They cite an NREL analysis of pyrolysis that suggests only 0.1 to 6 percent of the plastic waste undergoing pyrolysis can become new plastic. The NREL report also notes that:

“…the economic and environmental metrics of pyrolysis and gasification are currently 10 to 100 times higher than virgin polymers.”

     That certainly suggests that recycling plastic through pyrolysis and gasification is not worth the trouble and will likely cause more harm than good, both environmentally and economically. Pyrolysis is mostly used to turn plastic waste into fuels, highly toxic ones. In 2023, the EPA approved 18 new chemical mixtures derived from plastic waste for use as fuels while also acknowledging that some of these fuels present high risks of cancer. Later, they rescinded some of these approvals, noting the need for further research.

     Pyrolysis facilities also produce large volumes of hazardous waste. The table below from the NRDC report shows the hazardous waste generated from just three facilities. They note:

“If all 26 of the pyrolysis facilities that are currently proposed or under construction are actually built and put into operation, this could mean between 624,000 and 10.8 million additional pounds of hazardous waste generated in, transported through, and disposed of in communities across the country.”

     This hazardous waste is transported to storage and landfills, and transporting hazardous waste has its own risk factors. The map below from NRDC shows where the operating and proposed facilities are, and below the first map is a map showing routes of travel for the hazardous waste from just three facilities. Many of the locations of operating and proposed facilities are near vulnerable communities and are likely to become environmental justice concerns.

     Other methods of chemical recycling of plastic, such as solvent-based and solvolysis methods, do not burn it but dissolve it with toxic chemicals, which also creates significant environmental and health concerns. These also generate significant amounts of hazardous waste. Perhaps it is better to just landfill all plastic. NRDC calls chemical plastic recycling a “false solution,” and it is hard to disagree. Promoting other solutions to the problem, such as making the plastic less toxic to begin with and switching to more benign materials where possible, are better things on which to focus

     Pyrolysis facilities produce toxic air pollution in their local vicinity, but that may vary with the sophistication of the pollution abatement equipment. They have also been associated with noise pollution and unpleasant odors. Conditions such as these tend to reduce local property values.

     Operating plastic pyrolysis facilities have also struggled economically, with some filing for bankruptcy. The difficulty in making a profit also means that they will likely not provide much local tax revenue.

     The bottom line is that chemical plastic recycling is not really viable. ExxonMobil used to promote these methods, but they have proven thus far to be woefully inadequate in solving the problem at best, and toxic to local people and the environment with very little or no benefits at all at worst. Of course, research into chemical plastic recycling should continue. I do not believe that many of these proposed facilities should be built unless they can prove that they can overcome some of these difficult challenges to the flailing industry. Of course, landfills have their own substantial environmental concerns. I also think that of the so-called three R’s: reduce, reuse, recycle, perhaps reduce may have the most utility here. If we can somehow reduce the use of plastic, that would help, but plastic still has many advantages over other materials, including its low weight. The continued proliferation of plastic, microplastic, nanoplastics, and plastic manufacturing and recycling pollution is a problem that is not easy to solve and which threatens to get worse.

 

  

 

References:

 

Planned WV plastics recycling facility could hurt economy, public health. Nadia Ramlagan. Public News Service. October 8, 2025. Planned WV plastics recycling facility could hurt economy, public health

It's time we confront the ugly truth about plastic recycling. Opinion by Holly Kaufman. San Francisco Chronicle. October 8, 2025. It's time we confront the ugly truth about plastic recycling

“Chemical Recycling” Is a Toxic Trap:Chemical recycling is mostly plastic incineration and generates significant hazardous waste and pollution. Renee Sharp. Natural Resources Defense Council. March 11, 2025. “Chemical Recycling” Is a Toxic Trap

 

Polluted Tijuana River Causing Significant Air Quality Concerns on Both Sides of Border: New Study Demonstrates That Toxic Gases in the Water are Transferred to the Air in Turbulent Sections of River

      Air pollution from the heavily polluted Tijuana River is affecting both sides of the border area. The river passes through San Diego's South Bay Region before reaching the ocean. South Bay area residents have long complained about foul smells, and the water quality measured in the river has been very poor. The main causes of water and air pollution are untreated raw sewage and industrial waste. Highly elevated levels of hydrogen sulfide (H2S) have been found, likely due to the sewage. Peak concentrations of H2S that were some 4,500 times higher than what is considered typical for an urban area, along with the presence of hundreds of other gases, were found.

     The study, published in August in the journal Science, analyzed the results of air quality monitoring in the area. 

     Alex Fox of UC San Diego Today notes:

“From September 1-10, 2024, residents near the study’s air quality measurements in Nestor — close to Berry Elementary School — were exposed to levels of hydrogen sulfide that exceeded the California Air Resources Board’s one-hour average air quality standard for five to 14 hours each day.”

“We show here that while hydrogen sulfide is an excellent marker of the sewage impacting area residents, there are multiple sources of waste entering the Tijuana River and a multitude of other hazardous gases that area residents are potentially inhaling,” said Kelley Barsanti, an atmospheric chemist at NSF NCAR who led the analysis of additional gases detected at the site.”

     The abstract below explains some of the results and implications, including the implication that water pollution can be transferred to the air and become air pollution in turbulent sections of rivers.

     The authors note that:

“…many processes can transfer water pollutants to the air, including bursting bubbles in waterfalls, turbulence in rivers, aeration in wastewater treatment plants, toilet flushing, and breaking waves in coastal surf zones, which form aerosols in a process known as aerosolization.”

     The researchers identified a turbulent section of the river as an air pollution hotspot. This is where there are the most malodor complaints.

“On September 10, 2024, the Tijuana River’s flow rate dropped dramatically — from 40-80 million gallons per day to less than 5 million gallons per day — reducing concentrations of hydrogen sulfide and many other gases for the remainder of the study’s duration. Though authorities have not announced any official changes in the river’s management, the study authors surmised that “on September 10, a pump station in Mexico was activated.” Activating this pump diverted the wastewater flow, keeping it on the Mexican side of the border.”

     After the water was diverted, the H2S concentrations dropped, definitely tagging the river as the source of the airborne H2S and other gases. They also found that the number of complaints about maladies such as headaches, as well as complaints about odors, spiked on days when the H2S levels were highest. The graph below shows hourly and daily changes in H2S concentrations.

     The graph below shows changes (lower levels) in gaseous oxygenated hydrocarbons after the water was diverted.

     San Diego County has a program that provides free air purifiers for residents to use at night when H2S levels tend to be highest and when the wind speed is lowest. They also developed an online dashboard and an alert system that alerts residents when H2S levels exceed 30 parts per billion (ppb).

     This issue is also considered to be an environmental justice issue where disenfranchised and marginal communities tend to be most affected. 

    

References:

 

Researchers issue warning about toxic gases crossing US border: 'Hazardous'. Tina Deines. The Cool Down. September 16, 2025. Researchers issue warning about toxic gases crossing US border: 'Hazardous'

Tijuana River’s Toxic Water Pollutes the Air: New peer-reviewed study shows hydrogen sulfide levels exceeded California air quality standards. UC San Diego Today. Alex Fox. August 28, 2025. Tijuana River’s Toxic Water Pollutes the Air

Heavily polluted Tijuana River drives regional air quality crisis. Benjamin Rico, Kelley C. Barsanti, William C. Porter, Karolina Cysneiros de Carvalho, Paula Stigler-Granados, and Kimberly A. Prather. Science. Vol 389, Issue 6763. August 28, 2025. Heavily polluted Tijuana River drives regional air quality crisis | Science