Unlocking the Potential of the Pearsall Formation

The Pearsall Formation lies deep within the Gulf Coast stratigraphic column, positioned beneath some of the region’s most prolific producing intervals, including the Eagle Ford and Austin Chalk. While these overlying formations have long been the focus of exploration and development, the Pearsall remains comparatively underexplored—despite evidence of rich organic content and favorable thermal maturity in certain areas. Investigating this deeper stratigraphy offers a unique opportunity to identify untapped hydrocarbon potential, extend the productive life of mature assets, and uncover plays that may have been overlooked in the rush toward shallower targets. In today’s competitive exploration environment, such deeper, data-driven assessments are increasingly critical for unlocking new reserves and maintaining a competitive edge.

RFDbase in Action

GeoMark’s Rock, Fluid & PVT database (RFDbase) provides a powerful framework for isolating and evaluating source rocks on a formation-by-formation basis, allowing geoscientists to move beyond broad regional averages and focus on the intervals that matter most. In the case of the Pearsall Formation, every rock and oil sample in the database can be tagged to its precise stratigraphic unit, making it possible to quickly filter out non-relevant data and concentrate exclusively on Pearsall and underlying Silgo intervals.

Using this filtered dataset, our interactive dashboard brings the geochemistry to life—displaying TOC, Tmax, S1/TOC, Hydrogen Index (S2/TOC), Production Index and Oil Family trends across depth and geography. Each data point is color-coded by county, providing an immediate visual connection between subsurface geochemical character and geographic location. This integration of stratigraphic tagging, depth trends, and spatial context allows for targeted play assessments, rapid identification of promising zones, and a clearer understanding of how source rock potential varies laterally across the Gulf Coast.

With RFDbase as the backbone, exploration teams can assess maturity, kerogen type, and generative potential at a resolution that supports confident decision-making—reducing uncertainty and accelerating the path from dataset to drillbit.

Geochemical Insights - Pearsall & Silgo Formations by County

RFDbase Silgo & Pearsall Formation Source Rock Data

The Pearsall and underlying Silgo Formation samples from GeoMark’s RFDbase reveal clear geochemical trends across the Gulf Coast, with distinct differences between counties:

• Total Organic Carbon (TOC): Most samples show moderate to good organic richness, generally below 3 wt% but with localized higher values observed in Bee, Maverick and Webb counties.

  
  

• Tmax (Thermal Maturity): Maturity values range from immature (<435 °C) in all locations, early oil window (~435 °C) in Bee, Maverick, McMullen and Robertson counties, and gas window conditions (>470 °C) within Maverick and McMullen counties. This spread highlights potential for both oil-prone and gas-prone intervals within the Pearsall/Silgo section.

  
  

• Production Index (S1/(S1+S2)): PI values generally range from 0.2–0.6, with elevated values at depth in Bee, Maverick, McMullen and Webb counties—indicating advanced maturity and potentially significant hydrocarbon generation.

  
  

*PI should always be interpreted alongside Tmax and other maturity indicators—high PI in an immature rock may indicate contamination or migrated hydrocarbons. Additionally, in mature rocks, a high PI confirms active or past generation; in overmature rocks, it may be high because little S2 remains.

Overall, the Pearsall/Silgo system is gas-prone in its deeper, high-maturity sections (Maverick, Webb, Washington and McMullen counties), with select pockets of oil-prone potential in less mature areas (Maverick, Webb and Bee counties). The ability to pinpoint these variations—both vertically and laterally—underscores the importance of targeted exploration strategies.

Has GeoMark Identified Any Lower Cretaceous Oil Across the Region?

Yes, we sure have!

RFDbase Gulf Coast Oil Source Age Map - Lower Cretaceous Oils Highlighted in Red

Beyond source rock screening, RFDbase also enables direct oil-source correlation details through geochemical fingerprinting. GeoMark has analyzed and interpreted over 1,000 oil samples across the Gulf Coast, using detailed biomarker and isotopic data to assign each oil to its most likely source rock. From this extensive dataset, 71 oils have been confidently tagged as sourced from a Lower Cretaceous source rock.

Notably, in Southwest Texas, this Lower Cretaceous signature is particularly strong—providing compelling evidence that the Pearsall Formation has actively sourced hydrocarbons in the region. These correlations not only confirm the generative capability of the Pearsall but also help map migration pathways and identify potential charge areas. By integrating oil-source correlation with the rock-based maturity and richness data, explorers can target areas where the Pearsall is both a proven source and a potential direct contributor to hydrocarbon accumulations in shallower reservoirs. As we say here at GeoMark "MIGRATION HAPPENS".

Current Exploration Interest & Outlook

While the Pearsall Formation has historically been overshadowed by the Eagle Ford and Austin Chalk, several factors suggest it is gaining renewed interest. High-resolution geochemical data reveals that in certain parts of South Texas the Pearsall retains favorable maturity and richness profiles for liquid hydrocarbons. The strong oil-source link in Southwest Texas further boosts its prospectivity.

Beyond geochemistry, assessing phase behavior and reservoir pressures is a critical step in de-risking Pearsall exploration. Understanding how hydrocarbons will behave under reservoir and surface conditions directly impacts facility design, completion strategy, and economic outcomes. GeoMark’s extensive PVT database and in-house geochemistry & PVT services can provide this essential insight—delivering a complete subsurface evaluation that integrates geochemistry with fluid property analysis for any operator pursuing the Pearsall.

With operators increasingly looking deeper for untapped resources and leveraging analogs from other Lower Cretaceous plays, the Pearsall offers a compelling target for both new venture teams and those seeking to extend production from existing acreage.

With the right combination of geochemistry, oil-source correlations, and PVT insights, the Pearsall Formation is no longer just a deep line on a stratigraphic chart—it’s a tangible exploration opportunity waiting to be unlocked. The data is there, the evidence is strong, and the tools to de-risk the play already exist.

The next move is yours. If you’re ready to uncover what the Pearsall could mean for your portfolio, let’s put the science to work.