DATE: September 17th, 2026

SPEAKER: Tim Matava, Owner of Geological and Geophysical Integrated Modeling, Inc (GGIM, Inc)

TITLE: The Next Stage of Development of the Fruitland Coal in the San Juan Basin

TIME: 

5:30-6:30 Happy hour and dinner

6:30-7:30 Society business and presentation

7:30pm raffle to raise money for student dinners

LOCATION: Rm. 710, Sitter Family Hall, Fort Lewis College.

COST: TBA – Still negotiating pricing with caterer. Don't register yet.

RSVP DEADLINE: Friday, September 12th. 

ABSTRACT: The Fruitland Coal is the largest coalbed methane reservoir in North America and has been a prolific source of hydrocarbons in the San Juan Basin.  However, parts of this supergiant reservoir accumulation are approaching their expected ultimate recovery, setting the stage for the next phase of reservoir development. In this presentation I will discuss transitioning the reservoir from a hydrocarbon producing reservoir to a storage site for permanent sequestration of CO2. The emphasis of this presentation is on the geologic controls that make this such a unique storage site. 

I will begin with a review of the role of adsorption onto the coals and how more CO2 is adsorbed on the coals than methane and that the adsorbate is unconditionally stable. In every laboratory and field test Langmuir adsorption is generally presented as the controlling process; however, adsorption only describes the relationship between pressure and volume of adsorbate on the coal. The fundamental control on the adsorbate is the chemical potential of the adsorbate relative to the species in solution.  An understanding of the chemical potential of the adsorbate and how it varies with temperature, pressure, and species (e.g., the presence of methane) is critical for understanding the changes in the capacity of the coal to adsorb CO2 as the shallow part of the basin transitions from a producing reservoir to a storage reservoir.  It is the basis for an equation of state which describes the P, T behavior of the coal with mixed species. 

Injection histories from the extended field tests make clear that the Fruitland Coal has a robust dual porosity system that does not exist in age equivalent coals in some other basins. In a field test involving CO2 in the Western Canada Sedimentary Basin (WCSB), coal cleats swelled shut in less than two weeks ending the field experiment. Extended field tests in the Fruitland Coal showed no signs of decreased permeability after several months of injection at a high rate. A review of the basin history shows why so much storage potential exists in the Fruitland Coal that is lacking in other inland seaway basins with age equivalent coals such as the WCSB. The set of fractures in the Fruitland Coal is distinct from other fracture sets in the basin suggesting a stress history associated with uplift overlaid on existing cleats; consequently, swelling associated with adsorption does not close these fractures. 

A final prospective aspect of the Fruitland Coal as a CO2 storage site is that pre-development studies show that this section of the basin was originally overpressured. Meteoric charge from aquifers outcropping on the rim of the basin leads to overpressured reservoirs at the middle of the basin. Sequestering CO2 to a hydrostatic pressure relative to the well location ensures that as the basin recovers from dewatering associated with production then the stability of the adsorbate should increase with time. This is because the amount of either CO2 or methane adsorbed always increases with increasing pressure.

Ensuring CO2 containment will be the responsibility of New Mexico and Colorado regulators because both states are seeking primacy for these activities from the EPA. The strong coupling between pressure, temperature, and composition, however, provides reason to be optimistic that simpler, less expensive yet robust monitoring methods may be available instead of the standard large array of permanently placed seismic monitoring arrays. For monitoring near the wellbore, if the CO2 enters the surrounding sands and is unconstrained then fluid expansion leads to Joule-Thomson cooling where the leak occurs. If the CO2 is adsorbed on to the coal then the enthalpy of adsorption leads to reservoir heating. Away from the well a vertical seismic profile may be sufficient for monitoring a plume extending into the surrounding formation. A single fiber optic cable installed in the wellbore monitored for both acoustic and thermal responses may be adequate for these measurements. Both of these approaches require first modeling and then extended field tests to verify their efficacy.

In summary, the Fruitland Coal has had a long history as a supergiant hydrocarbon accumulation and long lived asset in the San Juan Basin. However, cumulative production in parts of the field is approaching the recoverable limit, so now is a good time to begin to address outstanding issues associated with converting the producing asset to a permanent storage site for CO2.   The amount of adsorbed CO2 will exceed the amount of methane produced and the adsorbed fluid will be unconditionally stable. However, developing cost effective monitoring methods requires planning both modeling and field tests.