What Two Years of Heat Flow Data Taught Us About the Wasatch Front

Two years ago we started a systematic heat flow survey along the Wasatch Front and into the eastern Basin and Range. We had public BHT records from oil and gas wells, some vintage temperature logs from the 1970s, and a hypothesis: the published geothermal gradient maps for this region were too conservative because they were interpolated from sparse data at the basin margins, not from measurements taken in the zones that actually matter for modular extraction.

The short version: we were right, but not in the way we expected. The gradient values were fine at depth. What the literature missed was the shallow-to-midrange thermal structure between 800 and 2,200 meters, which turns out to be the decision window for modular unit sizing.

What We Actually Measured

We pulled temperature data from 47 wells across a roughly 220-kilometer corridor from the southern Wasatch Front through the central Utah Basin. These were not new wells. They were existing completions from oil and gas exploration that had been dormant or plugged, wells from geothermal exploration programs in the 1980s that were never brought online, and a handful of water wells with deep temperature logs.

The work was not glamorous. Most of it was tracking down completion reports through state agency databases, contacting surface rights holders, and doing bottom-hole temperature corrections with the Horner method for wells where shut-in time was documented. Where it was not documented, we used regional thermal conductivity estimates and cross-checked against adjacent wells. When two independent correction approaches differed by more than 8 degrees Celsius, we flagged that data point and did not use it in the gradient calculations.

Of the 47 wells, 31 produced data we were confident enough to use. That is a 66 percent yield, which is about what you expect from legacy data in this region.

The Gradient Numbers

Published regional gradient estimates for the Wasatch Front hinterland generally run between 28 and 35 degrees Celsius per kilometer. Our corrected well data shows median gradients in the range of 38 to 44 degrees Celsius per kilometer across the formations we care about, with several sub-basins hitting 52 to 58 degrees Celsius per kilometer.

Those are not extraordinary numbers by global geothermal standards. The Salton Sea in California, or the wells Fervo is working in Utah's Milford area, are running gradients that make ours look modest. But here is the point the published maps miss: we do not need extraordinary gradients for modular extraction. We need usable gradients at accessible depths.

At a gradient of 42 degrees Celsius per kilometer, starting from a mean annual surface temperature of about 12 degrees Celsius, you hit 150 degrees Celsius at roughly 3,300 meters. That is within the practical range for binary ORC power generation. At a gradient of 52 degrees Celsius per kilometer, you hit the same temperature at around 2,650 meters. That is a meaningful difference in drilling cost, which is roughly linear with depth for the formations we are talking about.

The sub-basins with elevated gradients are not random. They cluster around Quaternary volcanic features and areas with documented shallow plutonics. This is not surprising to a geologist but it is information the interpolated published maps lose entirely.

What Surprised Us

The bigger surprise was not the gradient values themselves but the thermal structure in the 800 to 1,500 meter range. Several of our wells showed a reversal or plateau in the temperature profile at this depth, followed by a return to the expected gradient below it. This kind of feature typically indicates a permeable formation acting as a lateral heat conduit, drawing cooler recharge water from the basin margins and flattening the near-surface gradient.

For a conventional geothermal developer targeting fluid production, this is a complication. For our closed-loop approach, it is actually useful information: it tells us where we do not want to site a unit if we are trying to maximize thermal gradient, and it tells us where the thermal boundary conditions at depth are more predictable because the recharge zone insulates against surface temperature variability.

We found this thermal structure in 11 of the 31 usable wells, which is a high enough frequency that it needs to be a standard screening criterion in our site assessment process. We have added it.

Implications for Site Selection

The practical output of this survey is a probabilistic model of accessible formation temperatures across the corridor. We have binned the formations into three categories: high confidence above 130 degrees Celsius at or below 2,500 meters, moderate confidence in the 110 to 130 degree Celsius range at 2,000 to 3,000 meters, and lower confidence zones where the data is sparse enough that we would require a temperature log before committing.

The high-confidence zones are smaller than the regional maps suggest, but they are more concentrated around existing infrastructure, which matters for interconnection economics. The moderate-confidence zones cover a wider area and include several locations near industrial sites that have expressed interest in off-grid geothermal baseload.

We want to be direct about what this means for a prospective partner: the survey gives us a strong prior on where to put a modular unit, but it does not replace a site-specific temperature log. No basin-scale survey does. What it does is dramatically narrow the risk of siting a unit in a zone that will underperform. The difference between a 38-degree and a 44-degree gradient is the difference between a unit that generates power economically and one that is running at the lower edge of the binary cycle efficiency window.

What the Literature Gets Wrong

The published gradient maps we have been referencing are not wrong in a fundamental sense. They are correct for the purposes they were designed for: regional energy resource assessments that want a defensible average over large areas. The problem is that modular geothermal decisions are not made at the regional scale. They are made at the site scale, and the regional map tells you very little about what gradient you will actually encounter at a specific location 2,000 meters below a specific industrial campus.

We are not saying the regional literature should be replaced. We are saying it should not be the terminal step in feasibility analysis. It is the starting point. The survey work we have done over the past two years brings that starting point much closer to a real answer for the Wasatch Front corridor specifically. We will be extending this work into the western Nevada Basin and Range beginning later this year.

Open Questions

Two things we cannot yet answer with confidence. First, the lateral variation in gradient within individual sub-basins is not well-characterized. We have point measurements from wells, and the interpolation between them carries real uncertainty. A 5-kilometer jump between data points in a complex Basin and Range structure can hide fault-controlled thermal heterogeneity that matters at the site scale. Better characterization here requires either more well data or surface heat flow measurements, and we are pursuing both.

Second, we do not have good numbers on formation thermal conductivity across the depth range we care about. We have used published values for the general lithological categories, but basin fill conductivity in particular is quite variable and the published ranges are broad. This feeds uncertainty directly into the BHT corrections and into the temperature predictions at depth. Uncertainty here does not invalidate the survey but it does set a practical floor on how precise a pre-drill temperature prediction can be.

We are running with a working assumption of plus or minus 12 to 18 degrees Celsius on formation temperature predictions at 2,000 to 2,500 meters. That is enough precision to decide whether a location is worth a temperature log, which is the actual decision the survey is designed to support.

If you are evaluating a site in the Wasatch Front or eastern Basin and Range corridor and want to know where your location falls in our probability bins, reach out. We are happy to share what the data says.