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Inside method

China is drilling thousands of deep coal wells at record speeds, but the formulas needed to measure what comes out of them are still being argued over in university halls.

Clay-diorama editorial illustration related to Method And Device For Evaluating Production Proportions Of Different Gases In Deep Coalbed Methane Reservoir.

What changes in this design

Most people would assume that gas coming out of an underground well is a single, uniform substance measured simply by the total volume flowing to the surface.

The record describes factoring in water saturation, rock porosity, original reserve sizes, and daily reservoir pressure. By running these measurements through specific formulas after hydraulic fracturing, it figures out the separate daily volumes and percentage shares for adsorbed, free, and dissolved gases.

Different gases behave and flow differently underground. Knowing the exact daily breakdown helps reservoir managers understand where their energy is actually coming from and how the underground coalbed is responding over time.

Eleven million cubic meters a day

In 2021, a single test well in northern China began flowing one hundred thousand cubic meters of natural gas a day from a deep coal seam. By late 2025, that pilot had grown into more than seven hundred wells producing over 4.2 billion cubic meters a year. At the Daning-Jixian field, daily output recently reached a record eleven million cubic meters. When I look at the field numbers from the basin, the speed of the expansion is hard to miss. National reserves are estimated above forty trillion cubic meters, and proven deposits already top seven hundred billion cubic meters across fourteen basins.

The drillers are moving fast because deep coal seams hold immense volumes of energy. But drilling two thousand meters into coal is not like drilling shallow beds. In traditional shallow coalbeds, methane clings tightly to the coal surface as adsorbed gas, with negligible free gas in the spaces between. Down past 1,500 meters, extreme pressure and heat squeeze large volumes of free gas into natural fractures and open pores. Across China's deep basins, that free gas represents between ten and fifty-five percent of the total deposit.

A ledger for three gases

Free gas rushes up the pipe almost immediately, while adsorbed gas desorbs slowly as pressure drops over months and years. Dissolved gas in reservoir water behaves differently still. If you are managing a field, you need to know which gas is flowing on any given morning. On September 3, 2026, a patent application published under number US20260259346A1 offered a way to calculate those daily fractions.

The filing, carrying eighteen claims and six diagrams, lays out a computational method and device to track the reservoir after hydraulic fracturing. By calculating coalbed porosity and water saturation alongside daily pressure drops, the system estimates the original volumes of adsorbed, free, and dissolved gas. It then uses those baselines to determine the daily production rate and changing percentage of each gas coming up the wellbore.

The school in Shaanxi

What caught my eye in the published record was who owned the filing. It was not submitted by a national energy giant like PetroChina, even though PetroChina completed over two hundred deep wells by 2024 and aims for thirty billion cubic meters a year by 2035. Instead, the assignees are Xi'an Shiyou University and China University of Petroleum, Beijing.

Xi'an Shiyou University began in 1951 as a regional training college under the national petroleum administration before shifting to Shaanxi provincial oversight in 2003. It remains an applied engineering school. Having regional university labs file patent applications in Washington points to where the real work is happening. The field crews are drilling, but academic teams are left to invent the accounting systems needed to make sense of the flow.

Disagreements on the same rock

The formulas look neat, but real-world measurement is proving far messier. On test well B25, as we can see in the technical literature, conventional well-logging estimated free gas at 24.79 percent, while pressure-preserved core testing put it at 22.56 percent. A discrepancy of more than two percentage points on the exact same rock column sounds modest, but multiplied across a vast basin, it alters the commercial outlook of an entire project.

Another evaluation on well B24 combined nuclear magnetic resonance with isothermal adsorption tests, arriving at an adsorbed gas proportion between 76 and 83 percent. I suspect the real disagreement lies deeper than the math: downhole core samples inevitably bleed gas as they travel up to the surface, while electronic logs struggle to distinguish gas trapped in tiny cracks from gas bonded to coal. Nobody has settled which tool gives the true number.

The harder half of the problem

We often assume that industrial drilling follows established metrology, but deep coalbed methane works in reverse. China's existing reserve standards offer no rules for defining free-gas estimation units in deep rock, no cutoffs for net-pay thickness, and no standard parameters for deep porosity or gas saturation.

Academic reviews acknowledge that the geological accumulation mechanisms in deep coal remain poorly understood. Yet production is surging anyway, backed by a 98 percent well completion rate. With full-cycle costs exceeding shale gas benchmarks and no dedicated subsidies in place, operators are committing billions while fundamental reservoir physics are still being debated. That is a gap I found startling for a resource slated to deliver thirty billion cubic meters a year by 2035. The industrial buildout is already here, but the science of measuring it is still scrambling to keep up.

Sources

Reporting for this piece drew on the published filing and the references below.

The record, briefly. US20260259346A1, “Method And Device For Evaluating Production Proportions Of Different Gases In Deep Coalbed Methane Reservoir” A method and device for evaluating production proportions of different gases in a coalbed methane reservoir: it calculates coalbed porosity and water saturation after fracturing flowback, original adsorbed, free and dissolved gas reserves, average coalbed pressure and cumulative productions each day, then daily production rates and proportions of the three gases.

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