A Hall plot is a simple but powerful diagnostic chart for injection and disposal wells: it plots the running total of injection pressure over time against the running total of water injected, and the shape of the resulting line tells you whether the well is behaving normally, plugging up, or fracturing. It turns two ordinary SCADA measurements - rate and pressure - into a single curve whose slope is a health indicator. This guide explains how the Hall plot is constructed, how to read its slope and curvature, and why it is such a natural fit for SCADA-logged injection data.
Hall Plot in one line: A Hall plot is a diagnostic graph for injection wells that plots cumulative injection pressure, integrated over time, on the vertical axis against cumulative injected volume on the horizontal axis; the slope of the line reflects the well's resistance to injection, so a steepening slope indicates plugging and a flattening slope indicates fracturing or improving injectivity.
The horizontal axis of a Hall plot is cumulative injected volume - the running sum of every barrel the well has taken. The vertical axis is a cumulative pressure term formed by summing the injection pressure over time, effectively the area under the pressure-versus-time curve. Each point on the plot represents the state of the well at a moment, and as injection continues the point marches up and to the right, tracing a line. Because both axes are cumulative, the plot smooths out short-term noise and reveals the underlying long-term behavior that a raw rate-and-pressure trend can hide.
The key to reading it is the slope. The slope of the Hall plot line is proportional to the well's resistance to injection - essentially the inverse of its injectivity. When a well is behaving steadily, the Hall plot is a straight line and its slope is constant. Changes in that slope, not the absolute values, carry the diagnostic message, which is why the Hall plot is drawn cumulatively rather than as an instantaneous chart. This construction is a classic reservoir-surveillance technique precisely because it distills a well's entire injection history into one interpretable line.
A straight Hall plot means constant injectivity - the well is stable and accepting water the same way it always has. When the line begins to steepen and curve upward, it means each additional barrel is taking more pressure to inject, which is the signature of near-wellbore plugging by solids, scale, oil, or bacteria. A concave-up Hall plot is one of the earliest quantitative signs that water quality or the formation face is degrading, often visible well before the problem is obvious on a daily reading.
A Hall plot that flattens - its slope decreasing over time - means the well is accepting water more easily, which typically indicates the formation is fracturing or that a stimulation has improved injectivity. A flattening line is the fingerprint of injecting above the formation parting pressure, and because operating fractured can be prohibited by a well's permit, that change in slope is a flag to review the injection pressure. Read together, a steepening line warns of plugging and a flattening line warns of fracturing, so the single chart brackets the two opposite failure modes a disposal operator worries about most.
The Hall plot is unusually well suited to modern monitoring because it is built entirely from the two things an injection well's SCADA logs continuously anyway: injection rate, which integrates to cumulative volume, and injection pressure, which integrates over time to the cumulative pressure axis. Nothing extra needs to be measured. What the plot needs is a long, consistent, clean history of those two values, which is exactly what a well-run SCADA system provides.
Merobix, as a cloud SCADA, reads the digitized rate and pressure tags from the injection well's controller over a protocol such as Modbus or DNP3, and that continuously logged history is the raw material a Hall plot is constructed from. Because the diagnostic lives in the accumulated trend rather than in any single reading, having that data captured and available from anywhere is what makes routine Hall-plot surveillance practical. A remote operator can watch the plot steepen as a plugging warning, catch a flattening slope that suggests fracturing, and compare the behavior of many wells across a disposal network, turning raw logged data into a genuine well-health diagnostic.
The slope is proportional to the well's resistance to injection, which is the inverse of injectivity. A constant slope means a stable well, a steepening slope means the well is getting harder to inject into, and a flattening slope means it is getting easier. The changes in slope, rather than the absolute numbers, carry the diagnostic meaning.
When a well plugs, each additional barrel of water requires more pressure to inject, so the cumulative pressure axis climbs faster relative to cumulative volume and the Hall plot curves upward and steepens. That concave-up shape is one of the earliest quantitative signs of near-wellbore plugging by solids, scale, oil, or bacteria. It often appears before the problem is obvious in day-to-day readings.
Only two things, both of which an injection well's SCADA already records: the injection rate, which is summed into cumulative injected volume, and the injection pressure, which is integrated over time for the vertical axis. No special measurements are required. The value comes from having a long, consistent history of those two values at steady conditions.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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