Injectivity testing asks a practical question: how does the injection system and receiving interval respond as rate and pressure are changed under a controlled procedure? In CRI, the answer supports formation characterization, operating-window decisions and long-term surveillance. The test is not a generic field calculation that can be interpreted safely without the well, fluid and geomechanical context.
This control belongs to a connected operating system. Use the CRI engineering pillar, the integrated surface process and formation capacity and containment together; changing one boundary can move the constraint elsewhere.
Purpose of an injectivity test
A controlled test can establish a repeatable pressure-rate response and provide a baseline for later comparison. Published CRI programs repeat injectivity tests during operations to detect changes and support model recalibration. The exact sequence, fluid, step duration and interpretation method are project-specific.
Pressure-rate data must be clean
Record stabilized or procedure-defined rate and pressure, fluid properties, temperature where relevant, well configuration and measurement location. Transient data can be valuable, but it should not be mixed casually with steady or step-end values.
| Test record | Required basis | Reason |
|---|---|---|
| Rate step | Defined unit and time interval | Allows pressure-rate comparison |
| Pressure | Measurement location and reference | Separates unlike gauges and references |
| Fluid / slurry | Density, relevant rheology and batch identity | Hydraulic losses depend on the injected material |
| Well configuration | Valve and injection path state | Configuration changes alter the measured response |
| Timing | Synchronized timestamps and project hold/stabilization rule | Prevents mixing unlike transient and step-end data |
Pressure–rate indicators: useful only on a defined basis
A project may define a pressure–rate or injectivity indicator for surveillance, but the reference pressure, measurement location, fluid, well configuration and test procedure must be fixed. Fracture injection can be nonlinear, so a simple rate/pressure ratio is only a trending aid and cannot replace the approved pressure-transient or fracture interpretation.
Step-rate logic
Changing rate in planned steps can reveal changes in pressure response. A change in pressure-rate slope may indicate a change in system response, but it does not by itself identify fracture reopening or extension. Distinguish the approved injectivity, step-rate/fracture-extension and falloff objectives; interpret each using measured or reliably calculated bottomhole pressure on a stated datum, together with transient behavior, wellbore storage, hydrostatic and rate-dependent friction corrections, fluid properties and the project geomechanical model. If a defensible bottomhole-pressure basis cannot be established, do not assign a fracture-opening, reopening or extension threshold from the surface curve alone. Surface friction and changing fluid properties must be accounted for.
Repeat tests as surveillance
The value of a repeated test is comparability. If the procedure, fluid or measurement system changes, the trend can be misleading. Document deviations and use the same reference basis whenever practicable.
What the test does not prove
A good injectivity result does not by itself prove long-term containment or remaining disposal capacity. Those conclusions require the broader subsurface assurance program, including cumulative volume, pressure history and model-based assessment.
Operational interface
Surface personnel should know when a test is planned, what slurry or fluid is required, how to prepare the system and which data must be captured. Poor surface execution can compromise an expensive subsurface test.
Test preparation controls test value
Confirm the well configuration, fluid/slurry to be used, instrument status, planned rate steps, stabilization or hold criteria, data frequency and communication protocol before starting. A test with uncertain valve status or changing fluid properties can produce an apparently precise curve that is difficult to interpret.
Surface friction must be recognized
The measured surface pressure includes losses outside the formation. As rate changes, those losses can change substantially. Project interpretation may correct or model these contributions. Ignoring them can make a hydraulic change look like a formation threshold.
Repeatability is more valuable than a pretty curve
A surveillance test should be repeatable enough that changes over time are meaningful. Record deviations from the standard procedure. If a later test uses different fluid, equipment or step duration, the comparison should explicitly account for it rather than forcing both tests onto one trend.
Post-test handling
Preserve raw data, not only the interpreted result. Record calibration information, timestamps, units, fluid properties and operational notes. Raw data allows later re-interpretation as the geomechanical model evolves and protects against conclusions being detached from the conditions that produced them.
Operational decisions remain governed
A test may support an updated operating window, but changing injection limits requires the responsible project authority. Field personnel should not convert an apparent test threshold directly into a new maximum pressure or rate without the approved technical review.
Treat injectivity tests as controlled experiments inside the CRI assurance program. Their power comes from procedure, data quality and repeatability—not from a single calculated index.
Common questions
Is injectivity a constant property of a CRI well?
No. The observed pressure-rate response can change with fluid, well condition, fracture state and cumulative injection history.
Can a simple injectivity index replace step-rate interpretation?
No. A ratio can support trending, but it does not capture nonlinear fracture behavior or replace the approved interpretation.
Does a successful injectivity test prove containment?
No. Containment is assessed through the broader project-specific subsurface assurance process.
