CRI slurry design is a balance between carrying more waste per injected barrel and keeping the mixture processable, pumpable and compatible with the qualified injection system. Increasing solids loading can reduce carrier-fluid demand, but it can also change density, rheology, friction, settling behavior and the pressure required to move the slurry. The correct operating window is therefore established by project testing and operating response—not by a universal solids percentage.
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.
PSD is a distribution, not one particle size
A single maximum-particle statement hides the shape of the distribution. Coarse tails, agglomerates and foreign debris can matter even when an average size looks acceptable. Sampling should be representative and the measurement method documented so trends are comparable. PSD is a quality-control input; it is not proof that the well will accept the slurry.
Solids concentration changes the whole hydraulic problem
As solids concentration changes, slurry density and apparent rheology can change, and pump/line friction may change with them. Published field cases report different qualified density, rate and pressure windows because lithology, equipment and formations differ. Those case values should never be converted into universal SC DrillTech targets.
Rheology and suspension
The slurry must stay sufficiently homogeneous through mixing, hold time, transfer and injection. Rheology measurements can help track consistency, but the selected model and test conditions must be stated. A slurry that looks stable in a tank may still settle in a low-velocity line or during an extended shutdown.
Mass balance for batch preparation
For a batch, total slurry mass equals dry-equivalent solids plus all liquid associated with the as-received waste, added carrier fluid and approved additives. Define whether retained drilling fluid is measured separately or included in the carrier-liquid term so it is neither omitted nor double-counted. Volume-based field measurements require density information before they can be converted reliably to mass. This is why tank level alone is not a solids-loading measurement.
Worked screening example
Suppose a prepared batch has a measured total mass of 40,000 kg and independently estimated dry-equivalent solids mass of 8,000 kg. The mass fraction of solids is 8,000 / 40,000 = 0.20, or 20% by mass. This is only an arithmetic example—not a recommended CRI target. Real qualification must account for the actual waste, carrier fluid and project limits.
Sampling and QA/QC
Collect samples only from a designated, depressurized sampling point under the approved procedure. Do not loosen fittings, open pressurized containment or reach into moving equipment to obtain a sample; use the required PPE and exposure controls.
Define sample location, mixing condition, timing, test method and acceptance authority. Samples taken from a poorly mixed tank or immediately after a local addition can misrepresent the batch. QA/QC records should link the sample to the batch and injection record so later pressure behavior can be compared with the actual feed properties.
| QA/QC item | Basis to record | Why it matters |
|---|---|---|
| PSD | Sample point, timing, method and distribution | Links grinding result to settling and restriction risk |
| Solids concentration | Mass or volume basis stated explicitly | Prevents density from being mistaken for solids fraction |
| Density | Measured value and unit | Supports batch consistency and hydraulics |
| Rheology | Instrument, temperature and method | Makes suspension and pressure comparisons reproducible |
| Batch identity | Tank/time window linked to injection record | Connects QA/QC to pressure-rate response |
Compatibility and rejected material
The approved waste acceptance plan should identify materials that require segregation or special handling. Hard debris, oversized material or chemically incompatible waste can create risks that grinding alone does not solve. Rejection criteria are project-specific and should be explicit at the point of collection.
Density is not solids concentration
Two slurries can have similar density and different solids composition, especially when carrier-fluid density or retained drilling fluid changes. Density is useful for trending but should not be treated as a direct solids-concentration measurement unless the composition and calculation basis support that inference. When mass fraction matters, use a documented mass-balance or qualified laboratory method.
Residence time changes what "stable" means
A slurry prepared and injected immediately faces a different suspension challenge from a batch held during an injection interruption. Qualification should consider credible hold times, mixing state and restart conditions. A sample that remains homogeneous for a few minutes does not prove stability through an extended static period in tanks and lines.
Rheology measurements need a defined method
Report instrument, temperature, conditioning and model rather than publishing an isolated viscosity number. CRI slurries can be non-Newtonian and heterogeneous, so field readings are most useful as controlled comparisons. If a rheology target is part of the project specification, the test method and acceptance authority should travel with the number.
Water demand and waste minimization
Adding carrier fluid can improve handling but increases the volume that must ultimately be injected. The optimization is therefore not "add water until it pumps." Balance slurry quality, solids loading, mixing capability, friction, available water and disposal capacity. The optimum is project-specific and may change with waste type.
Link slurry data to injection response
The strongest QA/QC program does not end at batch release. Compare PSD, density, rheology and solids loading with the subsequent pressure-rate response. Over time this can identify which feed changes are operationally meaningful. Correlation does not prove causation, but it provides a disciplined basis for investigation and controlled adjustment.
The best CRI slurry is not the thickest or the finest. It is the qualified mixture that can be produced consistently, transported reliably and injected within the approved operating and containment envelope.
Common questions
Is 20% solids by mass the recommended CRI target?
No. The 20% figure in the worked example is arithmetic only. The qualified solids range is project-specific.
Does finer PSD always improve CRI performance?
No. PSD must meet the qualified requirement, but unnecessary grinding can reduce throughput and increase energy use without proving better injectivity.
What should a slurry QA/QC record contain?
At minimum, identify the batch, sample point/time, relevant slurry measurements, preparation conditions and the corresponding injection record.
