Overview
ISO 13503-6:2014 - "Petroleum and natural gas industries - Completion fluids and materials - Part 6: Procedure for measuring leakoff of completion fluids under dynamic conditions" - specifies a consistent laboratory method to measure fluid loss (leakoff) of completion fluids under dynamic (circulating) conditions. It applies to all completion fluids except those that react with porous media and is intended to reproduce downhole circulation and filter-cake formation behavior that differs from static testing.
Key topics and technical requirements
- Scope and applicability: Dynamic fluid-loss testing for completion fluids (excluding fluids that react with porous media).
- Cell types: Two cell geometries are defined - round cell (typical core: 25.4 mm length × 25.4 mm diameter) and proppant conductivity cell (core thickness ≥ 9.5 mm).
- Test parameters:
- Temperature: Measured to ±1 °C, stabilized to ±3 °C of test temperature; heat-up rate limits apply (inlet temperature within −5% to +3 °C of test temp within 15 min).
- Pressure: Differential pressure across the core controlled to ±5% of design pressure; backpressure typically ≥ 690 kPa (100 psi). For low-permeability cores a higher differential (example: 6 900 kPa / 1 000 psi) is recommended.
- Shear rate: Target shear rate across the core face is 40 s⁻¹ ± 25%; shear rate is calculated from flow rate (Q), gap height (h) and gap width (w).
- Test duration & sampling: Minimum duration 60 minutes with leakoff recorded at least one data point per minute.
- Permeability: Core permeability must be measured prior to test using a compatible fluid.
- Optional: Use of a shear-history simulator for shear-sensitive fluids (parameters: tubing length, ID, flow rate).
- Core preparation & fluids: Cores must be mechanically prepared to avoid permeability alteration and saturated with base or synthetic formation fluid (non-reactive if formation fluid unknown).
- Data reduction: Cumulative fluid loss per unit area (ml/cm²) is regressed against time and square-root(time) to obtain three leakoff parameters: dynamic coefficient (Cd) proportional to time, wall-building coefficient (Cw) proportional to √time, and spurt loss (S). Relationship: V = S + Cd·t + Cw·t^1/2.
Practical applications and users
- Who uses it: Petroleum/completion engineers, laboratory technicians, completion-fluid R&D teams, service companies, quality assurance groups and regulators.
- Why use it:
- To simulate downhole circulating conditions and predict fluid-loss behavior and filter-cake formation.
- To compare and qualify completion-fluid formulations, optimize additives, and select fluids for fracturing, stimulation and gravel-pack operations.
- To assess formation damage risk and proppant-pack interactions under dynamic leakoff.
- To provide standardized, comparable leakoff coefficients for engineering models and well-design decisions.
Related standards
Keywords: ISO 13503-6, completion fluids, fluid loss, leakoff testing, dynamic conditions, spurt loss, shear rate, proppant conductivity, petroleum industry.
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