Frontier Application | On-Site NMR Online Characterization of High-Temperature Thermal Stability in Completion Fluids for Oilfields

As oil and gas exploration extends into deeper, ultra-deep, and unconventional reservoirs, the downhole temperature environment becomes increasingly extreme. Completion fluids, which play a critical role in maintaining wellbore integrity and protecting reservoirs, must exhibit strong thermal stability at high temperatures. Their performance directly impacts well control safety, reservoir protection (permeability damage), tool service life (corrosion/deposition), and economic returns (non-productive time due to fluid failure).

As development moves toward high-temperature, high-pressure (HTHP) wells, with downhole temperatures exceeding 100°C and even 200°C, traditional completion fluid systems—such as brine-based and polymer-based fluids—face increased risk of thermal degradation. There is an urgent need for precise thermal stability evaluation methods. Current approaches, including HTHP aging cells and rheological testing, can only reflect macroscopic property changes and fail to provide insight into nanoscale phenomena like agglomeration, sedimentation, and degradation. These issues affect how nanoparticles and emulsifiers interact under high temperature—limiting formulation optimization. High-field NMR systems (>300 MHz) are expensive and not suitable for on-site deployment. In contrast, low-field NMR presents a new pathway for investigating the thermal stability of completion fluids.

Low-field NMR enables in-situ simulation of reservoir high-temperature environments and supports fast, quantitative analysis within minutes. By evaluating T₂ relaxation distributions, the dispersion stability of nano-materials can be rapidly assessed, allowing detailed insight into molecular-level failure mechanisms.

Case Study: Online Characterization of Thermal Stability in Completion Fluids Using Low-Field NMR

Experimental Materials:

Sample: Oil-based completion fluid

Instrument: Variable-temperature low-field NMR analyzer (VTMR20-010V-I)

Experimental Procedure:

1. Divide the oil-based completion fluid into a control group and an experimental group.

2. Store and test the control group at ambient temperature (25°C).

3. Subject the experimental group to online thermal aging at 150°C for 48 hours using the NMR instrument.

4. Compare T₂ relaxation results between the two groups to evaluate high-temperature thermal stability of the fluid.

Sample	T21	T22	T23
Control Group	20 ms (6%)	189 ms (54%)	512 ms (40%)
Experimental Group	15 ms (17%)	152 ms (40%)	598 ms (43%)

Through NMR relaxation analysis, we observe that the T₂₂ main peak of the control group appears at 189 ms (corresponding to the free oil phase). After 48 hours of aging at 150 °C, the experimental group shows a **leftward shift** of the T₂₂ peak to 152 ms, with a **reduction in peak area**, indicating thermal-induced structural change. The short-relaxation component T₂₁ increased by 12% due to degradation products of emulsifiers formed under high temperature. For the long-relaxation signal T₂₃, the high-temperature environment disrupted the oil–water phase equilibrium, leading to further water release and longer relaxation time.

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