Schlumberger recently introduced the MagniSphere high-definition nuclear magnetic resonance (NMR) logging-while-drilling (LWD) service and described it as the most accurate NMR LWD service, enabling real-time producibility analysis, optimal well placement, and improved production in the most complex reservoirs. A natural question might be: What does that really mean? And Schlumberger’s Well Construction Petrophysics Product Champion Benjamin Rouanet might start his answer with, “MagniSphere service provides automated, high-definition NMR data while drilling for complex reservoir evaluation to maximize hydrocarbon exposure and ultimately optimize production.” But that’s only the beginning.

So, this is high-definition NMR?

Yes, high-definition NMR data enables far more accurate petrophysical evaluation than traditional triple-combo or standard industry LWD NMR solutions in complex carbonate and clastic reservoirs. What’s exciting is that it provides the industry’s first simultaneous measurements of T₁ and T₂ distributions while drilling, delivering robust and reliable real-time petrophysical evaluation regardless of reservoir complexity. Integrating this data into an automated processing workflow provides operators vital information to characterize porosity distributions, permeable layers, and producible hydrocarbon. In turn, this enables precision geosteering and maximized reservoir contact.

What are T₁ and T₂ distributions and how does MagniSphere compare to legacy NMR LWD services?

T₁ and T₂ are time-based measurements. The NMR tool uses a combination of magnetic fields directly acting on the formation fluid hydrogen nuclei (protons), measuring their polarization time (T₁) or relaxation time (T₂). NMR solutions are then derived from the T₁ or the T₂ distribution at each depth. Today, the LWD industry legacy solutions are based on either the T₁ or the T₂ distribution, but not both. Having simultaneous T₁ and T₂ enables the most accurate characterization of the widest range of rock fabrics and fluid type.

The T₂ distribution better defines fast-relaxing fluids. That means you’ll have a higher definition of micro- to mesoporous environments and medium to heavy fluid types. 

On the other hand, T₁ distributions help characterize slower-relaxing fluids, which maintains this high definition within macroporous environment and lighter fluid type such as light oil, and gas.

The simultaneous T₁ and T₂ acquisition brings the additional benefit that the processing and interpretation workflow can be automated in real-time and recorded mode, ensuring consistent and reliable answers. Traditionally, the T₁/T₂ ratio is a single value user input, but when both T₁ and T₂ are available it can be determined directly from the raw measurements as a variable across the full distribution range. This enables the NMR answers to be delivered directly from the acquisition system in real time, enabling operators to make more informed geosteering decisions that maximize contact with the reservoir.

How does this work?

A static magnetic field is emitted by two permanent magnets located within the sensor assembly of the tool. Between the magnets is a turbine-powered antenna that transmits a radio frequency pulse into the formation.

The measurement comprises two stages, the first being when protons align (polarize) with the static magnetic field as the tool progresses through the formation. This polarization requires a specific time designated T₁.

The second stage is when the radio-frequency pulse induces a transverse magnetization that spins the protons perpendicular to the static magnetic field. The transverse magnetization decays, enabling the protons to relax back to their original state. Proton relaxation requires a specific time designated T₂.

It's important to mention that the tool features a 400-us echo, which is the shortest of all current LWD NMR solutions, ensuring that the fast-relaxing formation components are accurately characterized and enables enhanced resolution in carbonate reservoirs with complex microporosity profile and heavy fluids.

What about real-world application?

The Middle East is a challenging environment for any technology because of the complexity of its carbonates and clastic reservoirs, as well as the challenging drilling conditions that can make it difficult to acquire quality NMR data. Operators in this region often require real-time acquisition of NMR data to accurately geosteer at a high rate of penetration (ROP) in complex reservoirs; they also need reliable technology that can withstand the local drilling conditions.

A large operator completed a substantial number of runs using high-definition NMR LWD in multiple wells, accumulating high-quality, continuous LWD NMR data. This enabled accurate evaluation of the reservoirs by delivering permeability profile and pore size distribution and identifying the presence of various fluid types, such as light and heavy oil, tar, or water. Applications comprised multiple drilling environments, including exposure to lateral motion, shock and vibration, water-based and oil-based muds, and multiple BHA configurations.

An offshore operator also used MagniSphere service to drill an extended-reach horizontal section and accurately characterize the reservoir porosity and permeability profile, placing the well into the higher-quality pay zone—which is the outcome we strive to help our customers achieve.