Acquire quality NMR measurements and overcome challenging drilling conditions

Better well placement in the complex carbonate and clastic reservoirs found in the Middle East requires real-time acquisition of pore size distribution with accurate quantification of macro- and microporosity volumes, identification of permeable layers, and detection of heavy oil and tar.

Macroporous carbonates exhibit very long relaxing times, which are best evaluated using T1 measurements. T2 measurements are optimal for characterizing fast-relaxing formation components and enable best coverage of the relaxation time space with higher data density and higher vertical resolution. Low-gradient T2 can also be used to resolve longer relaxation time. Conventional LWD solutions provide either T1 or T2 distributions, but not both simultaneously. In the region, data must not only be acquired and processed in real time while drilling, but also in challenging environments where lateral vibration poses a challenge to the quality of NMR data.

Use high-definition NMR logging while drilling

Schlumberger developed MagniSphere high-definition NMR logging-while-drilling service for slimhole applications (wellbores <6 3/4 in). The service incorporates the latest digital and technological enhancements in NMR sensor design and characterization to improve sensitivity, accuracy, and precision of measurements. MagniSphere service simultaneously identifies T1 and T2 distributions while drilling, enabling the optimal characterization of a wide range of fluids, from light oil and gas to heavy oil and tar mats, along with a wide range of pore sizes, from macro- to microporous reservoirs.

Higher tolerance to lateral motion is another key advantage of MagniSphere service that results from an increased volume of investigation and additional motion-prevention methods that incorporate two built-in stabilizers to minimize antenna vibrations. A new NMR signal acquisition sequence and a short echo spacing enable better vertical resolution with enhanced precision in microporosity and heavy oil. Finally, MagniSphere service is also able to operate in high-salinity environments thanks to a newly designed receiver.

Successful deployment in multiple fields and conditions

The operator completed a large number of MagniSphere service applications in multiple wells, accumulating high-quality, continuous LWD NMR data. This enabled an accurate evaluation of clastic and carbonate reservoirs by measuring permeability profile, macro- and microporosity volumes, 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.

Technical details

Hursan, G., Silva, A., Van Steene, M, Mutina, A.: "Learnings from a New Slim Hole LWD NMR Technology," paper SPE 202897-MSD presented Abu Dhabi International Petroleum Exhibition & Conference, Abu Dhabi, UAE (9–12 November, 2020)