The next NFES meeting will be held at Solastranden Gård, Wednesday, 12th of February 2025, at 11:00.
The presentation “CORE SCANNER FOR ELECTRICAL PROFILING OF FULL-BORE CORES AT THE WELL SITE WITH ADVANCED PULSE ELECTROMAGNETIC TECHNOLOGY” will be given by Dler Mirza, from AkerBP.
Abstract
When freshly cut full-bore cores come up to the rig floor, petrophysicists are eager to know whether or not they have hit their objective. Should they continue coring or proceed with the drilling operation towards their next objective? Where are they on the structure when correlating to other wells in the field? We present a new core scanner instrument that can answer these important questions while the core is on the rig floor. The new scanner measures the resistivity and the dielectric permittivity of the cross section of the core. The output is a finely resolved survey along the axis of the core. The observed resolution is on the order of two centimeters. Later, we integrate resistivity and dielectric permittivity measurements with other petrophysical parameters from the core analysis to refine the formation evaluation results. We combine the resistivity and dielectric permittivity with lithology, porosity, and water resistivity in the Complex Refractive Index equation. The outcome is a finely resolved estimate of the water filled porosity and water saturation.
The new core scanner device includes a transmitter antenna and a receiver antenna located on opposite sides of the core. The assembly moves along the axis of the core. The transmitter antenna emits pulsed microwave signals, similar to radar pulses, operating in the mid GHz range. The pulses travel across the section of the core and reach the receiving antenna. Very fast electronics with advanced digitizing circuits convert the received signal into binary output. This enables us to apply sophisticated signal processing techniques. The first level of output includes the amplitude of the received signal and the travel time across the section of the core. Through joint inversion, we convert the amplitude and travel time into resistivity and dielectric permittivity.
We have recently tested the new device on a series of full-bore cores from wells offshore Norway. Naturally the core barrels were non-metallic to allow propagation of electromagnetic microwaves. The results showed good agreement between the resistivity from the core scanner instrument and the open hole logs, but with much finer resolution. In high resistivity intervals we observed, as expected, a difference due to resistivity frequency dispersion. At the other end of the scale, for formations below 1.5 ohm-m, the device in its present design lost the ability to provide accurate travel time. In reservoir sections charged with hydrocarbons, where the resistivity range was 1.5 ohm-m and above, we obtained a robust inversion yielding reliable resistivity and dielectric permittivity. The joint interpretation of resistivity and permittivity yielded a correct water filled porosity, in agreement with the classic open hole interpretation, but with finer resolution.
Bio
Dler Mirza is Subsurface Manager leading the Petrophysics Excellence team at Aker BP in Stavanger. He has an MS degree in reservoir engineering from the University of Stavanger. He joined Logtek AS in 2008 and Aker BP in 2019. He is the President for the Norwegian Formation Evaluation Society (NFES). His general interests are logging tool physics, petrophysical interpretation of reservoir properties, model building and wellbore data digitalization.