A complex of high-tech geophysical studies was implemented in the well No. 59 of the Machukhskoe field (DTEK Oil&Gas), which made it possible to estimate the reservoir properties of the main productive carbonate reservoir of the Tournaisian deposits at a qualitatively new level. This made it possible to confirm the designed productivity of the well No. 59 and the prospects for the development of the field as a whole.

One of such studies was the first work in Europe using Focused Magnetic Resonance (FMR) technology designed by Weatherford, which was successfully carried out by the company's representative office in Ukraine in cooperation with DTEK Oil&Gas specialists.

The study methodology is as follows: the FMR device uses a strong magnetic field to influence the hydrogen core in a given volume around the tool. Strong permanent magnets create a gradient magnetic field in front of the antenna to polarize the hydrogen core in the formation. The sensitive antenna of the tool is used as both a transmitter and a receiver. As soon as the formation is polarized, a high power pulse is applied to the antenna to "throw the cores over". Upon completion of the trigger, the antenna is brought into sensitive listening mode to measure the resulting RF field as the hydrogen cores return to their natural state. The effect is measured by FMR, has a direct connection with the structure of the pore space and the reservoir properties of the formation, while focusing allows one to obtain more reliable data, including from thin and settled rock layers.

Main advantages of the FMR device:

• High pressure and temperature range - 138 MPa and 177°C.
• The FMR probe is a focused sideward device designed to run eccentrically relative to the borehole wall. The sideward design reduces wellbore signal, allowing the tool to operate in highly conductivity fluids. Resistivity, only 0.015 Ohm·m, delivers satisfactory results.
• Focused probe design means one can run the tool of the same design with the appropriate deflectors and eccentralization equipment into any hole diameter.
• The device uses a permanent magnet gradient magnetic field and multiband operating frequencies from 900 kHz to 380 kHz to receive 16 different depths of study. Exploration depth ranges from 1.68 to 4.27 inches. Lower frequencies provide greater depth of study.
• The tool has powerful and flexible PDS activation options. The downhole tool can withstand multiple data logging sequences to record different types of magnetic resonance data. The data record can be modified while the tool is in the wellbore to perform multiple PDS records in one run. Flexible activations make it possible to optimize product quality for specific applications.

The sideward multifrequency focused nuclear magnetic logging (FMR) tool is manufactured using modern equipment and magnetic materials. The FMR has two unique and innovative features that provide improved performance compared to other devices:
(1) static magnetic field (Bo) focused into the formation with a 90 degree angle, which means a 25% constriction compared to standard tools;
(2) long echo sequences (also called porosity echoes) with a short TE of 0.4 ms.

The MRL technology is widely used in petrophysical appraisal of oil and gas fields since the 1990s. The MRL studies followed by post-processing variables such as T1, T2, D spectra and T1T2 and DT2 maps provided a new reliable way to appraise both rocks and fluids based on the MRL properties and their correlation with petrophysical variables. The fact that MRL can distinguish between porosity of clay bound water (CBW), bound volume index (BVI) and free fluide index (FFI, water or hydrocarbons) is unique to the MRL method, which is able to identify fluids using established physical principles, regulating relaxation mechanisms, which are characterized by the longitudinal and transversal relaxation times T1 and T2, respectively.

Key indicators and parameters determined by the FMR method:

• Precise porosity irrespective of lithology
• Pore size distribution (for pores filled with water with a radius of less than 100 microns)
• Indicator of rock quality
• Determination of fluid and saturation at different depths of study, subject to the resonance conditions, namely F= γ · Bo (where: γ is proton gyromagnetic coefficient, Bo is magnetic flux force)
• Indicators of viscosity and permeability
• Water and hydrocarbon saturation

Evgeniy Solodkiy, Head of the Department for Geology and Field Development at DTEK Oil&Gas, noted: “Innovative study was carried out in the well No. 59 of the Machukhskoe field, which is, in fact, the only PDS method for today to estimate the structure of the pore space and determine the permeability and effective porosity of rocks, to perform a high-quality detailing of the reservoir rock properties through the section compared to other well logging methods and also to reveale zones with improved productivity parameters throughout the open section and their ranking. This became the basis for detailing the geological and hydrodynamic models of the Machukhskoe gas condensate field. We updated the permanent geological and technological model of the field, localized zones and formations that were not covered or partially covered by development and optimized the further field development program.
The use of other specialized logging methods in this well, together with point measurement of reservoir pressures throughout the entire productive horizon, made it possible to adjust the well development technology with the application of optimal drawdowns in the conditions of fractured-cavernous carbonate reservoirs and, as a result, to obtain a high commercial well flow rate - over 400 mcm per day."

The article was prepared jointly by the team of DTEK Oil&Gas and Weatherford Ukraine, consisting of:

Evgeniy Solodkiy - Head of the Exploration Department, DTEK Oil&Gas

Artem Kutsolap - Chief Geologist, Head of the Geology Division of the Geology and Development Department, Naftogazvydobuvannya JSC

Lutfi Ablyakimov - Head of Geophysics Department, Weatherford Ukraine

Sergey Megidey - Head of Business Development with Private Companies, Weatherford Ukraine