Development and service of drilling fluid

Another well has been successfully drilled at Semyrenky field. Despite the fact that DTEK Oil&Gas annually puts in the service a number of new wells, this event is, actually, extraordinary.

It is not even due to the fact that the implementation of such high-yield project with the debit which is two times higher than the most daring expectations. The most important is that Well 79 of Semyrenky gas-condensate field made history as it has become the starting point for cardinal expansion of the borders for the utilization of HC-based drilling muds.

Hydrocarbon-based flushing fluid system Witer II has been successfully applied for drilling of the wells at DTEK Oil&Gas fields since 2017. During this period, the drilling of 11 wells was completed at the Semyrenky and Machukhy fields, where the utilization of HC-based drilling fluids was limited to the opening of the productive deposits of Lower Visean, Tournai and Famen. Most often, IEDM Witer II was used at the depths range of 5000 – 5100 m to 5600 – 5800 m and below.

At Well 79 of Semyrenky gas condensate field, for the first time in the practice of DTEK Oil&Gas, hydrocarbon-based drilling fluid IEDM Witer II was used to penetrate non-productive carboniferous sediments, in the interval of 3800 - 5120 m. This corresponds to the deposits of the Bashkir, Serpukhov and Upper Visean stages, where polymer inhibited water-based drilling fluid was earlier applied. The planned drilling time for this interval using water-based mud was 44 days.

The decision to change of the drilling mud type was made by DTEK Oil&Gas when the well had already been under drilling. It was assumed that the use of IEDM Witer II would increase the stability of rocks and accelerate drilling. At the same time, an increase in the cost of work was not expected, since DTEK Oil&Gas had its own volume of IEDM Witer II drilling fluid required to open the interval.

Filling the well with IEDM Witer II and drilling began on 02/05/2021, and already on 03/05/2021, that is, after 27 days, the design depth of lowering the casing- 5120 m was reached, and a week later, on 03/12/2021, the first section of casing was run and cemented.
Drilling mud parameters during the drilling of the entire interval were stable and fully compliant with the customized flushing program. As a result, mud treatment was not carried out while drilling and there was no additional consumption of chemicals. Significant financial savings have been achieved by changing the drilling fluid type.

Despite the fact that the density of the drilling mud was maintained in the range of 1.25 - 1.30 g/cm3, that is, less than the design density of the water-based mud equal to 1.40 ± 0.2 g/cm3, the wellbore was absolutely stable. Based on the results of geophysical studies, the well had a nominal diameter throughout the drilled interval. Now, there is no doubt that the use of IEDM Witer II ensures wall stability at a lower density than the one achieved by water-based drilling fluids.

This conclusion is extremely important for drilling and development of Ukrainian fields at great depths, which are at the final stage of operation and have abnormally low reservoir pressures. Today, when using water-based solutions, there is often a need for a significant increase in their density due to the loss of rock stability and wall collapsing. As a result, repression of productive strata increases catastrophically and can reach astronomical values of several hundred atmospheres. The use of high-quality oil-based drilling fluids, in particular IEDM Witer II, allows avoiding unnecessary weighting and creates conditions for high-quality drilling of productive formations with technologically acceptable repressions.

Thus, the successful application of IEDM Witer II in non-productive carboniferous deposits at Well 79 of Semyrenky gas condensate field creates a reliable foundation for further expansion of the boundaries for the application of oil-based drilling fluids and allows us to expect an even greater economic effect from their implementation when drilling Permian, Triassic and Jurassic deposits.

Picture – Borehole geometry tool diagram of the interval (3785 – 5125 м) of Well 79 Semyrenky that was drilled with utilization of OBM Witer II.

Upper part of diagram (3710-3785 m) – the interval that was drilled with utilization of water-based mud.



An information from DTEK Oil&Gas official web-site:

Half a million cubic meters of gas per day: DTEK Oil&Gas finished drilling of a new high-output well

DTEK Oil&Gas finished drilling of a 5450 m deep well No. 79 on Semyrenkivskyi area and received an inflow of over 460 thousand cub. m of gas and 120 t of condensate per day.

Innovational complex of geological exploratory works, including modern geological exploration and new technologies of geophysical data processing, helped to discover an undeveloped block of the field where the well was drilled. Exploration results helped to precise geological and hydrodynamic models of the field and to confirm perspectives of a further block development.

The well was drilled within 136 days, aligned with a planned period. Use of 3D geologic-mechanic modelling data and a correctly chosen drilling solution allowed to lower drilling risks and to raise quality of production layers’ revelation.

General Director of DTEK Oil&Gas Ihor Shchurov noticed: “Our company involves new technologies over the whole production chain consistently – from geological exploration and drilling to production and treatment of gas. This allows us to develop fields with complex geological conditions and drill high-output wells. So, thanks to modern technologies, since 2015 we have produced 1,5 bcm of gas additionally. This is a contribution of DTEK Oil&Gas to reaching of energy independence of Ukraine”.

We remind that in 2020 DTEK Oil&Gas produced 1,84 bcm of gas which became a new record of private gas production of Ukraine. In 2021, company plans to increase its production volume to 2 bcm of natural gas.