Development and service of drilling fluid

The exploration well, where we are starting our activity together with the Ukrainian-Belarusian company Service Oil, was drilled in 2014 in a frontier part of the field. According to the test results, it turned out to be far from being successful. Its productivity was low, and various methods of intensification proved themselves to be ineffective.
Today, geologists assume the presence of productive horizons at great depths. In order to test this hypothesis, it was decided to deepen the well by drilling a sidetrack.
The complexity, and even uniqueness, of this operation is determined by the depth of a sidetrack (5600 m) from the casing string Ø139.7 mm. The design depth is 6300 m. Drilling starts at the drilling mud density of 1370 kg/m3 with a gradual increase in weight up to 1520 kg/m3. The temperature at the design depth is 155 °C. 
We proposed biopolymer clayless drilling mud Biocar-TF to ensure the technical feasibility of implementing the designed hydraulic flushing program, to maintain the stability of rocks and high-quality formation exposure.
A distinctive feature of Biocar-TF flushing system is its weighting by means of a combination of highly soluble salts. As a result, even at the maximum design density, the content of solids in such mud will be lower than in any alternative system. As a result, the hydraulic resistance that occurs during wellbore flushing will be minimal. We expect that such approach will ensure the possibility of practical implementation of the designed drilling technology.
Biodegradable components are the basis of Biocar-TF flushing system which makes it absolutely environmentally friendly. The entire solid phase is acid-soluble. Speaking of the degree of inhibition effect on clayey rocks, Biocar-TF is very close to hydrocarbon-based solutions. The thermal stability of the system is 170 °C.


Fig. 1. Shear stress of clay-free biopolymer drilling fluids with different concentration of salts at increasing temperature (600 rpm). The inflection point of the curve characterizes the temperature at which polymeric agents begin their thermal degradation.


Fig. 2. Stability index of argillite (rolling test) of the Bioсar-TF filtrate model with different  concentrations of salts.


Fig. 3. HPHT Filtration of  the drilling fluid Biocar-TF (ρ = 1600 kg/m3). Temperature is 150 °С, ceramic disc 20 micron.
Fl150 =  9,8 ml / 30 min.

In Ukraine, there is a huge number of deep abandoned wells finished with Ø139.7 mm casing. In such wells, sidetracking is extremely difficult due to high hydraulic resistance during flushing. If the current activities using Biocar-TF system become a success, it will open the way for a large-scale restoration and possible deepening of the old-fund wells. In case of successful implementation, drilling of sidetracks allows solving geological and technical problems at significantly lower financial costs than in case of drilling new wells.