Development and application of solutions for temporary oil and gas wells-killing
G.R. Gieahpour, Ph.D. (Engineering),
V.M. Svitlytskyi, Full Prof., Full Dr.Sc. (Engineering),
O.O. Ivankiv, Ph.D. (Engineering),
V.B. Khomyn, M.S. (Engineering)
"Actual Oil & Gas Technologies", LL.C
Well killing process is often accompanied by the absorption of liquids, which significantly reduce the productivity of wells. In commercial practice, a large number of chemical reagents are used to treat killing fluids in order to reduce the fluids loss.
The damping ability of the killing fluids is characterized by the permeability recovery coefficient after the models interact with the core material. According to the results of studies, the changes in permeability recovery coefficient with the various surfactants which were added to the jamming composition are shown in Fig.1 as in the following.
Additives: 0.5%-1% nonionic surfactant; 0.5%-2 amphoteric surfactant; 3 - 0.75% anionic surfactants; 4 - 0.5% cationic surfactant; 5 - 0.75% cationic surfactant
According to the results, , when some additives such as 0.5% nonionic surfactants and 0.75 anionic surfactants on 20% activator solution were used, the recovery rate of permeability for sandstone and carbonate formations would be 76-90% and 67-94% respectively.
The microparticles form when the mentioned surfactant is added into the solution. As a result, their sedimentation rate increases, which avoids penetration into the pore space that leads to increasing of the permeability recovery coefficient.
For a carbonate core sample on the killing liquids, the dependence of the blocking solution absorption on the pumping pressure and the addition of 0.5 nonionic surfactants and 0.75 of anionic surfactants is also established (Fig. 2).
In accordance with graph analyses, the intensive absorption of solution occurs at the time when the fracture is filled with the killing gel, it decreases as the dehydrated gel mass forms, and also stops after the compression. When the solution pumping pressure becomes more than the pressure of the hydro-pressing, the growth of cracks rises and the process is repeated again. At lower pressure, the addition of anionic surfactants caused severe damages to the fractures like breaking them down. However, on the other hand, the breakthrough pressure increases. The termination of absorption begins at a pressure drop of up to 0.2 MPa, a second breakthrough occurs at the P = 10.2-10.5 MPa.
Additives: 1 - no additives; 0.5%-2 nonionic surfactants; 0.75%-3 anionic surfactants
Thus, it can be concluded the compositions that form gels to preserve the natural permeability of the layers can be used for well-killing.
The basis of the developed killing technology and development of the wells would be resulted experimental research and analysis of the literature data.
Several methods with various scheme of binding equipment and sequence of pumping were tested during the pilot tests. Since the formation of blocking composition is formed in the wellbore, cementing units are used to pump the reagents, which are attached to the well target assembly. Depending on the specific state of the well, the pumping of the initial components is performed jointly Pumping procedure during the operation of well-killing:
- The amount of used killing fluid must be equal to the tubing size
- Injection of 01.-0.15 m3 buffer liquid;
- Injection of 1-1.2m3 saline solution (brine);
- Injection of the buffer liquid again;
- Injection of 3-3.5m3 activator solution;
- Injection of the buffer separation liquid;
- Alternate injection of brine and activator solution
The solutions will be mixed and reacted at the bottom hole due to this pumping procedure.
If there is no packer in the well, the solution is pumped through the tee. Simultaneously, the reaction of the components occurs immediately and the blocking composition by the quenching liquid is forced into the bottom hole.
The well is sealed for 3-4 hours until the components of solution react completely.
The quality of blocking is established by the subsequent addition of technical fluid.
The practice of using the developed blocking composition indicated its advantages over other methods:
The results of pilots of well-killing fluids with compositions forming a gel
- There is no need for preliminary preparation of the killing liquid at the solution unit (mixing, grinding of the components);
- Full blocking of the bottom hole zone is achieved;
- Pre-workover debit is saved.
Pilot tests of blocking the bottom hole zone technology which was related to absorbing layers were carried out at the fields of "Ukrhazdobycha" the State Enterprise.
The feasibility of using the temporary blocking technology in the bottom hole well zone with various lower formation pressures have been investigated too (Oposhnyanske, Kotelevske, Timofeevskoye gas condensate field). In addition, this study is a novelty in petroleum engineering.
In the Timofeevskoye gas condensate field during the blocking composition pilot test, the formation pressures decreased to 66.9%. The purpose of carrying out workover services at the well 54 Timofeevka was the tubing replacement. Previously, the well was killed with a surfactant solution, which was accompanied by absorption (up to 100 m3), therefore it was decided to block the absorbing interval. The killing was carried out by consecutive pumping of the 10.6 m3 developed composition. After 12 hours, the well was discharged and it was determined that blockage of absorptions had been achieved, ensuring the full volume of work
The well 78 of the Kotelevsky gas condensate field was also killed by a separate batch feeding of the components of the blocking liquid. The pumping volume was 3.5 m3. Endurance (stability) on the face was 24 hours.
The absorption was eliminated. The workover services of the well carried out for 4 months, confirmed the absence of absorption of the killing liquid.
The technology of blocking with gel solutions has also been tested in case of the killing of well 75 of the Yablunovskoye gas condensate field for overhaul.
The gel composition was prepared in a container with a volume of 25 m3 with parameters: viscosity- 53 s, = 990 kg / m3.
The volume of 20 m3 of technical water was pumped into the well to obtain circulation. After that, 7 m3 of blocking composition was pumped through the piping (or tubing) and it was pushed to the perforation interval. The displacement pressure did not rise above 10 MPa. For borehole Killing (plugging), the well is maintained with a closed annular space for 12 hours. After the well discharge, it was established that absorption blocking was achieved, allowing for the workover services.
Process of wells piping arrangement with special equipment during work over and insulation is shown in Fig.3.
Figure 3. Scheme binding wells for killing:
1-steam generator; 2 - tanker; 3 - pump unit; 4 - wellhead equipment; 5 - lift
According to the results of pilot tests, it can be concluded that the developed method of blocking the production layer is reliable, simple, and ensures the preservation of the filtration properties of the layer regardless of the formation pressure. The created barrier sustained reprisals up to 20 MPa. After the workover , the wells were developed by various methods. In the process of inducing the inflow from the formation due to the attendance of surfactant in the killing liquid, effective cleaning of the bottom hole zone from the layer' plugging (killing) substances is ensured. The results of wells development in some locations of the State Enterprise "Ukrhazdobycha" after killing are presented in table1.
Thus, field studies have confirmed the effectiveness of the developed well killing technology with the use of solutions with high blocking ability, wide limits of control properties, abundant initial components, simplicity of preparation technology, and environmental friendliness.