Planned well kill operations
It is necessary to conduct some works on downhole equipment or reservoir during well commissioning. Measures can be either planned, as geological works, pumping equipment audit or another geological operations, or contingent, as pump replacement, tubing string (TBG) leakage etc.
Performing such kinds of works it is necessary to suppress the formation pressure to avoid oil, gas and water shows or so-called oil and gas outflow from the well.
Reverse pressure is provided by conducting advanced operations prior to setting up a workover team — planned well kill operations.
The well kill is the operation of placing a column of heavy fluid or composition of fluids of a certain density into a well bore in order to provide a wellbore pressure at the level, equal or above the reservoir pressure.
Kill fluid type depends on composition density calculations, providing enough reverse pressure, and chemicals, in accordance with laboratory test on reservoir minerals, reservoir fluids (formation water, oil, associated gas) compossibility.
Despite optimal kill fluid, a well kill method should also be taken (number of cycles, direction (method) of injection, injection speed, method of solution pushing to the bottom).
Depending on the type of pumping equipment, it’s setting depth, pressure and reservoir properties, the well kill is performed by replacing the borehole fluid with the kill fluid in one, two or more cycles to exclude KF heterogeneity in the borehole or its mixing with the borehole fluid.
A direct well kill method involves simply pumping the kill fluid directly down the well bore. Such a method has a number of advantages, such as a shorter operating time, a lower operating pressure, no reverse circulation of kill fluid and borehole fluids.
Reverse circulation involves kill fluid pumping into the annular space between production string and tubing string. The method is justified if it is not possible to knock down the pump circulation valve or if there are paraffin deposits blocking the tubing string.
The mud injection speed is determined by reservoir pressure. If high, injection is carried out at maximum speed, and if abnormally low, the injection should be carried out slowly, in order to avoid a kill fluid entry into the formation.
Well kill can be carried out both in standard and in complicated conditions (solution absorption, gas, oil and water inflow, high reservoir pressure well kill, multi-formation wells and wells with super-reservoirs).
Kill fluids with a specially calculated density are used for complicated well kill, with various modifiers designed to exclude the influence of this or that factor. To reduce the complications risks, jamming compositions are used to protect the oil reservoir from the possible negative effects of the kill solution. Jamming composition depends on the geological and technical workover conditions.
More than two thousand well kill operations in Russia are conducted by the Technotec Int. subsidiaries annually. One third of these are operations on complicated wells. The high demand for the Company’s services in the field of planned well kill speaks for the quality of the work performed, the level of technical competence and Company’s team’s professionalism.
