Focused acoustic stimulation (FAS) of the bottomhole formation zone (BHZ) is an environmentally friendly technology for increasing injectivity of injection wells and stimulation of production wells.
Decrease in bottomhole permeability is mainly due to:
- penetration of drilling fluid filtrate, mechanical impurities of the injected fluid or killing fluid into the pore space of the formation; deposition of high-viscosity oil components and clay particles on the surface of pore and perforation channels;
- formation of fixed liquid films on the surface of pore channels, which include adsorption and partially diffusion sub-layers.
The FAS technology is based on acoustic impact on the bottomhole zone and reservoir by frequencies of sound and ultrasonic ranges and promotes cleaning of perforation channels and bottomhole zone of the reservoir from colmatizing material, disruption of surface liquid layers, increase of waterflooding coverage, increase of oil displacement intensity by displacing agent, change of fluid phase permeability, acceleration of gravitational separation of oil and water.
At acoustic influence in the reservoir saturated with fluid, oscillations are excited, which are accompanied by significant alternating loads and are accepted by the saturating fluid, which contributes to solving the problems of enhanced oil recovery and intensification of oil production due to the following main effects:
- increase in filtration volumes of mobile fluid at the existing pore radius and pressure gradient due to the “piston” effect, which leads to an increase in fluid withdrawal;
- Involvement in the filtration process of fluid immobile at the existing pore radius and pressure gradient due to overcoming viscoplastic forces holding the fluid, which leads to intensification of oil extraction;
- reduction of oil viscosity due to destruction of its rheological structure by depolarization of molecules and weakening of intermolecular bonds, as a result of which phase permeability of oil increases, while for water it remains unchanged, which contributes to reduction of watercutting of production;
- overcoming surface tension forces and, accordingly, reducing the wetting angle between water and oil leads to an increase in the coefficient of oil displacement by water;
- segregation (separation) of oil and water in highly watered reservoirs due to acceleration of gravitational separation of phases of different densities in the acoustic field promotes redistribution of oil saturation and more complete oil recovery;
- manifestation of seismoelectric effect contributes to the destruction of near-wall fixed fluid layers, which have electrostatic nature and are represented by oil, so their destruction and involvement in the filtration process increases reservoir permeability and oil recovery factor;
- increase or restoration of permeability of the reservoir and bottomhole formation zone is achieved by cleaning of pore and perforation channels from mechanical impurities and high-viscosity deposits, as well as by disruption of surface liquid layers, which leads to an increase in the effective cross-section of pore channels and involvement of stagnant formation zones in the filtration process.
Tasks to be solved
- increase in injectivity of injection wells;
- levelling of injectivity profile and inflow profile in injection and production wells with the inclusion of low-permeability and zakolmatised formations;
- Intensification of production well flow by cleaning the perforation zone from dirt, mechanical inclusions, high-viscosity deposits, etc.
Advantages of FAS
- Localised and focussed exposure to specific zones of the reservoir;
- Safety for the production column and cement stone;
- Environmental friendliness of the method; Unlimited multiplicity of application;
- Extraction of colmatant from the bottomhole cavity;
- The technological process makes it possible to carry out treatment through the entire thickness of the pay zone without interruption of well operation and tubing string lifting and running on injection, flowing and gas lifted wells, and on mechanised wells to combine it with underground or workover operations.
