CLASSICAL HYDRO-SLOTTING PERFORATION TECHNOLOGY
Hydro-slotting perforation (HSP) it is a technology of opening casing, cement and productive formation in oil and gas wells by cutting of continuous deep longitudinal slots along the wellbore.
For the creation of slots is used a special HSP equipment, which cuts slots by rectilinear and constant movement of abrasive cutting jets along the wellbore without moving tubing.
Main idea of HSP technology:
opening a large casing’s area and creation of a large drainage penetration’s zone in the productive forma-tion (for good hydrodynamic connection well with the productive formation)
unloading annular compressive stress in the near wellbore zone (for increases of permeability and porosity, and accordingly increasing the productive inflow. Hydro-slotting perforation is the only method, supposed to unload annular compressive stress conditions around the wellbore
By classical HSP the whole process of cutting the casing, cement and formation carried out in a single indivisible cycle, and without cyclical addition of various chemical and mechanical additives. Classical HSP is absolutely environ-mentally friendly method (components used: sand and water).
Hydro-slotting perforation is the is the most effective technology of opening productive formation through the casing, and cement sheath with slicing long and deep longitudinal slots along the borehole.
Hydro-slotting perforation is an absolutely reasonably efficient technology for produce influx in the newly drilled wells, and for successful completion/recompletion of old low-producing oil and gas wells.
Hydro-slotting perforation is the only method, supposed to unload annular compressive stress conditions around the wellbore.
HSP technology refers to basic methods of initial opening casing, cement and productive formation (as some kinds of drilling, gun perforation, cumulative perforation, abrasive jet’s-point perforation, and some types of slotting perforations), and not refers to stimulation (optional) methods (as acoustic, acid, air, cavitation, chemical, electrical, frequency, gas, hydraulic, laser, magnetic, plasma, pneumatic, pulse, resonance, shock, steam, stress (overstress), temperature, thermal, ultrasonic, vacuum, vibration, wave etc.)
It is known, that one of the main causes of the declining production rate of oil and gas wells is the deterioration of rock permeability in the near wellbore zone (directly from the borehole walls). This occurs both during drilling and during operation(figure on the right). Study the role of this factor is still neglected.
Under the action of stress conditions (stress-strain states), and high overburden pressure occurs a significant reduction in permeability in the near wellbore zone, and in some cases close to zero. Oil or gas flow cannot penetrate into the well. Traditional methods of opening the productive formation did not consider this complicated situation in the near wellbore zone, and therefore not effective. Porous and fractured formations are subjected to compression, that deform rock mass, and reduce permeability. The depth has a significant influence on the stress-strain state of rock mass around wellbore. The more depth - more stress-strain states, the lower permeability, and as a result decrease of productive inflow efficiency.
The only possible solution in this situation, is to unloading the rock pressure from existing shear stresses conditions. In particular, the current decrease in near wellbore zone, the hoop stress. In practice, this can be achieved by cutting of extended deep slots along the borehole, in vertical section of wellbore. The first figure below shows that the borehole is surrounded by low permeable "cork" thickness which is approximately 50% of the radius of the well.
Cutting of vertical slots significantly changes the situation. The second and third figures below shows the intensity distribution of shear stresses in the near wellbore zone with two and four diametrically opposed vertical slots. The figure shows, that the slots almost twice reduce effect on the contour of the borehole shear stresses, and zone of reduced permeability is significantly decreases in sizes, and pushed into the interior of the reservoir.
At the bottom shows the unloading stress conditions charts for gun/cumulative perforation, and hydro-slotting perforation:
Charts and graphs of permeability and unloading stress conditions in the near wellbore zone before and after hydro-slotting perforation: