Research has shown that almost the main reason for fall production rate are the initial methods of opening casing, cement and productive formation, among which a leading position occupies gun perforation and cumulative perforation in the old wells.
INITIAL OPENING CASING, CEMENT AND PRODUCTIVE LAYER
REQUIREMENTS OF GEOLOGICAL MECHANICS
Geological Mechanics dictates quite specific requirements for the initial opening of casing, cement and productive formation.
WHICH TRADITIONAL METHOD TO MEET THESE REQUIREMENTS ?
COMPARISON OF TRADITIONAL METHODS
GUN / CUMULATIVE PERFORATION
Due gun or cumulative perforation occurs the impact, deformation of casing, destruction and formation of cracks in cement, that becomes longer and deeper especially after subsequent hydraulic fracturing, that promotes water flooding the producing formation.
Also gun or cumulative perforation creates a stable melted border, that promotes the formation of water plugs in near well-bore zone, that prevents entry of oil or gas to the well.
Very small opening area (0.5 ft.) and depth of penetration (0.5 ft.²).
WATER OR ABRASIVE JET-POINT PERFORATION
Abrasive jet-point perforation not deforms the casing, does not destroys the cement (keeps the integrity of the cement sheath), and does not forms the borders in the opening productive formation zone, but depth of penetration not exceeding 1 ft. (0.3 m).
More large penetration depth does not occur because reverse abrasive jet interferes with direct jet not allowing to penetrate deep into the productive formation and regardless of application time.
Abrasive jet-point perforation can wash out a large enough cavity in the productive formation.
If apply to abrasive jet a rectilinear constant movement, reverse jet will not interfere with the direct jet, and the depth of penetration will be much greater. But it will be hydro-slotting perforation technology.
MECHANICAL SLOT PERFORATION TECHNOLOGY (MSPT)
Hydro-mechanical (non-abrasive) slot perforation (HMSP) does not deforms the casing, does not destroys the cement (keeps the integrity of the cement sheath), and does not forms the borders in the opening productive formation zone.
Depth of penetration up to 2.5 ft. (0.7 m) and drainage opening area up to 9 ft.² per linear foot, or 2.5 м² per one linear meter.
The depth of the opening would be larger if with mechanical circular saws may be used abrasive.
With hydro-mechanical slot perforation technology can simultaneously cut two opposing slots. More number of simultaneously slots is not possible due to the complexity of the design combined jet-nozzles and disc cutting saws.
SLOT PERFORATION TECHNOLOGY (SPT)
Slot perforation technology (SPT) with abrasive component does not deforms the casing, does not destroys the cement (keeps the integrity of the cement sheath), and does not forms the borders in the opening productive formation zone.
Depth of penetration up to 5 ft. (1.5 m) maximum and drainage opening area up to 40 ft.² per linear foot, or 12 м² per one linear meter (with simultaneous formation of four slots).
HMSP and SPT are environmentally friendly and only the methods of the initial opening the casing, cement and productive formations with unloading stress conditions in the near wellbore zone.
Hydraulic fracturing is the most powerful method of opening a productive formation.
Hydraulic fracturing is possible only after prior opening of the casing (initial opening). It forms deep cracks and micro cracks, the direction of which defies prediction, integrates productive and unproductive formations, "pulls" the nearest water.
Very good results after HMSP and SPT, which sets the follow geometry for hydraulic fracturing (if there is no risk of flooding).
Comparative characteristics of the main initial opening methods clearly shows, that the most effective and meets the required of Geological Mechanics parameters are HMSP (hydro-mechanical slotting perforation) and HSP (hydro-slotting perforation).