We propose to restore wellbore productivity by means of radial drilling.
The new technology of non-damaging perforation developed by our team is intended for increase of the flow rate of producers, enhancement of the injection capacity of injectors and elimination of cones of water-gas-oil contacts due to expansion of the filtration area. This method is defined as a mechanical way of pay zone stimulation.
The quantity of hard to recover reserves in Russia is currently growing and makes approximately 70%. More than 80% of wells are being operated using electric centrifugal pumps and sucker-rod pumps. Mechanical production methods are far from always being effective due to a low performance factor of pump units that are utilized in marginal wells. There is a threshold value of the well flow rate, below which well production is either technically impossible, or economically unviable. By now, well production has been suspended in many wells because of absence of the fluid inflow, or because of a high water-cut of the product produced. Unprofitability of well production in wells with hard to recover reserves results in their suspension and abandonment; the number of such wells is approximately 25-30 thousand.
The main problem with old, marginal wells is the absence of proper and reliable connectivity in the “well-formation” system, which is caused by external impact on the bottom-hole area during well construction and operation: clogging of the reservoir by filtrate of drilling mud, slurry or killing fluid.
Damage zone of the bottom-hole area can vary from 4 to 8 meters.
Let us make a review of current widely used methods of well stimulation:
Perforation (cumulative, slotted, drilling) can make channels with the length of up to 2 meters but does not always go through wall packing areas. The actual recovery of a formation, which was drilled-in this way, is much less than the target estimated on the basis of simulation results and this is a typical situation.
Chemical methods of enhanced oil recovery (injection of acid) seems, at first sight, highly effective, but only in formations that are homogenous in terms of permeability. If there is even one layer with higher permeability, the chemical compound starts moving along it as the lowest resistance path, which significantly reduces the general contact area between the acid and the formation.
Jet radial drilling is a modern technology, developed and implemented by non-Russian companies. Due to physical effects of erosion and cavitation, the method enables to construct long radial channels. Though this technique makes it possible to go through the bottom-hole area, it has some crucial limitations: the channel cross-section is of irregular shape and re-entry into the channel is impossible; the channel trajectory cannot be measured and controlled – the movement is along the lowest resistance path, which creates a high risk of penetration into the formation water zone; the method works only in carbonate reservoirs and is not effective in terrigenous reservoirs, which was proved by field testing; this technique requires perfect quality of cementing in the kick-off point.
Drilling with Fishbones titanium needles is innovation (currently under R&D) of Norwegian experts. Prior to running in hole, it is necessary to remove a multi-meter section of casing, which takes a lot of time and money. Works only in carbonate reservoirs. Requires a perfect alignment in the well, otherwise a titanium needle will twine around the well. Re-entry into the drilled channel is impossible.
Frac is characterized by high costs and serious limitations in application (cannot be used in thin layers and in case of close occurrence of water-bearing horizons), requires high quality of cement bond and complete absence of behind-casing leaks. Crack propagation trajectory is estimated approximately, and it is not possible to make a precise forecast of the actual crack trajectory due to heterogeneity of lithological composition of a formation and other factors. That is why, even though this method is very effective, later a high growth of the well water-cut is observed and remedial cementing is necessary. Given the above, the frac technology is not applicable for most marginal wells, and operators have to look for other ways of their recovery.
Side-tracking is nowadays a widely used method of recovery of old wells. Applied only in thick sections of the pay zone (from 15-20 meters). Side-tracking is possible in intervals of close occurrence of water-bearing strata but this results in a significant increase of the cost, since very expensive completion technologies (cementing of individual liner’s sections, utilization of swellable and hydraulic packers) will be required. The long horizontal hole does not guarantee a high growth of the production rate, since only first 200-300 meters of the channel will be in action. Side-tracking, including rig-up and preparatory operations, takes several weeks and is very expensive (40-50 mln RUR).
The PERFOBUR system, created by our team, integrates advantages of modern effective techniques and does not have most drawbacks of competing methods.
The system has the following characteristics:
- Increase of the oil recovery factor by several times;
- Significant extension of the drainage radius of producers, helping to optimize the field
- development mode without well pattern in-filling;
- Can be applied in carbonate and terrigenous reservoirs;
- Ability to go through low-permeability bottom-hole areas;
- Effectiveness in thin layers (from 5 meters);
- Can be applied in formations with close occurrence of water-bearing horizons;
- Controlled trajectory;
- Up to 4 radial channels of various trajectories can be drilled on one spot;
- Ability of re-entry into the drilled channel;
- Possibility of combined well interventions: additional acid treatment and directional frac from a radial channel;
- Duration of the entire work package does not exceed 3 days;
- Usage of available customer’s infrastructure (workover rigs, equipment);
- Consists only of equipment pieces manufactured in Russia;
- Competitive price.
The main purpose of the Perfobur system is deep perforation of a pay zone during completion of the well construction or during workover.
Perfobur is an innovative solution that has no equals anywhere in the world. That is why we will do our best to describe herein details of the design and ways of application as simply and carefully as possible.