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V. N. Manyrin, R. Sh. Mufazalov (Russian Society of Oil and Gas Engineers, Moscow, Timurneftegaz Research and Production Company, Oktyabrskiy)

Problem number one for all oil producing regions is preserving the potential productivity of a bed during the drilling-in process. This problem is especially topical for mature fields, fields with low formation pressures, and fields containing highly viscous oil. Therefore, the most critical stage in well construction is good, clean penetration of the producing (oil-bearing) horizon, since the initial flow rate, the duration of effective well operation, and the oil recovery factor during field development are completely dependent on the cleanness and quality of the penetration.

Due to the special importance of the drilling-in phase during well construction or workover, these operations are performed by specialized teams in many foreign oil companies.

Causes of Problems
The current and widely used methods for drilling-in and completion are far from perfect from both the technical and technological viewpoints. In the majority of cases, they do not provide the best productivity index and oil recovery factor, especially in poorly productive reservoirs and fields in the late stages of production.

During initial drilling-in, the solid, fine phase of the drilling mud, cuttings, mud globules, and crystals of weighting agents and polymers penetrate the pores and cracks in the reservoir simultaneously with the filtrate. The penetration depth of the filtrate is several times greater than the depth of the perforations, and this is the primary cause of degradation of oil inflow into a well. This is generally the result of a mismatch of the physicochemical properties and rheological parameters of the drilling mud, as well as imperfections in the hydraulics program and the drilling-in conditions.

In its natural state, a reservoir is under uniform compression by rock, hydrostatic, and geostatic pressures. The natural pressure conditions are disrupted during drilling-in, with deformations and the onset of shear stresses. These stresses sometimes exceed the rupture strength of the rock, especially where the rocks are anisotropic and have differing values of elasticity, rupture strength, and volumetric expansion. The anisotropy leads to asymmetrical deformation stresses, primarily in the borehole environment, and fractures and cavities in areas where stresses are concentrated. Deformation anisotropy of the porosity and permeability occurs. This is the next cause of reduced inflow.

The problem is aggravated by the fact that penetration of the solid particulate phase by drilling mud filtrate and deformational changes in the reservoir occur simultaneously as it is penetrated, causing irreversible processes such as pinch-off and plugging. Carbonate reservoirs are the most sensitive to deformational changes due to their fissuring.



Analysis of Experience in Use of Technology
In recent years, searches for new methods for intensifying the drilling process and improving well flow rates have led to nontraditional methods for bottomhole zone treatment during the drilling and oil production process.

To solve this problem, specialists at Timurneftegaz Research and Production Company have developed reactive acoustic equipment and technology for drilling and penetration of the producing horizon of a well, and have obtained patents for this invention (1). The patented design comprises a drill bit with a reactive acoustic module. The use of this equipment and technology reveals fundamentally new approaches to solving this problem, and experience in drilling in various fields and regions has produced the following positive results:

• the rock boring efficiency is increased, and the drilling rate is increased by 40% to 90%;
• the service life of the drill bit in the well is prolonged and the headway per bit is increased by 50% to 80%;
• the diametral wear of the bit, especially the calibrating elements, is reduced significantly;
• the drilling mud is subjected to undulation during drilling. is homogenized, and its rheological properties are improved as a result;
• a thin protective screen is created around the borehole wall that prevents penetration of drilling mud and grout into the producing and water-bearing beds and thereby prevents their contamination (cleanness of the reservoir is ensured);
• minor (up to 15 m3/hour) lost circulation in the drilling process is prevented, and the probability of gas, water, and oil kicks and formation fluid crossflow during drilling is reduced significantly;
• the formation of blockages above the bit, cave-ins, and sticking of the bit when drilling in unstable rocks is prevented, and the quality of the wellbore is improved;
• the friction on the drill string in horizontal and directional sections of the wellbore is reduced significantly and the required load on the bit is ensured;
• the reactive acoustic tension when drilling a horizontal section of a wellbore is comparable to the required axial load on the bit, and ensures that it is loaded smoothly;
• the time required to complete wells into producing beds penetrated using this technology is 1.5 times less than the standardized time, while the flow rate is 1.5-2 times greater than the flow rate from a bed penetrated using the conventional technology.

Influence of Hydroacoustic Field on Filtration Processes
In view of the special importance of the drilling-in process, the influence of the hydroacoustic field on the filtration of the flushing fluid through cores with various permeabilities was studied. (2). The results of the studies of mud filtration through core samples under static and dynamic conditions and in a hydroacoustic field differ. The essence of the differences is the change in the filtration rate over time, since the changes in the velocity and volume of the flushing fluid filtrate are the primary indicators of the formation of a protective screen, i.e., of the degree of colmatation of the borehole wall. Fig. 1 provides curves of the filtration (colmatation) rate during time under static (1) and dynamic (2) conditions and under a hydroacoustic effect (3).

The studies of the filtration processes showed that under a hydroacoustic effect the formation of a protective screen is accelerated by a factor of 10 or more, as a result of which the filtration rate drops to near zero after 15-20 seconds, and the degree of colmatation reaches 92-96%, while the volume of filtrate penetrating the bed decreases by several orders of magnitude.

This degree of colmatation is achieved in 50-60 minutes under static and dynamic conditions. A mud cake is present under static and dynamic conditions, while under hydroacoustic effects there is no mud cake, and the thickness of the protective colmatation screen is 10-18 mm in the pores of the core samples studied.

Furthermore, the decolmatation (cleaning of the pores under the influence of hydroacoustic waves) was also studied [2]. Under hydroacoustic effects on the cores, the colmatation layer is cleared tens of times faster, until the permeability of the rock is completely restored.



Hydroacoustic apparatus and technology for well completion and stimulation of the inflow from a producing horizon were developed on the basis of the studies (see pic 3 of hydroacoustic device for well completion).

In particular, hydroacoustic generators for drilling with various active elements (vortex, toroidal, disk, diaphragm and parametric generators) operating with output parameter amplification were developed. The amplitude-frequency responses of hydroacoustic generators under various operating conditions were studied to create hydroacoustic devices with the required parameters and to select the optimum design. This work was performed at the Russian Academy of Sciences Machinery Science Institute (IMASh) [3] and the regional enterprise OTO Production Ltd., with the involvement of specialists of the Machine Acoustic Institute of Samara State Aerospace University [4]. It was found during this work that the output parameters of these devices are dependent on many factors: the type and geometrical dimensions of the active elements, the density, viscosity, quantity and flow rate of the active agent in the pores, and the counterpressure in the system. However, the most important fact is that the waves generated are nonlinear hydroacoustic waves with simultaneous generation of frequencies from 0.15 to 16 kHz. Figs. 4 and 5 show the amplitude-frequency responses of hydroacoustic devices for well drilling and completion under various operating conditions.





Application of Technology
This technology can be used in the rotary drilling process using various downhole motors, including electric drills for directional and horizontal drilling with drill bit diameters of 124 mm and larger. The photographs show reactive acoustic modules for drilling directional and horizontal wells using drill bit diameters of 124.0 and 215.9 mm and a diagram of the operation of a reactive acoustic module in a horizontal borehole.

According to the results of test well drilling in the Zyuzeyevskoye field by Tatnefteprom (Almetievsk) performed to determine the effectiveness of various technologies for penetrating producing formations containing highly viscous oil, the best results in terms of the specific productivity of a formation were achieved using hydroacoustic technology.

In addition, test wells were drilled to assess the effectiveness of various well completion technologies under the conditions of the Tatneft oil fields.

Thirteen preferred technologies were used, including hydroacoustic penetration technology. The results of the test well drilling were processed and analyzed by the TatNIPIneft Institute. According to the criterion used, the best results in terms of formation penetration effectiveness were obtained using the hydroacoustic technology: the specific productivity was increased by a factor of 3.8.

In the opinion of specialists from Saudi Aramco, where 100% of the wells are horizontal wells, as well as per the horizontal drilling engineering support provided by Sperry-San, where the trial operations were conducted, the hydroacoustic technology simplifies drill string guidance and trajectory correction, improves accuracy, and accelerates drilling.






Primary Parameters of Reactive Acoustic Device:

• diameters of drill bits used: 124 mm and larger;
• flushing fluid density: 900-2200 kg/m3;
• permeability of rocks drilled: 0.001-2.0 u2;
• with lost circulation of up to 30 m3/hour and pore size of 10-8 m;
• in any type of reservoir and unspecified formation temperature and hydrogen sulfide content;
• hydroacoustic wave frequency: 0.15-16 kHz;
• pressure: 1.5-6.0 MPa;
• drilling mud consumption: 0.020-0.035 m3/sec;
• pressure differential in device: 3.0-6.0 MPa;

Overall dimensions:
diameter: 120-295 mm;
height: 350-800 mm;
weight: 20-150 kg

Conclusion
The results of the comparative analysis show that the reactive acoustic equipment and technology is unique and has no analogs in world practice in terms of its ease of use, reliability, effectiveness, and multifunctionality. The hydroacoustic technology is now the basis for developing a whole series of devices using its technological principles in the oil producing, petrochemical, and other industries. They are all superior to traditional technologies. The developers are protected by patents in the Russian Federation, the leading nations of Europe, the USA, Canada and Japan.

It should be noted that the hydroacoustic technology used in various processes is exceptionally environmentally friendly and physiologically safe, which is very important for its widespread use in the fuel and energy sector.

References
1. RF Patents for Invention No. 2270315 and 2351731.
2. R. Sh. Mufazalov, R. Kh. Muslimov, L. R. Klimov et al. Hydroacoustic Equipment and Technology for Drilling and Penetration of a Producing Formation. Kazan: Dom Pechati Press, 2005, 184 pp., illustrated.
3. Wave Technology and Equipment. Edited by Russian Academy of Sciences Academician R. F. Ganiev. Moscow, Logos Press, 1993, 127 pp., illustrated.
4. Technical Report of Machine Acoustic Institute of Samara State Aerospace University under Contract No. 019 dated March 12, 2001 "Measurement of Amplitude-Frequency Responses of Downhole Generators".

Labels: Acoustic technology, Reactive, Reservoir Penetration, ROGTEC, Russian oil gas news

posted by The Rogtec Team @ 17:33 

2 Comments:

 Eugene said...

Enchanting technoloy. I would like to learn more of its applications. Very interested in propagating the tech here.
Could I ask R. Sh. Mufazalov or Lili for further direction?

19 September 2009 20:19  

 The Rogtec Team said...

Hi Eugene,

Many thanks for your interest. Please contact me on doug.robson@rogtecmagazine.com and we can put you in touch with the author.

21 September 2009 12:09  

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