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Improved Oil Recovery vs. Enhanced Oil Recovery

London Journal of Research in Computer Science and Technology
Volume | Issue | Compilation
Authored by Prof. Nikolay P. Zapivalov , NA
Classification: J.m
Keywords: NA
Language: English

Nowadays, the problem of enhanced oil recovery (EOR) and improved oil recovery (IOR) is a key problem in petroleum theory and practice. In world oil-and-gas practice, two different terms are in use: EOR (enhanced oil recovery) meaning intensive, forcible methods; and IOR (improved oil recovery) – advanced and moderate methods.

The enhanced oil recovery methods do not provide a scale effect. There are about 1500 active projects in the world using various EOR technologies, and their annual production build-up is estimated as 100-120 million tons. It is only about 2% of all produced oil in the world, which is equivalent to the total transporting and other losses.

In the USA, the “additional” oil recovery is kept at the level of 30-35 MT/Y and has not exceeded this threshold value since 1986. In 1986, there were 512 active projects and in 2008 there were 184, so there is an obvious tendency of a decrease. The situation in other regions of the world is much the same. In terms of the final oil recovery, at many oilfields the efficiency of EOR is very low or zero.

               

Improved Oil Recovery vs. Enhanced Oil Recovery

Prof. Nikolay P. Zapivalov

____________________________________________

ABSTRACT

In this chapter, the author presents a principally new scientific-technological paradigm of exploitation, preservation, and rehabilitation of petroleum resources.

An oil deposit in the Earth crust is considered as a self-organizing, living fluid-saturated system capable of restoring its balance. Active works during development of an oilfield produce a strong perturbation in the near-equilibrium system and substantially deform its natural parameters. In case of a moderate perturbation, the self-organizing system restores its balance; a prolonged or intensive perturbation considerably exceeding the critical threshold will destroy the system.  

Nowadays, the problem of enhanced oil recovery (EOR) and improved oil recovery (IOR) is a key problem in petroleum theory and practice. In world oil-and-gas practice, two different terms are in use: EOR (enhanced oil recovery) meaning intensive, forcible methods; and IOR (improved oil recovery) – advanced and moderate methods.

The enhanced oil recovery methods do not provide a scale effect. There are about 1500 active projects in the world using various EOR technologies, which only results in additional production of about 100-120 MT/Y. It is approximately 2% of the total of produced oil in the world – an equivalent of transporting and other losses.

In the USA, the “additional” oil recovery remains at the level of 30-35 MT/Y and has not exceeded this threshold value since 1986. In 1986, there were 512 active projects and in 2008 there were 184, so there is an obvious tendency of a decrease. The situation in other regions of the world is much the same. In terms of the final oil recovery, at many oilfields the efficiency of EOR is very low or zero.

However at present, development of oil-and-gas resources is usually aimed at immediate commercial return; therefore, all possible methods are used for accelerated intensification of oil and gas extraction, which in the longer term leads to the destruction of the oil deposit as a living system in the thermodynamic rock-fluid interconnection.

The only way out is to rehabilitate and revitalize such deposits as a whole or as separate productive zones. This will permit to restore the natural energy parameters of fluid saturated systems and also to provide a balanced proportion of hydrocarbons in fractures and porous matrix. Such individual fluid-dynamic cycles, based on self-organization of natural systems, can essentially increase the oil recovery.

Also, a review is presented of promising modern trends in technologies for sparing and moderate development of oilfields (Improved Oil Recovery instead of Enhanced Oil Recovery) aimed at longevity and high oil recovery.

Among the present-day innovative technologies for exploration and development of oilfields, such trends are worth noting as geofluid-dynamical, seismic-geophysical, geo-mechanical, and technological; besides, there are some ideas and projects not implemented so far. 

Keywords: oil production, dynamics of oilfield states, innovative methods and technologies, residual (hard-to-extract) oil, rehabilitation cycles. Hope for future cooperation.

Author: Institute of Petroleum Geology and Geophysics, SB RAS Russia, Novosibirsk, 630090, Koptyuga av., 3.

  1. INTRODUCTION 

Nowadays, the problem of enhanced oil recovery (EOR) and improved oil recovery (IOR) is a key problem in petroleum theory and practice. In world oil-and-gas practice, two different terms are in use: EOR (enhanced oil recovery) meaning intensive, forcible methods; and IOR (improved oil recovery) – advanced and moderate methods.

The enhanced oil recovery methods do not provide a scale effect. There are about 1500 active projects in the world using various EOR technologies, and their annual production build-up is estimated as 100-120 million tons. It is only about 2% of all produced oil in the world, which is equivalent to the total transporting and other losses.

In the USA, the “additional” oil recovery is kept at the level of 30-35 MT/Y and has not exceeded this threshold value since 1986. In 1986, there were 512 active projects and in 2008 there were 184, so there is an obvious tendency of a decrease. The situation in other regions of the world is much the same. In terms of the final oil recovery, at many oilfields the efficiency of EOR is very low or zero.

However at present, development of oil-and-gas resources is usually aimed at immediate commercial return; therefore, all possible methods are used for accelerated intensification of oil and gas extraction, which leads to the destruction of the oil deposit as a living system in the thermodynamic rock-fluid interconnection. In this paper, a principally new scientific- technological paradigm of exploitation, preservation, and rehabilitation of petroleum resources is described.

The author considers an oil deposit in the earth crust as a self-organizing, living fluid-saturated system capable of restoring its balance. Active works during development of an oilfield produce a strong perturbation in the near-equilibrium system, and substantially deform its natural parameters. In case of a moderate perturbation, the self-organizing system restores its balance; a prolonged or intensive perturbation considerably exceeding the critical threshold will destroy the system.  

The only way out is to rehabilitate and revitalize such deposits as a whole or as separate productive zones. This will permit to restore the natural energy parameters of fluid saturated systems and also to provide a balanced proportion of hydrocarbons in fractures and porous matrix. Such individual fluid-dynamic cycles, based on self-organization of natural systems, can essentially increase the oil recovery.

Also, a review is presented of promising modern trends in technologies for sparing and moderate development of oil fields (Improved Oil Recovery instead of Enhanced Oil Recovery) aimed at longevity and high oil recovery.

Among the present-day innovative technologies for exploration and development of oil fields, such trends can be distinguished as geofluid- dynamical, seismic-geophysical, geo-mechanical, and technological; besides, there are some ideas and projects not implemented so far.

  1. GEOFLUID-DYNAMICAL ASPECTS; CRITICAL THRESHOLD OF PERTURBATION

Any accumulation of hydrocarbons (fluid- saturated system) is an unsteady system. Depending on various fluctuations and bifurcations, it can be equilibrium or non-equilibrium. The natural accumulations of hydrocarbons can enlarge or grow smaller, or even fully collapse (disappear) in relatively short geological time periods. In fact, it is a self-organizing system.

It is necessary to distinguish two states of an oil deposit in the earth crust: natural state formed before human intervention, and natural- technogenic state during the process of active exploration and development. The active works during the development of an oilfield produce a strong perturbation in the near-equilibrium system and substantially deform its natural parameters. In case it is a moderate perturbation, the self-organizing system restores its balance.

It is especially important at the late stages of the oilfield life.

A prolonged or intensive perturbation considerably exceeding the threshold will destroy the system. As a result, the formation pressure drops, production rate falls off, the layer is watered out, and even its mineral composition changes.

The perturbation threshold can be estimated through the draw-down pressure. The author has established that the optimal draw-down pressure (formation pressure, FP – bottom-hole pressure, BHP) must not exceed 5÷8 MPa (FP – BHP ≤ 5÷8 MPa). This value is almost universal and applicable for all types of reservoirs and many oilfields. It is apparently illustrated in Fig. 1.

Fig. 1.

  1. Indicator diagram and dependence of productivity index (Ipr) from draw-down pressure in wells. Nizhnevartovsky oil fields, West Siberia.
  2. Indicator diagram for well 43 in Barsu-kovsky oilfield, Belarus.
  3. Description of fluid-dynamic parameters of carbonate reservoirs of porous-fractured type. Correlation between skin-factor and depression (draw-down) at the wells of Beshtentyak oil field, Kirgiz-stan.

The main features of any living system are its energy potential and working capacity. Any oil reservoir is an open fluid-dynamic system with variable exergy and versatile gradients of mass-and-energy transfer. Their threshold values are determined by the boundary parameters of the system at any given moment of time [1].

It is established that the actual reserves of oil and gas can be replenished in the process of oilfield development. It is possible in two cases.

  1. An active present-day process of hydrocarbon generation is proceeding in the layer. This case was proved in the Mexican bay, Eugene Island oilfield, and also in other regions. An additional feeding (inflow) with newly formed portions of hydrocarbons is possible from both inside and outside the system.
  2. An individually adjusted moderate development is carried out, with regular periodic rehabilitation works. In this case, a balanced exchange of fluids proceeds between the matrix (block) and filtration channels of the layer. Also, equilibrium is observed between the rock pressure and formation pressure [1, 3].

There are many examples throughout the world demonstrating a renewal of activity in the well after some period of rehabilitation (rest) of the whole oilfield or its separate blocks.

(N.P. Zapivalov, Novosibirsk, Russia)

  1. SEISMIC-GEOPHYSICAL METHOD. DYNAMIC-FLUID MODELS (DFM)

Parameters of a fluid-saturated medium of a discrete structure are, by their physical character, functions of elastic modules and of the current stressed state. Therefore, the most appropriate method for estimating the gradient pressure may be based on a complex analysis of the seismic parameters and other geologic and geophysical data [4].

The results of applying DFM-technologies at various world basins showed the possibility to define (prognosticate) the location of the maximum fluid-saturation zones (foci) with a sufficient reliability. The application of DFM-technologies is illustrated in Fig. 2.

Fig. 2: Map of differences of fluid-dynamic parameters [5]

DFM-technology can be effectively applied at all stages of oilfield exploration and development including the process of monitoring; it has already proved successful in various regions. The technology is aimed at mapping the productive zones (foci) with active fluid cross-flows.  

(V.B. Pisetsky, Yekaterinburg, Russia)

  1. GEO-MECHANICAL TECHNOLOGY 

4.1 Method of directional unloading of the reservoir (rock loosening) 

The idea of the rock-loosening method [6, 7] is to create stresses in the well vicinity so as to form multiple new micro- and macro-fractures, by way of non-uniform directional unloading of the reservoir. The unloading is performed through a pressure relief in the well and choosing a special bottom-hole design. This newly generated system of fractures functions as a new network of filtration channels, with a permeability considerably exceeding the initial one.

It should be noted that the rock-loosening method impacts the bottom-hole area in the range up to ten well radii. This accounts for the high effectiveness of the method in development of the producing wells and repair works at the injection wells.

In 1954-1955, S.A. Khristianovich developed a theory and methodology of hydraulic fracturing of oil reservoirs, which up to now remains one of the most effective methods of oil production intensification. In 1990, Khristianovich suggested a totally new approach to the problem of rock deformation, with a gradual decrease of the formation pressure.

Rock sample tests were carried out at the Institute of Problems in Mechanics RAS, at an ITCTS experimental station (Independent Triaxial Compression Testing System). The results demonstrated a remarkable phenomenon concerning the influence of the bottom-hole depression increase on the rock permeability of the well vicinity. Depression of 6 to 9 MPa proved to decrease the rock permeability. It is especially evidently shown in sandstones with high clay content. It presumably results from plastic deformation of clays due to the tangential stresses appearing in the reservoir: they tend to «close» the filtration channels. This corroborates the thesis of geofluid-dynamic critical perturbation threshold 5÷8 MPa suggested above [8].

This deterioration in the rock permeability of the well vicinity lowers the well productivity. Actually, the effect of a sharp decrease in the well flow-rate due to higher depressions has been frequently observed in practice; there even appeared a special term for it: collapsing of a reservoir.

The mechanism of the DUR method (directional unloading of the reservoir) is that of the hydraulic fracturing method, but inverted vice versa.

With the rock-loosening method, development of a well can be conducted simultaneously with rehabilitation of the reservoir permeability in the bottom-hole area. No additional equipment or additional up-and-down operations are required. Thus, both time and expenses needed for the well development essentially decrease while the quality of the works increases.

The rock-loosening method is applicable at any depth of formation. It can produce a considerable economic effect at oilfields where the costs of well drilling and development are high, say at the sea shelf.

It can be supposed to be a most sparing and effective method.

(S.A. Khristianovich, Yu.F. Kovalenko, V.I. Karev, Russia)

4.2 Gasgun®: technology of stimulating wells with solid propellants 

The necessity to optimise the impact on the bottom-hole area resulted in creating an effective technology with the use of solid propellants – Gasgun® technology. The technology is developed by the research team of The GasGun Inc. Co. headed by Dr. R.A. Schmidt [9].

Three various ways of stimulating the reservoir are compared at Fig.3a: explosion, hydraulic fracturing, and the Gasgun® method. The experimental and field tests have shown the Gasgun® method to be the most effective one. Fig.3b shows schematically a typical fracture pattern produced by the Gasgun® technology in the bottom-hole area of a reservoir. A principal feature of the Gasgun® technology is the use of solid propellants creating oscillating gaseous jets in the perforated well or even in the open hole.

Fig. 3 

  1. Schematic dependence between pressure and time for three various stimulation methods.
  2. Typical fracture pattern produced by the Gasgun® method in underground experiment.

With the use of solid propellants, large quantities of high-pressure gas can be produced. The burning characteristics of solid propellants can vary in a wide range; through appropriate adjusting of the burning intervals, multiple radiating fractures can be produced in the restricted treatment zone. Their structure will have a number of obvious advantages as compared with the results of the conventional hydraulic fracturing method.

For the last ten years, the Gasgun® method has been already used over 4,000 times in the USA, Canada, Europe, Africa, and Middle East, with the well depth 70 to 3,000 m. Promising results are shown for sandstone, limestone, dolomite, shale, coal, chalk, marlstone, and diatomite.

The developers claim that Gasgun® stimulation has the following advantages as compared with hydraulic fracturing:

  • Minimal vertical fracture growth out of the productive zone;
  • Multiple circumferential and radiating fractures;
  • Selected zones stimulated without the need to set packers off;
  • Minimal formation damage from incompatible fluids;
  • Homogeneous permeability for injection wells;
  • Minimal onsite equipment needed;
  • Much lower costs.

This technology undoubtably must be tested in West Siberia in the terrigenous Mesozoic as well as in the carbonaceous Paleozoic, and surely in other regions of the world as well.

(R.A. Schmidt, The GasGun Inc, the USA)

V.    NOVEL IDEAS AND PROJECTS NOT IMPLEMENTED SO FAR 

  1. Metasomatic dolomitisation: A possibility of applying nano-technologies to form highly- productive reservoirs (artificial metasomatosis).

Oil and gas occur in various natural reservoirs including dolomites, which contain 40% of all the world oil reserves. By changing the architectonic pattern of voids and cavities, dolomitisation can increase the pore volume in compact limestones. This increases not only porosity but also permeability.

It is known that the radius of a calcium ion (Ca2+) is 0.99 Å, or 99 nm, while the size of a magnesium ion (Mg2+) is 0.66 Å, or 66 nm. So, when Calcium is replaced with Magnesium, an additional empty space appears (fractures, caverns etc.). Hence, natural nano-dimensional metasomatic processes facilitate the formation of high-rate collectors, especially in the Phanerozoic carbonate rocks.

The Maloichskoe oilfield (West Siberia) discovered in 1974 is one of the best-studied oilfields. The main productive horizon is at the depth 2794-2850 m and consists of carbonaceous rocks, namely limestones and dolomites. This oilfield clearly shows the focal character of dolomitisation, which is eventually the key factor in forming the well productivity. A specific feature of such foci (western and south-western parts of the oilfield, wells 9, 6, 117, 2) is active secondary dolomitisation across the Middle Devonian reef. The areas with high-rate wells apparently prove to coincide with the western facial-tectonic zone (Fig. 5).

Fig. 5: 3D-seismic survey map of the Maloichskoe oilfield (West Siberia)

It should be noted that metasomatic foci have no definite stratigraphic referencing, and their morphology normally cannot be viewed in terms of folded forms analysis and the superposition law.  

It is possible to initiate an accelerated technogenic process of metasomatic dolomitisation so as to create (renew) highly-productive foci at an oilfield. In fact, it will allow managing the process of an oilfield development and increase the oil recovery factor.

For these purposes, we should first determine the composition of the carbonate materials and formation water. The technology of injection of magnesium-containing liquid, or nano-particles of granular magnesium, is unlikely to prove too difficult. As a result, the specific surface of pores and cavities will increases; the fluid cross-flow from the block matrix to the fractures will intensify, and even active formation of new hydrocarbon masses will start. Also, this will stimulate the percolation processes; the well productivity and the actual oil recovery factor will increase. In certain cases, the process of induced and accelerated dolomitisation (metasomatosis) may be supported with certain wave or thermal stimulation.

In case it is successfully applied, this technology can considerably improve the duration of oilfield development and the total oil recovery factor.

(N.P. Zapivalov, Novosibirsk, Russia)

2. Laser-based technologies

These days, the attention is focused on novel breakthrough technologies for studying subsurface resources, geological prospecting, and oil-and-gas production. In a longer prospect, laser-based technologies are supposed to allow almost 100% oil extraction at any oilfield, without environmental pollution [10].

A. Lenetsky, Director of the Research and Production Company «Bereg», claims that the method suggested by the Company is a conceptually new one and has no world analogues. They suggest using laser instead of conventional rock drilling tool. A laser tool does not destroy the rock but rather fuses it; besides, it can pass at an angle, and therefore penetrate into hard-to-reach places. The technology will make it possible to restore old oilfields from which oil cannot be extracted any more through conventional methods.

In 2012 an American start-up company, Foro Energy, also announced that they have developed a technology of laser application in oil production. Their method involves rapidly cracking the surface of hard rocks with a high-energy laser. Foro Energy representatives assert that during the test run they managed to send a laser beam of 20 kW through a fibre-optical channel for a distance of 1.5 km. With the Foro technology, the intensive laser strike destructs the hard rock in such a way that no further difficulties arise afterwards when a mechanical drilling tool is used. This method can 10 times improve drilling effectiveness. Industrial tests of the technology will take place as soon as in 2014.

Saudi Aramco Company reports [11] that their Advanced Research Center has developed a new perforation method using laser technology. This method is supposed to make Saudi Aramco the first to introduce in-situ laser perforation to the petroleum industry.

A direct application of laser perforation will facilitate hydraulic fracturing in open-hole horizontal wells (oriented fracturing), which can greatly enhance the wells’ productivity. This technology may show significant advantages as compared with conventional perforation technologies, because it does not involve compaction in the rock.

Specialists of Saudi Aramco are sure that the in-situ tests of laser perforation in the well will make a ground for further research in petroleum engineering, including laser drilling.

(Foro Energy, USA; Saudi Aramco, Saudi Arabia)

  1. CONCLUSIONS 

  1. A principally new scientific-technological paradigm is suggested for developing, saving, and replenishing oil-and-gas resources, with the account of the critical stability threshold of the system in order to provide for the fluid-dynamic balance. This approach will make it possible to save for long the active oil resources; they can be replenished at the expense of newly formed hydrocarbon masses and soft sparing methods of improving oil recovery without destroying the composition, structure, and properties of the fluid-dynamic productive strata.
  2. For successful prognosis, effective prospecting and long-term development of oil fields, it is necessary to take account of the latest geo-dynamics of the Earth crust including its behavior in the gradient terms. For these purposes, satellite survey and mapping should be used in various modifications as well as other monitoring technologies.
  3. Optimisation of the sparing methods and techniques should be adjusted depending on the individual features of the object.  

REFERENCES

  1. N.P. Zapivalov, I.P. Popov Попов. Fluid-dynamic models of oil-and-gas deposits. – Novosibirsk: Geo, 2003. – 198 p. (in Russian)
  2. A.N. Reznikov. Geosynergetics of oil and gas. – Rostov-on-Don: Publishing house «ЦВВР» («Centres of valeology of Russian higher educational establishments»), 2008. (in Russian)
  3. N.P. Zapivalov, V.I. Lobov. Geofluid-dynamic methods in managing the stressed-deformed state of oil-saturated reservoirs and well productivity. – Geodynamics and Stress State of the Earth's Bowels: Proceedings of International Conference, Institute of Mining Engineering, Novosibirsk, Oct. 6-9, 2003. – Pp. 447-454. (in Russian)
  4. V.B. Pisetski. Prognosis of fluid-dynamic parameters of a basin based on seismic data. – Yekaterinburg: Ural State Mining University, 2011. (in Russian)
  5. Zapivalov N. P., Pisetski V. B. New geo-fluid dynamics method for mapping active fluids in oil-and-gas saturated strata // DEW: Drilling and Exploration World. – India. – August 2012. – Vol. 21, No 10. – P. 55-60.
  6. S.A. Khristianovich, Yu.F. Kovalenko, Yu.V. Kulinich, V.I. Karev. Improvement of productivity of oil wells using the geo-loosening method // Oil & Gas EURASIA. – 2000. – № 2. – P. 90-94.
  7. V.I. Karev, Y.F. Kovalenko. Stress condition control as a method for a perfect well drilling // Oil & Gas EURASIA. – November 2012. – №11. – P. 16-19. (in Russian).
  8. N.P. Zapivalov. Dynamics of oilfield life // Bulletin of Tomsk Polytechnic University. – Tomsk: 2012. – V. 321. – No. 1. – P. 206–211. (in Russian).
  9. Schmidt R. A. Fracturing with solid propellants offers advantages over traditional stimulation // DEW: Drilling and Exploration World. – India. – October 2009. – P. 47-51.
  10. «Kapital» of December 11, 2013. http://kapital.kz/economic/24434/v-rossii-nauchilis-dobyvat-neft-s-pomocshyu-lazera.html (in Russian)
  11. http://theenergyinfo.com/ServiceDetails.aspx?ID=60 (Information Agency theen ergyinfo.com)



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