Lecture 5 Thermal Thermic EOR methods Thermal

Lecture 5 Thermal, Thermic EOR methods

Thermal methods are divided into: Thermophysical Injection of hot water Injection of steam Injection of hot water with chemical reagents Cyclic steam well treatment 2. Thermochemical In-situ combustion 1.

Thermal EOR methods are applied for the deposits: Containing high-viscosity oil; When the reservoir temperature is close the temperature of oil saturation by paraffins; For bituminous deposits of clays.

Physical processes, happening during oil displacement by heat-transfer agents. The peculiarity of the application of thermal methods is that along with hydrodynamic oil displacement the temperature of the deposit increases. There is formed an additional heat oil displacement front by hot water. Hydrodynamic displacement front passes ahead the heat displacement front, because the heat transfer from the heat-transfer agent that is used to heat viscous oil occurs not at once The increase of oil, water and rock temperature leads to the decrease of oil viscosity, change in the ratio of oil and water mobility to the change of relative permeabilities, residual oil saturation, to the evaporation of light fractions; there is occurred thermal expansion of the reservoir (varies porosity, the fluids volume that fills it, i. e. saturation).

Oil displacement by hot water and steam Hot water and steam, in other words – heat-transfer agents, are produced in steam generators (boilers) of high pressure and are injected into the formation through the injection wells of special construction and with special equipment designed for operation in the conditions of high temperatures. The disadvantage of using of surface steam generators provides high level of heat losses (temperature) in the surface communications and in the well bore. During the movement of the heat-transfer agent in the reservoir there are happened the heat losses through the top and the bottom of the reservoir. To reduce heat loss there should be chosen the formations with the thickness of more than 6 meters, applied rectangular well pattern with the distance of up to 100 -200 m between the injection and producing wells. The perforation interval is chosen in the middle part of the reservoir; the pipes are isolated; steam generator is situated to the wells as close as possible.

The method of heat margins According to this technology instead of a continuous injection of fluid after its penetration into the reservoir over time there is injected water at the reservoir under the conditions of the reservoir temperature. There is created a heated area (heat margin) in the formation, which moves from the injection well to the producing wells under the influence of cold water injection to the formation.

There are formed three displacement fronts in the reservoir when oil is displaced by the heat margin: 1 - hydrodynamic – the displacement of not heated cold oil by water; 2 - heat front – the displacement of the heated oil of the reduced viscosity by hot water; 3 –the displacement front of hot oil by cold water.

The method of heat margins The use of heat margins injection reduces oil recovery compared in comparison with the continuous heat-transfer agent, but it takes considerably less energy to prepare steam or hot water.

Combined technologies of enhanced oil recovery of high-viscosity oil deposits. Professor Kudinov V. I. and his colleagues has developed and embedded the advanced methods of thermal stimulation with the changing of time cycles and with the use of chemicals for enhanced oil recovery in the complex in structure reservoirs in "Udmurtneftegaz"

The technology of impulsive metered thermal stimulation (IMTS) considers cyclic variable injection of heat-transfer agent and cold water in certain proportions to the reservoir. The advantage of IMTS consists in the limit of the injected to the reservoir heat-transfer agent up to the effective temperature. This technology is applied for fractured-porous reservoirs (Warren – Ruth model). When the cycles of steam-cold water injection are repeated then steam penetrates in the porous blocks and after condensation displaces preheated oil in the fissures. The modification of the IMTS method is the application of this technology with the pauses before cold water injection. The pauses allow to ensure an additional oil inflow from the blocks to the fissures. This technology resembles the cyclic steam treatment of the producing wells. But the injection is carried out in the injection wells.

Thermal-polymer reservoir treatment (TPT) The TPT technology is based on the injection of heated up to the temperature of 90 -950 C of the PAA (polyacrylamide) solution with concentration of 0. 05 -0. 1%. The viscosity of heated water solution of polyacrylamide is 1. 5 -2 m. Pas The viscosity of oil in the system of cracks decreases, a part of hot solution, mainly hot water permeates the blocks, improves the hydrophilicity of the rock, increases oil mobility, and thus it leads to oil displacement

Thermal-polymer reservoir treatment (TPT) During this technology there is a complex or simultaneous physical treatment of three methods: 1. hydrodynamic, 2. physical - chemical 3. thermal. When water polymer solution moves through the reservoir it gets cold; its viscosity increases and becomes comparable with viscosity of the displaced oil. The displacement coefficient is increased.

Cyclic steam treatment of producing wells Cyclic steam treatment of producing wells refers to the methods of production stimulation (PS). When cyclic steam treatments there is injected steam to the producing well by the volume of 100 -300 tones per 1 m of formation thickness during 15 -20 days. Then the well is terminated for 10 -15 days for the heat redistribution, capillary counterflow oil displacement of low-permeability interlayers (LP) in high-permeability interlayers (HP). Further the well is being operated to achieve the maximum cost-effective production rate for 2 -3 months.

Cyclic steam treatment of producing wells (physical essence) 1. 2. 3. The physical essence of the process consists in the following: steam dilutes high-viscosity oil, increases the oil mobility factor. Depending on the change of temperature and pressure the steam transits first of all into two-phase state of steam - water, then after condensation, into hot water, intruded into the lowpermeability interlayers, reducing the oil viscosity there. After well termination as well as with the cyclic flooding, the water begins to displace oil from the LP to the HP. At the third stage of the well operation – the bottom -hole pressure falls, oil withdrawal increases due to its greater mobility.

In-situ combustion (ISC) is based on the ability of hydrocarbons (in this case, oil) to enter into a chemical reaction with oxygen. In the result of combustion in the reservoir a large amount of heat is emitted, the physical properties of the reservoir fluids and rocks are changed. Unlike the othermal methods of enhanced oil recovery ISC allows to remove technical problems and heat loss, which arise when generating it on the surface and delivering to the formation of the heat-transfer agent by injection.

In-situ combustion The process of in-situ combustion is carried out at the well bottom that is called a fireflood well. The oxidizer (usually air) is pumped to the injection well with simultaneous heating of the bottom-hole formation zone using downhole electric heater, gas burner, incendiary chemical mixtures, etc. Due to this the exothermic oil oxidation reactions are accelerated, which eventually lead to the creation of the combustion process in the bottom-hole formation zone. In the process of combustion the heavier fractions of oil, called coke (gas carbon), are burnt. The rest part of the oil is heated to reduce viscosity, density, increase oil mobility. The lighter fractions transform into the vapor phase and participate in the displacement of the liquid heated oil. For different geologic-field conditions the coke’s concentration can be 10 -40 kg per 1 m 3 of the reservoir. This important parameter of the combustion process is recommended to determine experimentally in laboratory conditions. It is established that with the increase of density and viscosity of oil the coke’s concentration increases, and at high values of permeability of rocks it decreases. It is believed that during the combustion of coke the heat in the quantity of 29 -42 MJ/kg is emitted.

There are three main types of insitu combustion: dry, wet , super wet.

Dry-situ combustion At a dry-situ combustion to maintain the combustion process it is necessary to pump only air. The main share of the generated heat in the formation (80 % or more) remains in the area behind the combustion front and gradually dissipates in a surrounding rocks of the formation. This heat has some positive impact on the process of displacement of not covered by the burning process adjacent parts of the reservoir

Wet-situ combustion The combination of in-situ combustion and flooding is called wet-situ combustion. The essence wet combustion is that the injected along with the air in certain proportions water, evaporating in the surrounding zones of the combustion front, transfers the generated heat to the area ahead of it; as a result, extensive zones of warming-up, formed by the areas of saturated steam and condensed hot water in this area are developing The process of the in-situ steam generation is one of the most important distinguishing features of the wet combustion, determining the mechanism of oil displacement from the reservoir

Super wet combustion During super wet combustion the cold water intrudes into the combustion zone before the full burn out the oil, remained as a fuel. In this case, the heating and evaporation of water, heat recovery and its generation in the result of oxidation reactions are concentrated in a single area. Water velocity is determined by the injection rate. It will be significantly higher than the velocity of the combustion front. Thus, significant cost reduction of air on oil production can be achieved by means of super wet combustion. To maintain super wet combustion process it is necessary to use small concentration of fuel. So using the method of super wet combustion is associated with the significant prospects of oil recovery enhancement, containing oils of low viscosity, including the oils after the flooding.

The main disadvantages of oil displacement methods with the help of in-situ combustion include: The necessity of the environmental protection and utilization of combustion products measures implementation; The necessity to take measures to prevent corrosion of the equipment; The possibility of the gravitational effects influence and decrease, as a result, of the sweep coefficient by thermal stimulation.

Thermal-gas method of treatment. The method of thermal-gas treatment (TGT) refers to thermal methods. It is applied on the fields of light oil with high temperatures of above 650 C and high reservoir pressures. As for the in-situ combustion the products of oxidation: nitrogen, carbon dioxide, and the light oils fractions are the displacing gas agent, mingling with oil, and ultimately increasing its mobility. It contributes to the oil recovery factor increase, especially in the development of the fields with difficult-to-recover reserves.

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