Enhanced recovery of hydrocarbon through supercritical wet combustion, gravity stable in deep heavy-oil reservoirs

Abstract

Method to enhance the recovery factor by injecting simultaneously or alternately air and water through a well, which is located in the top part of a heavy-oil reservoir showing dip and by producing fluids through a vertical or horizontal well, which is located in the formation lower part, resulting in a gravity stable burning front (GSAI or Gravity Stable Air Injection) at high temperature and pressure.

Description

TECHNOLOGICAL SECTOR

This patent is related to the production and increase of recovery factor of heavy-oils in deep reservoirs by injection of air and water or steam.

STATE OF THE ART

One of the main problems in air injection, increased by major sand thicknesses and few vertical permeability barriers, is the displacement of this gas toward the top part of oil-bearing stratum, known in English as overriding combustion gases, caused mainly by the difference in gas- and oil-mobility. This causes a preferential channel for air, generally in the top part of the reservoir, leaving a considerable sand zone without being altered by combustion and promoting a high production of oxygen in producing wells

Therefore, this invention is intended to utilize the formation dip to enhance gravitational fluids segregation by maximizing the contact zone between water and air, increasing burning front area and producing a stable advance thereof and higher time of cold production by displacement of original oil bank of the reservoir. Additionally, due to the high pressure and temperature conditions present in the reservoir, the injected water will reach the supercritical condition in the proximity of the burning front enhancing transport properties and the physicochemical improvement of the fluids, similarly to what is described in US patent 2009/0206007 A1 and WO 2009/085436 A1.

The features of coke deposition in a reservoir are the basic parameters for the design in the application of combustion process in situ. The coke is the fuel that supports the burning front resulting from thermal cracking and the distillation of crude oil near the combustion zone. The amount of deposited coke is a function of API gravity, saturation and mobility of crude oil, the pressure and reservoir mineralogy, being more in heavy-oils, less mobile, under high pressure. (SPE 75207, JCPT Volume 38, No.8). The coke deposition determines the quantity of air required for the burning front advance; if the deposited coke is excessive, which is often the case of heavy-oils, a big quantity of air is needed to burn it completely reducing the economic viability of the process and limiting the applicability thereof to deep heavy-oils reservoirs.

A strategy to overcome these disadvantages is the process of wet combustion, referred to in patents U.S. Pat. No. 3,520,363 and CA 872041. In this process, the mechanism of coke formation and, therefore, the air requirement are reduced by improving the crude oil mobility through transferred heat by steam. When the wet combustion is carried out under supercritical conditions for water, part of the deposited coke reacts with water under such condition through reforming and water-gas shift (WGS) reactions, producing hydrogen and carbon oxides, as Vostrikov et al. 2007 (Ind. Eng. Chem. Res. 46, 4710-4716; Energy & Fuels, 21, 2840-2845) shows. This reduces the amount of coke and, therefore, the oxygen consumption needed for its combustion.

A phenomenon contributing to the oxygen consumption reduction arises because water under supercritical conditions behaves as an excellent organic solvent. This behavior is well known in the state of art (J. Phys. Chem. B, 107, 12307-12314). Because of this property, water under supercritical conditions passing through burning front dissolves crude oil light fraction (maltenes) preventing these undergo thermal cracking by burning front and being converted to coke. Evidence thereof can be noted in experimental results of Watanabe et al. research, 2010 (The Journal of Supercritical Fluids Volume 53, Issues 1-3, Pages 48-52).

Besides coke deposition, another parameter concerning air volume in combustion process in situ is the efficiency of oxygen utilization (Intevep, Procesos Térmicos de Extracción de Petróleo, 1987), which depends on the controlling reaction regime, which is defined by the temperature range at which the reactions are performed. Most researchers put reaction regimes into two categories: low temperature reactions, LTO, and high temperature reactions, HTO (DOE. BC14994-21).

In an ideal combustion operation in situ for heavy-oils, coming first reaction regime is HTO, wherein fuel reacts with oxygen at a temperature higher than 343° C. to produce carbon dioxide and water. At lower temperatures (LTO) certain fraction of oxygen reacts with the crude oil to form oxygenated compounds (acids, ketone, alcohols, among others) assisting crude oil polymerization, increasing its viscosity, causing blocking problems in the reservoir (DOE., PC, 9 1 008-0374). This kind of condition can be reached if the oxygen supply is insufficient or if the heat losses in burning front are excessive, as it would happen during a wet combustion with an excessive water supply.

One way of attenuating the LTO regime problem is improving the oxygen transport in combustion zone. This can be reached by wet combustion under supercritical condition, wherein water shows the property of dissolving oxygen in big quantities, as it is shown in the document DOE., GA-C24239. On the other hand, as it is reported in the literature, fluids under supercritical conditions show very good diffusivity, high heat capacity and low viscosity. Accordingly, in a low permeability reservoir undergoing wet combustion process under supercritical condition, water can diffuse beyond the burning front transferring heat and reducing crude oil density and viscosity by dissolution. Thus, hydrocarbon mobility is significantly improved, even compared to conventional in situ wet combustion, with the additional benefit of a better fluids distribution in the reservoir, even if this is heterogeneous.

Regarding heavy-oil quality improvement through treatment with water under supercritical condition, patents US 2010/0314583A1 and WO 2009/085436A1 show two kinds of processes by which a crude heavy-oil with significant sulfur, heavy metals and nitrogen content is treated, admixed with supercritical water in continuous reactors. As a result, an improved crude oil, with higher API gravity and lower sulfur, nitrogen and heavy metals content, is obtained. According to patent WO 2009/085436A1 author, the API gravity increase is owing to cracking reactions, whereas the heavy metals and sulfur reduction is owing to metal or sulfur oxidation in hydrocarbon. Also, in the patent US 2010/0314583A1 the author concludes that some sulfured components react with carbon monoxide to produce carbonic sulfide. The benefits shown in these patents are also obtained in in-situ combustion processes due to the fact that they are carried out with the same components (ACSC and crude oil) under the same supercritical conditions of water.

DESCRIPTION OF THE FIGURES

FIG. 1 corresponds to a supercritical wet combustion process, gravity stable according to the present invention.

GENERAL DESCRIPTION OF THE INVENTION

This invention is intended to increase the recovery factor through air and water injection, simultaneously or alternately through a vertical injection well located in the top part of heavy-oil reservoir formation showing dip and producing fluids via vertical or horizontal well located in the lower part of the formation, causing a gravity stabilized burning front (GSAI or Gravity Stable Air Injection) at high temperature and pressure.

Under high pressure and temperature conditions, present in the reservoir, either because of its initial condition or because of the previous air or other fluid injection, the injected water reaches supercritical condition in the proximity of burning front, obtaining improvement of its transport properties and its effect on present reactions kinetics. These phenomena increase recovery efficiency and result in a decrease of energetic requirements related to other in-situ wet combustion processes.

This process provides the benefit of a less air requirement, better control of burning front advance, higher scanning efficiency and higher cold production time for displacement of the reservoir original oil by produced combustion gases and steam, latter effect resulting in a better control of the producing wells integrity.

The invention comprises the following aspects:

1. Simultaneous or alternated air and water injection through vertical injection well in the top part of a reservoir showing dip

• • Air is injected through the injection well which is drilled in the formation upper part.
  • Water is injected simultaneously or alternately. Water injection starts once the existence of a stable burning front is determined.

2. Oil production through a vertical producing well, located in the reservoir lower part and perforated in the formation lower part or a horizontal well, the horizontal section thereof is in the producing formation lower part.

3. Generation of a burning front in the proximity of the injection well face by spontaneous or artificial ignition.

4. Displacement of the burning front from the reservoir top part until its lower part in a fluids gravitational segregation stable process.

5. Generation of water supercritical condition, injected in the proximity of the burning front owing to the reservoir condition or by pressurization thereof under pressures higher than 22.1 MPa and temperatures higher than 380° C.

• • Under this condition water is hydrocarbon soluble in situ, whereby the sweep efficiency of the zone located before the burning front is increased. This causes the decrease of residual oil saturation causing less coke generation and less air requirement.
  • Water under this condition, in a hydrocarbon combustion process, concerns present reactions causing less coke production and thus less air requirement compared to typical combustion process, either wet or dry.
  • Water under this condition and in the presence of minerals present in the rock improves metals and sulfur removal from the hydrocarbon, increasing produced fluid quality.

DETAILED DESCRIPTION OF THE INVENTION

The process requires drilling vertical injection well 3, located in the top part of the structure and perforated in the formation upper part 4. Furthermore, drilling a vertical or horizontal producing well 8, located in the lower part of the structure and perforated in the formation lowest part 7. The process requires that the reservoir pressure be higher than water critical pressure, i. e. 22.1 MPa, otherwise the process starts with the fluid injection allowing reservoir pressurization.

Once pressure condition of the process is reached, ignition procedure starts, which comprises an oxidizing gas injection 1 through injection well 3. Once the ignition has been reached, either artificially or spontaneously, the well is monitored in order to determine the availability of a burning front, stable at HTO regime; afterwards, oxidizing gas and water injection 2 starts simultaneously or alternately. Oxidizing gas and water can be injected in variable ratios depending on well characteristics, either more oxidizing gas than water or more water than oxidizing gas, or equal amounts of water and oxidizing gas.

Oxidizing gas can be air, oxygen or mixtures thereof, whereas water can be fresh water, brine, formation water, sea water, carbon dioxide-saturated water or mixtures thereof. In some instances, injected water can be in the form of steam.

Due to the well configuration and to the formation dip because of fluids gravity segregation, injected oxidizing gas and produced hot gases migrate towards the formation upper part 5 and the heaviest fluids, as water and hot oil, flow towards the lower part thereof 7 to be extracted through the boreholes 8 located in the lower part or in the producing well horizontal section 9. These fluids go up through the producing well to be brought to surface facilities 10.

Due to well configuration and with the help of gravity forces, the process according to the present invention produces a better distribution of oxidizing gas and a more stable advance of burning front 6, preventing overriding effect, achieving higher sweep efficiency and thus higher recovery factor. Furthermore, supercritical condition reached by water in the proximity of burning front 6 has a positive influence on displacement phenomena, reaction mechanisms and kinetics, thus obtaining less air requirement and higher fluids quality improvement compared to a typical in-situ wet combustion process.

Claims

1. Method for enhanced heavy hydrocarbon recovery from deep reservoirs with dip, in which injection well in the reservoir top part and producing well in the lower part have been drilled, comprises comprising the steps of:

a) injecting oxidizing gas through the injection well;

b) forming a burning front by spontaneous or induced oxidizing gas ignition;

c) monitoring the burning front until the stabilization thereof is determined;

d) injecting water and oxidizing gas through injection well;

c) Extracting extracting fluid oil through producing well, located in the formation lower part;

wherein the well is under a pressure higher than or equal to 22.1 MPa.

2. The method according to claim 1, wherein water and oxidizing gas are injected simultaneously.

3. Method The method according to claim 1, wherein water and oxidizing gas are injected alternately.

4. Method The method according to claim 1, wherein a greater water proportion than that of oxidizing gas is injected.

5. The method according to claim 1, wherein a greater oxidizing gas proportion than that of water is injected.

6. The method according to claim 1, wherein equal amounts of water and oxidizing gas are injected.

7. The method according to claim 1, wherein water is injected in liquid form.

8. The method according to claim 1, wherein water is injected in form of steam.

9. The method according to claim 1, wherein water is selected from the group consisting of fresh water, brine, formation water, sea water, carbon dioxide-saturated water or mixtures thereof

10. The method according to claim 1, wherein oxidizing gas is selected from air, oxygen or mixtures thereof.

11. The method according to claim 1, wherein if the pressure inside the well is lower than 22.1 MPa, an inert gas is injected until the pressure inside the well reaches at least 22.1 MPa before the step of oxidizing gas injection.