Patent Application
20130020080
This disclosure relates to methods of extracting hydrocarbon materials from subterranean geological formations.
As energy consumption rises, alternative sources of oil to traditional oil wells are developed to meet consumption demand. For instance, one alternative oil source is oil shale. The oil shale is removed from subterranean geological formations and then processed at the surface to extract the oil from the rock. The extracted oil is subsequently refined using conventional refining techniques.
In the illustrated example, the method 20 generally includes steps 22, 24 and 26, although it is to be understood that each of the steps 22, 24 and 26 may include any number of sub-steps in order to carry out or facilitate the primary steps 22, 24 or 26. In the example shown, step 22 includes the action increasing permeability of a low permeability hydrocarbon-containing subsurface region. The increase in permeability creates a plurality of well sub-regions that include a first well sub-region and a second well sub-region that is located vertically below the first well sub-region. The second step 24 includes the action of heating the first well sub-region to extract liquid hydrocarbon materials that then gravimetrically flow from the first well sub-region to the second well sub-region. The third step 26 includes the action of transporting the liquid hydrocarbon materials from the second well sub-region to the surface, for example.
The method 20 will be further described with reference to
In the illustrated example, the well arrangement 40 is configured relative to a surface region 42 and a subsurface region 44. The subsurface region 44 includes a low permeability hydrocarbon-containing subsurface region 44a that is generally located between a near subsurface region 44b and a far subsurface region 44c. That is, the low permeability hydrocarbon-containing subsurface region 44a is at a depth that is between the near subsurface region 44b and the far subsurface region 44c. In some examples, the subsurface region 44a is at a depth of 500 to several thousands of feet.
In this example, three well sub-regions 46a, 46b and 46c are created within the low permeability hydrocarbon-containing subsurface region 44a by increasing the permeability of the subsurface region 44a. For instance, each of the well sub-regions 46a, 46b and 46c are created by rubblizing the subsurface region 44a. The subsurface region 44a is rubblized using horizontal well strings, hydraulic fracturing and/or by using a compressed gas or supercritical gas. The rock fractures to form a rubble bed of broken rock, which increases the flow area for the hot working fluid, increases the rock surface area for heat transfer, and reduces the size of the rock dimension or diameter for affecting diffusion and expulsion of the liquid oil from the rock pores. In general, techniques of rubblizing are known and, given this description, one of ordinary skill in the art will recognize suitable rubblizing techniques to meet their particular needs.
As shown, the first well sub-region 46a is fluidly connected to the surface region 42 by injection duct 48a, the second well sub-region 46b is connected to the surface region 42 by collection duct 48b, and the third well sub-region 46c is fluidly connected with the surface region 42 by vent duct 48c. In that regard, the first well sub-region 46a is considered to be an injection well sub-region, the second well sub-region 46b is considered to be a collection well sub-region and the third well sub-region 46c is considered to be a vent well sub-region. In the illustrated example, the injection well sub-region and the vent well sub-region are at substantially equivalent subsurface depths.
The injection duct 48a and the vent duct 48c are connected by a surface battery 50 to recirculate a working fluid through the subsurface region 44a. In the illustrated example, the surface battery 50 includes a condenser 52, a turbo-compressor 54, a separator 56 and a gas source 58.
A downhole combustion heater 60 is located within the injection duct 48a below the surface region 42. The combustion heater 60 is located in close proximity to the first well sub-region 46a for enhancement of thermal efficiency in conveying heated working fluid into the first well sub-region 46a. The close proximity allows for the efficient generation and transport of the heat without suffering heat losses in the long transport of the working fluid from a remote surface heating facility. An additoinal benefit of the close proximity is where the subsurface region 44a is very deep, under a body of water, under permafrost, or a combination of these conditions.
The downhole combustion heater 60 operates to heat the rubblized material within the first well sub-region 46a to extract hydrocarbon-containing materials from the oil shale or other oil-bearing material. The combustion heater 60 distributes the heated working fluid into the first well sub-region 46a to slowly heats the shale and release (i.e., by the process of catagenesis) liquid oil. The heating profile with regard to time and temperature can be adjusted such that catagenesis of the kerogen to oil or oil and gas products is controlled.
In one example, the combustion heater 60 is used to heat the first well sub-region 46a to a temperature of 350°-450° C. (662°-842° F. In a further example, the target heating temperature is approximately 350° C.-400° C. (698° F.-752° F.). The given temperature range thermally decomposes kerogen to a light, low viscosity liquid oil by very slowly heating the first well sub-region 46a. In comparison, surface retorting of mined rock is conducted at much higher temperatures for much shorter times.
In one example, the combustion heater 60 is a vitiated, pressurized combustor unit that is designed for high thermal output, such as a combustor that is of similar design to a gas or liquid fueled rocket engine.
Depending on the type of oil-bearing material in the subsurface region, the extracted hydrocarbon-containing materials are liquid hydrocarbon material, gaseous hydrocarbon material or both. The extracted liquid hydrocarbon material flows downwards into the second well sub-region 46b, where it subsequently transported through collection duct 48b to the surface region 42.
After initial heating of the first well sub-region 46a to extract and drain liquid hydrocarbon material, the temperature in the first well sub-region 46a is optionally slowly increased to more efficiently release hydrocarbon gases and condensable liquids and to produce additional liquid oil by the thermal decomposition of any residual bitumen products. In one example, fuel gases that are extracted are used to fuel the combustion heater 60.
The working fluid that is heated and provided into the first well sub-region 46a is a non-degrading fluid, such as carbon dioxide, methane, nitrogen or mixtures thereof. That is, the working fluid does not decompose into other shorter chain molecules that can otherwise foul the surfaces of the combustion heater 60 or the pores within the wells. In a further example, the working fluid is a compressed gas or supercritical gas.
The heated working fluid provided from the turbo-compressor 54 to the combustion heater 60 and into the first well sub-region 46a circulates to the third well sub-region 46c. The extracted gaseous hydrocarbon materials are carried with the working fluid into the third well sub-region 46c and are vented through the vent duct 48c to the surface region 42.
The condenser 52 condenses any condensable hydrocarbon materials within the vented gas and the separator 56 subsequently separates the condensed fluids, such as liquid oils and water. The remaining gaseous material is made up substantially of the working fluid, which is then conveyed to the compressor 54 for recirculation through the combustion heater 60 into the first well sub-region 46a. A combustible gas, such as oxygen, is provided from the gas source 58 into the injection duct 48a for combustion in the combustion heater 60.
Experimental modeling of the method 20 using the disclosed working fluids suggests that the well can be heated to the desired temperature and oil released from the rock over a reasonable period of field production life (e.g., 10-15 years). In some examples, the parameters that influence the production rate are thermal losses within the formation and within the length of the injection ducts (minimized by the downhole combustion heater 60), volumetric rate of circulation of the heated working fluid, temperature of the injected working fluid, and the geometric character of the rubblized rock.
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.
