Wet electric heating process

Details Wet electric heating process Wet electric heating process

2001-12-10

2003-10-14

Bagnell, David (Department: 3672)

Wells

Processes

Electric current or electrical wave energy through earth for...

C166S060000, C392S301000

Reexamination Certificate

active

06631761

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for producing hydrocarbons from a subterranean formation. More specifically, the invention relates to a method of using wet electric heating to facilitate hydrocarbon production, and more particularly, producing hydrocarbons having pre-heated viscosities of about 100 centipoise or greater.
BACKGROUND DISCUSSION
Much of the hydrocarbons produced under primary methods (i.e., non-thermal processes) has a viscosity, ranging from about 0.5 centipoise (“cp”) to about 100 cp. Because of this relatively low viscosity, a significant percentage of the oil in place (“OIP”) in the subterranean formation can be produced without resorting to thermal processes. Typically the percentage of the OIP that can be produced under primary methods will range from about 3% to about 30%.
However, there are significant deposits having higher viscosity hydrocarbons with pre-heated viscosities in the range from about 100 cp to about 1,000,000 cp or even greater. Typically, for a subterranean formation containing hydrocarbons with a pre-heated viscosity of about 100 cp to about 1,000 cp, roughly 3 to 10% of OIP can be recovered using conventional primary techniques. To produce beyond that percentage, of course, requires one or more processes, including among others, thermal processes (i.e., secondary recovery).
For convenience, hydrocarbons with pre-heated viscosities in the about 100 cp to about 1,000 cp range will be referred to herein as “heavy oil,” while hydrocarbons with pre-heated viscosities in the range of greater than about 1,000 cp to about 1,000,000 cp or greater will be referred to herein as “super heavy oil.” One of the more common types of super heavy oil is tar sands, also known as oil sands or bituminous sands.
Tar sand deposits are impregnated with dense, viscous hydrocarbons and are typically a mixture of sand, water and bitumen. Bitumen is a hydrogen-deficient oil that can be upgraded to a commercially desirable hydrogen to carbon ratio by carbon removal (i.e., coking) or hydrogen addition (i.e., hydrocracking). The sand component in a tar sands deposit is primarily quartz, which is typically about 80% to 85% by weight (“wt”) of the deposit, while the remainder is bitumen and water, which comprises about 15 wt % to 20 wt % of the tar sands.
Worldwide tar sand deposits can provide an enormous resource of hydrocarbon reserves. In September, 1982, during the Proceedings of the Second International Conference on Heavy Crude and Tar Sands (Caracas, Venezuela), R. F. Meyer and P. A. Fulton estimated the total bitumen in place globally as 4.07×10
12
barrels (“bbl”) (about 4 trillion bbl). Of this total bitumen in place, they estimated about 2.4×10
12
bbl in seven deposits in Alberta, Canada, about 1×10
12
bbl in four deposits in Venezuela, about 5.6×10
11
bbl (0.56 trillion bbl) in Russia and about 3.4×10110 (0.034 trillion bbl) in 53 deposits in the United States.
Of course, because of bitumen's high viscosity and the intimate mixture bitumen forms with sand and connate water, tar sand deposits and other super heavy oil deposits cannot be exploited using primary oil recovery techniques. Therefore, the super heavy oil (e.g., bitumen) has often been mined, presuming the deposit is at a sufficiently shallow depth, or otherwise produced using a non-mining, but enhanced recovery, process.
Non-mining processes that may be used include thermal and non-thermal processes. Non-thermal processes can include cold production (i.e., sand production) and solvent injection, while thermal processes can include in-situ combustion or a hot aqueous fluid injection and displacement or drive process using hot water, steam or a steam/solvent mixture. But typically a hot aqueous fluid, such as hot water or steam, is used to reduce oil viscosity and displace the oil. For example, one common heavy oil or super heavy oil recovery technique involves steam injection, followed by a steam “soaking” phase and subsequent recovery of the reduced viscosity oil, also known as huff-n-puff or cyclic steam stimulation (“CSS”). Huff-n-puff or CSS can also be combined with an electric heating process to provide additional heat and viscosity reduction.
For example, in U.S. Pat. No. 3,946,809 (Mar. 30, 1976), Hagedorn suggests that CSS should be followed by electric heating so that brine can be injected into the region where the oil was displaced under the CSS process. Specifically, Hagedorn's proposed process involves four steps: (1) CSS, which is terminated when there is interconnection of CSS heated zones between wells; (2) producing oil and water; (3) injecting high conductivity fluid into CSS heated zones; and (4) completing wells as electrodes and allowing current to flow between wells to increase the temperature of oil not heated in CSS. And more specifically, Hagedorn suggests that the volume of high conductivity fluid should be sufficient to displace substantially all water condensed from steam from the CSS heated zones. But Hagedorn warns that “the volume should not be so great, however, as to displace substantial amounts of high-electrical-resistivity connate water from the unheated portion of the reservoir” (col. 6:1-4).
As discussed in more detail below, it is well understood by those skilled in the art of thermal oil recovery processes that when steam is injected into a formation, it will rise forming a conical bowl steam zone around a vertical well. See for example, Boberg, T. C.
Thermal Methods of Oil Recovery
John Wiley & Sons, 411 pgs.; pg. 166; 1988 and Butler, R. M.
Thermal Recovery of Oil and Bitumen
Prentice Hall, 528 pgs., pg. 258-259; 1991.
So, Hagedorn suggested either prohibiting or restricting the amount of electrolytic or high conductivity fluid (e.g., brine solution) introduced into the unheated portion of a reservoir, where oil was still substantially in place, was important in practicing an electric heating process. This was understandable since it was generally believed by Hagedorn and others skilled in the art then, and up to now, that increasing the electrode zone's effective radius was, alone, the critical factor to effectively electrically heat a formation, while ignoring electrode zone spacing, geometric shape and spatial orientation effects. However, surprisingly and unexpectedly, the inventors have discovered that, by properly accounting for electrode zone spacing, geometric shape and/or spatial orientation effects in substantial accordance with the detailed description provided below, a target region in a formation heating will be more diffuse than in a conventional electric heating process, like Hagedorn's for example, that fails to properly account for spacing between electrode zones, geometry effects (e.g., electrode zone surface area and shape) and/or electrode zone spatial orientation.
For example, in a CSS configuration, such as Hagedorn used, it is important to ensure that an electrolytic or high electric conductivity fluid is in place in both the unheated, as well as any previously heated portions of the reservoir, contrary to what Hagedorn, in fact, taught. Put another way, beyond the electrode zone's size, it is also important to ensure that the spacing, geometric shape and/or spatial orientation of the electrode zone formed with the injected electrolytic fluid has a suitable combination of surface area and shape for eliminating or reducing, among other things, unwanted “edge” effects. “Edge” effects lead to undesired small volume “hot spots” (i.e., more intensely heated regions), rather than relatively more diffuse heating between electrode zones, like that generated with the inventive WEH process more fully described below.
Consequently, while Hagedorn and other proponents of electric heating processes in oil formations have focused primarily on the electrode zone's size, they have, in the meantime, overlooked and/or incorrectly assessed the effects that electrode zone spacing, geometric shape and/or spatial orientation would have on significantly improving

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