US 3432205 A
Description (OCR text may contain errors)
March 11, 1969 c, E, HOTTMAN ET AL 3,432,205
SULFUR STEAM DRIVE Filed Dec. 8, 1966 INVENTORS:
CLARENCE E. HOTTMAN PIETER VAN MEURS 111M 1 @vglm THEIR AGENT United States Patent 3,432,205 SULFUR STEAM DRIVE Clarence E. Hottman and Pieter Van Meurs, Houston,
Tex., assignors to Shell Oil Company, New York, N.Y.,
a corporation of Delaware Filed Dec. 8, 1966, Ser. No. 600,176
US. Cl. 299-4 Int. Cl. EZlc 41/14, 43/00; E21b 43/24 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to mining sulfur. More particularly, it relates to mining sulfur by circulating hot fluid through a sulfur deposit and recovering sulfur that is melted and entrained by the circulated fluid.
For many years sulfur has been mined by the Frasch process. In the Frasch process, hot water is injected into an upper portion of the sulfur deposit and molten sulfur is produced from a lower portion. Particularly in respect to olfshore locations, the operating costs tend to be disadvantageously high due to a need for purifying and heating a relatively large volume of hot water. The volume of the hot water must fill all of the space that was previously occupied by sulfur. A more recently proposed process utilizes at least two horizontally spaced wells and injects a hot gas, e.g., the gas produced by heating fluid recovered from a petroleum reservoir, along with the hot water. This minimizes the amount of water that is required, but it requires both the fortuitous location of a petroleum reservoir and the compression and injection of a large amount of hot gas. The amount of gas is large because it is used as an expanding gas cap that displaces the hot water and molten sulfur in a downward direction, so that the sulfur deposit is progressively depleted from the highest to the lowest levels within the deposit.
In accordance with the present invention, at least two Wells are opened into the lower portion of a sulfur deposit. Fluid communication between the wells is established along a path that extends through the lower portion of the sulfur deposit. This is preferably accomplished by a fluid circulation in which a fluid having a temperature below the melting point of the sulfur and a density at least equaling that of water is forced to flow from one well to the other along a generally horizontal path through the sulfur deposit. An aqueous liquid is heated, softened and flowed between the wells at rates that are adjusted to maintain a substantially constant temperature along the path of fluid communication between the wells. The temperature of the circultaing liquid is increased to between 250 to 350 F. At this temperature the sulfur will soften and become a mobile liquid. Preferably, the circulating aqueous liquid is converted to circulating steam. Sulfur is entrained in the circulating hot aqueous fluid and is recovered by separating it from sulfur-containing aqueous fluid that flows into a production well.
In completing the wells into a sulfur deposit, in order to operate the present process, conventional procedures and equipment can be utilized. It is generally preferable to use a relatively high ratio of production wells to injection wells. Thermal insulation can advantageously be applied to the injection and production tubing strings that are installed in the wells.
While establishing a fluid communication between a pair of wells in accordance with the present process, although substantially any fluid having the specified temperature and density can be circulated between the wells, it is generally preferable to circulate an aqueous liquid at the ambient surface temperature. During such a circulation of relatively cold fluid, the injected fluid and any connate water that is present are substantially the only mobile fluids in the sulfur deposit. When, for example, a cold aqueous liquid is injected at a depth within the lower portion of the deposit while fluid is produced from another point at the same depth, the injected liquid displaces any connate water that is present and flow is soon established along a substantially horizontal path that extends through the lower portion of the deposit along substantially the shortest distance between the points at which fluid is injected and produced. In a preferred procedure, the permeability of such a substantially horizontal path between the Wells is increased to the extent required to provide a channel capable of conveying aqueous liquid through the lower portion of the deposit at the rate exceeding one-tenth barrel per minute. Although some sulfur deposits are relatively permeable earth formations, it is often desirable that the natural permeability be improved by fracturing, acidizing, or the like techniques for increasing the permeability of an earth formation.
After the above type of fluid circulation has been established through a path of fluid communication between a pair of wells, an aqueous liquid is heated, softened and flowed between the wells at rates that are adjusted to maintain a substantially uniform temperature along the path between the Wells. During this operation, the fluid flow rate preferably exceeds one-tenth barrel per minute. The aqueous liquid may be initially pumped into the injection well at about the ambient surface temperature and then heated at a rate that is controlled in the manner described below. At the outset, the aqueous liquid can be any pure, brackish or briny water that is non-scaling at the reservoir temperature. However, as the temperature of the injected aqueous liquid is increased, the liquid should be softened to the increasing extent required in order to provide a water that is non-scaling at the temperature to which it is being heated.
The rate at which the water is heated to temperatures that exceed the reservoir temperature is controlled to cause a substantially uniform heating up of the flow path between wells. This is preferably accomplished by measuring temperature properties of the fluids being injected and produced and adjusting the heating rate so that, at a selected flow rate, the measured values are indicative of the existence of a temperature gradient of less than about 1 F. per foot along the path between the wells. The temperature property measurements can utilize conventional methods and equipment. Such measurements can be made at the downhole locations at which the fluids leave an injection well and enter a production well, or can be made at surface locations and corrected for the tempera ture changes that occur during the flows through the well conduits.
Such a substantially uniform heating up of the flow path between the wells is continued until the circulating fluid has a temperature between about 250 and 350 F. at which the sulfur in the deposit is a mobile liquid. The aqueous liquid which is circulated at such a temperature melts sulfur in and adjacent to the flow path and the liquid sulfur becomes entrained in the stream of hot liquid or is displaced toward the production well by the drag forces of the stream. The resulting extraction of sulfur converts the flow path to a channel of sulfur-depleted earth formation. The channel of sulfur-depleted earth formation has a permeability that is materially greater than that of the undepleted sulfur deposit.
In the present process, the fluid that enters the production well is primarily a mixture of hot water and liquid sulfur. This fluid is preferably produced from the bottom of the well at a rate that maintains a relatively low pressure near the bottom of the well. Such a bottom hole pressure can advantageously be about the pressure of saturated steam at a temperature at which the sulfur is a liquid, e.g., about 50 p.s.i.g., where the sulfur is liquid at about 300 F. The fluid that enters the production well may be produced by conveying it to the surface by means of conventional devices or techniques such as pumping, gas lifting, or the like.
The produced fluid is preferably maintained at a temperature exceeding the melting point of the sulfur until the fluid has reached a surface location. At a surface location the sulfur may be recovered by separating it from the other components of the fluid by means of conventional procedures. For example, sulfur can be recovered by flowing the produced fluid into open containers from which the aqueous components are allowed to overflow and/ or evaporate to leave a deposit of solidified sulfur.
In the operation of the present process, a sulfur deposit is depleted progressively from the bottom to the top as sulfur is melted and extracted by the hot aqueous fluid that is circulated between the wells. This extraction leaves a channel of preferential permeability that expands vertically until it encompasses substantially the entire thickness of the sulfur deposit. Such a vertical expansion is facilitated by the gravity segregation of the components of the fluid in the channel. The molten sulfur, which is denser and more viscous than the aqueous fluid, tends to move down while the hottest and lightest portions of the aqueous fluid are moving up and over the sulfur and cooler portions of water. Such an upward migration of the hottest component (preferably steam) increases the tendency for sulfur to be extracted from the roof of the channel, and causes the channel roof to move up through the sulfur deposit until the movement is stopped by contact with an overlying earth formation. In the present process, gas compression costs are minimized. If any gas is used, it is used merely to gas-lift the sulfur-containing aqueous fluid from the bottoms of the production wells.
In conducting the present process, after the temperature within the flow path between the wells equals the temperature of steam at the injection pressure required to maintain an adequate rate of flow, the hot aqueous fluid that is circulated is preferably injected in the form of low quality steam, dry steam, or super-heated steam. In offshore locations the water that is heated and circulated or converted to steam can comprise sea water. The low quality steam that is used can advantageously comprise a steam of the type produced by the process of US. Patent 3,193,009. Where steam is used the water consumption is low relative to the amount required where the sulfur is extracted by hot water. The amount of water required to produce suflicient steam to fill the space that was previously occupied by sulfur is much less than the amount of water that is required to fill the same space.
The drawing illustrates equipment which is suitable for practicing a preferred embodiment of the present invention. As shown, a sulfur deposit is located between a pair of non-productive earth formations such as a cap rock-11 and a base rock 12. The sulfur deposit is penetrated by an injection well 13 containing perforations 20 and a production well 14 containing perforations 19. The wells are opened into fluid communication with the lower portion of the sulfur deposit.
The injection well 13 contains a tubing string 15 containing perforations 21 which has a lower portion that extends into fluid communication with a hot geopressured aquifer 16 and is provided with valve means 17 for controlling the flow of fluid from the aquifer. As is described in US. Patent 3,258,069, such a geopressured aquifer can advantageously be utilized as a source of hot water and/ or steam. In a preferred procedure for operating the present invention, water from the aquifer is expanded to form steam that supplements or supplants steam which is supplied to the tubing string 15 from a surface-located, water-heatin g device, not shown.
In using the illustrated equipment to initiate the operation of the present process, a relatively cool fluid, preferably an aqueous liquid that it non-scaling at the temperature of the sulfur deposit, is injected through well 13 with valve 17 closed and fluid is produced through well 14. If the natural permeability of deposit 10 is low, for example, if it is difficult to inject fluid into the sulfur deposit at a rate exceeding about one-tenth barrel per minute, it may be desirable to fracture and/or acidize the deposit. When fluid is injected and produced through the respective injection and production wells and the volumes of fluid being injected and prouced involve the production, through a well such as 14, of an appropriate proportion of the input, through a well such as 13, a path of preferred fluid communication, such as path 18, has been established between the wells.
When such a path of preferred flow between the wells has been established, an aqueous liquid is circulated through the path by injecting it through well 13 with valve 17 closed and producing it through well 14. The circulating aqueous liquid is treated to provide increasingly hot liquid that is non-scaling at increasingly high temperatures and is circulated and heated at rates that are correlated to maintain a substantially constant temperature along the flow path 18. The correlation of the heating and circulating rates is preferably accomplished by measuring the difference between the temperature of fluid flowing through the wells 13 and 14 and adjusting the heating rate as required to maintain a difference that correlates with a temperature gradient that is significantly less than 1 F. per foot while maintaining a flow rate that is significantly greater than one-tenth barrel per minute.
The controlled heating and circulating of the aqueous liquid is continued until the temperature of the circulating liquid has attained a temperature at which the sulfur in the deposit melts and becomes a mobile liquid. At this time, the circulating fluid is converted from a liquid to a steam, which may be a low quality steam, i.e., steam mixed with liquid, a dry steam, or a super-heated steam.
In a preferred procedure, the heating and circulating is accomplished by softening and heating sea water by flowing it through ion exchangers or other water softening means and a once-through water-heating device. Using such procedures, the circulating heated fluid is relatively slowly converted from liquid to steam by gradually in creasing the fluid residence time within the heating unit without changing the pressure or temperature of the circulating fluid. In general, the rate at which the circulating fluid is converted from liquid to steam is preferably controlled by measuring the behavior with time of the temperature of the fluid that enters a production well, such as well 14, and maintaining a conversion rate that maintains a substantially constant temperature.
In a particularly suitable procedure for operating the present invention, the supply of the steam which is circulated through the path 18 is, at least in part, switched from a surface-located water-heating device to a means for flashing steam from the hot pressurized water of a geopressured aquifer, such as aquifer 16. In the illustrated arrangement, a valve means 17 is operated to expand the water from the aquifer to steam having a pressure and temperature equaling that of the steam being circulated through the path 18. The volume of the steam derived from the aquifer is increased as that from a surface-located water heater is decreased until most or all of the circulating steam is derived from the aquifer. In addition to materially reducing the cost of generating the steam to be circulated into the sulfur deposit, as is indicated in U.S. Patent 3,258,069 and copending patent application Ser. No. 530,222, filed Feb. 25, 1966, the equipment and techniques for obtaining steam from such hot geopressured aquifers, provide means for recovering byproduct hydrocarbons and/ or minerals from the water contained in the aquifer.
We claim as our invention:
1. A sulfur mining process which comprises:
(a) opening at least two wells into the lower portion of a sulfur deposit;
(1)) establishing preferential fluid communication between the wells along a path extending through the lower portion of the sulfur deposit the fluid having a temperature below the melting point of sulfur and a density at least equal to that of water, the flow path of said fluid from one well to another and through the sulfur deposit being essentially horizontal;
(c) circulating an aqueous liquid along the path beween the wells while heating, softening, and flowing the liquid at rates adjusted to maintain a substantially constant temperature along said path;
((1) heating the circulating liquid to a temperature between about 250 and 350 F. at which the sulfur in the deposit melts and becomes a mobile liquid and then converting the circulating fluid from a liquid to a steam at between 250-350 F.; and,
(e) recovering sulfur by separating it from fluid that flows into at least one production well.
2. The process of claim 1, wherein (a) aqueous liquid is circulated along the path between the wells at a rate exceeding one-tenth barrel per minute; and,
(b) the circulating liquid is heated at a rate adjusted to maintain a temperature gradient of less than 1 F. per foot along the path between the wells.
3. The process of claim 1, wherein (a) aqueous liquid is circulated along the path between the wells while heating the liquid by softening sea water to the increasing extents required to provide briny water that is non-scaling at the increasingly higher temperatures to which it is being heated; and,
(b) the circulating fluid is converted from a liquid to a steam by converting the circulating hot briny water to a low quality steam in which the liquid phase is a briny water that is non-scaling at the temperature of the steam.
4. The process of claim 1, wherein (a) at least one well in the vicinity of the sulfur deposit is completed into a geopressured aquifer having a pressure and temperature that exceeds the pressure and temperature at which steam is to be circulated through the sulfur deposit and is equipped for flowing liquid from the aquifer through means for expanding it into steam having the pressure and temperature at which steam is to be circulated through the sulfur deposit;
(b) the circulating aqueous liquid is initially converted from a liquid to a steam that is generated in a surface-located water-heating means; and,
(c) subsequently, at least a portion of the steam being circulated from the surface-located Water-heating means through the sulfur deposit is supplanted by steam which is obtained by expanding water from the geopressured aquifer.
References Cited UNITED STATES PATENTS 988,995 4/1911 Frasch 299-4 2,808,248 10/1957 Prokop et al 299-4 2,947,690 8/1960 AxelrOd 299-6 X 2,991,987 7/ 1961 Heinze 299-4 X ERNEST R. PURSER, Primary Examiner.
U.S. Cl. X.R.