US 3357490 A
Description (OCR text may contain errors)
a G. HOLMES 3,357,490 R AUTOMATICALLY INTRODUCING COOLANT Dec. 12, 159E? APPARATUS FO INTO AND SHUTTIIJG DOWN WELLS Filed Sept. 30, 1965 BILLY G. HOLMES INVENTOR BY Z ATTORNEY.
United States Patent APPARATUS FOR AUTOMATICALLY INTRODUC- ING CUQLANT INTO AND SHUTTING DOWN WELLS Billy G. Holmes, Lancaster, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Sept. 30, 1965, Ser. No. 491,541 5 Claims. (Cl. 166-53) ABSTRACT OF THE DISCLOSURE This specification discloses a system for automatically introducing a coolant into a well and shutting in the well if the well temperature is not reduced as desired. The system includes a downhole temperature sensing means and associated control circuitry which functions to inject a coolant into the well in response to a high temperature condition. If the temperature is not reduced to a desired lower level, the system automatically closes a valve, shutting in the well.
This invention relates to systems for prolonging the useful life of production wells utilized in thermal recovery processes and more particularly to systems for automatically introducing a coolant into such wells in order to maintain the temperature therein below a preselected level.
Thermal recovery techniques, in which hydrocarbons are produced from carbonaceous strata such as oil sands, tar sands, oil shales, and the like by the application of heat thereto, are becoming increasingly prevalent in the oil industry. Perhaps the most widely used thermal re covery technique involves in situ combustion or fire flooding. In a typical fire flood, a combustion zone is established in a carbonaceous stratum and propagated within the stratum by the injection of air or other combustion supporting gas through a suitable injection well. As the combustion supporting gas is injected, products of combustion and other heated fluids in the stratum are forced away from the point of injection toward production zones where they are recovered from the stratum and withdrawn to the surface through suitable production wells.
One difliculty experienced in fire flooding has been the failure of downhole well equipment due to the high temperatures which are sometimes reached in the production Wells. These high temperatures, which are due to burnthrough of the flame front in the production Well and/ or the flow of hot fluids from the stratum, may cause deterioration or failure of the well equipment such as the liner, casing, or tubing string, and may in some instances lead to fire or explosion within the well.
In order to overcome the deleterious effects of such high temperature conditions, it has been proposed to introduce a coolant such as water into the production well in order to maintain the temperature therein below a preselected level. Since obvious disadvantages are attendant to the indiscriminate injection of coolant into the well, steps normally are taken to introduce selectively the coolant only in response to characteristics indicative of undesirably high bottomhole temperatures. A common expedient, for example, is to monitor the temperature of the production eflluent at the wellhead and inject water into the well when a significant temperature rise is noted. Techniques such as this are not always as effective as might be desired, particularly in those cases where burnthrough occurs in only a small section, because of the relatively high temperature gradients caused by poor heat transfer conditions which usually exist within in situ combustion production wells. The poor heat transfer conditions within such wells are due to the predominantly gaseous nature of the production fluids. For example, temperature measurements carried out in a typical in situ combustion production well revealed a normal wellhead temperature of about 275 F. while the bottomhole temperature at 1200 feet was about 800 F. In order to offset such high temperature gradients it has been proposed to position a temperature sensing element in the lower portion of the production tubing string. However, in this position the sensing element is exposed to the relatively high abrasive action of the fluids within the tubing string and is subject to early failure.
In accordance with the instant invention, there is provided a system for automatically introducing a coolant such as water into a production well in response to even a highly localized burn-through within the well and for shutting down the well automatically in the event the introduction of the coolant fails. to bring the well tempera ture below a specified level.
In carrying out the invention, a temperature sensing means is disposed in the well in the vicinity of the producing stratum. The temperature sensing means produces .a first condition such as an electric signal in response to a specified temperature in the well and thereafter produces a second condition such as the absence of the electric signal in response to a temperature less than the aforementioned specified temperature. Flow control means are provided for introducing a coolant into a suitable passage within the well, such as the annulus between the well casing and tubing, in response to the first condition and for restricting the introduction of the coolant into the well passage in response to the second condition. Additional flow control means are provided for the tubing string or other production passage for shutting in the well in the event the temperature sensing means fails to produce the aforementioned second condition within a specified time period. Thus, in the event the introduction of coolant fails to bring the well to a safe temperature level, the well will be shut in thus preventing extensive damage to the downhole production equipment therein.
In a preferred embodiment of the invention, the temperature sensing means is positioned at a location exteriorly of the tubing string and in'the flow path Within the well of substantially all of the products recovered from the stratum. This will prevent excessive wear of the sensing means and yet will insure that the system will detect burn-through of even a small reservoir zone as soon as it occurs. The coolant thus will be added to the hot area without undue delay.
For a better understanding of the invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which:
FIGURE 1 is an illustration partly in section of a production well installation embodying the present invention; and
FIGURE 2 is a schematic illustration of one form of control circuit for the installation shown in FIGURE 1.
With reference to FIGURE 1, there is shown a Wellbore 10 extending from the surface 12 of the earth through the overburden 14 and into a carbonaceous stratum 16. Well 10 is provided with a casing 18 which is closed at its upper end by a suitable closure 19 and which is cemented to the surrounding formations as indicatedby reference numeral 21. The casing 18 and surrounding cement sheath 21 are provided with perforations 23 which define an open production interval 24 within the stratum. Products from the stratum are recovered from the well through a production passage defined by a tubing string 25 which as shown extends from a point adjacent the bottom of the stratum through the closure means 19 of the casing. Tubing 25 is closed at its upper end by a suitable closure means 27 and is provided with an outlet line 28 through which the recovered products are delivered to a suitable treating or storage facility (not shown).
It will be recognized that the well completion illustrated in FIGURE 1 is exemplary only and that the invention may be utilized in a well completed by any suitable technique. For example, the well may be completed with an uncemented slotted liner or even openhole with the casing set to the top of the production interval. These and other completion procedures are well known to those skilled in the art and will not be discussed further.
Disposed in well and located in accordance with the instant invention is a temperature sensing element 30. Element 30 is supported on a cable 32 and sends signals via suitable communications channel such as cable 32 to a suitable controller 34 in response to certain temperature conditions within the well. Controller 34 functions to regulate the operation of a motor valve 36 in line 28 and a pump 38 fluidly interconnected with the annular passage defined by the tubing and casing by means of a coolant input line 40.
The operation of the system is as follows. Products of a thermal recovery process being carried out in stratum 16 flow into the well through perforations 23 and into tubing 25 through the open lower end 25a thereof and thence upwardly to the surface where they pass into line 28. In the event element 30 senses a specified temperature, e.g., 450 F., it functions to produce a first condition such as an electric signal which is transferred via a conductor in cable 32 to controller 34. Controller 34 then acts in response to this condition to activate pump 38 which pumps coolant such as water from a source (not shown) through a check valve 42 in line 40 into the well. In most cases the coolant will be injected directly into the annulus of the well at the surface as shown. However, it will be recognized that the coolant may be introduced through a line such as tubing string positioned in the well parallel to the production tubing. This usually will not be preferred because of the expense involved in providing the additional passage within the well. Pump 38 continues operating until element 30 senses a temperature less than the specified temperature at which time it produces a second condition, e.g., the absence of the aforementioned electric signal. Controller 34 then acts in response to this second condition to deactivate pump 38, thus terminating the injection of coolant into the well.
The instant invention also includes a fail-safe system in the event the injection of coolant fails to bring the bottom-hole temperature down to the desired level. If the coolant fails to reduce the well temperature satisfactorily within a redetermined time, e.g., one hour, controller 34 functions to close normally open valve 36, thus preventing withdrawal of products through tubing 25 and shutting in the well. Simultaneously or shortly after the closing of valve 36, controller 34 also acts to terminate the action of pump 33, thus halting the flow of coolant into the well.
Of particular importance in accordance with a preferred embodiment of the invention is the location of the temperature sensing element. As noted above, the prodnets of ran in situ combustion drive are predominantly gaseous in nature and heat transfer within the well is relatively poor. In addition, heat transfer within the well primarily is by convection with only a relatively small amount by conduction and radiation. In the preferred embodiment of the invention, therefore, the temperature sensing element is positioned in close proximity to the stratum and at a location in the flow path Within the well of substantially all of the products recovered through the open production interval of the well. In the case where the tubing inlet is at or, as shown in the drawing, below the lower level of the production interval, this is accomplished by positioning element 30 within a zone extending from a location in the well adjacent the lower level of the production interval to a location adjacent the inlet of the tubing string. Preferably, the heat sensing element is located at the lower level of the production interval in order to offsetthe effect of the high temperature gradient within the well. With element 30 in this position, all of the fluid produced from the stratum flows over the sensing element as it travels to the inlet 25a of production tubing 25. As can be seen from the drawing, if element 30 were placed a substantial distance above this point, e.g., at the location indicated by broken line 31, products from the stratum below this location would not flow over the sensing element. Little if any heat transfer from this zone to the sensing element would take place by convection and the element would be relatively unresponsive to a hot zone in the lower portion of the production interval.
In most cases, it will be preferred to locate the inlet of the tubing 25 at or below a location adjacent the lower level of the production interval. This will permit the withdrawal of fluids, liquid as well as gaseous, from the well without the necessity of maintaining a fluid column over part or all of the face of the stratum. However, under some circumstances, it may be desired to locate the inlet of the production passage at a point intermediate the upper and lower levels of the production interval or even at a point at or above the upper level of the production interval.
Regardless of the location of the inlet of the production passage, element 30 should be positioned at a location such that substantially all of the fluid produced from the stratum will flow past the location of the temperature sensing element. For example, if the inlet 25a of tubing 25 is intermediate the upper and lower levels of production interval 24, temperature sensing element 30 should be positioned at a location adjacent the inlet.
In those instances where the production tubing is landed at a level in the well at or above the upper level of the production interval, the temperature sensing element is positioned within a zone extending from a location in the well adjacent the upper level of the interval to a location adjacent the inlet of the tubing. Preferably, element 30 will be positioned at a location adjacent the upper level of the production interval 24 because of the relatively high temperature gradient within the well. However, in the event difficulty is experienced in positioning element 30 at this location or for other suitable reasons, element 30 may be positioned at any point above the upper level of the production interval, but not higher than a location adjacent the inlet of the production tubing. In general, the temperature sensing element should not be placed more than about 30 feet from the open production interval.
Regardless of its elevation within the well, the temperature sensing element preferably is positioned at a location exteriorly of the tubing string as shown. From the standpoint of convenience of handling such as in insertion and retrieval, it would seem desirable to place the sensing element within the tubing string. However, it has been found that the production fluids from in situ combustion drives often are highly charged with abrasive particles such as sand and coke and that a sensing element placed within the production string is subject to excessive wear because of the high velocity of the particle-charged fluid stream within the tubing passage. With the sensing element placed exteriorly of the production string where the cross-sectional flow area, such as the annulus, is greater and the fluid velocity lower than in the tubing, abrasive wear of the sensing element is reduced.
With reference to FIGURE 2,-there is shown one form of control circuit for the instant invention. Element 30 as shown comprises a normally open switch 30a which is disposed in a circuit leading from a suitable power source 46 to ground. Switch 30a may be of a conventional bimetallic type which. is closed at or above a specified temperature, e.g., 450 F., and open below this temperature. When switch 30a senses a temperature at or above the specified level, it closes, thus completing a circuit through a relay 48. When relay 48 is energized, it acts to close its contacts 48a and 4811. With contact 48a closed, an alarm circuit is energized and an alarm signal indicative of a hot spot within the well is produced. The alarm circuit may comprise simply a visual alarm beacon 49 as shown or other suitable means such as, for example, telemetering means for sending an alarm signal to a central headquarters. Upon closure of contact 48b, a pump motor 38a is energized through a circuit traced from power source 46, contact 4812, and a normally closed contact 536. Pump 38 then will function to introduce coolant into the annulus between the casing and production string. Coolant will continue to be introduced into the well until the temperature thereof is lowered to a suificient level to permit switch 30a to open, thus breaking the circuit through relay 48. Contact 48b then is opened and the pump motor is de-energized. This cycle of operation will be repeated in the event the well again heats up to a suflicient level to close switch 30a.
As noted above, the instant invention also includes fail-safe means for shutting down the well in the event the injection of coolant fails to bring the bottomhole temperature down to the desired level. The fail-safe operation of the system is accomplished by means of a timing device such as that designated in FIGURE 2 by the reference numeral 52. Timer 52 comprises a cam 52a driven by a timer motor 52b, a normally open cam switch 520, and a relay 53 having associated contacts 53a, 53b, and 530. Upon closure of contact 48a, timer motor 52b is energized and rotates cam 52a in a clock wise direction. If switch 30a is not opened within the specified time period, e.g., one hour, allowed for the introduction of coolant to bring the well to the desired temperature level, cam 52a will rotate to a position such that it closes switch 520. Upon closure of switch 520, an energizing circuit is completed through a valve actuating solenoid 36a. With valve solenoid 36a energized, valve 36 is closed, thus shutting in the well. The energizing circuit for valve solenoid 36a also includes a suitable well shut-in alarm such as a beacon 54.
When switch 520 is closed, the relay 53 is energized and acts to open contacts 53a and 530 thus de-energizing the timer motor 52b and the pump motor 38a, respectively, and to close contact 53b which is shunted across cam switch 52c. The timer 52 is of a conventional power-off reset type which includes a reset clutch (not shown) which acts to reset cam 52a to the starting position shown upon de-energization of the timer motor 52b. Switch 52c will of course be opened when the timer is reset, but the circuit to signal means 54 and valve solenoid 36:! will remain energized due to the closed shunt contact 53b. The valve 36 will remain in a closed position shutting in the well until a reset button 56 is pushed, thus opening the circuit to relay 53.
As noted above, timer 52 is of the power-off reset type which is reset to the starting or zero position each time the energizing circuit of the timer is opened. Thus, when the introduction of coolant into the well brings the temperature therein to a sufliciently low 'level to enable switch 30a to open within the time limit set into the timer, relay 48 will be deenergized thus opening contact 48a and resetting timer 52 before it times out to close switch 520.
It will be recognized that rapid opening and closing of switch 30a may result in on-ofl cycling of pump 38 at undesirably close intervals. In most instances, a satisfactorily long time interval between the opening and closing of switch 30a will result from the time required for coolant to travel from the surface to the depth of the stratum and to bring the well temperature down to the desired level. However, in those instances where the 6. system is found to produce undesirably rapid cycling of the pump, suitable means may be included in the circuit of FIGURE 2 for maintaining pump motor 38:: energized for a specified time period, notwithstanding the opening of switch 30a within this time period. Such means may take the form of a timer (not shown) which functions to hold the energizing circuit to motor 38a closed for a specified period after closure of switch 30a. If, at the end of this period, switch 30a is open, pump motor 38a will be de-energized and the introduction of coolant into the well will be terminated. Also it may be desirable in some instances to continue the introduction of coolant into the well for a time after the Well is shut in. This may be accomplished by providing suitable timing means (not shown) in the circuit of FIGURE 2 which functions to hold the energizing circuit to motor 38a closed for a specified period after the closure of valve 36.
In many instances, a single temperature sensing element will be sufiicient to detect accurately and timely the occurrence of a hot spot within the well. However, in some instances, for example, Where production is from a relatively thick stratum, it may be desired to utilize a plurality of vertically spaced temperature sensing elements. This may be accomplished utilizing the circuitry of FIGURE 2 simply by connecting such additional temperature sensing elements as are required in parallel with switch 30a and in series with relay 48.
The temperature sensing elements may be spaced at such intervals as conditions and experience dictate. Usually, however, it will be preferred to locate them at intervals of not more than about 30 feet in view of the relatively high temperature gradient that normally exists within the well.
The temperature sensing element or elements may be mounted on the tubing 25 rather than on a separate line 32 as shown. The separate supporting means is preferred, however, in order to permit withdrawal of the sensing elements for repair, inspection, etc. without pulling the tubing. Line 32 preferably takes the form of a conventional armored electrical cable. In this case, the circuit for the sensing element may be formed by connecting one side of the switch 30a to the insulated conductor or hot line and grounding the other side to the armor.
In the embodiment of the invention illustrated, coolant injection is initiated in response to undesirably high temperature Within the well and terminated when the well temperature is reduced to a satisfactory level. However, the invention may be utilized in a system in which coolant is continuously flowed into the well and automatically increased or decreased as necessary to control the temperature. For example, input line 40 may be connected intermediate casing 18 and check valve 42 with a second line (not shown) through which coolant from a secondary source is continuously circulated into the annulus. In this case the rate of flow of coolant into the well will be increased by activation of pump 38 and thereafter decreased to its formed level when the pump is deactivated within the specified time period provided for in the fail-safe operation of the system. In the event the well is shut-in by closure of valve 36, all coolant flow into the well preferably is terminated similarly as in the illustrated embodiment. In either embodiment, coolant is introduced into the annulus in response to a first condition produced by the temperature sensing means and the introduction of coolant is restricted, i.e., either decreased or terminated, in response to a second condition.
While in the embodiment of the invention illustrated switch 30a closes to indicate a high temperature condition, it will be recognized that a normally closed switch which breaks in response to a high temperature may be used. However, a normally open switch is preferred since it provides a measure of fail-safe protection for the system. In this regard, temperatures in the well sufficiently high to damage the switch would also normally cause a short in the switch circuit, such as for example, by melting the insulation between the conductor and armor on the cable 32. This of course would result in the system responding in the same manner. as if switch 30a were closed as in normal operation.
Heat sensing elements other than the switches disclosed herein also may be used in the instant invention. For example, element 30 could take the form of a thermistor, in which case valve 36 and pump 33 or other suitable flow control devices could be made to operate in response to quantitatively different voltage signals rather than the absence and presence of an electric signal as in the illustrated embodiment. Bimetallic switches are preferred, however, because of their simplicity and reliability.
Having described specific embodiments of the instant invention, it will, be understood that further modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.
What is claimed is:
1. In a well having an open production interval in a carbonaceous stratum and adapted for recovery from said stratum of products of a thermal recovery procedure, the system comprising:
means forming in said well a first passage having an inlet within said well for the withdrawal of said products therefrom,
means forming in said well a second passage for the flow of coolant within said well,
temperature sensing means in said well in the vicinity of said stratum for producing a first condition in response to said means sensing a specified temperature and for producing a second condition in response to said means sensing a temperature less than said specified temperature,
first flow control means fluidly interconnected with said second passage for introducing a coolant into said second passage in response to said firs-t condition and for restricting the introduction of said coolant into said second passage in response to said second condition, and
second flow control means fluidly interconnected with said first passage for preventing withdrawal of said products therefrom in response to said second condition failing to occur within a specified time period after the occurrence of said first condition.
2. The system of claim 1 wherein said first-named flow control means terminates the introduction of said coolant into said second passage in response to said second condi r 8 said tubing string and in the flow path within the well of substantially all of said products recovered through said open production interval for producing a first condition in response to said, means sensing a specified temperature and for producing a second condition in response to said means sensing a temperature less than said specified temperature, first flow control means fluidly interconnected with said second passage for introducing a coolant into said second passage in response to said first condition and for restricting the introduction of said coolant into said second passage in response to said second condition, and
second flow control means fluidly interconnected with said tubing string for preventing withdrawal of said products therefrom in response to said second condition failing to occur within a specified time period after the occurrence of said firstcondition.
4. The system of claim 3 wherein said first-named flow control means terminates the introduction of said coolant into said second passage in response to said second condition failing to occur within said specified time period.
5. In a well having an open production interval in a carbonaceous stratum and adapted for recovery from said stratum of products of a thermal recovery procedure, the system comprising:
means forming in said well a first passage having an inlet within said well for the withdrawal of said products therefrom,
means forming in said well a second passage for the flow of coolant within said well,
an electric circuit connected to a source of electric power and extending into said well, normally open switch means in said circuit and located in said well in the vicinity of said stratum for closing said circuit in response to a specified temperature whereby an electric signal is generated in said circuit,
first flow control means fluidly interconnected with said second passage for introducing a coolant into said second passage in response to said electric signal and for restricting the introduction of said coolant into said second passage in response to the termination of said electric signal, and
second flow control means fluidly interconnected with said first passage for preventing withdrawal of said products therefrom in response to the continuation of said electric signal for a specified time period.
References Cited UNITED STATES PATENTS 1,539,667 5/1925 Halagarda 137-79 2,133,962 10/1938 Shoemaker 13779 X 2,506,936 5/1950 Murray 137-79 X 3,013,609 12/1961 Ten Brink 16639 3,120,267 2/1964 Bayless 16653 3,202,219 8/1965 Parker 166-64 X 3,227,215 1/1966 Marx 166-53 CHARLES E. OCONNELL, Primary Examiner.
IAN A. CALVERT, Assistant Examiner.