Method for Determining Borehole or Cavity Configuration Through Inert Gas Interface

1. Field of the Invention

This invention relates to the measurement of boreholes and underground caverns. In particular, this invention relates to the configuration of a borehole at certain depth intervals with the use of an inert gas, such as nitrogen interfaced by determining the change in the weight of the gas from its source.

2. General Background

In the oil and gas industry, and in other related industries where there are storage caverns and the like within the earth for storing minerals such as oil, natural gas, sulphur, etc., these caverns, often being at a great depth beneath the surface of the earth, are reached through the use of boring a borehole from the surface of the earth down into the cavern. The borehole, of course, would accommodate the flow of minerals that are to be stored in the storage cavern both downward, and the movement of the minerals up through the borehole as the minerals are utilized. After a certain depth, these boreholes are simply holes drilled within the earth and have no pipe or casing to support the walls which may serve to prevent erosion or the like of the walls of the borehole. That being the case, in the preparation of the cavern by inserting salt water, or in the insertion of or the retrieval of the liquid minerals that are flowing through the borehole, the walls of the borehole become eroded, and the borehole itself may be in such a state that it is no longer effective in being used as a conduit for the passage of minerals and the like into the cavern.

Therefore, it is essential in the storage of such minerals and the preparation of the cavern, that the boreholes are carefully monitored in order to determine whether or not the borehole is in the proper shape that it is not so eroded that it is ineffective in its use. Likewise, often the configuration of the cavern itself is measured in order to determine the extent of erosion of the cavern.

One known process for measuring the configuration of the borehole is to use an inert gas such as nitrogen gas and insert it down the hole. The pressure of the gas is measured as it leaves its source, and a measurement is attempted in order to determine how much gas is being used to fill a certain void within the borehole. What is utilized in the present state of the art is a measuring device which is marketed under the trademark of a "Barton Guage" which records the number of inches of nitrogen being pumped out of the tank. This particular method falls very short of being in the least bit accurate, and is totally ineffective. At present, both governmental and industry requirements are such that the amount of inert gas being used to measure the configuration of the borehole must be within five pounds of the actual amount being pumped down the hole, and under the present method, this determination is ineffective.

There have been several patents which speak to the measurement of pressure, etc. either down the borehole or methods of determining the size of an orifice, the most pertinent being as follows:

U.S. Pat. No. 2,374,154 issued to C. B. Moore entitled "Comparator Gauge" teaches the use of a type of pneumatic guage for recording demensions of an internal bore at successive locations down the borehole. Essentially, the apparatus includes a transmitter head with a pressure transmitter within on the end of a flexible tube which is able to extend the length of the bore to be measured. It further provides an air compressor which supplies pressurized fluid to a receiver through the supply pipe to pressure regulators. The fluid supplied to the transmitter head is then delivered through the bore to the fluid pressure chamber. The apparatus then provides a readout of the pressurization within the bore which is then transmitted onto a chart as the transmitter is moved down periodically the borehole. This apparatus in no way measures the configuration of the borehole due to the change in the weight of the measuring medium such as in this case, nitrogen.

U.S. Pat. No. 2,513,374 issued to C. Stead, et al entitled "Measuring Apparatus for Gauge Determination of Dimensions of Bodies with Flow of Fluid Under Pressure From an Orifice" teaches the use of a measuring apparatus which has the capability of gauging dimensions of bodies by comparison with those of a master or standard, and determining the deviation from the "standard." The apparatus uses a Venturi means for providing differential fluid pressure for efficient operation of a gauge meter such as air and to permit bi-manual manipulation adjustment of a valve to 0 for comparatively measuring the dimensions of the body. In the claims of this particular patent, there is claimed a Venturi means as part of the combination for responding to the differential pressures and verifying the dimensions of the orifice being engaged.

U.S. Pat. No. 1,919,546 issued to H. W. Fletcher entitled "Method and Apparatus for Testing Internal Diameter of Tubes" teaches the use of a device for testing the uniformity of the internal diameter of tubes so that inequalities within the internal walls of the tubes may be found. The invention is carried out by noting the amount of fluid that leaks past a cylinder of uniform diameter that moves within the tube. This is quite unlike the invention which relys on the interfacting of the layer of nitrogen with the atmosphere as it moves down the hole and conforms itself to the irregularities within the borehole. Please note also in the claims that there is claimed a gauge piston form to fit the tube loosely, and the other mechanisms which relate to this type of measurement.

U.S. Pat. No. 2,669,864 issued to O. C. Brewster entitled "Pneumatic Bore Gauge" is basically an improvement patent upon pneumatic bore gauges of that time by having the ability to use a bore head to obtain the results of a two-range diameter of the hole. As with the other patent, what is required in this patent is an apparatus having a head which goes down the bore hole for determining the shape of the hole. And there appears to be no language in the patent which does teach the use of this particular apparatus down an oil well bore and is simply a patent on an improved bore head.

U.S. Pat. No. 4,000,655 issued to Jones entitled "Measuring Devices for Bores and Ducts" teaches the use of a means for measuring the irregularities on the inner surface of a pipeline by having a fluid filled envelope whereby the surface of the envelope would fill the irregularities of the hole. There would be a means for sensing the pressure variations within the envelope.

U.S. Pat. No. 3,456,504 issued to C. C. Bombardieri entitled "Samping Method" teaches the use of a method for analyzing a subsurface formation by introducing two types of fluid at a selected ratio and analyzing the fluid following their injections into the formation.

U.S. Pat. No. 3,502,169 issued to J. E. Chapman, III entitled "Sonic Borehole Televiewer Apparatus" teaches the use of an electrical instrument for situating within a borehole and the apparatus responding to changes in the emissions within the hole and recording a record of the surface of the borehole wall.

U.S. Pat. No. 4,155,248 issued to Wagner, et al entitled "Method and Apparatus for Determining the Pressure Drop and Circumference of Filter Rods" teaches the use of a method for determining the circumference of and the pressure drop of filter rods for cigarette filters or the like.

U.S. Pat. No. 3,841,152 issued to Guest entitled "Drilling Conditions Monitor" teaches the use of a system which produces a digital readout for recording the pressure of the fluid circulating in the well bore and in doing so to detect a "kick" shortly after it occurs and take corrective action in order to prevent a blowout.

U.S. Pat. No. 3,712,129 issued to Rhoades entitled "Simplified Wellbore Pressure Testing Apparatus" for determining the bottom hole pressure in an oil well by use of a combination of instruments and recording the change in the pressure.

U.S. Pat. No. 4,250,947 issued to Heilhecker, et al entitled "Apparatus and Method for Detecting Abnormal Drilling Conditions" is done by monitoring mud volume of the mud system or the rate of change in the mud volume for detecting the abnormal conditions when the rate of makeup mud addition differs from the rate of solids removed from down the hole.

The preferred embodiment of the method and apparatus of the present invention solves the problems encountered in the present state of the art in a simple and straightforward manner. What is provided in the present invention is a method for determining the erosion of a borehole or cavity by providing a source of liquid inert gas, preferably nitrogen, placing the inert gas in a storage tank, and suspending the storage tank so that one may determine the actual weight of the nitrogen as it is withdrawn from the tank in liquid state. There is further provided hydraulic means for lifting or lowering the storage tanks suspended from a weight cell as a tank is placed into use or non-use. Further, the liquid nitrogen is pumped from the storage tank with the use of a reciprocating pump, and converted into gaseous nitrogen (in the state of 100.degree. F.,) and is injected into a borehole or the like. The nitrogen gas is then allowed to flow under a certain pressure down the borehole, and due to the properties of nitrogen gas, the nitrogen interfaces at a horizontal plane as it moves down the borehole. There is further provided a wire line means for measuring the movement of the nitrogen down the borehole, and the wire line enables to determine the position of the interface at predetermined intervals, preferably one foot intervals down the hole. There is further provided a digital readout means, which electrically records the change in weight of the nitrogen tank as the nitrogen is pumped down the hole. Upon the nitrogen reaching one-foot intervals, the weight of the nitrogen is recorded from the digital readout, and is manually plotted as the nitrogen moves down the borehole. Therefore, knowing the amount of weight of nitrogen utilized in a particular interval, i.e. one foot, and the temperature of the nitrogen, and the pressure of the nitrogen in the hole, one can determine the area that that nitrogen is occupying in the hole. That being the case, when erosion has occurred within a particular one-foot area, a greater amount of nitrogen would be utilized, and therefore, one has a reading onto the extent of the erosion within the hole at that particular interval. There may be further provided computer means for receiving the information from the digital readout and the temperature weight and pressure of the nitrogen, and providing a graphic readout of the shape of the borehole as the nitrogen moves down the borehole and interfaces therein.

Therefore, it is an object of the present invention to provide a method for determining the errosion within a cavern or borehole.

It is a further object of the present invention to provide a method for accurately determining the shape of a borehole through the calculating of predetermined qualities of an inert gas as it moves between predetermined intervals down the borehole.

It is still a further object of the present invention to provide a system whereby a change in weight of an inert gas stored in a tank enables one to calculate the erosion that has occurred within an underground cavity.

It is yet a further object of the present invention to provide an apparatus for storing liquid inert gas, weighing the inert gas, moving the inert gas from storage to the cavern to be measured, and providing a readout means for determining the change in the weight of the inert gas as it moves down the borehole.

It is still a further object of the present invention to provide a method for determining the shape of a borehole by providing an inert gas under a given pressure, temperature, and flow rate, and determining the weight of the inert gas at certain intervals down the borehole, and further calculating and graphing the shape of the borehole from these factors.

In order to accomplish the above stated objects of the present invention, it is a feature of the present invention to provide an inert gas such as nitrogen for pumping down a borehole in order to measure the shape of the borehole.

It is an additional feature of the present invention to provide a means for storing the nitrogen in the liquid form and providing an apparatus for accurately weighing the nitrogen to provide a given weight of the nitrogen prior to extraction from the storage tank.

It is yet a further feature of the present invention to provide a digital readout means for monitoring the change in the weight of nitrogen as it is pumped down the borehole.

It is still a further feature of the present invention to provide a pumping means to pump the liquid nitrogen from the storage tank into the borehole as gaseous nitrogen.

It is still a further feature of the present invention to provide a wire line means in order to determine the depth of the movement of the interface of the nitrogen down the borehole at predetermined intervals.

For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numbers and, wherein:

FIG. 1 is an overall view of the preferred embodiment of the apparatus utilized in the preferred embodiment of the method of the present invention.

FIG. 1 best illustrates the preferred embodiment of the apparatus utilized in the method of the present invention. There is illustrated in FIG. 1 borehole and/or cavern 10 which is the subject matter to be measured under the present method. As is illustrated, borehole 10 would have its starting point at ground level 12 and would in most cases for a reasonable distance down as indicated by numeral 13 be a straight sided borehole, having remained intact for a certain distance down the hole. However, as further illustrated, there is a possibility, and often it is the case, that the straight walls as indicated by numeral 13, the borehole would become eroded due to the passage of minerals, salt water or the like up and down and up the borehole, with erosion areas 14 and 15 being illustrated in order to show the extent of erosion that may occur down the borehole. As was stated earlier, it is imperative that in the safe use of these boreholes in order to fill the storage cavern 16, that the extent of the erosion 14 and 15 be determined accurately. The result of this determination may result in the drilling of an additional borehole due to the fact that the present borehole is non-usable.

The preferred embodiment of the apparatus and the method utilized in the present invention is illustrated in order to accomplish this result of accurracy in measurement of erosion. There is provided storage tank 20 which is a special tank, known in the art, which can withstand cryogenic temperatures and pressures for the storage of various types of fluid. In this particular case, tank 20 would be filled with liquid nitrogen gas in the preferred embodiment, and storage tank 20 would be placed within framework 22 so that tank 20 is securely mounted for further use in the process.

After being filled, the tank 20 and framework 22 is set within weighing frame 24 which comprises a pair of vertically disposed stabilizing beams 26 and 28 placed on either end of the tank, and held into position with horizontally disposed beam 30 which is secured to the upper most ends of beams 28 and 26, thus providing a hanging frame for tank 20 and framework 22. The entire frame and tank containing nitrogen gas is then weighed and the beginning weight is thus determined before the measurement begins. As is seen in the drawing, the upper half of beams 26 and 28 are slideably movable so that the framework is able to adjust up and downward as will be further illustrated.

There is further provided extender wire 32 and 34 which are connected at four corners of the framework 22, and are connected at a single point midway along beam 30, to provide a means for suspending tank 20 and frame 22 from horizontal beam 30 during the process.

In order to provide upward and downward movement of suspended tank and frame 22, from horizontal beam 30, there is further provided a pair of hydraulic cylinder 36 and 38 which, are typical hydraulic cylinders, with the hydraulic arms 39 and 40 having upward and downward movement from the pressure of the hydraulic fluid within cylinders 36 and 38. The upper ends of the hydraulic arms 39 and 40 are integrally attached to the end portions of horizontal beam 30, so that the upward and downward movements of arms 39 and 40 imparts upward and downward movement to horizontal beam 30 as indicated by arrows 41. Hydraulic cylinders 36 and 38 are manually controlled by hydraulic power unit 42 which provides hydraulic fluid through lines 43 and 44 to hydraulic cylinder and provide upward and downward movement as the case may be.

At that point of connection between extended lines 32 and 34 to horizontal beam 30, there is provided a weight cell 50 which, when the tank 20 and frame 22 is suspended from beam 30, the weight cell indicates the total weight of the unit being suspended from the framework. This total weight is received by electrical digital readout means 52 via electrical line 53, and readout means 52 digitally reads out the total weight of the suspended unit, and will read out any change in the weight as the weight is decreased or increased during the process.

In the actual process, once the tank 20 and framework 22 has been suspended from beam 30, and a digital readout of the total weight from readout means 52 is determined, the liquid nitrogen, which is pressurized within tank 20 is released through line 54, and through the use of reciprocating pump 56, the liquid nitrogen is converted into gaseous nitrogen, preferably under 80.degree. to 100.degree. F., and at a predetermined pressure, the gaseous nitrogen is then transported into borehole 10, via line 54.

The gaseous nitrogen at that temperature, once entering borehole 10 will move down the borehole 10 with a very concise horizontal interface at point 58, so that as more nitrogen gas is pumped, the interface 58 continues to move down borehole 10. In order to accurately monitor the position of the interface as it moves down borehole 10, there is provided wire line 60 which is a conventional wire line and has a means 61 for recording the position of interface 58 at given intervals within borehole 10. In the preferred embodiment of the present invention, the position of interface 58 down borehole 10 is measured (at one foot or more intervals), and these intervals would be determined by the use of wire line means 61. An operator, who is monitoring the movement of wire line 60 down the borehole, informs a statistician the position of wire line 60 at each interval, at which point the statistician records the digital readout of the weight of the nitrogen unit, which would be a reduced weight as more nitrogen gas is being pumped into the borehole.

Of course, when the interface reaches an erosion point such as point 62, since there is a greater width to borehole 10, at this point, a greater loss weight of nitrogen would be recorded at this interval than would have been at earlier intervals when borehole 10 was in the normal configuration. That being the case, the statistician would record this greater weight loss as he would continually down the movement of interface 58 down borehole 10, until nitrogen interface 58 has reached the point that the test is completed.

Following the recording of the various weight changes down the borehole during the test, given the known pressure of the nitrogen gas, the temperature of the gas, and the weight change in the gas, one is able to calculate the area that that gas is occupying, and thus able to plot the configuration of the walls of the borehole.

There may be further provided computer means wherein the information of the gas pressure, temperature, and weight is entered into the computer, and the computer would calculate the area involved, and graphically represent the shape of the borehole on a screen or the like as provided by the computer.

(Of course, if some turbine-type differential flow meter were to be perfected which would have the capacity to measure the flow of an inert gas, such as nitrogen, down a borehole, and would be able to maintain itself within the required degree of accuracy as is required in the industry, one would be able to accurately measure the flow of the gas, without having to depend on the actual total weight of the liquid nitrogen that is loss from the tank in order to plot the configuration of the borehole and/or the crown of the cavern 16 during the measuring process.)

As ancillary use, following the completion of the test, often times the nitrogen gas is maintained within the borehole on the presence, and from the change in the pressure of nitrogen gas over an extended period of time, one may determine the amount of leakage that is occurring within the borehole, and thus because of leaks which have developed down the borehole, the bore hole, other than the erosion factor, may be unusable if in fact there is great deal of leakage occurring from the walls or the outer most top portion of the borehole.

There is provided for further edification a chart which represents the use of the nitrogen down the borehole, and the results of those tests as the nitrogen moves down the borehole.

As illustrated in the above graph, as examples of the method utilized in the present invention, if the starting weight of the liquid nitrogen is shown as 10,036 pounds in column 1, a total of 44 pounds would occupy a twenty foot interval in the borehole, injected at 607.2 S.C.F. at a depth of 1780 feet. Moving down the column, at a depth of 1900 feet the amount of nitrogen necessary to occupy the same twenty foot interval is measured at 84 pounds injected at 1159.2 S.C.F. The results of this differential in the two examples illustrate that in the latter case, the borehole or cavity has eroded to an area whereby substantially twice the amount of gaseous nitrogen is required to occupy that same twenty foot interval. As this measurement is taken at consecutive predetermined intervals to a predetermined depth, one then is able to plot, either manually or with the aid of a computer the visual configuration of the borehole or cavity throughout the entire depth.

Because many varying and different embodiments may be made within the scope of the inventive concept taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.