US3911741A

US3911741A - Pneumatic fluid weighing device

Info

Publication number: US3911741A
Application number: US469876A
Authority: US
Inventors: Robert W Rochon; Jr Joseph W Sneed
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-01-16
Filing date: 1974-05-14
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14

Abstract

An apparatus for weighing drilling fluid being pumped into a well and for weighing the drilling fluid returning from the well during drilling operations. A pair of pneumatic conduits are connected in parallel relationship with their one ends communicating with a source of air under pressure for bubbling a constant supply of air through the tubes. The other ends of the conduits are open and are spaced from each other a distance of 8.35 inches. When used to weigh the drilling fluid being pumped into the well a float device is connected to the tubes for floating the tubes in vertical position in a drilling fluid suction tank. When used to weigh drilling fluid returning from the well a housing having an outlet opening in the bottom portion thereof surrounds the conduits and is connected on the outside of a shaker box and receives drilling fluid from the shaker box through an opening in the shaker box which communicates with an opening in the housing. A differential pressure recording device is connected between the pneumatic tubes and the air source.

Description

United States Patent [191 Rochon et al.

[ Oct. 14, 1975 PNEUMATIC FLUID WEIGHING DEVICE [76] Inventors: Robert W. Rochon, 4436 Blanco Road, San Antonio, Tex. 78212; Joseph W. Sneed, Jr., 5706 Ben Casey, San Antonio, Tex. 78240 22 Filed: May 14, 1974 211 App]. No.: 469,876

Related US. Application Data [63] Continuation of Ser. No. 324,099, Jan. 16, 1973,

Primary Examiner.lerry W. Myracle Attorney, Agent, or FirmCox, Smith, Smith, Hale & Guenther Incorporated ABSTRACT An apparatus for weighing drilling fluid being pumped into a well and for weighing the drilling fluid returning from the well during drilling operations. A pair of pneumatic conduits are connected in parallel relationship with their one ends communicating with a source of air under pressure for bubbling a constant supply of air through the tubes. The other ends of the conduits are open and are spaced from each other a distance of 8.35 inches. When used to weigh the drilling fluid being pumped into the well a float device is connected to the tubes for floating the tubes in vertical position in a drilling fluid suction tank. When used to weigh drilling fluid returning from the well a housing having an outlet opening in the bottom portion thereof surrounds the conduits and is connected on the outside of a shaker box and receives drilling fluid from the shaker box through an opening in the shaker box which communicates with an opening in the housing. A differential pressure recording device is connected between the pneumatic tubes and the air source.

6 Claims, 4 Drawing Figures U.S. Patent Oct. 14, 1975 Sheet 1 of2 3,911,741

FIG. 2

U.S.P1tent Oct. 4,1975 816612012 3,911,741

FIG.3

FIG. 4

PNEUMATIC FLUID WEIGI-IING DEVICE This application is a continuation of US. Pat. application Ser. No. 324,099 filed on Jan. 16, 1973, expressly abandoned upon filing this application.

BACKGROUND OF THE INVENTION This invention relates to an apparatus for accurately determining the unit weight of drilling fluid being pumped into a well during drilling operations and for determining the weight of the drilling fluid returning from the well during drilling operations.

During the drilling of a well in the quest for hydrocarbons using the rotary method of drilling, it is necessary to pump or circulate a drilling fluid, known in the art as drilling mud downwardly through the drill pipe to which the drill bit is attached and outwardly through the drill bit into the annulus formed by the drill pipe and the wall of the well bore for return upwardly through the annulus to the surface.

A container known as a suction tank contains the drilling fluid for pumping through the drill pipe into the well. The circulating drilling mud exits from the drill bit returning to the surface through the annulus between the drill pipe and the wall of the well bore and out into a shaker box where the cuttings which are drilled up are separated from the returning drilling fluid. The drilling fluid then flows from the shaker box via a settling tank back to the suction tank for return to the well. The drilling mud is essential to a well drilling operation as it serves to carry away the cuttings from the drill bit to facilitate drilling and act as a medium for transporting the cuttings from the drill bit area out of the well bore to be separated from the mud via shaker or settled out in a mud pit at the top of the well prior to recirculation. The primary function of the drilling mud is to act as a stopper in the well by exerting hydrostatic pressure on the bottom of the well according to the specific weight of the drilling mud thereabove to balance or overcome the formation pressure in order to prevent blowouts. The pressure of the formation adjacent the drill bit, or bottom-hole pressure must also be taken into consideration because this pressure must be sufficient to sustain the hydrostatic pressure of the mud in order to prevent loss of circulation, that is the loss of the mud as it escapes into the formation due to the pressure exerted by the mud column being substantially greater than the formation pressure itself. It is therefore essential that the pressures in the well bore, i.e. the formation pressure and the hydrostatic pressure of the drilling mud be maintained near balanced condition. The drilling mud also acts as a sealing means on the well bore by caking on the surface of the bore to seal the bore and prevent the drilling mud from flowing out into porous formation material.

It is necessary that the drilling mud must be of sufficient weight to balance against the force of any upwardly acting hydrostatic pressure such as the pressure of gas, water, or oil which may be exposed in drilling and at the same time the drilling mud should not become so heavy that it enters the formation causing a loss of circulation. As conditions vary in the course of 'drilling, the weight of the drilling mud has to be varied constantly to meet these changing conditions. For instance, if the gas sand is penetrated the gas in the bore space will become a part of the drilling fluid. As the fluids are pumped out of the hole the gas expands, mud flows out of the hole at a faster rate than it enters and the mud weight becomes considerably lighter. Such a condition must be detected immediately as remedial action may be necessary by the addition of weight material to the drilling fluid otherwise the fluid might not contain the forces of the formation pressures reacting upwardly thereagainst with the consequence that a blowout may occur.

The use of excessive ,mud weight to provide a large factor of safety against blowouts was previously used as a standard drilling procedure. Of course, as mentioned previously, such an overbalance may result in a loss of circulation where the formation pressures are incapable of withstanding the over-balanced hydrostatic pressures of the drilling mud. For reasons of economy, a new drilling concept of balanced pressure drilling was adopted and it became essential that continual accurate measurement of the mud weight be maintained at all times during the drilling operation. Balanced drilling grew out of the need for more economy in the drilling operation, since less dense drilling mud allows faster drilling with less wear on the equipment. Since balanced pressure drilling reduced the factor of safety against blowouts which resulted from excess mud weight it becomes imperative that accurate and continuous mud weights into and out of the well be logged since the best evaluation of bottom hole conditions is to continuously determine the absence or to accurately measure the volume of gas entering the hole. Such a determination will provide information essential to maintaining minimum mud weight to balance the bottom hole pressures and prevent blowout conditions.

Mud weight, the key to well safety, is the most valuable information on the drilling well yet it has been the most neglected. There has never been a problem of knowing when there was a lot of gas since it could be detected by smelling, tasting and visual observation and the development of gas detecting equipment was directed to the identification of the sub-sensory or small amounts of gas. No appreciable progress was made in the measurement of large quantities of gas and the standard practice of checking mud weights today is the use of the hand balance device for periodic checks. Several types of continuous mud weighing devices have been developed, however, due to their limitations, it is estimated that only one well out of a hundred has a continuous mud weight device. The prior devices have consisted of mechanical and float devices with moving parts and pressure differential devices. Both the measurement of the mud weight in at the suction tank and the mud weight out of the shaker box has had its problems. The use of pneumatic tubes in the shaker box were affected by the excessive turbulence of the mud flowing into the shaker box and the box would fill with cuttings and stop up the tubes. In the suction tank on the mud discharge side, excessive changes in the level of the mud in the tank would leave the permanently placed pneumatic tubes out of the mud. Problems were also compounded by changes in submersion depths which affected the other properties of the mud such as the viscosity and gell strength.

It is recognized that a continuous accurate measure of the amount of gas entering the formation is valuable information for properly balancing a well during the drilling operation. Drilling for hydrocarbons is hazardous as evidenced by frequent blowouts which cause considerable air and water pollution and general ecological damage. Blowouts result from the unknown relationship between f; nation pressures and the weight of the drilling mud which is predetermined for formation pressure containment and penetration control. The mud weight determinations are initially based on historical data for a particular formation which of course is only an approximation and it is therefore essential that accurate and continuous determinations be made of the drilling fluid exiting from a well since the mud weight out of the well is a reflection of the bottom hole pressure relationship and the content of the formation being drilled up.

Many devices have been developed to give advace warning of potential trouble in the drilling of a well so that remedial action may be taken to minimize the trouble and control the well. The basic warning and indication of trouble is the relationship between the input drilling mud and the output drilling mud, i.e. the weight per unit volume and the volume per unit time of the mud at the entrance and at the exit from the well. If the volume of the returning drilling fluid is less than that of the input drilling fluid, the formation is taking the drilling fluids which is commonly referred to as a loss of circulation wherein the drilling mud enters the forma tion faster than it is pumped into the well. The sooner this condition is determined, the easier it is to seal off the zones that are taking the fluids. If more mud comes out of the hole than is pumped in, formation fluids such as salt water, gas or oil are entering the bore hole. When fluids enter the bore hole, mud containing pressures are inadequate since the fluid entering the hole will mix with the drilling mud being pumped into the well and lighten the weight of the mud column of the mixture being pumped out of the well. To make an accurate determination of the gas entering the formation, a new U-tube detector was invented for accurately and continuously measuring large quantities of gas entering the formation. This device, which measured the weight of the mud returning from the well bore prior to gas aeration at atmospheric pressure was difficult to set up and maintain.

SUMMARY OF THE INVENTION The present invention consists of an apparatus for accurately measuring the weight of the drilling mud being pumped into the well and accurately determining the weight of the mud being pumped out of the well and continuously logging the information on a time chart so that an accurate determination can be made as to changes in the mud weight resulting from bottom hole conditions. The determinations of mud weight in and mud weight out require two measurements, one of which is made on the suction tank which contains the drilling fluid being pumped into the well and the other measurement is made on the shaker box which contains the drilling fluids returning from the well. The basic apparatus for making both determinations is essentially the same except for slight modifications in its arrangement on the suction tank and shaker box, respectively. The apparatus of this invention consists of a pressure differential densiometer in which the weight of the fluid is measured by the difference in pressure between two pneumatic tubes submerged in the drilling fluid, both tubes having an independently controlled air supply. The pressure of the air in each tube is regulated to the same rate and the flow is metered so that both tubes have the same volume of air at equal pressure flowing into the mud being measured. The air outlet ends of the tubes are positioned at exactly 8.35 inches apart which represents the weight of water in pounds per gallons. Therefore when the weight of the drilling fluid is increased or decreased the pressure differential at the ends of the submerged tubes will increase or decrease by 1 inch of water pressure for each pound per gallon increase or decrease in the weight of the drilling fluid. This permits direct reading in pounds per gallon on a pressure differential recording device.

Prior attempts to use pressure differential pneumatic tubes for measuring the weight of fluid returning from the well have not been successful because of the shaker box turbulence and plugging tubes with the cuttings being returned from the well.

It is an object of this invention to solve the problems previously encountered with the use of pressure differential tubes on the shaker box by enclosing the tubes in a housing and mounting the housing on the outside of the shaker box. The housing communicates through an opening in the side of the housing with the interior of the shaker box via an opening in the wall of the shaker box and a restricted discharge opening in the bottom of the housinginsures that the housing will remain full of drilling fluid thereby insuring accurate weight determinations regardless of the turbulence inside the shaker box itself. This also eliminates the problem of tube plugging from the cuttings since the cuttings are excluded from the tube housing.

The use of pressure differential tubes on the suction tank for determining the weight of mud being pumped into the well has encountered many difficulties also. Excessive changes of the level of the drilling fluid in the suction tank oftentimes leaves pneumatic tubes permanently positioned in the tank completely out of the drilling fluid and thereby failing to record the drilling mud weight. Fluctuations in the level of the drilling fluid in the suction tank causes substantial changes in the submersion depth of the pneumatic tubes. This results in error in the recorded mud weights due to changes in mud viscosity and gell strength which vary with mud depth.

It is a further object of this invention to provide a means whereby the pneumatic tubes will be maintained at a constant submersion depth in the suction tank regardless of variations in the level of the drilling fluid in the tank.

Other and further objects and advantages of the pres ent invention will become apparent from the detailed description of the preferred embodiment.

BRIEF DESCRlPTlON OF THE DRAWINGS FIG. 1 is a schematic sectional view of a drilling rig including pumps, well bore, suction tank and shaker box' with the present invention included therein.

FIG. 2 is a schematic partial section view disclosing the specific arrangement of the pneumatic tubes connected to the air supply means and recording device.

FIG. 3 is a vertical section view of the apparatus of this invention as modified for use on the shaker box for weighing drilling fluid returning from the well.

FIG. 4 is a perspective view partly in section, of the apparatus of this invention mounted in the suction tank and modified for use in weighing drilling fluid being pumped into the well.

DESCRIPTION OF THE PREFERRED EMBODIMENT As can be seen from FIG. 1, a derrick 2 has been illustrated as mounted over the well bore 3 which is being drilled by the drill bit 4 connected to drill pipe 5 which is in turn connected to a swivel 6, a travelling block 7 and the hoisting lines 8. This drill pipe is rotated by rotary table 9 which receives its power from a suitable source. The well bore 3 as indicated is being filled with a drilling mud 10 which is forced downwardly by pump 12 through a hose 14 and into the upper end of the drill pipe 5. The mud is picked up by the pump 12 from the suction tank 21 via conduit 22 shown partly in schematic form in FIG. 1. Well casing 11 exits from the bore 3 in known manner and has a blowout preventer 23 mounted on top of said casing with a bell nipple 24 mounted on top of the blowout preventer 23. The drilling mud circulates upwardly in the casing within the annular space between the casing 11 and the drill pipe 5 and will rise to a level such as in the casing depending upon the rate of circulation which is being maintained by the pump 12. The discharge flowline 16 allows the drilling mud to discharge from the well bore and into the shaker box 17. The drilling mud exits from the shaker box over a vibrating screen 19 and into settling tank 25. The drilling fluid then travels from the settling tank 25 via conduit 26 and into the suction tank 21 to be recycled into the well via conduit 22.

The pneumatic fluid weight device 31 and 31' is shown modified for use on the shaker box 17 and the suction tank 21 respectively.

As shown in-FlG. 2, the basic pneumatic fluid weight device of this invention consists of a pair of

pneumatic tubes

32 and 33 connected in parallel relationship. The exit end of the

pneumatic tubes

32 and 33 are spaced apart by a distance d which is exactly equal to 8.35 inches. The

tubes

32 and 33 communicate with conduits 34 and 34' respectively which are connected to a source of compressed air 40 connecting air to the conduit at a pressure of approximately 3 psi. The low pressure is used to maintain a constant flow of air through the tubes with a minimum amount of friction and the flow is maintained constant in each tube by means of flowmeters 35 and 35'. The

air supply conduits

34 and 34 communicate with the air supply source 40. A cap member has openings 29 and 29' with adjusting

sleeves

52 and 52 mounted therethrough. The adjusting sleeves 52 and 52' are provided with adjusting screws 53 and 53'.

Tubes

32 and 33 extend upwardly into the adjusting

sleeves

52 and 52 respectively and are maintained in proper selected position by means of adjusting

screws

53 and 53. The inlet ends of the

tubes

32 and 33 are connected to the air supply lines 34 and 34' by suitable connecting means. As previously explained, the discharge ends of the

pneumatic tubes

32 and 33 are maintained apart a distance d which is exactly 8.35 inches. Since a gallon of water weighs 8.35 pounds, a change of 1 pound per gallon in the drilling fluid is reflected in a differential pressure of one inch of water. This differential pressure is reflected on the recording device 41 which may be calibrated to record drilling fluid weight changes as inches of water which is directly equal to the weight change in pounds of mud per gallon.

As shown in FIG. 3, the fluid weight device 31 is modified for use on the shaker box 17. A housing 36 encloses the

pneumatic tubes

32 and 33. The housing has an inlet opening 37 through its side for communicating with a source of drilling fluid such as the shaker box 17 as shown in FIG. 1. The housing is provided with an opening 38 at its bottom for discharging drilling fluid from the inside of housing 36. The discharge opening 38 is smaller than the inlet opening 37 in order to keep the housing 36 full of drilling fluid. A water supply line 39, connected to a water'supply source (not shown) communicates with the outlet opening 38 for use in cleaning the outlet opening.

As shown in FIG. 1, the fluid weight device 31 is connected to the outside of shaker box 17 and communicates via an opening in the shaker with the interior of shaker box 17 through the inlet opening 37 provided in the housing 36.

FIG. 4 discloses the fluid weight device 31 modified for use in the suction tank 21. The apparatus is essentially the same as described with reference to FIG. 2 except that the housing 36 has been eliminated and float means 42 have been added. The

tubes

32 and 33 are connected in parallel relation by means of the cap member 30 and adjusting sleeves 52 and 52' as previously described. The housing 36 is replaced by a float means 42 consisting of

air chambers

43, 44, 45 and 46 which are connected by means of suitable connecting

rods

47, 47' and 48, 48' to a connecting ring 49. The

tubes

32 and 33 extend downwardly through the ring 49 so that the cap member 30 rests inside the ring 49 and maintains the

tubes

32 and 33 in vertical alignment.

Tubes

32 and 33 are connected to flexible conduits 51 and 51' which in turn communicate with

air supply conduits

34 and 34. The floating

chambers

43, 44, 45 and 46 float on the surface of the drilling fluid in the suction tank 21 and maintain the

tubes

32 and 33 at constant submersion depth regardless of changes in the depth of the drilling fluid in the tank 21. While it is not essential that the float means be anchored, I prefer to provide an anchor means consisting of a collar 56 connected to the ring 49 by means of anchor bar 57. An L-shaped pivot rod 54 is connected at one end to a C-clamp 55. The C-clamp 55 connects the pivot rod 54 to the side of the tank 26. The collar 56 is positioned over the pivot rod 54 for anchoring the fluid weight device in proper position in the tank while allowing it to rise and fall with the changing depth of drilling fluid. The operation of the device is exactly the same as previously described.

Having now described a preferred embodiment of my invention what I claim is:

1. An apparatus for weighing drilling fluid at a shaker box comprising a pair of pneumatic tubes mounted in parallel relationship, each of said tubes being open at one end and communicating with a source of pressurized air at the other end said open end of one tube being vertically spaced a pre-determined distance from the end of the other tube, control means for delivering and maintaining a constant and equal rate of air flow to each of said tubes, housing surrounding said pneumatic tubes with an inlet opening in the side of said housing for receiving said drilling fluid from an opening in the side of said shaker box, discharge opening in the bottom of said housing, said discharge opening being smaller than said inlet opening to maintain a level of said drilling fluid in said-housing substantially equal to the level in said shaker box, flow of said drilling fluid through said housing means being over the open ends of said pneumatic tubes immersed in said drilling fluid.

2. The apparatus of claim 1 wherein said housing means includes a cap member having a pair of spaced openings therethrough, an adjusting sleeve is mounted over each of said openings and extend upwardly from said cap member in parallel relationship, each of said pneumatic tubes extends through a respective one of said adjusting sleeves and said space openings and an adjusting screw extends through the wall of each of said adjusting sleeves to frictionally engage said pneumatic tubes and maintain said tubes in position relative to each other with their ends vertically spaced apart a predetermined distance.

3. The apparatus of claim 2 wherein said predetermined distance is 8.35 inches.

4. The apparatus of claim 1 wherein a water supply line communicates with said housing adjacent the discharge opening to periodically clean said housing means.

5. An apparatus for weighing drilling fluid comprising a pair of pneumatic tubes mounted in parallel relationship, each of said tubes being open at one end and communicating with a source of pressurized air at the other end, said open end of one tube being vertically spaced from the end of the other tube,

a cap member having a pair of spaced openings therethrough, an adjusting sleeve mounted over each of said openings and extending upwardly from said cap member in parallel relationship, each of said pneumatic tubes extends through a respective one of said adjusting sleeves and said spaced openings, an adjusting screw extending through the wall of each of said adjusting sleeves to frictionally engage said pneumatic tubes and maintain said tubes in position relative to each other with their open ends vertically spaced apart a predetermined distance, I

float means connected to said pneumatic tubes, said float means comprising a plurality of air chambers surrounding said tubes, said air chambers being fastened around a connecting ring with said pneumatic tubes extending vertically through said ring with said cap member resting on top of said connecting ring and maintaining said pneumatic tubes in vertical alignment.

6. The apparatus of claim 5 wherein an anchor means is connected to said float means, said anchor means comprises an anchor rod connected at its one end to said connecting ring and extending outwardly therefrom and a collar connected to the other end of said anchor rod.

Claims

1. An apparatus for weighing drilling fluid at a shaker box comprising a pair of pneumatic tubes mounted in parallel relationship, each of said tubes being open at one end and communicating with a source of pressurized air at the other end said open end of one tube being vertically spaced a predetermined distance from the end of the other tube, control means for delivering and maintaining a constant and equal rate of air flow to each of said tubes, housing surrounding said pneumatic tubes with an inlet opening in the side of said housing for receiving said drilling fluid from an opening in the side of said shaker box, discharge opening in the bottom of said housing, said discharge opening being smaller than said inlet opening to maintain a level of said drilling fluid in said housing substantially equal to the level in said shaker box, flow of said drilling fluid through said housing means being over the open ends of said pneumatic tubes immersed in said drilling fluid.

3. The apparatus of claim 2 wherein said predetermined distance is 8.35 inches.

5. An apparatus for weighing drilling fluid comprising a pair of pneumatic tubes mounted in parallel relationship, each of said tubes being open at one end and communicating with a source of pressurized air at the other end, said open end of one tube being vertically spaced from the end of the other tube, a cap member having a pair of spaced openings therethrough, an adjusting sleeve mounted over each of said openings and extending upwardly from said cap member in parallel relationship, each of said pneumatic tubes extends through a respective one of said adjusting sleeves and said spaced openings, an adjusting screw extending through the wall of each of said adjusting sleeves to frictionally engage said pneumatic tubes and maintain said tubes in position relative to each other with their open ends vertically spaced apart a predetermined distance, a float means connected to said pneumatic tubes, said float means comprising a plurality of air chambers surrounding said tubes, said air chambers being fastened around a connecting ring with said pneumatic tubes extending vertically through said ring with said cap member resting on top of said connecting ring and maintaining said pneumatic tubes in vertical alignment.