US3364494A - Drilling system recorder - Google Patents

Description

Jan. 16, 1968 T. B. DELL INGER ET L DRILLING SYSTEM RECORDER Original Filed June 25, 1961 6 Sheets-Sheet l T T T T T T T x I in g 2 g l a K IO F58 f 8% i i: 55 fi lo g LU f E;

FOOTAGE DRILLED BY BIT FIG. I Thomas B. Dellinger, Alexander B. Hildebrondt, Ralph D. Lynn INVENTORS myQ/LAM ATTORNEY Jan. 16, 1968 T. B. DELLINGER ET AL 3,

DRILLING SYSTEM RECORDER Original Filed June 23, 1961 6 SheetsSheet 2 l l m 1 w E 3' E o 932 i Lu v E 8 FOOTAGE DRILLED BY BIT o l ::-:-z-1=.; {1h} Thomas B. Dellinqer, Alexander B. Hildebrandt, Ralph D. Lynn INVENTORS A TTORNEY Jan. 16, 1968 T. B. DELLINGER ET A DRILLING SYSTEM RECQRDER 6 Sheets-Sheet 3 Original Filed June 23, 1961 F IG. 3

Thomas B. Dellinqer, Alexander B. Hildebrundt, Ralph 0. Lynn INVENTORS ATTORNEY Jan. 16, 1968 11 DELUNGER ET AL 3,364,494

DRILLING SYSTEM RECORDER Original Filed June 25, 1961 I 6 Sheets-Sheet4 C I76 /--l32 Thomas B. D ellinger, Alexander B. Hildebrondt, Ralph D. Lynn INVENTORS ATTORNEY Jan. 16, 1968 DELLINGER ET AL 3,364,494

' DRILLING SYSTEM RECORDER Original Filed June 23, 1961 6 Sheets-Sheet 5 FIG. 5

Thomas B. Delllnqer, Alexander B. Hlldebrundt, Ralph D. Lynn INVENTORS BY%%M A TTORNE Y Jan. 16, 1968 DELUNGER ET AL 3,364,494

DRILLING SYSTEM RECORDER Original Filed June 25, 1961 6 Sheets-Sheet 6 COST FACTOR PER FOOT DECREASING O H 03 m O I p- O. LLI T FIG. 6

Thomas B. Dolllnger, Alexander B. Hildebrundt, Ralph D. Lynn INVENTORS A TTORNE Y I te States Patent ()ffice 3,364,494 Patented. Jan, 16, 1968 3,364,494 DRILLING SYSTEM RECORDER Thomas B. Dellinger and Alexander B. .Hildebrandt, Tulsa, Okla., and Ralph 1),, Lynn, Houston, Tex., as signers to Esso Production Research Company, a

corporation of Delaware I 9 Original application June 23, 1961, Sen, Nou I 19,087o D1 vided and this application May 25, 1966, Sern Noo 4. Claims, (Cl, 346-30) ABSTRACT OF THE DISCLOSURE This is a division of Ser, No, 119,087, filed June 23, 1961, and now abandoned.

This invention relates to the drilling of boreholes into the earth, It relates particularly to a system for deter= mining when a drill bit used for drilling such boreholes should be replaced,

In the art of. drilling wells for the production of oil and gas, the most commonly used method is the socalled rotary drilling method: In. the rotary drilling method, a drill bit is suspended at the lower end of a string of drill pipe which is supported from the surface of the earth: The drill string is conventionally formed of many joints of drill pipe, each joint usually being about 30 feet long. As the hole is deepened, additional joints of drill pipe as needed are connected into the string, A drilling fluid is forced down through. the drill string, through the drill bit, and back up to the surface through the am nulus between the drill pipe and the walls of the bore hole. While the drilling fluid serves primarily to carry the rock cuttings from the drill bit to the surface, it also serves to lubricate and cool the drill bit, The drill bit obtains its rotary motion. from the drill pipe which is rotated from the surface, It is known that the rate of penetration of a drill bit can be increased by increas ing the force of the drill bit on the bottom of the bore hole. The penetration of the drill bit is also influenced. by the rate at which the drilling fluid is forced through the drill bit and by the rate of rotation of the bit, The sharpness of the bit, of course, also etfects the drilling rate,

It is the usual practice in order to obtain optimum drilling conditions to apply constant force on the drill bit and rotate the bit at a constant speed, Then as the bit becomes dull, the drilling rate gradually decreases, In such a situation the universal question in rotary drill ing operations which the driller has to resolve is-= when should the bit be replaced or pulled? .lThis is a question for which it has been most difiicult to obtain. an, answer; i.e., it has been most diflicu'lt to determine when in drill ing operations the time or moment that a bit should be replaced by another bit,

It is most important to note that the pulling or re placing of a bit in rotary drilling is considered a major operation; that is especially for the deeper depths of drill ing, This is true because the many joints of pipe which have been connected to make up the drill string must be pulled two or three joints at a time (depending on the size drilling rig used) and disconnected and racked in order to remove the bit to the surface, When the new or replacement bit is put into operation, it is placed on. the lower end of the lower joint of the drill pipe (or drill. collar) and the disconnected sections or joints must be reassembled so that the bit can be lowered to the bottom of the borehole, In the deeper wells this pulling of the bit can amount. to a several-hours job ranging from 2 to 10 or more hours depending upon the depth. And, of course, during the time when the bit is being removed and replaced, drilling or advancing of the bore= hole is stopped, In effect. then, an expensive and elab= orate drilling system and its crew are inoperative inso= far as advancing the borehole is concerned inasmuch as their time is entirely consumed in pulling the bit and replacing it, It is thus most important that a bit be changed only when it has drilled its optimum total foot age.

Normally records are kept of each bit and the time which the bit was in drilling operation, From these records it is possible to calculate mathematically the average cost per foot for the bit, However, these calcula= tions are made some time after the bit has been pulled and do not directly aid in determining the moment a particular bit should be changed, Presently there is no system whereby the driller can easily determine the moment a bit should be changed while he is drilling so that the bit can be used to drill its optimum total foot age, no more, no less, Under present practices the driller is largely forced to rely upon hunches to determine when he changes the drill bit, After elaborate calculations are made after the bit has already been pulled, the driller can then be told when the bit should have been changed, but that of course is too late What the driller needs is a system whereby he can tell more accurately when the bit should be changed at the approxi= mate moment it needs to be changed, This invention, are plained in detail hereinafter, discloses such a system, such that the driller can replace the drill bit at the proper time, i.e.. at the time when the bit has drilled its opti= mum footage or distance,-

The economical. optimum. drilling time that a bit should be changed is at a point in time when the cost per foot (considering the total footage drilled by a bit) reaches a minimum. This point in time can be determined as drilling progresses by observing the ratio of .K+! to 1 wherein. t the drilling time, preferably in hours, which. the bit is on the bottom of the borehole, f=the footage drilled by the bit, usually in feet but can be other linear units, and K is the preparatory time of the unit, i.e. time when the drilling unit is performing operations ancillary to the actual turning of the drill bit, K includes trip time plus the equivalent bit cost time and is con ventionally in hours, In this regard, trip time includes the approximate time which it takes to remove a bit from. the bottom of the borehole and replace it at the bottom of the hole with a new hit The approximate time re quired to change a bit at any depth range can be deter= mined fairly accurately by those sldlled in the art, The bit cost equivalent time is readily determined by divid ing the cost of the bit by the cost of the drilling unit per hour, It is a common practice of owners of drilling units to charge a certain rate per hour for their drilling units depending upon such factors as location and size unit required, A. cost per hour is usually agreed upon prior to commencement of drilling, When the bit advances the length of a joint of pipe, an additional joint is added, Drilling, i.e. rotation of the bit, is briefly stopped for this connection time This connection time is rather short; however an estimation of the connection time can be included in In the invention disclosed herein the ratio, or an indication thereof, of K+t to f is continuously recorded as drilling progresses. Thus, there is a record of the cost per footage drilled by a particular bit at any instance during its drilling time. When a bit is first placed in the bottom of the borehole and. drilling is started. the ratio of 16+! to f (or cost per foot drilled by the bit) is quite high; this is so because K is rather large compared to the footage drilled which starts at zero. However, as drilling progresses, the ratio decreases until the optimum footage has been drilled. At this point the bit has worn dull to the point where any additional drilling with that bit would cause the average cost per foot drilled by that bit to in crease. At the time the ratio of K+t to f stops decreasing is the moment that optimum drilling footage has been reached for that bit. At that time the bit should be changed.

Further objects and a better understanding of this in vention may be had from the following description taken. in conjunction with. the drawing in which;

FIG. 1 illustrates a chart upon which a drilling curve has been placed;

FIG. 2 is similar to FIG, 1 with the exception that a representative lithological 10g has been placed to the left of the chart;

FIG. 3 illustrates an apparatus upon which the drilling [chart of FIG. 1 or FIG. 22 is placed so that a drilling curve is recorded thereon as drilling progresses;

FIG. 4 illustrates another apparatus for use in practic ing this invention;

FIG. 5 illustrates a chart for use with the apparatus of FIG. 4; and

FIG. 6 illustrates another chart for use with the apparatus of FIG. 4.

A chart for use in this invention is shown in FIG. 1. The ordinate of the chart is footage drilled by the bit, or in keeping with the nomenclature given above, this repre-= sents f. The units of the ordinate are conveniently in feet. The abscissa of the chart is time or 1. Of course, if. desired, the ordinate can be in time and the abscissa in feet. The time is normally divided into trip time, bit cost equivalent time and drilling time. This is represented by K+t. The trip time as shown on the chart is the approximate time required to pull a bit from the bottom of a borehole and replace it with a new bit. Bit cost equivalent time is the cost of a new bit which is being used to drill the borehole divided by the cost per hour of the drilling unit. The trip time and bit cost equivalent time are added together and are included in K or the time which must be accounted for before drilling commences. If the total anticipated connection time is substantial when compared to trip time and bit cost equivalent time, or when compared with drilling time, it is also preferably included in K. Thus drilling time, as plotted on the chart of FIG. 1, begins at a point 10 on the chart. The following is an example of arriving at a value for K for a drilling unit. costing $50.00 per hour and for a bit beginning drilling at 5000 ft. in a partially drilled well. For a bit costing $187.50 the equivalent time is 187.50/50 or 3.75 hours. An estimate of the footage the bit can drill is made by one skilled in the art, and for this example is assumed to be approximately 250 feet. The average time for a round trip, or time required to pull a string of drill pipe and re place it, at a depth of 5250 is used for trip time. An average time required for a round trip to that depth is typically about four hours. K. in this example is equal to 3.75 +4.00 hours or 7.75 hours. In 250 feet about eight connections are required. If each connection requires four minutes the connecting time is about 32 minutes. If the connection time is desired to be included, about .5 hour is added thus making K- -8.25 hours. Error in the estimated footage that a bit will drill normally does not greatly affect this system, particularly at greater depths.

Also shown in FIG. 1 are a plurality of radial lines 12A to 12N. Upon reflection, it will become apparent that these radial lines are constant cost per foot lines, since equal intervals along the abscissa (or time coordinate) of FIG. 1 are directly translatable into dollars or other monetary units. In other words, if. it costs the same amount of money to drill each foot of hole (represented along the ordinate axis of FIG. 1.), it follows that a. record.

in FIG l of the footage drilled by a bit, which. is drilling at a constant cost per foot at each point along the drilled hole, will be a. straight line originating at the origin of FIG. 1 and extending at a constant slope across FIG. 1. It will be recognized, of course, that boreholes character ized by a constant cost per foot of hole drilled are a rarity and that, in actual practice, the cost will vary as indicated by trace 14 in FIG. 1. Thus when drilling curve 14, which is shown on FIG. I, crosses a radia line it represents a certain fixed average cost per foot drilled to that. point regardless of where the drilling curve 14 crosses the radial line with respect; to drilling time.

As shown above. the average cost. per foot is proportional. to

Kit)

If the ratio.

iii? 1 remains constant with variable time and depth, it defines a radial line. The ratio is really equivalent to the cotangent of the angle a formed by such a radial line, such as 12A, with the abscissa. The cost per foot for a particular radial line equal to the cotangent. of the angle or which that line makes with the abscissa times a proportionality constant. If desired, a value of the cost per foot can be placed on the chart for each radial line.

On the chart in FIG. 1. drilling curve 14 begins at a. time from the origin equal to K. and. includes trip time plus bit cost equivalent time, as indicated at point 10. The radial lines 12A through. 12N extend outwardly from the origin of the graph, that. is at. zero time and at zero footage. The radial lines shown on FIG. 1 are equally spaced. However, they can be spaced in any order desired. .A particularly desirable arrangement of the radial lines is to have the difierence in cost per foot represented by any two adjacent radial lines equal. to the difference in cost in. any other two adjacent radial lines on the graph. The number of radial lines which a chart. contains should be suificient so that it is readily apparent when. drilling curve 14 becomes tangent with a radial line.

As drilling continues, curve 14 continues to rise and for some time the cost per foot drilled continues to decrease. The cost per foot drilled by the bit at any instance during its run is K-l-t (trip time plus bit cost. equivalent: time plus drilling time divided by f (the footage drilled) times a proportionality constant. As drilling continues, the bit dulls and the rate of drilling rate falls off. Eventually curve 14 becomes tangent to a radial line, shown as 12G in FIG. 1 at the time T At the time T the drilling cost per foot drilled. has reached its minimum value. If drilling is continued, curve 14 drops oil as indicated by a dotted line 16 and the cost: per foot begins to increase. The cost. of drilling the entire borehole will also be greater than if each. bit were changed at its optimum. footage. Therefore, it is apparent that the bit should be changed at. time T That is, when. line 14 becomes tangent with radial line 12G. Thus, it is quite clear that whenv the drilling curve 14, becomes approximately tangent to one of. the radial lines, it is then time to change the bit.

The system of this invention is very easy to use. There are no time consuming calculations to be made. The system is so straightforward that only a matter of a few minutes is required to instruct a driller on how to use the chart and its accompanying apparatus.

As shown. above, the cost. of drilling a. borehole per foot and thus the total cost increases if a. bit is used beyond a certain optimum distance. In addition to costing rnore per foot. of drilling, if a. bit s used too long, there is a serious danger that it will wear to the point that a cone of the roller bit. will be lost in the borehole. As these cones are extremely hard, ordinary drilling equipment cannot be used to drill through them. Therefore, if a cone is lost in the borehole, either a fishing job must he done to regain or remove the cone from the borehole or else the hole must be side-tracked. Either of these operations is very costly and time consuming, and thus are to be avoided.

Attentionis now directed to FIG. 3 which illustrates a recording means upon which the chart described above in FIG. 1 can be placed so that drilling curve 14 is recorded as drilling progresses. Illustrated thereon is a housing member 20 and an upper shelf 22 with intermediate shelf 24 and a floor 26. On the upper shelf 22 is mounted a pickup drum or spool 28 mounted on axis 30. Drum 28 is biased in the direction of the arrow so as to keep line 34 which is wound about drum 28 in a taut condition. Line 34 extends downwardly around a sheave 36 which is mounted on axle 38. Sheave 36 and and axle 38 are mounted in the lower part of housing 20. Line 34 from drum 28 goes downwardly around sheave 36 and back upwardly through a hole 40 in the top of the housing to a connection on the kelly (not shown) so that line 34 then unwinds in an amount sufficient to follow the movement of the drilling string as it is lowered as the hole is drilled deeper. Sheave 36 and its axle 38 then rotate in response to the movement of line 34 which is responsive to the lowering of the drill string as drilling progresses deeper. Shaft 38 is connected through a manually operated clutch 42 to shaft 44. The end of shaft 44 goes into gear box 46 which has an adjustable gear ratio adjustable by handle 48. Gear box 46 has a power outlet shaft 50 which is connected through a manually operated clutch 52 to shaft 54, Mounted on shaft 54 opposite clutch 52 is a cam sheave 56. A line 58 is attached to the periphery of sheave 56 at 60.

Mounted above intermediate shelf 24 is a recording drum 62 upon which is mounted a recording chart 64 such as illustrated in FIG. 1 and described above. Drum 62 is driven by a manually controlled clock motor 66 through clutch means 68, which serves to connect and disconnect shaft 70 of clock motor 66 and shaft 72 supporting drum 62.

A travelling block; 74 is slidably mounted upon horizon= tal support rods 76 which are supported from intermediate shelf 24 by end supports 78 and 80. Travelling block 74 is resiliently biased. toward the left by resilient means such as spring 82, which is connected at one end to end member 78 and at the other end to travelling block 74. Mounted above travelling block 74 is pen holder 84 and pen 86. Travelling block 74 and its associated parts are arranged such that when it is in its extreme left-hand position, pen 86 is at the zero footage mark on chart 64. Line 58 from peripheral sheave 56 to travelling block. 74 crosses over to sheave 88 which is mounted on end support member 80'.

In operation, a chart such as illustrated in FIG. 1 is placed upon recording drum 62.. Pen 86 is placed at point on the abscissa which represents time, from the origin of the chart, equal to K... In this position the drilling curve is ready to begin at the proper place and time and at zero footage. As drilling progresses, line 34 is pulled upwardly 'by'the lowering of the drill string and sheave 36 is thus rotated. The rotation of sheave 36 is directly proportional to the drilling or deepening of the borehole. As sheave 36 rotates, the rotational motion is transferred through clutch 42 to gear box 46. Gear box 46 has an outlet drive shaft 50 which rotates proportionally to the rotation of shaft 44 in accordance with the selected gear reduction of gear box 46. Shaft 50 is connected through clutch 52 and its rotational motion is transferred to sheave 56. Then as drilling progresses line 58 pulls travelling block 74 to the right a distance representative of the instantaneous position of the drill bit. Thus a curve 14 is formed on record 64. Simultaneously with the commencement of drilling operations. (i.e. rotating the hit against the borehole hottom), clock motor 66 is started so as to rotate drum 62 at a constant speed. As drum 62 rotates at a constant speed, pen 86 is pulled to the right to represent the depth that the drill bit has drilled at the particular time indicated on the chart. During down time the clock is dis= engaged from. driving the chart and the chart is stopped. If drilling is only momentarily interrupted for adding an other joint of drill pipe and connecting time was not included in K, the clock can continue to drive the chart, thus in effect including connecting time. When another joint of pipe is added, clutch 42 is disengaged to permit line 34 to follow the kelly without such travel being indicated on the recording chart. During connecting time clutch 52 remains engaged so as to hold pen 86 in its proper position.

Referring to FIG. 1', drilling curve 14 becomes tangent with one of the radial lines as at 12G and which occurs at time T at which time the bit needs to be changed. This is indicated at the approximate moment in the run of the drill bit and not at a later time after calculations have been made or other charts consulted, etc. This system permits individual bit evaluation as well as an evaluation of one bit based upon experiences with other bits.

Attention is now directed to FIG. 2- wh-ich illustrates a chart similar to the one in FIG. 1 with the exception that a lithological log has been placed to the left of the co-ordinate graph. This log, when available, can prove to be quite useful. Development wells are wells which are being drilled in an area in which other wells have already been driiled. In a development well a log can be taken from an adjacent well. which has already been drilled in the area and in which the formations drilled through were noted. If the well being drilled is a wildcat well, that is one in which there are no other wells close by, then a log can sometimes be obtained from geophysical information or subsurface geology which may indicate possible form'a tions. The log on FIG, 2 illustrates one taken from a nearby well and shows an interval from. 2,000 feet to 4,000) feet. In the particular scale of FIG. 2 then, each square represents 200 feet for the drill bit as the footage scale then is 0 to 2,000. It will of coursebe understood that these values are merely for purposes of illustration only. Shown on the log is an extremely hard formation. identified by the numeral 90.

In operation, the chart shown on FIG. 2 is placed on recording drum 62 in a manner similar as the chart of FIG. 1. The pen 86 is set to begin at zero footage and at K time from zero. As drilling progresses, a drilling curve 92 is recorded on the chart. When the drill bit reaches the hard format-ion 90, that is a formation which is very difficult to drill through, the drilling slows down consid erably. In some cases the drilling may slow down sufli= ciently so as to indicate that. the drilling curve is tan-gent to one of the radial lines as illustrated in. 94. .When this occurs, it appears that it is time to change the drill bit. However, the hardness of the formation 90 shown on the log suggests that this is a false indication and that drilling should continue. Drilling continues and. when the bit passes through the hard formation 90, the average cost per foot again. begins to decrease until at a time T drilling curve 92 becomes tangent with one of the radial, lines at which time the drill bit should be changed.

In the description above in regard to FIG. 1, it is shown that when drilling curve 14 became tangent with one of the radial lines such as 12G that this is the optimum foot age for the bit to drill. If one considers the angle a which is formed between a line defined by the instantaneous point on the drilling curve and the origin of the graph. and the abscissa, it is seen that this angle continues to in= crease as drilling progresses "until it reaches a maximum. which is coincident with the point at which drilling curve 14 becomes tangent with the radial line. The optimum drilling footage is indicated by measuring a as drilling progresses and noting when it ceases to increase. A. suit" 7 able apparatus for recording the angle a as drilling progresses is shown in FIG. 4.

Illustrated thereon is a housing 100 having a top 102, a shelf 104 and a base 106. Supported within housing 100 is a horizontal rod 108 and a vertical rod 110. These rods are supported by support means 112 at a 90 angle, slid ably mounted on slide rod 108 is sliding block 114. Block 114 is driven by clock 116 through clutch 118, take-up spool or sheave 120, and line, 122 which is fastened to spool 120. Line .122 is fixed to sliding block 114 at point. 124. The end of line .122 opposite take-up spool or sheave 1-20 is secured to another take-up spool or sheave 126 which is biased to maintain line 122 in. tension. The ar row on take-up sheave 126 indicates the direction of the bias. Clutch 11 8 is conveniently a hand-operated clutch which can be engaged and disengaged manually.

Mounted upon take-up sheave 120 is gear 128. A gear 130 which meshes with gear 128 is attached to a vertical rod 132 which extends upwardly through shelf 104. Rod 132 is mounted in a rotatable and non-axial movable relationship with shelf 104 and anchor 134 which is sup ported from the wall of housing 100. The upper end of rod 132 has affixed thereto an indicator 136 which points to a circular scale 138. This indicator 136 is especially useful for resetting sliding block .114 so that the proper value of K can be set at the time drilling commences.

Mounted on vertical rod 110 is a sliding block 140. Sliding block 140 is affixed to line 142. Line 142 is responsive to the vertical movement of the drill string and of course the drill bit as it drills deeper. The end of line 142 below block. 140 is secured to a take-up spool 144 which is biased to maintain line 142 in tension. The line 142 above block 140 is secured to a spool 146 which is driven by shaft 148 from gear box 150. An axis 152 extends from gear box 150. Mounted on axis 152 is sheave 154. A line .156 similar to line 34 (FIG. 3) passes around sheave 154 and up to take-up spool 158 which is biased in the direction of the arrow, Gear box 150, sheave 154, line 156 and take-up spool 158 are similar respectively to gear box 46, sheave 36, line 34 and take-up spool 28 shown in FIG. 3.

Mounted parallel to vertical rod 110 is shaft 160 hav ing keyway 162. Shaft 160 is rotatably mounted in trav-= elling block 140. Mounted about shaft 160 is a gear 164 which has a key 166 which slidably fits in keyway or slot 162. Gear 164 is .rotatably supported from housing block 140 and travels with. block 140 as that .block moves verti cally. Mounted on the upper end of shaft 160 is a roller 168. The rotational position of sheave 168 then follows the rotational position. of beveled gear 164.

A slotted bar 172 is pivotally attached to pivot 174 to sliding block 140. Mounted about pivot 174 and rigidly or non-rotata'bly attached to sliding bar 172 is gear 176 whose teeth mesh with the teeth of gear 164. Pin 170 is mounted through the slot of bar 172 to sliding block 114. The diameter of the head of pin 170 is greater than the width of the slot in the bar 172. Pin 170 is mounted on sliding block 114 such that when sliding block 140 is in its lowermost position, the center or axis of pin 170 is on the same level with the axis of pin 174; in other words, when sliding block 140 is in its lowermost position, bar 172 is parallel with rod 108.

In FIG. 4 there is a right. triangle which has three points, namely the axis of pin 170, the axis of pin 174, and point 178 which is the axis of pin 174 when bar 172 is horizontal or parallel to rod 108. The base leg of the right triangle then is from point 178 to point 170. 'Point 178 is fixed and point 170 moves with respect to time. The base of the triangle then is representative of K+i. The value of K being the same as hereto-fore described. The other leg of the right triangle is from point 178 to point 174. This value is comparable and representative of f. Thus a is the angle between bar 172 and the lower leg defined between points 178 and .170. The other acute angle of that triangle then. is a supplement of a or 90 minus a. The change of rotation of gear 176 is directly proportional to the change of angle a.

Mounted on upper shelf 104 of the housing is a rotating chart drum. 180 mounted on shaft 182. Mounted on drum 180 is a. chart. 184 such as illustrated in FIG. 5 or FIG. 6. Also shown mounted on shelf 104 is a clock motor 186 which through manually operated clutch 188 drives shaft 182 and in turn, drum 180. Also shown on shelf is gear 190 which is mounted on shaft 148 of gear box 150. In relation with. gear 190 is gear 192 Which is afiixed to shaft 194.. Shaft 194 is connectable to shaft 182 through manually operated clutch 196. In operation if it is desired that drum 180 rotate at a. constant rate withv respect to time, then clutch 188 engages shaft 182 with clock motor 186 and clutch 196 is disengaged. If on. the other hand, it is desired that; drum 180 rotate proportionally to the rate of drilling, then clutch 196 engages shaft 194 with. the shaft 182 of drum 180 and clutch 188 is disengaged so as to disengage clock 186.

Also mounted on shelf 104 are support. members 198 and. 200.. Mounted between these two support members are two parallel. slide rods 202 and 204.. Mounted on rods 202 and 204 is a travelling pen carrier .206. A pen. 208 is supported therefrom in a manner to contact chart 184. Travelling pen carrier. 206 is biased by resilient means 210 toward support member 200 or to the right. .A. line 212 is fastened to sheave 168 and at. the other end to travelling carrier 206. The particular rotatable position of sheave 168 is representative of the angle a. Thus, as sheave 168 rotates, it likewise moves pen 206 proportionally.

A typical chart for use with apparatus of FIG. 4 is shown in 5. The abscissa there is a from 0 to 60 and the ordinate is time, preferably in hours. When it. is desired to use the chart of FIG 5 on the apparatus of FIG. 4, the chart is placed upon. drum 180 and both. clutches 196 and 188 are disengaged until drilling oper= ations are to commence and then only clutch. 188 is en gaged. This is so that the chart will be driven at a con stant rate by the clock motor. However, before drilling operations start, sliding block 114 is set at a point equal to K. This is readily accomplished. by disengaging clutch 118 and rotating indicator 136 until the desired K is indi= cated. on scale 138.. Then the axis of pin will be the required distance, representative of K, from point 178. Travelling block 140 will automatically go to its lowest position due to the bias of take-up spool. 144 when the tension is relieved on line 156 as blockv 112 is arranged to stop the downward travel of block. 140 at the correct position. When bar 172 is horizontal, 1x equal to zero and pen 208 is at its right-hand position which coincides with the zero angle marker on the chart. In. the embodiment shown, the chart sheave 168, and gears 164 and 176 are all designed and calibrated such that. the righthand side of the chart. equals zero degrees and the left-hand side equals a. selected angle- Which is preferably about 60. When drilling is readyto commence, clutches 118 and 188 are engaged so that clock. motor 116 can start driving pin 170 to the right so that. the lower leg equals plus I and as drilling progresses, travelling block 140 is moved up wardly so that the upright leg of the triangle is represent ative of the summation f. The position. of bar 172 then is seen to be at all times representative of a. At: the same time that. clutch 118 was engaged, clutch 188 was engaged so that clock motor 186 will start driving chart. drum 180.. Drum. rotates and pen 208 records the angle a. Re ferring to 5 drilling continues until the curve 202 becomes tangent with one of the angle lines as at angle 48, at time T This is the time that. the bit should be changed as at that time it. has reached its optimum drilling footage. Any further drilling by that bit will increasethe average cost per foot thus making the holemore costly to drill,

Sometimes it. will be desired to record angle a". with a chart whereby the ordinate is depth. drilled. This can easily be assomp h. the pparatus of FIG, 4- 1m mam ner similar to that described above in regard to FIG. except that clutch 188 is disengaged and clutch 196 is engaged so that drum 180 is driven at a rate proportional to the advancement or deepening of the borehole. A chart such as shown in FIG. 6 is especially useful for this. The chart of FIG. 6 has the ordinate which is depth drilled. Also placed along the side of the chart is a drillers or lithological log which has been obtained from information derived by drilling other Wells in the area similarly as on the chart of FIG. 2. For purpose of illustration an extremely hard formation 216 is shown on the log. As drilling continues, curve 214 also is made on the graph. At a depth D the curve flattens out. This at first glance would indicate that the optimum footage has been reached, however, by noting the hard formation 216 it would be expected that the drilling rate would decrease and as soon as the hard formation 216 has been drilled through, the curve starts to increase again until at a depth D, it becomes essentially tangent with one of the vertical lines on the chart. The vertical lines can represent the angle a as shown on FIG. 5 or the lines can be given a cost value as indicated in FIG. 6 since in addition to indicating an angle they are constant cost lines similarly as the radial lines of FIG. 1 and FIG. 2. The cost per foot drilled which each line represents is proportional to the cotangent of the angle which the line represents. The radial lines of FIG. 1 and FIG. 2 can also be given cost values.

Having cost per foot drilled indicated on the radial lines, or constant cost lines is quite useful. For example, it permits a direct comparison by the driller between two different bits used to drill in the same or similar formation. A first bit. is used and drills until it has reached its optimum footage. The cost per foot for that bit is indi-= cated by the constant cost line on a first chart with which the drilling curve became tangent. The first bit is then replaced by a second bit of another type which drills until it reaches its optimum footage and is likewise pulled. The cost per foot for the second bit is indicated on a second chart. The cost per foot for the two bits are compared and the more favorable bit used in further drilling in that particular formation.

While there are above disclosed but a limited. number of embodiments of the system of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept hereinv disclosed. It is therefore desired that only such.

10 limitations be imposed on. the appended claims as are stated therein.

What is claimed is:

1. An apparatus for recording information indicating when a bit has drilled its optimum footage within a borehole which comprises in combination: a first red; a second rod forming a angle with the first rod; a first travelling block slidably mounted on said first rod; a second travelling block slidably mounted on said second rod; means for moving said first travelling block responsive to the advancing of the borehole; means for moving said second travelling block responsive to time; a bar pivotally mounted near one end to said first travelling block; means slidably connecting said second sliding block to said bar: a first circular gear pivotally attached to said first travelling block on the same pivotal axis as said longitudinal. bar; said first circular gear being responsive to the rotational movement of said bar about its pivotal axis; a second circular gear meshing with said first circular gear and being carried by said first travelling block; a recording medium; means to move said medium responsive to time; a recording pen movable perpendicular to the movement. of said medium; means to control the position of said pen responsive to the rotational position of said second circular gear.

2. An apparatus as defined in claim '1 in which means to move said recording medium is a clock motor.

3. An apparatus as defined in claim 1 in which the means to drive said recording medium is responsive to and proportional to the movement of said first. sliding block.

4. An apparatus as defined in claim 1 including means to adjust the position of said second sliding block.

References Cited UNITED STATES PATENTS 1,282,553 10/1918 Eaton .2... 235-6]'. 1,435,389 11/1922 Gross u--- ..s- 235-61 1,450,410 4/1923 Cox nu 235-61 2,096,995 10/1937 MiZell "up.-. uuuuuu 73--151.5 2,287,819 6/1942 Nichols "nu".-- 346-428 2,309,675 2/1943 Schlomann et al. u M l 235--6l. 2,935,87l 5/1960 Pearson ...-........,....Wn..l 73151.5

RICHARD B. WILKINSON, Primary Examiner.

J. W. HARTARY, Assistant Examiner.

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