US3899926A

US3899926A - Method and apparatus for continual compilation of a well data log

Info

Publication number: US3899926A
Application number: US268399A
Authority: US
Inventors: Elard L Haden
Original assignee: Continental Oil Co
Current assignee: ConocoPhillips Co
Priority date: 1972-07-03
Filing date: 1972-07-03
Publication date: 1975-08-19
Anticipated expiration: 1992-08-19

Abstract

A method and apparatus for obtaining a data indication log while drilling a well, such data log providing lithology indication of subsurface strata while the actual drilling operation proceeds. The apparatus consists of plural sensing and computational equipment interconnected so that well fluid conductivity readings, well fluid circulation rate, well fluid temperature, and drill pipe penetration rate are continually monitored in relation to constant data as to borehole size, drill pipe size and the volume of the bottom assembly equipment; all effective variables and constants being continually calculated to provide an output log which is comparable to a resistivity log, calculated data being output at the well-site to provide continual substrata indications relative to the drilling operation.

Description

United States Patent Haden Aug. 19, 1975 3,530] l() 9/ l 970 Beloglazov 73/153 Primary ExaminerJerry W. Myracle Attorney, Agent, or FirmWilliam J. Miller [75] Inventor: Elard L. Haden, Ponca City, Okla.

[73] Assignee: Continental Oil Company, Ponca ABSTRACT City, Okla. A method and apparatus for obtaining a data indica- [22] Fikid: July 3 1972 t on log while dr1ll1ng a well, such data log providmg lithology mdlcatlon of subsurface strata wh1le the ac- [21] Appl. No.: 268,399 tual drilling operation proceeds. The apparatus consists of plural sensing and computational equipment 52 us. c1. 73/153 f fluld f read [51 1 E2) 47/00 mgs, well fluid c1rculat10n rate, well fluld temperature, 58 Field of Search 73 153; 175 and i penetrm'on rate are Commuuny 9 tored 1n relation to constant data to borehole s1ze, [56] References Cited drill plpe size and the ,volurne ofthe bottoin aseembly I r H equlpment, all cffectne Vdfldblfih and conhtants bemg LNlrtD STATES PATENTS continually calculated to provide an output log which 3314974 9/1940 Hayward 73/153 is comparable to a resistivity log, calculated data being 3389b 7/1942 sufzm 4 73/153 X output at the well-site to provide continual substrata 2,346,203 4/1944 ZillkOWSk) t. 73/153 indications relative to th Operation- 3,386,286 6/1968 Moore 73/153 3,462.76] 10/1969 Horeth et al H 73/153 X 8 Claims, 4 Drawing Figures 26 MUD paw/p 2@ l f 22 MUD I -44 W4 M l 4 f 1/ J 5a 4a 4a 69 L 5 73 D/FFGREA/T/AL OIFFEEEA/ 77,44 MUD AMPL/F/EE AMPLIFIER WWW/w" COA/SMA/TS PM I 50 reMpae/z was 54 a2 ao l 7 FLU/D FLU/0 DRILL PM? CON/WNW), C/ECgjfig/OA/ PEA/Efflg/ON 69 L i i 40 HOLE 0,4771 COMPUTER M4 95 Dfi/LL -l08 p/ z- SIZE 02/22. 5 M L VOL UME RL'CUE/JIE METHOD ANII) APPARATUS FOR CONTINUAL COMPILATION OF A WELL DATA LOG BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates generally to the monitoring of well drilling operations and. more particularly, but not by way of limitation. it relates to a method for continually compiling a meaningful data log during the drilling operations.

2. Description of the Prior Art The prior art includes numerous methods and types of apparatus for compiling downhole log records of a well bore. but most previous teachings in this technology have utilized down hole devices utilized as a separate operation with the borehole cleared. Thus. it was mandatory to pick up the drill pipe and drilling equipment. a lengthy and expensive operation, and then utilize a separate equipment including cable and rigging to position various forms of borehole sensing device down within the hole in order to effect readings. Such testing procedures, or logs as they are referred to in the art. were of varied nature which included earth sample logs. mud logs. electric logs, radioactivity logs. and miscellaneous logs capable of giving a characteristic read ing relative to various substrata encountered along the borehole. Included within the miscellaneous classification are such as acoustic logs. caliper logs, temperature logs. dipmeter surveys. etc.. all of which required down hole equipment which. of necessity. had to be lowered into the borehole as a separate and time-consuming operation in order to effect sensing and transmit the usable readings to a surface meter or recording instrument.

There have been recent attempts to compile porosity logs and pore pressure logs through normalization of drilling data at the rig site while the drilling operation was proceeding. A gas saturation log has also proven feasible utilizing the similar approach. However, there has not yet been devised a suitable method or structure for keeping a continual resistivity or conductivity log. herein termed pseudo-resistivity log. which maintains a running data compilation during actual well drilling procedure. i.e. simultaneously with well fluid or mud circulation, drill bit activation, etc.

SUMMARY OF THE INVENTION The present invention contemplates a method and apparatus for compiling a data log during drilling operations to provide continual indication of borehole lithology. In a more limited aspect. the invention consists ofa plurality of sensing devices each adapted for deriving indication of specific variable parameters of the drilling operation. including mud conductivity. temperature. mud flow rate. mud particle content. etc.. such sensing outputs being processed and adapted for input to a computational device which also receives constant data pertaining to the bore hole and down hole equipment. A computational equipment either analog or digital. then evaluates all data in proper relationship to maintain a continuous log of desired bore hole data while actual drilling takes place.

Therefore, it is an object of the present invention to provide method and apparatus for deriving a selected data indication of borehole lithology during actual drilling procedure.

It is also an object to provide a method for deriving relative data indication of sub-strata along a borehole at greatly reduced expense.

It is still another object to enable derivation of a lithology log indication of pseudo-resistivity. temperature and the like without the necessity of a separate. time'consuming operation.

Finally, it is an object of the invention to provide apparatus for continually identifying subsurface strata onsite during the drilling operation and eliminating the need for various other separate logging operations.

Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially schematic block diagram of a system constructed in accordance with the present invention;

FIG. 2 is a block diagram of one form of resistivity derivation circuitry as may be utilized in the present invention;

FIG. 3 is a block diagram of an altemative form of resistivity derivation circuitry; and

FIG. 4 is a flow diagram of data procedure which may be utilized on site for compiling a pseudo-resistivity log.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1. a data log may be compiled at a drilling rig through utilization of a system 10 situated at the drilling site adjacent a well bore 12 and the related surface assembly I4. Surface assembly 14 is representative of the usual surface drilling equipment as is well-known for well drilling operations.

Included with the surface equipment are a drilling fluid or mud pump 16 receiving mud via flow line 18 from a mud reconditioning equipment 20 which may take the form of the various well-known apparatuses, i.e. shale shakers. cyclone separators, and the like. Drilling mud returning from borehole 12, as by upward travel through the casing annulus. flows via outcoming mud flow line 22 to a suitable reservoir or mud pit 24 which may include provision for cuttings settling and the like. and the drilling mud from mud pit 24 is passed through flow line 26 to the mud reconditioning equipment 20.

In conventional manner, drilling mud at predetermined pressure is driven by the mud pump 16 through entering mud flow line 28, i.e. including the stand pipe. rotary hose. swivel. etc. (not shown), for passage through the rotary table and down through the drill pipe string 30. At the bottom of borehole 12, the drilling mud is passed internally through a drill collar 32 for entry into a selected form of drilling bit assembly 34 whereupon released drilling mud with cuttings pick-up flows upward through the borehole or casing annulus 36 for exit through the return mud flow line 22 to the mud pit 24.

The data logging system 10 includes an on-site computer 40 of general or specialized type. and a plurality of sensing and data input devices each designed to derive a specific variable parameter for input to computer 40 in whatever the specified data or electrical signal form. An indication of resistivity is derived through a pair of

conductivity sensors

42 and 44 which provide outputs via

lines

46 and 48 to differential amplifier 50.

The

conductivity sensors

42 and 44, specific structure to be further described below, derive conductivity readings from the entering mud (to the well) and the out-coming mud. respectively. to provide output indication via

lines

46 and 48 to differential amplifier circuitry 50. The in-going mud conductivity reading is ap plied through a conventional storage stage 51 to be delayed by the time of mud circulation through the downhole portion of the flow. Thus. comparison readings are made for the same portion of mud at the two selected points of its circuit. Storage 51 is controlled from computer as will be further described. Differential amplifier then provides an output via line 52 which may indicate conductivity difference, and a fluid conductivity stage 54 provides suitable output on line 56 to computer 40 which is an indication of relative conductivity G (or the reciprocal resistivity R) of the mud as it includes drilled cuttings. particles, sediment, etc. Such relative conductivity indication is directly relatable to resistivity.

In order to give reliable credence to such relative conductivity or resistivity indication, it is necessary to take into consideration a number of variable parameters as well as a plurality of constants so that the resistivity indications can be made reliable and meaningful relative to the particular substrata which is being drilled at that time. Thus, data derived from the mud flow line is assembled to indicate the rate of drilling fluid or mud flow through analysis of data as to the rate of drill pipe penetration and various constants such as bore hole diameter, drill pipe size and the volume of the bit assembly and drill collar.

A temperature indication is derived from a suitable sensor 58, e.g. a thermocouple in contact with the mud, as inserted in the entering mud line 28 to provide indication via line 60 to a differential amplifier circuitry 62. A second temperature sensor 64 in out-coming mud line 22 provides indication of returning mud temperature via line 66 for alternate input to differential amplifier 62. lngoing mud temperature indication is stored for circulation time in storage 67 under control of computer 40. Practically. storage stages 51 and 67 may be comprised of a unitary device of conventional design under computer control as indicated by line 69. An amplified difference signal is then present at lines 68 for input to a temperature stage 70 which prepares or formats the differential output indication for input via line 72 to computer 40. Temperature stage 70 may be any of various well-known data preparation stages which transform the differential output into proper constitution for input in accordance with requirements of computer 40. Thus, it may be an analog operational amplifier stage or an analog to digital converter stage, depending upon the type of computational equipment utilized at computer 40.

The drilling fluid or mud circulation rate is also input to computer 40 as derived directly from mud pump 16 by a suitable sensing device 74. Sensing device 74 may be a conventional form ofdirect metering output which provides electrical output on line 76 by reading directly from the rotational components of mud pump 16. Mud flow indication on lead 76 may then be applied to such as an integrator 78 to provide an average flow indication whereupon such output is applied via line 80 to a fluid circulation rate stage 82 to provide output rate information in proper format or signal form for input via line 84 to computer 40. Still another variable, drill pipe penetration rate may be sensed by a suitable sensing device 86 to provide indication via line 88 through a drill pipe penetration rate formatting stage 90, and the properly prepared rate data or signal is supplied via line 92 to computer 40. The penetration rate sensing device 86 may be such as a conventional form of pulsing device providing pulse output in proportion to downward drill pipe movement or, alternatively, the drill pipe penetration data can be periodically updated through a simple manually operated device within access of the rig floor personnel.

It has also been found that in some cases it is necessary to enter still additional variable parameters relating to the mud dilution factor or particular drilling fluid constituencies. A dilution factor may be calculated using input constant data to determine earth material drilled per unit time or per foot. In many areas the percentage of cuttings recovered will decrease with depth. Thus, in order to account for the dilution of drilled material as penetration rates change, an evaluation of the amount of cuttings recovered at the shale shaker or such in mud conditioning 20 can be conveyed via suitable mud constants flow stage 94 for input to computer 40. Derivation of the mud constants may be automatic, by suitable sensing and signal determinative stages, or the information can be derived through continuous or periodic weighing of cuttings recovered on the shale shaker followed by appropriate data input to computer 40.

Constant data is also input to computer 40 via hole data stage 96, drill pipe size stage 98 and bottom as sembly volume stage 100. The hole data stage 96 merely inputs the constants relating to the borehole diameter versus the length of the borehole, the volumetric consideration of which provides mud volume when considered in relation to drill pipe inside diameter and the volume displaced by drill collar 32 and bit assembly 34.

Computer 40, being continually supplied with all variable and constant parameters, is able to provide an output indication of conductivity, or the reciprocal resistivity, continually and in relation to the bit contact area 102 as previously penetrated. That is, arrival of fluid from the hole bottom may take as much as an hour or more. Simultaneous mud resistivity readings or temperature indications must be delayed by a time which is a function of mud flow volume down the borehole and the fluid or mud circulation rate as derived from mud pump 16. Such delayed comparison is effected either by the inherent capabilities of computer 40, or by active storage stages 41 and 67, as will be further described below. Output from computer 40 may then be present on line 104 to a conventional form of log recorder 106 which will provide a continuous indication of pseudo-resistivity, temperature or such versus borehole depth. it may also be desirable to record indication of all or selected ones of the variable parameters relative thereto. and further forms of output from computer 40, may be made available via line 108 to a data output device 110. Data output device 110 may be such as a wellknown form of computer printout mechanism or a recorder providing an output in selected dif ferenc coordinates.

The data logging system 10 may be utilized to provide relative data indications of various parameters. Thus, resistivity data may be compiled to generate what may be termed a pseudo-resistivity log of the borehole.

Temperature corrections may be utilized in compilation of the pseudo-resistivity log. or a meaningful log may be constructed primarily utilizing temperature data alone. Recent findings indicate that a temperature log can be one of the best indicators of geo-pressure along a borehole.

FIG. 2 illustrates a particular form of circuitry wherein resistivity may be derived continually for a determinable bottom hole depth. Resistivity data is derived for out-coming mud flow line 22 for comparison with prior derived resistivity data from entering mud flow line 28. Proper delay insures that differences of resistivity data will be continually derived for essentially the same unit portion of the fluent mud material. The out-coming mud flow will of course contain cuttings, sediment and other solid and fluid materials which will serve to alter the resistivity data, such alteration being indicative of the form of strata at the borehole bottom, i.e. the penetration point at the time the particular material was drilled loose.

A suitable form of d-c generator 1 provides output current at a designated d-c potential on lead 112 for connection to each of

electrodes

114 and 116, in the entering and out-coming mud flow lines, respectively. Lead 112 is also connected through each of equal value current limiting resistors 118 and 120 to respective reference inputs of

d-c amplifiers

122 and 124. An additional pair of

sensing electrodes

126 and 128, disposed in the mud flow lines opposite the

respective electrodes

114 and 128, provide

inputs

130 and 132 to respective sense inputs of

d-c amplifiers

122 and 124. Thus, the

d-c amplifiers

122 and 124 operating from the same reference provide output in the form ofa d-c signal output wherein the amplitude of the output signal is a direct indication of the difference in conductivity between the two flow lines.

Output from (Le amplifier 122 is then applied through a switch 126:! to a suitable storage 134 which is operated under control of a circulation rate generator 136 to provide signal storage for the proper delay time of mud circulation. Switch 126ub is provided in order to illustrate that certain forms of operation will allow disabling of entering mud flow sensing, as there are many operations which will permit sensing of outcoming mud flow only thereby to derive meaningful resistivity information.

The storage 134 may be any of various analog devices, e.g. an endless wire or tape recorder synchronized as to desired mud circulation time through either transport speed control or read out head position as controlled in response to circulation rate generator 136. The circulation rate generator. driven as to pulse rate by the mud pump, and serving to control the speed of the recorder of storage 134 as a function of pulse repetition rate, such circuitry and storage technique being well-known in the art. Delayed output from storage 134 is then present on lead 138 to one input of a differential amplifier 140. An output d-c signal from outcoming mud amplifier 124 is present on a lead 142 to the remaining input of differential amplifier 140. A reference d-c voltage is applied from current limiting resistor 118 via lead 144 to provide a reference bias to differential amplifier 140. The switch section 12617 (shown open) can be actuated to interconnect leads 144 and 138 and provide reference potential to a reference input of differential amplifier 140 when the circuitry is operated in a single flow line mode of operation, as previously referred to.

Output from the differential amplifier is in the form of a difference signal proportionate to the difference in conductivity as between entering mud containing no cuttings and the same unit portion of mud material when detected as out-coming mud flow. The differential conductivity signal on a lead 146 may then be applied to a suitable form of operational amplifier 148 which serves to provide a reciprocal output. or the equivalent of a relative resistivity measure, as present on output lead 150. Such resistivity measure can also be further evaluated relative to the mud dilution factor for correction to a standard condition, e.g. cubic feet of rock per barrel of mud.

An alternative output on lead 146 may be applied to an analog/digital converter 152 such that coded, digital output is present on a lead 154 to terminal 156. A digital indication of conductivity difference at terminal 156 may then be utilized variously for further data derivation. Thus, digital output at terminal 156 may be applied to suitable formatting circuitry of well-known type to prepare digital data for input to the associated computer equipment. In the case of utilization of an analog computational machine, the time-analog signal present at the lead 150, and indicative of relative resistivity, can be applied directly for input to the computer as a time-varying continuous parameter.

FIG. 3 illustrates an alternative form of circuitry for processing the resistivity or conductivity data, such digital circuitry probably being more readily adaptable into the frame work of equipment presently used in the art. A change in voltage, A15 indicative of mud flow entering the well, for example derived from d-c amplifier 122 of FIG. 2, may be applied at input 160 to analog to digital converter 162 which converts the AE signal to digital form of preselected bit representation for input to digital storage 164. Digital storage 164 may be any of the conventional digital storage devices, tape, core, counter array, etc. A AE signal indicative of mud flow out-coming from the well, is applied at an input 166 to analog to digital converter 168, and the output from converter 168 is applied directly to a difference network 170.

Each of analog to

digital converters

162 and 186, and digital storage 164 are maintained under the control of clock circuit 172 via lead 174, and a circulation rate generator 176 is also controlled in accordance with the output of clock 172. Clock 172 may be any conventional form of pulse generator having the desired repetition rate for control of

converters

162 and 168 and digital storage 164. The circulation rate generator 176 may be constituted of conventional pulse delay circuitry wherein pulse output is delayed for a predetermined time, in this case the time as derived for mud circulation from the entering sensing point to the outcoming sensing point, whereupon a pulse output is provided via lead 178 for input to digital storage 164 to output the delayed AE (mud flow entering) data via line 180 to the difference network 170.

Each of analog to

digital converters

162 and 168, and digital storage 164 are maintained under the control of clock circuit 172 via lead 174, and a circulation rate generator 176 is also controlled in accordance with the output of clock 172. Clock 172 may be any conventional form of pulse generator having the desired repetition rate for control of

converters

Difference network 170 serves to receive the instant out-coming mud AE digital signal simultaneous with the properly delayed entering mud AE, digital signal to derive a difference digital signal as output on a line 182 to the related output devices, in this case an R data output 184 and a selected form of recorder 186. Thus, the AE- data could be directly recorded at this stage as a relative indication of resistivity, or the data could be applied to R data output 184 for derivation of conductivity G or the reciprocal resistivity R, for further application as input to the associated computer equipment located on-site.

Most accurate compilation and recording of data is probably enabled through utilization of a digital processing scheme. Also, digital computer equipment of either general or specialized purpose type is readily available in the art at present. Therefore, a total digital scheme utilizing an on-site digital computer and associated peripheral readout recorder may be the primary selection. FIG. 4 illustrates a data flow diagram which will enable utilization of such digital computational equipment.

Input conductivity data is presented at input stage 200, and this could be such data as derived at R data output stage 184 of FIG. 3. The computational scheme may be effected utilizing either conductivity or resistivity data, or temperature data as will become apparent. The conductivity quantities are reciprocal, and such data. as properly formatted and applied to input stage 200, would then be processed through a processing stage 202 which would include inputting on constants relative to hole size. drill pipe size, bottom assembly volume and the like. This annotation stage merely sets the constant parameters relative to the borehole and connecting mud line length, if any exists, between the upper borehole casing and the point of sensing; and these constants determine the total amount of drilling fluid or mud volume within the operating system which, in turn. will enable calculation of the circulation time of a given unit portion of mud. In the case where temperature log data is to be established. the data is input through flow stage 202 via line 203, as will be further discussed.

The process then proceeds to processing stage 204 wherein final determination as to mud volume is made through consideration of the instantaneous vertical length of the drill pipe. i.e. the data for depth of penetration. Time data is input at stage 206 to a predefined process stage 208 wherein calculation is effected utilizing all input constants and drill pipe vertical length to derive the drill pipe penetration rate relative to mud volume within the borehole. Flovv stage 210 their re ccives input data relative to fluid circulation parameters. and predefined process stage 212 calculates total drilling fluid flow rate through the predetermined portion of the flow system length.

Operational inputs as to temperature corrections and fluid data may also be considered at this point. Temperature data applied at input stage 214 is passed through a stage 216 to determine any temperature correction which may be required or advisable in the particular operation. Thus, if the data output is a parameter other than temperature, e.g. resistivity, affirmative output via line 217 from decision stage 216 supplied temperature correction data through the main process flow. If the final data, is a temperature log, data flow is via line 203 for input of temperature data at the initial processing flow stage 202.

Similarly, fluid data derivation at input stage 218 and rock and cutting data from stage 220 may require alterations, and in such case the processing stage 221 determines fluid constants, or variations from fluid constants, for further input to the main data flow. Input to stage 222 considers such variables as drilled cuttings removal, amount of rock drilled, amount of material dispersed, etc. The total fluid flow rate as calculated in predefined processed stage 212, as well as any temperature data correction and/or fluid data correction, are input to a predefined process stage 222 wherein final calculation is made as to the final bottom hole fluid data, i.e. a fluid resistivity, temperature or such selected measurement indicative of a relative data value at the predetermined strata.

Data output from flow stage 222 is then output in selected form, as for example to a suitable form of storage 224 and/or print out device 226, to provide a logtype continuous record of the printing operation relative to relative resistivity or pseudo-resistivity indication as derived throughout the drilling process. Other ancillary data as indicated by stage 228, such as substrata soil type, time notations, porosity indications, gas content indications, and the like may be entered for printout on the final record within stage 226. It should also be understood that the well parameter evaluations as variously derived heretofore, and as particularly directed to resistivity and temperature data, can also be used to identify and correct other measurements, e.g. redox potential, pH, specific ion concentration, color,

etc.

The foregoing discloses novel method and apparatus which enables compilation of a relative data indication or well bore log continuously, at the well site, throughout a drilling operation. The present invention enables compilation of valuable information as to lithology during the drilling operation and is capable of calculating various factors including an accounting for time difference of measurements taken (i.e. as between entering and outcoming drilling fluid), and the system can make corrections for temperature, pressure changes, changing penetration rate versus the mud dilution factor, etc. Any and all calculatable data inherently present relative to the operation ma be input to the final compilations; however, the number ofthese factors may be specifically limited in order to obtain a designated form of highl reliable relative resistivity or pseudo-resistivity (or temperature) log of the borehole Changes may be made in the combination and arrangement of elements as heretofore set forth in the specification and shown in the drawing; it being understood that changes ma v be made in the embodiments disclosed without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

l. A method for deriving a continuous pseudoresistivitv log indication of selected sub-strata through which a bore hole is being formed utilizing drilling equipment with drilling fluid circulation equipment. comprising the steps of:

continually deriving first electrical resistivity measurements from the drilling fluid entering said bore hole;

storing said first electrical resistivity measurements for a duration equal to circulation time ofa drilling fluid.

continually deriving second electrical resistivity measurements from the drilling fluid out-coming from said bore hole;

deriving a difference resistivity between said stored first electrical resistivity and the second electrical resistivity measurements:

continually deriving an indication of drilling penetration depth. and periodically deriving an indication of penetration depth change;

generating an indication of the total drilling fluid volume in the bore hole as well as the drilling fluid circulation rate a function of time to determine the amount of time for a unit portion of drilling fluid to circulate from the bore hole bottom to the bore hole top; and

recording said differential resistivity measurement on a time base delayed by said amount of time for a given portion of fluid to circulate from bore hole bottom to bore hole top in order to provide an out put display of electrical resistivity versus bore hole depth.

2. A method as set forth in claim 1 which includes the steps of:

deriving a drilling fluid dilution factor which is a coefficient indicating the relative consistency of said drilled borehole material; and

applying said dilution factor to said difference resistivity for recording such that a pseudo-resistivity log is compiled for said borehole.

3. A method for deriving a pseudo-resistivity log of sub-strata through which a bore hole is being formed utilizing drilling and drilling fluid circulation equipment. such pseudo-resistivity log being compiled using an automatic electronic data processing machine. the method comprising the steps of:

sensing entering drilling fluid to said bore hole at a first sensing point to derive first relative resistivity data for drilling fluid present at said second sending point; storing said first relative resistivity data for a duration equal to circulation time of said drilling fluid;

sensing out-coming drilling fluid from said bore hole at a second sensing point to derive second relative resistivity data for drilling fluid present at said second sensing point:

comparing said stored first resistivity data and said second resistivity data to derive a difference resis tivity data;

sensing bore hole penetration depth for evaluation with constant data as to bore hole diameter and volume of bore hole drilling equipment to derive total drilling fluid volume in circulation for input to said data processing machine;

sensing the rate ofdrilling fluid circulation for input to said data processing machine;

deriving time delay data representative of the time during which a given unit portion of drilling fluid will progress from the bore hole bottom to the outcoming drilling fluid sensing point; and applying said difference resistivity data to said data processing machine to generate an output indication constituting a pseudo-resistivity log of resistivity which is directly related to bore hole penetration depth. 4. A method as set forth in claim 3 which is further characterized to include:

sensing the difference in temperature of entering and out-coming drilling fluid and entering the tempera ture change data into said data processing machine as a periodic correction factor to output said pseudo-resistivity log as a function of temperature. 5. A method as set forth in claim 3 which is further characterized to include:

deriving a dilution factor proportional to size and amount of drilled earth material present in said out-coming drilling fluid and entering said dilution factor into said data processing machine as a periodic correction factor to output said pseudoresistivity log as a function of said dilution factor. 6. Apparatus for deriving a pseudo-resistivity log of earth sub-strata through which a bore hole is being formed by utilization of drilling and drilling fluid circulation equipment. comprising:

first sensing means including an electrical power source for deriving a first resistivity indication from the drilling fluid entering said bore hole; means for generating output indication of the circulation time of a unit portion of drilling fluid in said fluid circulation equipment; storage means for storing said first resistivity indication for a duration equal to the circulation time of said drilling fluids; second sensing means including an electrical power source for deriving a second resistivity indication from the drilling fluid out-coming from said bore hole; comparator means deriving a difference resistivity indication from said stored first resistivity indica tion and the second resistivity indication; means for indicating the instantaneous depth of said bore hole: means including a recorder receiving said difference resistivity indication and providing an output record of resistivity in relation to instantaneous bore hole depth. 7. Apparatus as set forth in claim 6 which is further characterized to include:

means sensing temperature of entering drilling fluid; means storing said temperature indication for a duration equal to said circulation time; means sensing temperature of out-coming drilling fluid; and means for comparing and deriving differential tem perature and recording output indication of temperature versus bore hole depth. 8. Apparatus as set forth in claim 7 which is further characterized in that:

said means including a recorder for providing output record of said resistivity and temperature is a digital data processing machine with peripheral display.

Claims

1. A method for deriving a continuous pseudo-resistivity log indication of selected sub-strata through which a bore hole is being formed utilizing drilling equipment with drilling fluid circulation equipment, comprising the steps of: continually deriving first electrical resistivity measurements from the drilling fluid entering said bore hole; storing said first electrical resistivity measurements for a duration equal to circulation time of a drilling fluid; continually deriving second electrical resistivity measurements from the drilling fluid out-coming from said bore hole; deriving a difference resistivity between said stored first electrical resistivity and the second electrical resistivity measurements; continually deriving an indication of drilling penetration depth, and periodically deriving an indication of penetration depth change; generating an indication of the total drilling fluid volume in the bore hole as well as the drilling fluid circulation rate as a function of time to determine the amount of time for a unit portion of drilling fluid to circulate from the bore hole bottom to the bore hole top; and recording said differential resistivity measurement on a time base delayed by said amount of time for a given portion of fluid to circulate from bore hole bottom to bore hole top in order to provide an output display of electrical resistivity versus bore hole depth.

2. A method as set forth in claim 1 which includes the steps of: deriving a drilling fluid dilution factor which is a coefficient indicating the relative consistency of said drilled borehole material; and applying said dilution factor to said difference resistivity for recording such that a pseudo-resistivity log is compiled for said borehole.

3. A method for deriving a pseudo-resistivity log of sub-strata through which a bore hole is being formed utilizing drilling and drilling fluid circulation equipment, such pseudo-resistivity log being compiled using an automatic electronic data processing machine, the method comprising the steps of: sensing entering drilling fluid to said bore hole at a first sensing point to derive first relative resistivity data for drilling fluid present at said second sending point; storing said first relative resistivity data for a duration equal to circulation time of said drilling fluid; sensing out-coming drilling fluid from said bore hole at a second sensing point to derive second relative resistivity data for drilling fluid present at said second sensing point; comparing said stored first resistivity data and said second resistivity data to derive a difference resistivity data; sensing bore hole penetration depth for evaluation with constant data as to bore hole diameter and volume of bore hole drilling equipment to derive total drilling fluid volume in circulation for input to said data processing machine; sensing the rate of drilling fluid circulation for input to said data processing machine; deriving time delay data representative of the time during which a given unit portion of drilling fluid will progress from the bore hole bottom to the out-coming drilling Fluid sensing point; and applying said difference resistivity data to said data processing machine to generate an output indication constituting a pseudo-resistivity log of resistivity which is directly related to bore hole penetration depth.

4. A method as set forth in claim 3 which is further characterized to include: sensing the difference in temperature of entering and out-coming drilling fluid and entering the temperature change data into said data processing machine as a periodic correction factor to output said pseudo-resistivity log as a function of temperature.

5. A method as set forth in claim 3 which is further characterized to include: deriving a dilution factor proportional to size and amount of drilled earth material present in said out-coming drilling fluid and entering said dilution factor into said data processing machine as a periodic correction factor to output said pseudo-resistivity log as a function of said dilution factor.

6. Apparatus for deriving a pseudo-resistivity log of earth sub-strata through which a bore hole is being formed by utilization of drilling and drilling fluid circulation equipment, comprising: first sensing means including an electrical power source for deriving a first resistivity indication from the drilling fluid entering said bore hole; means for generating output indication of the circulation time of a unit portion of drilling fluid in said fluid circulation equipment; storage means for storing said first resistivity indication for a duration equal to the circulation time of said drilling fluids; second sensing means including an electrical power source for deriving a second resistivity indication from the drilling fluid out-coming from said bore hole; comparator means deriving a difference resistivity indication from said stored first resistivity indication and the second resistivity indication; means for indicating the instantaneous depth of said bore hole; means including a recorder receiving said difference resistivity indication and providing an output record of resistivity in relation to instantaneous bore hole depth.

7. Apparatus as set forth in claim 6 which is further characterized to include: means sensing temperature of entering drilling fluid; means storing said temperature indication for a duration equal to said circulation time; means sensing temperature of out-coming drilling fluid; and means for comparing and deriving differential temperature and recording output indication of temperature versus bore hole depth.

8. Apparatus as set forth in claim 7 which is further characterized in that: said means including a recorder for providing output record of said resistivity and temperature is a digital data processing machine with peripheral display.