US2739475A

US2739475A - Determination of borehole injection profiles

Info

Publication number: US2739475A
Application number: US311017A
Authority: US
Inventors: Theodore J Nowak
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1952-09-23
Filing date: 1952-09-23
Publication date: 1956-03-27
Anticipated expiration: 1973-03-27

Description

March 27, 1956 4T. J. NowAK DETERMINATION OF BOREHOLE INJECTION PROFILES 2 Sheets-Sheet ll Filed Sept. 23, 1952 4 derramar' fum/- March 27, 1956 Filed Sept, 25, 1952 T. J. NOWAK 2,739,475

DETERMINATION oF BoREHoLE: INJECTION PROFILES 2 Sheets-Sheet 2 kami/mu ina/Mr United States Patent DETERMINATION OF BOREHOLE INJECTION PROFILES Theodore J. Nowak, Whittier, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application September 23, 1952, Serial No. 311,017

6 Claims. (Cl. 73-152) This invention relates to a method for logging well bores especially well bores, employed forntheinjectignf uids such as gases or liquids intiperiiieible underground strata." Particularly, this invention relates to the determination of the absloluteinjection profile in the secondary recovery of crude petroleiri""d'thlike.

Fluids are injected into permeable underground formations through a borehole penetrating such formations in several well-known types of operation. These operations include the underground storage of gases and secondary recovery operations in which gases or liquids such as water are employed to displace other valuable fluids through the permeable strata into a production well. The thus displaced iluids .are then recovered from the latter well usually by conventional pumping techniques. The secondary recovery operations are ordinarily resorted to only when the primary recovery processes, such as ilowing and pumping, have become uneconomical.

In the secondary recovery processes, a plurality of wells are drilled into and through the permeable subsurface strata containing valuable fluids. These wells are ordinarily spaced in a horizontal plane in a regular geometric pattern. For example, an injection well may be surrounded by 3, 4 or 6 production wells spaced at the corners of a triangle, square or hexagon, respectively. An injection fluid, such as gas or water or other specialized ud, is injected into the injection well, passes into and through the various permeable strata penetrated thereby and drives the valuable fluids present in such strata toward the surrounding production wells. Often the geologic structure of the Huid-containing formations is such that a plurality of permeable strata exists. Each stratum of the plurality may vary in thickness as well as in fluid permeability and thus the injection uid will pass at different rates into the different strata.

lt is highly important to the proper operation of these secondary recovery processes to be able yto ascertain exactly the locatio f each permeable stratum accepting fluid from th'we'l bore as well as the ratesadt whichfluid,

entersxervgrious strata;

Conventional spinner logs and the like are often used to locate points of ingress or egress of iluids in secondary recovery processes. These logs are subject to a number of serious problems. `The great majority of well bores are provided with casings to support the walls of the borehole. These casings are perforated along the casing length, supposedly opposite a permeable stratum into which uid injection is desired. Leaks in the casing at points other than the perforated sections appear in the spinner log as an injection point. Any vertical flow of injection iluid between the casing and the borehole wall which occurs after passage of the uid through the perforations and before entry into a permeable stratum renders a spinner log inaccurate as regards the true position at which the injection fluid enters the permeable formation. The spinner log is not subject to this disadvantage in an uncased well bore. However, it is a serious disadvantage in the usual cased injection borehole.

ICC

The present invention is directed to an improved method of logging a borehole into the earths crust and through which fluids are passed for injection into one or more permeable subsurface strata. The method permits the 5 determination of the absolute location or depth and the absolute thickness of the permeable strata receiving fluid from the bore and in addition permits a determination of the absolutewratewofiluidflowinw each such stratum. The subsequent descriptionl will be conducted relative to the logging of an injection well through which Water is passed into a permeable petroleum-containing formation to eifect the secondary recoveryof' Vthe crude petroleum. It should be understood, however, that the method may likewise be employed for the determination of injection profiles of gas entering underground reservoirs, secondary recovery processes using gas drive or in processes involving the injection of any other uids into underground strata.

Two highly important features of the present invention include the ability of the method to perform with high accuracy in uncased as well as in perforated cased boreholes. Another important feature is that the method permits the distinguishing of the rate of fluid injection into adjacent permeable strata which have differing iluid permeabilities; that is, strata not separated by irnpermeable strata.

It is a primary object of this invention to provide an improved method for logging boreholes. e

A more specific object of this invention is to determine the injecting; -gle in a well bore through which fluids are passedfll penetrated by the bore.

A more specific object is to provide a method for the highly accurate determination of the absolute length of a section of a well bore throughout which tluid passes from the bore into an underground permeable stratum as Well as a highly accurate determination of the rates tvyzhiclsiichjuidsgenter\@e.perrneablestrata.

One specific application of the present invention is in/j the determination of the location of water entry into sub?` surface petroleum-containing strata and therelativedis- .tributign of the injected gtegintoa plurality of. permeable strat.\-*-"" 'l Other objects and advantages of this invention will become apparent to those skilled in the art as the description thereof proceeds.

Briefly, the method of the present invention involves the accurate temperaturglgggu@ of an injection Well bore under" variousmoperating conditions and a comparison of the temperature logs so obtained to determine the limits of the various permeable strata receiving uid from the injection well bore as well as the liitiveminjection fluid In the present invention, accurate measurements of the temperatures of the fluid at various depths Within the Well bore are performed. One such temperature log is run during steadypstate injection of id. One or more such logs'arerun 'after the lnjectionwell iswshut in, e. g., the ow of lluid is stopped and no fluid is"`all6we'd to ilow through the borehole. A comparison of the temperature variations under injection and shut-in conditions permits a determination of the volumetric ow rate of injection fluid into the permeable underground strata.

The normal temperature of subsurface strata progressively increases with depth, often rising to 25W-300 F. at 10,000 foot depths and to higher values at greater depths. These temperatures are generally in excess of the temperatures at which the injection fluid is introduced into the injection well. Consequently, as the injection proceeds and the uid ows downwardly through the well bore toward the permeable strata, it is heated and the surrounding strata are cooled to temperatures below the 1 jection into permeable underground strata l normal geothermal temperatures (defined below). When injection is stopped and the well is shut in, the cooled portions of the strata adjacent the well bore and the stationary fluid therein are reheated by heat flowing radially inward by conduction from the uncooled outer reaches of penetrated formations toward the bore axis. The temperatures will eventually reassume the normal geothermal temperature gradient if the well is shut in A over a prolonged period.

Ordinarily the temperature of the subsurface rises roughly F. per thousand feet of depth along this geothermal gradient. There are several ways in which the geothermal gradient may be established. In an oil field in which a great number of wells have previously been drilled, a correlation of the bottom hole temperatures and depth of as many such wells as possible may be made. A measurement of the bottom hole temperature just following completion of the well is the most desirable since thermal disturbances at this point are then at a minimum. The geothermal gradient may also be determined by running a highly accurate temperature log through the bore after the bore has come into thermal equilibrium with the subsurface; that is, after a relatively long period of non-use during which no fluid flow through the bore has been effected. Typical geothermal gradients are shown as curves in Figures 2-4.

An accurate determination of the geothermal gradient for the reservoir under consideration is an important step of the present invention.

One step in the method of this invention is the determination of the injection temperature gradient through the borehole or at least through that part of the borehole embracing the strata receiving fluid therefrom. This temperature log indicates the changes in temperature of the injection fluid as it traverses the borehole. In most cases the fluid, when introduced, is at a higher temperature than the temperature of the formation through the first few hundred feet of depth of the well and in this region the injection fluid loses heat into the formation and is cooled. However, with increasing depth the normal or geothermal temperature of the subsurface rises and heat is received by the injected fluid and it rises in temperature. This heat is conducted radially inward toward the borehole axis.

When a permeable stratum deeplltlrejnhsu.fwnd v d'm flow f heat by condu il@ s halt o ra ized by the radial ou d flow of injemm remains unheated as indicated by constant temperature between the top and the bottom of the permeable stratum. From this constant temperature noted in the log which is run to determine the injection gradient, the upper and lower limits h1 and h2 of a permeable stratum receiving fluid from the well bore may be accurately located. This is true even though the fluid entering such permeable strata leaves the casing at a point above or below the particular stratum and enters the stratum after flowing vertically for some distance between the casing and the borehole Wall. In such a case the constant temperature portion ofthe injection gradient appears opposite the permeable strata receiving the fluid even though that portion of the casing is not perforated. Such injection gradients are shown as curves 42 in Figures 2 and 3 and curve 60 in Figure 4.

is-o the rapiditm Another step of the improved logging method of this invention involves slruttingzin the injection well; that is, terminating the flovr'cfjction fluid for a period of time during which Ano fluid is added or removed from the borehole. During this time one or more additional temperature logs of the borehole, or at least that part of the borehole which penetrates all the permeable strata, are run to determine one or more shut-in temperature gradients.

Intervals of as low as a few hours to as high as 30 or 40 days, when permissible, may separate the shutting in of the well and the running of the log to determine the shut-in gradient. r lQurrinU.. theshut-in period, the

,radial outward flow of injection Dtid througlmlpetrmeable "strataisreltrcedcioi andwcoiisequent y 'here' is Y zing effect --@Legen t e no al inward flow of heat by conduction through themous subsurfacTfr/atttzvard the borehole axis, which latter has been reduced in temperature by the prior flow of injection fluid. During this shit-*in period, therefore, the fluid temperature vyl(imirltl'bglfends v tomrise'l as the nor lali-*inward radialwrow oY heatrproceedsl" The temperature of thevinjection fluid within the well bore un er s ut-in conditions tends to rise more slow1`y`t fltliHFfftl-ie borehole than do the tem eratures o wthe mrmwmm'memme recmmfac ttFtadaUUtWard-f flow has absorbed heat from and cooled the permeable strata a relatively great distance from the bore axis whereas no such extensive cooling occurs in the impermeable strata through which no fluid flow occurs. The formation temperature in the permeable strata at a point any given distance from the well is therefore substantially less, due to the cooling influence of the injection fluid passing therethrough, than the temperature of an impermeable formation directly above or below this point and at the same distance from the well bore. Thus the flow of heat by conduction radially inward toward the borehole axis is very substantially slower in the cooled permeable strata into which injection fluid has passed than opposite the impermeable strata into which no fluid flows. Consequently, the fluid temperatures within the bore opposite the permeable strata rise more slowly after the well is shut in. The

curves

50 and 52 in Figures 2 and 3 and curve 62 in Figure 4 are typical shut-in gradients.

From an inspection of the shut-in gradient, confirming evidence of the presence of a permeable stratum receiving fluid from the well bore is found in the form of relatively low temperature portions of slow heating corresponding to the constant temperature portions of the injection gradient.

Certain boundary heating effects are noted in the shutin gradient at points corresponding to the upper and lower limits of the permeable strata. These boundary effects are caused by vertical heat flow from the warmer impermeable strata above and below a given permeable stratum into which the injection fluid passes. These boundary effects prevent the formation of sharp temperature changes in the shut-in gradient opposite the upper and lower limits of the permeable strata and hence, with one presently discovered exception, the limits of the permeable strata are determined from the injection gradient where sharp indications of constant injection fluid temperature appear.

The one exception referred to above is found in those cases in which two permeable strata are encountered side-by-side and not separated by a layer of impermeable rock, the two permeable strata having different fluid permeabilities. Under such conditions, the shut-in gradient shows a relatively sharp temperature anomaly opposite the point on the borehole axis at which the permeable strata of different permeability are in contact. This temperature anomaly is more clearly indicated and discussed in connection with Figure 4 and is of great importance since no dependable indication of this point is ordinarily obtained from the injection gradient.

After following the above described steps in obtaining the injection gradient and one or more shut-in gradients by temperature logging the well bore, the exact upper and lower limits of the permeable strata receiving fluid from an injection well bore may be located. In addition, the points at which two immediately adjacent permeable strata of differing fluid permeabilities are in contact may also be determined. The foregoing determinations have been proven accurate whether the borehole is uncased through the permeable interval or is provided with a perforated casing through this interval or is partly cased and partly uncased. These logging steps permit what might be called a qualitative determination of the presence of permeable fluid-receiving strata; that is, the location of the upper and lower limits of such strata. The additional steps by which a quantitative determination of injection rates are described below.

The geothermal temperature gradient is a smooth curve, the temperatures rising uniformly with depth from the surface. The injection temperature gradient is also a fairly smooth curve, with the constant temperature portions opposite permeable strata receiving uid discussed above. The shut-in temperature gradient is also a smooth curve except opposite the permeable strata, the temperatures Ts at any given depth rising regularly with time from the injection value Ti to the normal geothermal value Tg. The regular portions of a given shut-in gradient are smooth, but opposite the permeable strata anomalously low temperatures are noted due to the cooling effect of the radial outward uid ow therein. A simple extrapolation of the regular portions of the shut-in gradient opposite the impermeable strata across the temperature anomalies opposite strata receiving fluid gives the extrapolated equivalent shut-in temperatures Tes which would be expected from the shut-in gradient opposite the permeable fluid-receiving strata had no radial outward fluid ow taken place. At a given depth in a permeable stratum the shut-in temperature anomaly AT is Tos -Ts and is due solely to the cooling effect on the permeable stratum of fluid injected thereinto from the bore. It is proportional to the rate of such fluid injection into the differential stratum thickness at the given depth. The integral of AT as a function of depth h of the permeable strata is proportional to the volumetric rate of fluid injected into the whole stratum prior to shut-in. These temperature gradients and the anomalies referred to are more clearly shown in Figure 2 decribed below.

The mathematical relationships which are employed in the determination of the injection profiles from the shut-in temperature anomalies AT and the permeable strata depth limits h1 and h2 are simple.

At a given depth h in the permeable strata and after a given time following shut-in operation, the temperature anomaly AT is equal to:

AT=VTeSTs (l) or the difference between the expected shutain temperature Tes and the actual shut-in temperature Ts. The change of the value of AT with depth h through the permeable stratum is readily determined from the actual and the extrapolated shut-in gradients referred to above, thus AT is a known function of depth h.

Should extrapolation be difficult, a pseudo expected shut-in temperature gradient Tes in Figures 3 and 4 may be used instead by drawing a curve parallel to the geothermal gradient in the permeable interval and passing through the point on the shut-in gradient corresponding to the upper depth limit of the upper permeable stratum. Subtantially the same results are obtained.

As indicated above, it has been found that the integral of AT as a function of the depth of the permeable stratum h is proportional to the volumetric flow of injection fluid into the stratum. The integrated product A is:

h A=fh Ac/[(fmdh (2) and the individual stratum injection rate Q is:

Q=kA (3) wherein k is a proportionality constant. The integrated product A according to Equation 2 is the area between the extrapolated equivalent shut-in temperatures Tes and the actual shut-in temperatures Ts between the depths of the upper and lower permeable stratum limits h1 and h2.

The sum of the integrated products A is equal to:

EA or EA=A1+A2+A3 An (4) The sum of the volumetric injection rates Q into each permeable stratum equals the fluid injection rate Qo at the well bore inlet, or:

Q0=Q1+Q2+Q3 Qn (5) Substituting Equations 3 and 4 in Equation 5 the total injection rate Q0 is:

The individual volumetric injection rates are then directly calculable from Equations 3 and 6 and are equal to:

etc.

The drawings, discussed below, clearly illustrate the various temperature gradients discussed above and indicate the anomalous temperature differences AT between the extrapolated or expected shut-in temperature Tes and the actual logged shut-in temperature Ts opposite the permeable strata receiving fluid.

The total injection rate Qo multiplied by the ratio of the integrated product for a given stratum to the total integrated products for all strata is equal to the individual injection rate as indicated in Equations 7 and 8.

The temperature logs are ordinarily plotted as depth in feet as ordinate against temperature as the abscissa and the integrated temperature difference with respect to stratum thickness through each permeable stratum is readily determined for such logs; that is, it is equal to the anomalous area between portions of the equivalent and actual shut-in gradients which lie between the depth limits corresponding to the upper and lower depths of the particular stratum. These temperature gradients are conveniently recorded automatically on a temperature recorder of the moving chart type, which are well-known and commercially available, wherein the chart moves in position corresponding to the depth in the well bore of the temperature sensitive device employed to measure the Huid temperatures therein.

The method of the present invention as outlined above and the nature of the data obtained and the nature of the various temperature gradients referred to above are shown more clearly in the accompanying drawings in which:

Figure l is a schematic view in'cross section of an injection well showing the method of temperature logging,

Figure 2 indicates the appearance of the geothermal, injection and shut-in gradients obtained in the method of this invention,

Figure 3 is an expanded portion of curves in Figure 2 which are enclosed in the dotted rectangle, and

Figure 4 is an enlarged view showing in detail the temperature data obtained in logging a permeable stratum containing two adjacent permeable strata of different permeability.

Referring now more particularly to Figure l, well bore provided with casing 12 extends from the earths surface 14 down to and through two

permeable strata

16 and 18 separated by an impermeable stratum 20. The casing opposite the permeable strata are provided perforations 22 which permit the injection of injection fluid into the permeable strata. Injection fluid is introduced at the top of the well through line 24 at a rate controlled by valve 26 and flows down the bore, through the perforations into the permeable strata.

A temperature sensitive device indicated generally at 28 is suspended within well bore 10 by cable 30 which passes upwardly through the top of the well bore over sheave 32 and onto cable drum 34. Through slip rings, not shown, temperature recorder instrument 36 is connected to cable 3i). A temperature log is obtained by passing temperature sensitive means 28 through the well bore in contact with the injection fluid and the temperature indications obtained are plotted as a function of position or depth within the well bore by instrument 36. The temperature sensitive means may be moved slowly through the well bore or may be halted every few inches or every few feet while the temperature reading is obtained and recorded. The latter method is preferable since a more highly accurate temperature reading is thereby obtained.

Referring now more particularly to Figure 2, this figure is disposed to the right of Figure l in such a position that the temperature data appearing in Figure 2 correspond to the temperatures existing at points within casing 10 horizontally to the left in Figure l. In Figure 2 the locations of

permeable strata

16 and 18 are indicated at the left. Curve 40 shows the geothermal gradient normally existing through the undisturbed formations. Curve 42 indicates the injection gradient which is the variation in temperature of the injection uid, under constant flow rate conditions, with depth through the well bore. As is apparent, the upper portion of curve 42 indicates a drop in temperature which is usual in view of the fact that the injection fluid is generally warmer than the geothermal temperature just below the surface. The central part of the curve indicates a gradual warming of the injection fluid as it passes through deeper formations at increasing temperatures. That portion of curve 42 indicated generally as 44 is a zone through which fluid injection into permeable stratum 16 takes place, counteracting the normal geothermal heating effect and resulting in a constant temperature from the top to the bottom of this stratum. That portion of curve 42 indicated generally as 46 appears opposite impermeable stratum in which the normal geothermal heating occurs resulting in a slight temperature rise. That portion of curve 42 opposite permeable stratum 18 is indicated generally as 48 and through which the constant temperature characteristic of fluid loss is noted. The lowest portion of curve 42 shows a relatively rapid approach of the fluid temperature toward normal geothermal temperature at the bottom of the casing where little if any fluid liows.

Curves

50 and 52 indicate the shut-in temperature gradients after periods of 3 and 8 days respectively. In the upper three-quarters of each of these curves it is noted that the normal geothermal heating radially inward in the absence of injection fluid flow down through the bore causes the fluid temperatures within the well bore to rise from those of curve 42 and gradually approach the normal geothermal gradient as indicated in the upper threequarter portion of curve 40. However, the points opposite

permeable strata

16 and 18, into which injection fluid has been flowing and which has been cooled thereby, it is noted that a substantially lower degree of heating has taken place due to the fact that these strata have been extensively cooled due to fluid injection. The temperature log therefore obtained in actually determining these shut-in gradients exhibits a pronounced anomaly in temperature at positions in the bore corresponding to these permeable strata. These temperature anomalies are indicated by those solid portions of

curves

50 and 52 opposite

permeable strata

16 and 18 and to the left of the shaded areas. Had no permeable strata been present at these points, the shut-in gradients 5'0 and 52 would have included the dotted (extrapolated) portions to the right of the shaded areas. The normal geothermal heating takes place opposite impermeable stratum 20 so that those portions of curves S0 and 52 opposite this strata indicate the normal approach during shut-in toward the geothermal temperatures indicated by curve 40.

Referring now to Figure 3, an enlarged view in greater detail of the lower portion of the curves in Figure 2 is shown. The curves and portions thereof are designated in Figure 3 by the same numbers employed in Figure 2. The anomalous difference between Ts and Tes is clearly shown, this difference being AT referred to in Equation l. Whereas during 3 days shut-in, the temperature Ti would be expected to rise to a value of Tes, it only rose to a value TS and the difference AT is a measure of permeable strata cooling due to the injection fluid ow thereinto.

The determination of the location of the upper and lower limits In and h2 of

permeable strata

16 and 18 are obtained from the injection gradient, curve 42. Point a" is determined at the uppermost extremity of the straight or constant temperature portion of curve 42 opposite permeable stratum 16. The lower extremity of permeable strata 16, designated b" is determined where the inflection occurs near the lower extremity of the constant temperature portion of curve 42 or at the lower end of the sharply curved portion of curve 42. The slight curvatures above points a" and b" are caused by boundary effects resulting from vertical flow of heat. These points may be more accurately located in curve 42 than in curves or 52 and therefore the determination ot the upper and lower extremities In and hz of permeable stratum 16 is made from the injection gradient 42. A horizontal line drawn through points zz" and b" through the shut-in gradient, curve 50, defines the upper and lower dcpth limits on that gradient. An analogous determination of the limits of stratum 18 and any others is made as just described.

The normal geothermal temperatures existing at the depths /11 and h2 for

strata

16 and 18 appear on geothermal gradient 40 as points a, b, c and d. The integrated product A, as defined by Equation 2 given above, for stratum 16 is equal to the area bounded by a', a, b and b which is designated as A1 for shut-in gradient 50. In Figure 3, this area is the upper cross-hatched area. The total integrated product 2A is the sum or area A1 plus the area bounded by c', c", d' and d which is designated as A2 and is the integrated product for stratum 18. This is indicated as the lower cross-hatched area in Figure 3. The sum of the integrated products or areas A1 and A2 is in this example equal to EA, since only two permeable strata receive fluid. According to Equation 7, therefore, the injection rate Q1 into permeable stratum 16 is equal to the total injection rate Qo times the ratio of A1 to 23A. Obviously, the analogous calculation for the determination Q2, the liow rate into stratum 18, is Q0 times the ratio of A2 to EA.

A check determination of the shut-in gradient may be made after 8 days, for example, in which case shut-in curve 52 and extrapolated equivalent temperatures are employed in the same way. Good agreement is nearly always obtained between such check determinations when careful temperature logging procedures are employed.

Referring now to Figure 4, the nature of the data obtained when two adjacent

permeable strata

64 and 66 are encountered is shown. The geothermal gradient again appears as curve 40. The injection gradient is shown as curve 60. A single shut-in gradient is shown as curve 62 and again the anomalous temperature difference AT between the expected values of Tes and the actual values TS is indicated by a shaded area. The depth limits of permeable stratum 64 are indicated at h1 vedeva and ha, the upper and lower limits of adjacent permeable stratum 66 are indicated as h2 and h3. No normal geothermal heating during shut-in would be expected between the adjacent permeable strata at depth h2 due to the absence of an impermeable stratum therebetween. However, it has been found that the temperature rises during shut-n operation opposite these permeability discontinuities causing a higher temperature to appear at point b" corresponding to the line of demarcation between the

adjacent strata

64 and 66 at which the permeability changes. This effect is highly important since the injection gradient shows no deflection at point b" and thus the depth h2 is determined in this one exceptional case from the shut-in gradient 62 opposite the location of point b.

The relative injection rates of

strata

64 and 66 are determined according to the procedures outlined above; that is, the integrated product for stratum 64 is determined from area A3 bounded by points a', a, b, and b' and the integrated product corresponding to stratum 66 is determined from area A4 bounded by points b, b", c" and c'. The sum of A3+A4 is equal to 2A in Equation 6. The individual injection rates Q3 and Q4 are determined by multiplying the total injection rate Q in barrels per day times the ratio of A3 and A4 respectively to EA as described above.

As an example of the present invention, data are given, below in tabular form, which were obtained during the logging of an injection well, designated as Callender No. 90, located in the Dominguez oil field of Southern California. Prior to shutting in the total injection rate Qo was slightly over 990 barrels per day of oil eld brine. The well was logged to determine. the injection gradient according toV this invention. The well was then shut in for a period of 6 days and then again logged to determine the shut-in gradient. The permeable strata were found between depths of 5900 feet and 6365 feet and three principal injection zones appeared. The shut-in gradient was extrapolated across this interval and the magnitude'of the temperature anomalies AT ranged as high as 20 P. at the 6080 foot depth. The areas A were calculated for each 20 foot interval. The individual injection rates Q1 in barrels per day for each 20 foot intervaly 'were calculated according to Equation 7 and then calculated over to a volume per day per foot of depth basis. In the table below column l is the mean depth of theinterval considered, column 2 lists the upper and lower limits h1 and h2 of the interval, column 3 lists the integrated products (see Equation 2) A for each interval, and-columns 4 and 5 list the individual injection rates for each interval and rate per foot of interval respectively. i

Table Injection Rates in Mean Depth Depth Limits Integrated Interval of Interval, of Interval, Product It. ft. A, sq. in.

B./D. B./D./ft.

5, 910 5. 900-5, 920 0. 122 5. 95 0. 298 5. 930 5. 920-5, 940 0. 317 l5. 47 0. 774 5, 950 5, 940-5, 960 0. 44 21. 45 1.073 6, 010 6, OOO-6, 020 1. 41 68. 9 3. 445 6, 030 6, O20-6, 040 1. 62 79. 1 3. 955 6, 050 6. 040-6, 060 2. 04 99. 6 4. 980 6, 070 6, 060-6, 080 2. 04 99. 6 4. 980 6, 090 6, 080-6, 090 1. 82 88. 9 4. 445 6, 270 6, 260-6, 280 1. 76 86. 0 4. 30 6, 290 6, 280-6, 300 1. 73 84. 5 4. 225 6, 310 6, 300-6, 320 2. 20 107. 5 5. 375 6, 330 6, 320-6, 340 2. 20 107. 5 5. 375 6, 352 6, 340-6, 365 2. 58 126. 0 5. 03

The injection profile is obtained by plotting the incremental injection rate in barrels per day per foot in column 6 of thev table above against the depth of the increment. f

The continuous thermometric procedures usually employed to log bores involve moving the temperature sensitive element through the bore at velocities of from 40 to feet per minute. This has been found unsatisfactory in the method of this invention because the definition of the anomalies is lost. As much as a 50 foot error due to the thermal lag of the device has been noted.

A semi-continuous procedure has been found necessary wherein the temperature sensitive device is lowered at a rate of 500 feet per minute to a point just above or below the injection interval. At this point the device is stopped for a period of at least 10 minutes to attain thermal equilibrium. Then the injection interval is logged by passing the device through the permeable interval in increments of from l to 50 feet depending upon the thickness of the interval. In California oil sands of over 100 feet thickness, incremental depths of l0 to 25 feet are satisfactory while in other thinner sands an increment of 5 feet is employed. In any interval, the smaller increments give greater definition of the various injection strata.

At each incremental depth the temperature sensitive device is held stationary for a period of at least 3 minutes to reach local thermal equilibrium, the temperature reading taken and recorded, manually or automatically, and then the device is moved through the next increment and the temperature reading repeated. It has been found that injection intervals of several hundred feet in thickness c an be successfully logged with high degrees of accuracy in this semi-continuous manner in a period of a few hours and that no substantial temperature change occurs at a given point during that time.

Another requirement for successful logging to determine the shut-in gradient is that the injection well be shut-in for a certain period to allow all backow in the bore to cease prior to determination of the shut-in gradient. In most cases this period of delay should exceed 5 hours and preferably l0 hours or more should elapse. This period will vary with individual well bores.

The accuracy of temperature measurements is preferably as high as possible, being at least to the nearest 0.5 F. and preferably to the nearest 0.1 F. An Amerada gauge has been found satisfactory when used according to the semi-continuous method described above.

If possible temperature sensitive devices, such as thermocouples, thermopiles or others based on different principles, may be employed if greater accuracy may be obtained. Instruments correct to the nearest 0.l0 F. or better are highly desirable.

It is to be understood that the foregoing description and illustration of the method of this invention have involved the injection of a fluid which is at a lower ternperature than the underground permeable strata so that the strata are cooled and the fluid is warmed as it passes through the borehole. This is not a limitation of this invention because in cases where heated fluids are injected and pass through the borehole at temperatures above the normal geothermal temperatures, the fluids will be cooled and strata are heated. The injection gradient then appears to the right of the geothermal gradient, the same constant temperature portions thereof appear opposite permeable fluid receiving strata, and after shut in the fluids in the bore-hole opposite the impermeable strata cool more rapidly than uid opposite the permeable strata which have been extensively heated by the heated injection fluid. Analogous temperature anomalies appear in the shut-in gradients and the same calculations apply to determine the individual injection rates, e. g. the injection prole.

Further, the method of this invention is applicable to liquid or gaseous injection fluids because analogous thermal relationships have been found to apply.

A particular embodiment of the present invention has been hereinabove described in considerable detail by way of illustration. It should be understood that various other modifications and adaptations thereof may be made by those skilled in this particular art without departing from the spirit and scope of this invention as set forth in the appended claims.

I claim:

l. A method for determining the injection profile of an injection borehole penetrating an underground interval containing fluid permeable strata which comprises continuing the injection fluid ow downwardly through said borehole and into said strata at a steady rate; measuring the variation of injection fluid temperature within said borehole during injection by lowering a temperature sensitive device to a point adjacent the permeable strata within said borehole, holding it stationary for at least 5 minutes, moving said device through successive incremental depths opposite said permeable strata, holding said device stationary for at least 3 minutes at each incremental depth, recording the fluid temperature at each depth whereby the temperature variation with depth is established as an injection temperature gradient and whereby the precise upper and lower depth limits of the permeable strata receiving fluid are established from constant temperature portions of said injection gradient; subsequently shutting in the well for a period sufficient to terminate all back flow therein, then measuring the variation of the injection'uid temperature within said borehole in the absence of injection uid flow by the steps as employed to determine said injection temperature gradient thereby establishing a shut-in temperature gradient having temperature anomalies therein at depths corresponding to the permeable strata whereby the area of said anomalies bounded by the actual and the expected shut-in gradients and bounded by the upper and lower depth limits for each incremental depth of permeable stratum establishes the injection profile in terms of the incremental volumetric injection rate Q for each incremental depth of permeable stratum from:

(wherein Q1 is the incremental injection rate for the first incremental depth of permeable stratum, Qu is the total volumetric injection rate into said borehole, A1 is the incremental area of the temperature anomaly in the shut-in temperature gradient corresponding to the first incremental depth of permeable stratum, and EA is the total anomalous area opposite all of the permeable strata); and continuing the injection fluid flow into said borehole.

2. A method for determining the injection profile f a well bore through which injection fluids are passed into permeable underground strata penetrated thereby which comprises determining the injection temperature gradient within the well bore while continuing the fluid injection, shutting in the well for a period sufficient to terminate all fluid flow therein, next determining at least one shut-in temperature gradient within said bore in the absence of fluid ilow; said gradients being determined by the steps of lowering a temperature sensitive device to a point adjacent the permeable interval, suspending it at said point to attain thermal equilibrium therein, then passing said device through said well bore opposite the permeable interval, recording the indicated temperature of the fluid therein as a function of depth in said bore to establish said shut-in and injection temperature gradients; and then continuing the injection of said injection uid into said well bore; the precise depths of the upper and lower limits of each permeable stratum being established by constant temperature portions in said injection gradient, said shut-in gradient having anomalous regions through the depths corresponding to each permeable interval, the injection profile in terms of successive injection rates Q for each incremental depth difference in a permeable stratum being calculated from:

(wherein Q1 Qn etc. are incremental volumetric injection rates for each incremental depth difference in a permeable stratum, Qo is the total fluid injection rate into the well bore and into all the permeable strata penetrated thereby, A1 An are the anomalous incremental areas between said shut-in gradient and the expected shut-in gradient consisting of an extrapolation of said shut-in gradient through the anomalous temerature regions thereof, said areas being further bounded by the upper and lower depth limits of each incremental depth difference in a permeable stratum, and EA is the total of all the anomalous incremental areas A).

3. A method according to claim 2 in combination with the step of continuously measuring the depth of the points at which said temperatures are measured, and recording said temperatures as a function of depth within the well bore to record said injection and shut-in temperature gradients.

4. A method for determining the injection profile of a well bore through which injection uids are passed into permeable underground strata penetrated thereby which comprises determining the injection temperature gradient within the well bore while continuing the fluid injection, shutting in the well for a period of at least 10 hours to terminate all uid ow therein, next determining at least one shut-in temperature gradient within said bore in the absence of fluid flow; said temperature gradients being determined by lowering a temperature sensitive device to a point adjacent the permeable interval, suspending it at said point for at least 10 minutes to attain thermal equilibrium, then positioning the device successively through the permeable interval at a plurality of points separated by known incremental depth differences, recording the indicated temperature after holding said device stationary at least 3 minutes at each successive point, said temperatures being plotted as a function of depth within said borehole to obtain said shut-in and injection temperature gradients, and then continuing the injection of said uids; the precise depths of the upper and lower limits of each individual permeable stratum receiving fluid being established from the upper and lower limits of constant temperature portions of said injection temperature gradient; the injection prole being determined from the incremental in jection rates Q for each incremental thickness of said permeable strata which in turn are established from:

@FaQ-] ere.

(wherein Q1 Qn etc. are the incremental volumetric injection rates for said incremental thicknesses of permeable strata, Qo is the total uid injection rate into said well bore, A1 An etc. are areas of anomalous regions in said shut-in temperature gradient and which are bounded by shut-in gradient and the expected shutin gradient obtained by extrapolating the shut-in gradient through the anomalous temperature region thereof and further bounded by the upper and lower depth limits of each incremental thickness of the permeable strata, and 2A is the total area of the anomalous incremental area A).

5. A method for determining the injection prole of a well bore through which injection fluids are passed into permeable underground strata penetrated thereby which comprises determining the geothermal temperature gradient through the permeable interval, determining the injection temperature gradient within the well bore while continuing the fluid injection, shutting in the well for a period of at least l hours to terminate all lluid ow therein, next determining at least one shut-in temperature gradient within said bore in the absence of uid ow; said injection and shut-in gradients being separately determined by the steps of lowering a temperature sensitive device through the well bore to a point adjacent the permeable interval, suspending it at said point for at least minutes to attain thermal equilibrium, then positioning the device successively at a plurality of points separatedby incremental depth differences opposite the permeable interval penetrated by said well bore, recording the temperature indicated at each successive depth point after holding said device stationary for at least 3 minutes at each of said points, and continuing the injection iluid flow into said well bore; said injection temperature gradients having anomalous regions of constant temperature and said shut-in gradients having anomalous temperature regions thereon corresponding to the depths of each permeable stratum, the precise depths of the upper and lower limits of each permeable stratum receiving iluid being established by the upper and lower limits of said anomalous constant temperature regions in said injection gradient, the incremental injection rates Q for each incremental depth difference in each individual permeable stratum being calculated from:

(wherein Q1 Qn etc. are the incremental injection rates for successive incremental thicknesses, l n in the permeable interval, Q0 is the total tluid injection rate into all the permeable strata and is equal to the injection rate into said well bore, A1 An are the incremental anomalous areas between the shut-in gradient and a pseudo expected shut-in gradient consisting of a line drawn parallel to said geothermal gradient and extending through the precise upper depth limit of the permeable stratum, said incremental anomalous areas also being bounded by the incremental depth differences for each incremental anomalous area 1 n, and 2A is the total of all the anomalous incremental areas A).

6. A method of determining the injection profile of an injection borehole penetrating underground permeable strata which comprises continuing the flow of injection iluid through said injection borehole at a steady rate, measuring the Variation in injection iluid temperature Ti with depth in said borehole to obtain an injection temperature gradient at least through the permeable interval, shutting in the injection borehole to terminate tluid flow therethrough, remeasuring at least once the Variation in injection fluid` temperature Ts with depth of the stationary injection fluid present in said well bore to obtain at least one shut-in temperature gradient, and then continuing the injection iluid ilow; the upper extremity of each of said permeable strata penetrated being precisely established at a depth h1 below which Ti remains substantially constant, the lower extremity of each of said permeable strata being precisely located at a depth h2 at the inflection point below each constant temperature portion of said injection temperature gradient, an equivalent shut-in temperature gradients Tes being obtained by extrapolating said shut-in gradient through the anomalous temperature region thereof between depths h1 and h2, the incremental volumetric injection rates flowing into incremental thicknesses of the permeable strata being obtained from the relation:

(wherein Q1 Qn etc. are the incremental volumetric injection rates into each incremental thicknesses 1 n in the permeable interval, Qn is the total volumetric injection fluid rate in the borehole, A1 An etc. are equal to the integral of T es-Ts as a function of depth between the incremental depth limits h1 and h2 for each incremental thickness of each permeable stratum, and 2A is the sum of all the integrals of T es-Ts corresponding to all the permeable strata).

References Cited in the le of this patent UNITED STATES PATENTS 2,050,128 Schlumberger Aug. 4, 1936 2,172,625 Schlumberger Sept. 12, 1939 2,242,612 Leonardon May 20, 1941

Claims

5. A METHOD FOR DETERMINING THE INJECTION PORFILE OF A WELL BORE THROUGH WHICH INJECTION FLUIDS ARE PASSED INTO PERMEABLE UNDERGROUND. STRATA PENETRATED THEREBY WHICH COMPRISES DETERMINING THE GEOTHERMAL TEMPERATURE GRADIENT THROUGH THE PERMEABLE INTERVAL, DETERMINING THE INJECTION TEMPERATURE GRADIENT WITHIN THE WELL BORE WHILE CONTINUING THE FLUID INJECTION, SHUTTING IN THE WELL FOR A PERIOD OF AT LEAST 10 HOURS TO TERMINATE ALL FLUID FLOW THEREIN, NEXT DETERMINING AT LEAST ONE SHUT-IN TEPERATURE GRADIENT WITHIN SAID BORE IN THE ABSENCE OF FLUID FLOW; SAID INJECTION AND SHUT-IN GRADIENTS BEING SEPARATELY DETERMINED BY THE STEPS OF LOWERING A TEMPERATURE SENSITIVE DEVICE THROUGH THE WELL BORE TO A POINT ADJACENT THE PERMEABLE INTERVAL, SUSPENDING IT AT SAID POINT FOR AT LEAST 10 MINUTES TO ATTAIN THERMAL EQUILIBRIUM, THEN POSITIONING THE DEVICE SUCCESSIVELY AT A PLURALITY OF POINTS SEPARATED BY INCREMENTAL DEPTH DIFFERENCES OPPOSITE THE PREMEABLE INTERVAL PENETRATED BY SAID WELL BORE, RECORDING THE TEMPERATURE INDICATED AT EACH SUCCESSIVE DEPTH POINT AFTER HOLDING SAID DEVICE STATIONARY FOR AT LEAST 3 MINUTES AT EACH OF SAID POINTS, SAND CONTINUING THE INJECTION FLUID FLOW INTO SAID WELL BORE; SAID INJECTION TEMPERATURE GRADIENTS HAVING ANOMALOUS REGIONS OF CONSTANT TEMPERATURE AND SAID SHUT-IN GRADIENTS HAVING ANOMALOUS TEMPERATURE REGIONS THEREON CORRESPONDING TO THE DEPTH OF EACH PERMEABLE STRATUM, THE PRECISE DEPTHS OF THE UPPER AND LOWER LIMITS OF EACH PERMEABLE STRATUM RECEIVING FLUID BEING ESTABLISHED BY THE UPPER AND LOWER LIMITS OF SAID NAOMALOUS CONSTANT TEMPERATURE REGIONS IN SAID INJECTION GRADIENT, THE INCREMENTAL INJECTION RATES Q FOR EACH INCREMENTAL DEPTH DIFFERENCE IN EACH INDIVIDUAL PERMEABLE STRATUM BEING CALCULATED FROM: