CN1206837A - Method for measuring earth stratum density - Google Patents

Method for measuring earth stratum density Download PDF

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CN1206837A
CN1206837A CN 98108288 CN98108288A CN1206837A CN 1206837 A CN1206837 A CN 1206837A CN 98108288 CN98108288 CN 98108288 CN 98108288 A CN98108288 A CN 98108288A CN 1206837 A CN1206837 A CN 1206837A
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detector
neutron
density
gamma
rock stratum
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M·L·埃文斯
J·M·霍伦卡
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Anadrill International SA
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Anadrill International SA
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Abstract

Apparatus for determining the density of underground formations surrounding a borehole, such as a wireline logging tool or a logging-while-drilling tool, includes a neutron source for irradiating the formations from within the borehole and at least one detector which detects neutrons and gamma rays in the borehole resulting from the irradiation of the formations with neutrons. Multiple detectors can also be used to separately detect neutrons and gamma rays. Detected neutron and gamma ray signals are each analyzed and combined to determine the density of an earth formation.

Description

Measure the method for earth stratum density
The application is that on February 12nd, 1996 application, sequence number are that the part of 08/599712 application continues, this application has become No. 5608215 United States Patent (USP)s that are entitled as " method and apparatus of measuring earth stratum density ", and this patent is application on September 19th, 1994, be entitled as " method and apparatus based on accelerator that is used to measure drilling well simultaneously ", application number and be the part continuation of 08/307894 application, it has become No. 5539225 United States Patent (USP).
The present invention relates generally to the exploration of the earth formation of near surface, more specifically to the density measuring method that is used to carry out based on neutron accelerator.In the broadest sense, some aspect of disclosed technology relates to wireline logging and measures the technology of drilling well simultaneously.
Utilizing neutron flux to come measurement ring with the decay of the variable in distance of distance neutron source when wireline logging is known around the voidage of the earth formation of the near surface of drilling well boring.Particularly superthermal logging tool is sensitive for hydrogen density in the rock stratum or concentration.Because hydrogen normally finds in the liquid of rock stratum, the quantity of the void content in hydrogen concentration and the rock stratum thereby that is voidage relevant.Yet for the voidage of appointment, the increase of basement rock density (keeping same base lithification composition) can cause that epithermal neutron Detector count rate (for example being spaced apart 60 centimetres for the source to detector) reduces.If erect image for the basement rock density voidage increase of appointment will take place like that, can produce this variation along identical telegoniometer digit rate.Therefore, neutron voidage measurement itself can not be measured the not voidage of the rock stratum of principal component significantly.
Therefore, usually in wireline logging, by moving second downhole cartridge, be scattered in in the neutron voidage is measured the identical depth direction interval of downhole cartridge, carry out the volume density of the rock stratum paid close attention to and measure according to gamma-ray Compton from electronics.The increase of density causes that also the Detector count rate in the density downhole cartridge reduces.On the other hand, if increase for the basement rock density voidage of appointment, then the Detector count rate of density downhole cartridge increases.Therefore in the variation aspect basement rock density and the voidage neutron voidage and Compton diffuse density downhole cartridge are had good effect, this effect can be revised by the X plot of the response of two kinds of downhole cartridges.By utilizing this X plot, the physics problem can be resolved, and can measure the variation of basement rock density and composition (lithology).Because air inclusion also influences the response of neutron voidage and density downhole cartridge in the basement rock void volume, the X plot by neutron/density in some cases, existence that can detected gas.
Yet common volume density measuring technique needs gamma ray projector, is typically 137The Cs isotope source.From shining safe viewpoint, this radio chemistry radioactive source has significant disadvantages.This point will be paid close attention in the application scenario of measuring drilling well simultaneously especially, makes the loss and the ratio that cause the source probably more be difficult to recover in the wireline logging operation in this occasion condition of work.In fact, the prior art patent major part of above-mentioned measurement drilling well simultaneously mainly concentrates on and prevents leakage or missed these chemoluminescence sources of recovery.
Though the cable voidage downhole cartridge based on accelerator is known, for example, it is reported by No. 4760252 United States Patent (USP)s authorizing people such as Albast, also practical at present, in order to carry out density logging, need ratio 137The another kind of Cs gamma ray projector economy is based on the radioactive source of accelerator.Therefore there is for based on accelerator the demand of (can eliminate to the demand in chemoluminescence source in the conventional volume density downhole cartridge) downhole cartridge.
The invention provides some apparatus and method, they are included in the neutron accelerator of the high energy (preferably 14Mev (electron-volt)) in the drilling tool that removes with rope or the part of the drill collar in drill set, and at least one gamma ray detector and at least one neutron detector, perhaps for the single detector of neutron and gamma-rays, they and accelerator separate, around being used for measuring around the radiation that causes of the neutron irradiation of earth formation and indicate stratum density.Utilize known statistical technique (for example multicomponent linear regressioning technology of weighting or response surface method) that the neutron of detection and the gamma-rays of detection are handled, so that form density measurement by neutron that detects and gamma-rays influence.
In a preferred embodiment, installing one is used to monitor the detector of the nearly spacing of neutron source flux in this downhole cartridge, the superthermal thermal neutron detector of an important intermediate reach in response to the rock stratum hydrogen concentration and a gamma ray detector in response to the spacing far away of stratum density.The detector output of nearly spacing is used for other detector output the carrying out normalization to establishing because of the source strength fluctuation.To export through the epithermal neutron detector output of normalized intermediate reach with through the detector of normalized spacing far away and carry out combination, its mode is similar to the X plot of conventional neutron voidage one density, so that obtain the measured value of the gas of rock stratum voidage, volume density and lithology and/or detection.According to drilling depth applicatory, angle or orientation in boring, measure and record.
The detector of nearly spacing preferably utilizes the epithermal neutron detector of the material shielding of slowing down-intercept neutrons, and this material is insensitive for the neutron that comes from the rock stratum basically.Can comprise Mev level neutron detector in addition, for example by high Z material shielding 4He detector or liquid scintillator neutron detector.The epithermal neutron detector of intermediate reach can be one that constitutes in the similar a plurality of detectors that separate of detector array.This array can comprise a plurality of similar superthermal detector that separates along periphery around the inwall of drill collar.In array, also can comprise one or more gamma ray detector and/or thermal neutron detector.If desired, each detector of array can be along vertically separating in order to improve vertical resolution.The detector of spacing far away is gamma ray detector preferably, but also can comprise a high energy (＞0.5MeV) neutron detector, for example 4He or liquid scintillation bulk detector.In addition, the γ that can install a spacing far away penetrates the neutron detector of a detector and a spacing far away.Under the situation that adopts liquid scintillator, it can be configured and can detect neutron and gamma-rays.The measured value that neutron that detects and gamma-ray signal can provide stratum density independently.Can also be with these signal synthesis, to produce the stratum density measured value.
Under the situation of measuring drilling well simultaneously, a side of the best coaxial alignment of detector of neutron accelerator and nearly spacing and deflection drill collar is to adapt to the drilling fluid passage at the opposite side of drill collar.In order to improve sensitivity for the rock stratum, the recline inwall of drill collar of the best off-centre of each detector of array, and the back side shielding neutron that boring and drill collar transport that reclines.The detector of spacing far away is preferably coaxial and coaxial with the detector of nearly spacing with accelerator.Also conductively-closed is mobile to prevent along the neutron of boring and drill collar for it.Preferably, each neutron detector in array sees through window, so that improve sensitivity and raising investigation depth for the rock stratum in the face of being provided with neutron.In the preferred structure of subwindow comprise in the material that is coated on boron or other intercept neutrons for example titanium of low scattering cross-section material so that the neutron in the drill collar that will bleed is reduced to minimum.Can also form the external neutrons absorption layer, the place is formed with perforate in the neutron position of window, so that further reduce the neutron that flows in the drill collar.According to another kind of neutron window structure, transverse layers and/or longitudinal layer that the material by intercept neutrons constitutes can be housed, in drill collar so that decay wherein vertically and/or the neutron of circumferential flow.
Except above-mentioned crossplot technique, if desired, the detector output of can also centering equally spaced detector output and spacing far away is handled, so that obtain the out of Memory paid close attention to.For example, curve slowing-down time that is produced by each epithermal neutron detector of array can obtain the measured value in voidage and gap, and by obtaining the information relevant with the chemical constitution of rock stratum to carrying out spectrum analysis in the gamma-rays power spectrum of the gamma ray detector place of array record.Can carry out this spectrum analysis according to output in addition as the detector of the spacing far away that detects gamma-ray detector.Thermal neutron detector output is useful during in mensuration macroscopic capture cross section, rock stratum with in measurement clearance.Output also can be measured thermal neutron macroscopic capture cross section or its relevant thermal neutron fall time constant according to gamma ray detector.These additional measured values can use separately, or use when explaining basic X plot image.
The present invention detects by the neutron accelerator source and shines neutron in the rock stratum.The detector place that these neutrons separate at least one and source is detected.The present invention also utilizes neutron and the gamma-rays that produces in the nuclear reaction of inside, rock stratum, and in fact this rock stratum is used as and " once " source in downhole cartridge " secondary " gamma ray projector of comparing of chemical source for example.The neutron that is penetrated by accelerator penetrates drilling fluids and around the formation rock of downhole cartridge.These neutrons are with the atoms of elements nuclear reaction that constitutes this downhole cartridge, drilling fluids and rock stratum and produce the gamma-rays that returns the detector that advances to downhole cartridge inside.Perhaps by inelastic scattering or owing to heat capture can produce gamma-rays.The gamma-rays that is produced by the reaction of any type can be used as the secondary gamma ray projector, in order to density measurement.Yet, when formation characteristics changes, must in fact keep constantly in the position (degree of depth) of the secondary source of inside, rock stratum, otherwise the gamma-ray number change that is detected may be because the variation of secondary source position rather than stratum density change causes.The degree of depth in the rock stratum of penetrating thermal neutron depends on the size of the hot cross-section of rock stratum.It can sharply change with the concentration of the atomic nucleus with high absorbent capacity in rock stratum or drilling fluids (for example boron and chlorine).Therefore, the hot cross-section of drilling fluids and rock stratum is obviously depended in the position of the secondary gamma ray projector of heat capture.On the other hand, even because the non-resilient reaction of fast neutron produces the gamma-rays formation characteristics when changing also can produce in this identical zone (" focus).This effect is because two kinds of factors.At first, the fast neutron cross section difference of most of elements only is about 2 factors, and it is insensitive relatively that the gross section that makes rock stratum/boring changes for composition.Secondly, because it is very little in dissimilar rock intermediate change to constitute the concentration of the oxygen of essential element of most of sandstone type rocks and oxygen, almost be constant for the fast neutron cross section of most of sandstone type rocks.Be actually stable with regard to the position that has guaranteed the stiff gamma ray projector of secondary like this.
The intensity of secondary gamma ray projector depends on two kinds of factors (except the solid angle influence) neutron attenuation and concentration of oxygen atoms.By the neutron of source emission and the nuclear reaction in downhole cartridge, boring and the rock stratum.Because absorption and scattering drop to than low-lying level, fast neutron is attenuated.Because most of inelastic cross sections have high threshold value (being several MeV), the reduction of neutron energy is equivalent to because the absorption that the gamma-ray generation that is slackened causes.Therefore, the fairly obvious ground of the intensity of secondary gamma ray projector (by index) depends on for producing the number of the available high-energy neutron of non-resilient gamma-rays.Therefore, for adopting this density measure that carries out to comprise to the accurate correction of neutron attenuation to the influence of the intensity of secondary gamma ray projector.In addition, secondary source intensity is proportional with the atomic concentration of the material that should be used as the secondary gamma ray projector.Because the rock stratum is a gamma ray projector, clearly, to measure for stratum density, the non-resilient gamma-rays of oxygen is preferred source.At least owing to two kinds of reason this point are sure.At first, because oxygen is the abundantest constituent in the sandstone type rock, and its concentration only changes slightly to different rocks, and its use only needs very little correction for density measure.Secondly, oxygen sends the non-resilient gamma-rays of several high energy, utilizes simple energy discriminating and does not need the more frequency spectrum deconvolution of complex form, just can be easy to differentiate these gamma-rays by making gamma-rays take place to disturb.
Can proofread and correct the neutron attenuation effect by the signal that utilizes the state that reflects the fast neutron flux that produces non-resilient gamma-rays secondary source.By utilizing at the independent fast neutron detector of downhole cartridge inside providing, thereby can realize this point to independently monitoring of fast neutron decay.More briefly, by utilize this fact promptly with downhole cartridge in the neutron reaction of various compositions reaction cause forming stiff and gamma-rays epithermal capture, can disturb the fast neutron decay.For example, produce non-resilient gamma-rays with the fast neutron of iron in downhole cartridge reaction, its intensity changes in a kind of mode similar with excite the non-resilient gamma-ray neutron of generation in oxygen one secondary gamma ray projector.The gamma-rays that is produced by iron is very outstanding in non-resilient gamma-rays frequency spectrum, and therefore is easy to use and need not complicated frequency spectrum Deconvolution Technique.In addition, with the epithermal neutron of crystal counter in downhole cartridge reaction be known, can form a kind of signal with pine for the quite similar mode effect of minor voidage measurement.Because this crystal background comprises total non-resilient gamma-rays frequency spectrum of 50%-90% usually, the correction signal that produces the state that reflects fast neutron flux is not difficult.This can be as a kind of neutron attenuation correction signal of such density measure.
Introduce the present invention below with reference to accompanying drawings, wherein:
Fig. 1 is the synoptic diagram of an embodiment of " the simultaneously-measured piercing drill " that constitute according to the present invention represented with the part block diagram form, wherein and comprise the drill set that is hung by the rotary drilling platform;
Fig. 2 is the part vertical sectional drawing of expression in schematic form, and expression comprises an embodiment of the underground survey assembly of neutron accelerator and relevant each radiation detector;
Fig. 3 is the horizontal sectional view of being got along the section line 3-3 among Fig. 2, represents the optimum position of the detector of nearly spacing with respect to drill collar;
Fig. 4 is the horizontal sectional view of being got along the section line 4-4 among Fig. 2, subwindow in a kind of structure of expression array type detector and relevant each with respect to drill collar;
Fig. 5 is a local horizontal sectional drawing, the another kind of structure of expression array epithermal neutron detector and relative middle subwindow;
Fig. 6 is the local vertically sectional drawing of another embodiment of underground survey parts, another embodiment of subwindow in the expression;
Fig. 7 is the outside drawing of being got along the line of observation 7-7 among Fig. 6, the surface structure of the middle subwindow shown in the presentation graphs 6;
Fig. 8 is and Fig. 7 similar in appearance figure the surface structure of another embodiment of subwindow in the expression;
Fig. 9 is the synoptic diagram of wireline logging electrode system according to an embodiment of the invention;
Figure 10 is the graph of relation for the oxygen atom density and the rock stratum electron density of some rock stratum;
Figure 11 is for the oxygen counting rate of rock stratum that Figure 10 paints and the graph of relation of rock stratum electron density;
The present invention has special effect aspect wireline logging and the simultaneously-measured DRILLING APPLICATION two.Fig. 1-8 represents simultaneously-measured drilling technique of the present invention.
As shown in Figure 1, a platform and derrick 10 are located at the top of boring 12.It is inner and comprise a drill bit 16 in its lower end that drill set 14 is suspended in boring.Utilize universal stage 18 rotation drill set 14 and drill bits 16 fixed thereon, this universal stage by one not expression the device power supply and be connected the square kelly 20 of the upper end of drill set.Utilize a hook 22 that is fixed on the conveying device (not shown) to hang drill set.Be connected on this hook through a swivel 24 these square kellys, this swivel makes drill set this hook rotation relatively.In addition, drill set 14 and drill bit 16 can utilize one " top drive " type rig to be rotated by ground.Drilling fluid or mud 26 are contained in the mud sump 28 of contiguous derrick 10.Pump 30 is injected into the drilling fluid pressurization in the drill set through the aperture in the swivel 24, so that flow downward (as with shown in the flow arrows 32) through the center of drill set 14.Drilling fluid flows out drill set through some apertures in drill bit 16, and circulation upwards in the annular space between the periphery of the outside of drill set and boring then is as by shown in the flow arrows 34.Therefore, drilling fluid lubricating drill bit and take the landwaste of rock stratum to ground surface.On this surface, drilling fluid turns back to mud sump 28, so that recycle.
Preferably near drill bit 16 bottom hole assembly (totally marking with label 36) is installed in drill set 14, it comprises and is used for measuring processing and canned data and the various parts that are used for communicating by letter with ground surface.Best, this bottom hole assembly is located in the scope of several drill collar length of drill bit 16.In bottom hole assembly configuration shown in Figure 1, a stabilizator shank collar part 38 is located immediately at the top of drill bit 16, then is drill collar part 40, another stabilizator shank collar part 42 and another drill collar part 44 in the upward direction.This configuration of drill collar and stabilizator safety drill jig only is illustrative, certainly adopts other configuration mode.To depend on drilling condition in the embodiment shown in Fig. 1 for the needs of stabilizator safety drill jig or demand, each component part of underground survey assembly preferably is located in the drill collar part 40 of stabilizator shank collar part 38 tops.If desired, these ingredients can near or away from drill bit 16, for example or in stabilizator shank collar part 38 or 42, perhaps in drill collar part 44.
This bottom hole assembly 36 also comprises and is used for communicating by letter with ground data and controlling the remote observing and controlling assembly (not shown) of communicating by letter.
This bottom hole assembly 36 preferably also comprises conventional detection and handles and use the electronic installation (not shown), it comprises microprocessor system (having relevant storer, clock and timing circuit and interface circuit), can carry out timing controlled to accelerator and DATA REASONING sensor, storage is from the data of survey sensor, deal with data and event memory, and any required partial data is coupled to remote observing and controlling part, be transferred to ground.In addition, data can be stored in the down-hole and fetch at the place, ground when the shifting out of drill set.Be applicable to that this purpose electric circuit in well device did introduction in 4972082 and No. 5051581 United States Patent (USP)s.Be electrically connected and signal conveys for ease of surveying between the part in measurement component, data snooping and processing element and data, it is located adjacent one another that these parts are preferably in the drill set position.Be difficult for can adopting the data communication system in above-mentioned No. 5235285 United States Patent (USP)s under the situation about realizing, it can realize data communication and communicating by letter from the down-hole to ground in the short-range.Utilizing battery or utilizing provides the down-hole turbine generators of power to provide power supply for the down-hole electronic installation by drilling fluid.
The preferred embodiment of expression underground survey parts in Fig. 2-4, the part of drill collar shown in it 40 is around stainless steel tool body 54.Drill collar can be any suitable size, for example 8 " and external diameter, 5 " internal diameter.See as clear in Fig. 3 and 4, in housing 54, be formed with the slurry channel 56 of a longitudinal extension, be used for carrying drilling fluid downwards by drill set in a side of housing 54 longitudinal axis.With the outside of housing 54 neutron accelerator 58 control and the high-pressure electronic device packaging part relevant with it are set prejudicially, and the detector 62 of coaxillay aligned nearly spacing.This accelerator D-T type preferably well-known in the art (14 million-electron-volt) source.
The detector 62 of nearly spacing should be mainly with to the mode of rock stratum minimum influence in response to accelerator.For this reason, detector 62 can comprise an epithermal neutron detector, and for example one 3He proportional counter, its position insert highdensity screen layer near accelerator in the middle of being provided with.The sensitive volume of detector 62 is covered by cadmium or other high thermal-neutron capture cross-section material (not shown), so that improve detection threshold to superthermal magnitude.Be preferably in except near also utilizing screen layer 64 on all surface the part of accelerator 58 around detector 62, this screen layer 64 is by moderation of neutrons-neutron absorb composite material, and the boron carbide (or other 1/V type absorbing agent) that for example is dispersed in epoxy resin (or other hydrogenous material) bonding agent (" B4CE ") combines.In No. 4760252 United States Patent (USP)s (quoting here can be for reference), introduced about being used for this nearly spacing 3The more detailed information of the structure of the screen layer of He detector and performance.
In addition, nearly detector 62 can be the detector of higher-energy (MeV one million-electron-volt), for example 4The He detector, by tungsten, than heavy metal or other height-Z screen layer around so that detector and rock stratum shielding and multiplication are incided the number of the neutron of the non-rock stratum on the detector.Produce multiplier effect and be since high Z material big (n, 2n) and (it is transformed to the neutron that two or three are less than about 6MeV with the 14MeV source neutron, wherein for n, 3n) cross section 4The He scattering cross-section is big.Therefore, high Z screen layer has not only reduced the sensitivity for the nearly detector signal of the neutron of rock stratum scattering, but also neutron source (14MeV) neutron flux along this downhole cartridge is decayed effectively.
As what introduce below, each detector as spacing far away shields with B4CE (or material of similar slowing down absorption), the moderating power of the hydrogen in B4CE can be used for further reducing the energy of neutron, simultaneously, and the receptivity of the boron low-energy neutron flux that is used to decay.Shielding material, high Z's is very crucial near the material of neutron source and the putting in order of B4CE material (or similar material) of following, because just can not shield high-octane neutron effectively by opposite order.
The detector 62 of nearly spacing is eV (level) detector or MeV (level) detector, it should be such surveying energy, the displacement of nearly detector and the resultant effect of shielding, promptly will make detector output is insensitive relatively to the rock stratum voidage, and proportional with the neutron flux from accelerator basically.Nearly 62 of detectors can be used for making other detector output normalization because of the strength fluctuation influence in source.
A plurality of detector 66a, 66b, 66c and 66d (or claim array) position is closed on the detector 62 of this nearly spacing on vertically.This array comprises one and preferably comprise more than one epithermal neutron detector and at least one gamma ray detector at least.Can comprise alternative one or more thermal neutron detector.Just as shown in FIG. 4,2 superthermal detector 66a and 66b, a thermal neutron detector 66c and a gamma ray detector 66d are arranged.Can install detector or its mixing of varying number if desired.
The fundamental purpose of epithermal neutron detector 66a, 66b is to measure enough near the epithermal neutron flux in the rock stratum that separates a place of neutron source, so that make to heavier rock stratum element for example the influence of the detector output of these yuan vegetarian refreshments effective density major parts such as oxygen, silicon, carbon, calcium reduce to minimum, or at least obviously reduce, perhaps obviously strengthen the influence that hydrogen is exported for detector in the rock stratum.Locate like this, the response of epithermal neutron detector will depend primarily on hydrogen index, and lithology only has residual influence.In order to improve sensitivity, can be for the rock stratum 3The superthermal detector 66a of He proportion expression counter, 66b desired positions are very near the drill collar wall and the conductively-closed back side, shown at 68a and 68b, so that reduce the boring neutron response, this shielding material is preferably identical with the nearly detector 62 previous shielding materials of introducing, i.e. cadmium of Bao Fuing and B4CE.With more complete introduction, neutron sees through window 70a and 70b is preferably formed in the drill collar, so that further improve detector sensitivity and bigger probing depth is provided as below.
As shown in FIG. 4, epithermal neutron detector 66a, 66b and relevant window are preferably opened along the circumferencial direction cadmium of drill collar 40, be used to improve the angle or azimuthal resolution.Can adopt the circumferential interval of any required detector.Though shown detector 66a, 66b distributes by identical longitudinal separation apart from accelerator 58, can be in order to improve vertical resolution by different one or more additional detectors of longitudinal separation installing.In 4760252 and No. 4972082 United States Patent (USP)s, introduced in more detail along circumferentially and the detector array that separates of level, and with the structure relevant further details of each detector and their screen layer.As the high spatial resolution that the slowing down of being introduced is measured, make that the measurement of bearing according to slowing-down time of the present invention is had special significance and value in No. 4972082 patents.Should be pointed out that source/detector of being introduced is at interval at the drilling tool that removes with rope in 4760252 and No. 4972082 patents.Should form long slightly interval at the same time in the drilling well downhole cartridge of Ce Lianging, this is to consider such fact, and each detector is observed the rock stratum by drill collar.
Same thermal neutron detector 66c can be the band shielding 3He proportion expression counter shown at 68C, is removed beyond the cadmium clad that the rock stratum side is omitted, and is similar to superthermal detector 66a, 66b, so that detector is sensitive for the rock stratum thermal neutron.Neutron sees through window 70C and can be located in the drill collar 44 near thermal detector 66C.Can install additional thermal neutron detector as required, so that obtain required level and/or vertical resolution.Can be from the output signal 66 (c) of thermal neutron detector 66c according to handling of in the relevant portion of No. 4760252 United States Patent (USP)s, being introduced, so that obtain thermal neutron voidage measured value and/or obtain rock stratum sigma and clearance measurement value according to the disclosure of No. 5235185 United States Patent (USP)s.
Gamma ray detector 66d can comprise the detector of any suitable type, and for example NaI, BGO, CsI, anthracene etc., but ortho-silicic gadolinium (GSO) detector of cerium one activity preferably are as disclosed at 4647781 and No. 4883956 United States Patent (USP)s.As disclosed in these patents, the most handy boron is around the GSO detector, so that reduction heat and epithermal neutron are to the influence of explorer response.In addition, can between accelerator 58 and GSO detector 66d, insert-tungsten and or other high density screen layer (not shown) so that reduce the high-energy neutron flux incide on the detector.
Though do not give expression, should understand and to be provided with suitable timing and control circuits, so that according to pulse mode control operation accelerator 58 and selective control detector 66d as required, so that detect stiff gamma-rays and/or capture gamma-rays.The energy measuring scope is preferably wide, for example from 0.1 to 11MeV.The fundamental purpose of detector 66d provides stiff gamma-rays and/or captures gamma-ray power spectrum and the energy window counting rate.Particularly, this power spectrum can be carried out spectrum analysis, so that produce the relevant information of elemental composition of the rock stratum that is surveyed with quilt.
In No. 5440118 United States Patent (USP)s, introduced the optimization technique that is used to analyze from the frequency spectrum data of gamma ray detector 66d, so that obtain element spectrum and lithological information.In brief, utilize the least square frequency spectrum method of fitting to analyze inelastic scattering gamma-rays frequency spectrum, so that determine that supposition appears at influence that the coherent element contrast in the chemical element in the unknown earth formation produces and to the influence of the frequency spectrum of the measurement that obtains by this rock stratum.Relevant non-resilient yield to silicon, calcium and manganese is calibrated, so that provide for the direct estimated value of the volume ratio of each concentration of element of those elements in this rock stratum and each element or relevant rock type for example sandstone, lime stone and rauhkalk.The indication of degree of the dolomitized of rock stratum is provided for the ratio of the relevant non-resilient yield of magnesium and calcium.Also can determine to obtain the out of Memory relevant thus according to non-resilient yield with the rock stratum lithology from the calibration estimated value of each elemental yield of measured thermal capture gamma-rays frequency spectrum for the calibration of silicon and/or calcium.
Can obtain epithermal neutron slowing-down time and to the measured value in the downhole cartridge gap of distance the wall of a borehole by the output of epithermal neutron detector 66a, 66b.Because a large amount of steel is arranged as the long-life storage trap for neutron in drill collar 40 and housing 54, detector 66a, 66b obviously reduce for the sensitivity of epithermal neutron slowing-down time.Therefore in drilling well in order to measure the slowing-down time of epithermal neutron, detector 66a, 66b are very important with respect to the suitable location of drill collar 40, with the middle subwindow 70a, the 70b that form appropriate configuration and detector 66a, the 66b of suitably back side shielding.As shown in Figure 4 and point out above, detector 66a, the 66b of volume-sensitive preferably is installed in very near on the inwall of drill collar 40 and directly relative with separately middle subwindow 70a, 70b in the drill collar tool body 54.Preferably each detector is also at two ends with except carry out back side shielding (utilizing B4CE or suchlike thing) on all sides of the side of drill collar.Window 70a, 70b preferably by be covered by titanium in the boron or other high strength, low scattering cross-section material constitutes.In order further to reduce the inlet that enters drill collar 40, the boron carbide layer 72 with hole that the position with window 70a, 70b is complementary is preferably formed in the outside of the drill collar 40 in the detector area.Simulation test and experimental data show, according to locate in such a way, each detector of shielding and windowing, epithermal neutron is slowly than time highly sensitive in the detector that does not have window or outside boron screen layer with respect to the curve of voidage.
As expression in addition in Fig. 5, own by detector 74 being inserted drill collar 40, the boron carbide back side screen layer 76 and the outside boron carbide layer 72 of employing and the coupling of hole as shown in FIG. 4 can further improve detector sensitivity.Though this comprehensive convenient, detector is exposed, bigger damage risk is arranged, also need the machine work drill collar to form the detector container.
As a kind of another program that sees through window 70a, 70b for the neutron that adopts boron to seal, as shown in Figure 4, by forming the transverse layers of boron or other high absorption cross section material, the slowing-down time and the counting rate sensitivity that can improve epithermal neutron detector 66a, 66b in the drill collar 40 in the zone of epithermal neutron detector.In Fig. 6-8, represented this point.Fig. 6 drill collar wall and of reclining of representing to setover by the epithermal neutron detector 78 that is shielded by the back side shown in Figure 4.A plurality of horizontal boron carbide layers 80 are inserted in the drill collar wall, and they reach detector as " soft blind window " so that neutron energy lateral travel is passed drill collar therein, stop that simultaneously neutron flows along drill collar.The appearance graphic of the silicon carbide layer 80 in Fig. 7 presentation graphs 6.The figure of in Fig. 8, having represented another kind of boron carbide layer 82.This figure is used for and will longitudinally and circumferentially reduces to minimum by the neutron current of drill collar, but does not disturb cross flow.Therefore, boron carbide layer 80 and 82 function are as superthermal and middle subwindow thermal neutron detector basically.
As shown in Fig. 6-8, the employing of neutron absorbing layer have been found that for be reduced in low scattering cross-section material for example the neutron current in the titanium be particular importance, this is to being desirable as the drill collar material in the DRILLING APPLICATION of measuring at the same time, because it is to the suitable penetrability of neutron, but because density is lower, it can not make parallel with drill collar or decay to and identical degree with steel reached along the middle subdivision of its circumferential movement.For more effective, boron carbide layer also can be included in the tool body 54 of accelerator side, or on the both sides of neutron detector.
Come reference overall measurement modular construction as shown in FIG. 2 again, the detector 84 of spacing far away is located at the downstream of the detector array 66a-66b of the neutron shield layer 86 with insertion placed in the middle.Detector 84 and screen layer 86 are preferably coaxial with accelerator 58.According to the present invention, the detector 84 of spacing far away can be selected the location with respect to neutron source, so that be sensitive to pass relatively at a distance the neutron of MeV (level) energy (or, be preferably as the gamma-rays by the neutron of MeV (level) injection) in the rock stratum.Because compare with the neutron of KeV (keV)-eV (electron-volt) level energy, the motion of the neutron of MeV level energy has reduced for the sensitivity of rock stratum hydrogen index and has improved sensitivity to the density of heavier rock stratum element, the response of detector 84 is subjected to the strong influence of rock stratum effective density consumingly, and, influence the lithology of rock stratum because between density and basement rock type, have confidential relation.
Best, detector 84 comprises GSO gamma ray detector a kind of as that introduced in above-mentioned 4647782 and No. 4883956 United States Patent (USP)s, though, detectors such as for example anthracene of any suitable type, NaI, BGO, CsI can adopt, as long as can realize the statistical property and the energy resolution of the counting rate of permission.Preferred energy measuring scope is from 0.1MeV to 11MeV.In addition, the neutron detector to the neutron sensitivity of MeV scope (for example＞0.5MeV) can adopt.Preferred neutron detector is 4He type or liquid scintillation type.
Under the situation that adopts gamma-rays as the detector 84 of spacing far away, the screen layer 86 that inserts placed in the middle is preferably the material of B4CE or similarly moderation of neutrons-absorption.If adopt MeV (level) neutron detector, the preferably high Z material of screen layer 86, tungsten for example, the detector 62 of removing nearly spacing also utilizes high Z material to shield 4He (or other MeV class survey device) in addition.Under latter event, screen layer 86 should be B4CE or analog also, so that make full use of around the advantage of the above-mentioned degraded neutron effect of the high Z shielding material of the detector 62 of this nearly spacing.
Though the detector 84 of this spacing far away can be gamma ray detector or MeV level neutron detector, gamma ray detector is preferred, because gamma-rays ratio neutron in some cases has sensitivity preferably for gas.In addition, as recited above about array gamma ray detector 66d, the employing of gamma ray detector makes it possible to carry out spectrum analysis, so that obtain the elemental composition of rock stratum and the information of lithology.This spectrum analysis can two sides of the detector 84 of array type detector 66d and spacing far away or only a side locate to carry out.The output of arbitrary (or two sides) gamma ray detector can be used to obtain capture-measured value of cross section or its relevant thermal neutron constant slowing-down time (τ) for the rock stratum macroscopic view of thermal neutron (∑) in addition.Can adopt any known being used to obtain the technology of ∑ or τ for this reason.In addition, be under the situation of gamma ray detector at the detector 84 of spacing far away, if stipulated space or other condition, can omit the array gamma ray detector.
If desired, can install the detector (not shown) of second spacing far away.If like this, preferably its position is coaxial and approaching with it with detector 84.If detector 84 is gamma ray detectors, the detector of second spacing far away is neutron detector preferably, and is as the same against it.
Though specifically expression is not appreciated that above-mentioned each detector comprises amplification, shaping pulse, power supply and other required circuit entirely, so that produce the output signal that reflects the ray that is detected.All these circuit all are known in the present technique field.
In the embodiment that comprises two far detectors, detect neutron at a far detector place, detect gamma-rays at another far detector place.The neutron signal that is detected can be according to the technical finesse of introducing in No. 5539225 United States Patent (USP)s.The gamma-rays signal that is detected can be according to the technical finesse of being introduced in No. 5608215 United States Patent (USP)s.Can be with these two kinds of signal synthesis to utilize known inverse transformation technology (for example multiple linear regression of classical weighting (WMLR) technology or response surface method) to produce stratum density information according to neutron and gamma-rays signal.This WMLR technology in the present invention can be that this WMLR technology of being introduced in 08/532133 the U.S. Patent application (quoting here can be for reference) is similar to application number.
Can handle by variety of way from the signal that is contained in the several detectors in this downhole cartridge, so that obtain the information of required petrophysics aspect.(quote here can with reference to) can obtain the further details of this processing in No. 5539225 United States Patent (USP)s.
Fig. 9 represents the synoptic diagram of wireline logging downhole cartridge embodiment of the present invention.This downhole cartridge can be obtained by Schlumberger company as the RST-B downhole cartridge, and it comprises the downhole cartridge main body 100 that can reduce He log well by a drilling well in a usual manner.For clear, steel cable cable, remote-controlling electronic device and uphole equipment are omitted.One aforesaid substantially 14MeV D-T accelerator neutron generator 110 is in downhole cartridge main body 100 inboards.Near and far detector 130,140 is separated through a shadow zone 120.Each detector 130,140 comprises scintillator crystals 132,142 for example GSO (as being fit to or BGO or LSO), relevant photomultiplier 134,144 and can export the electronic device package part 136,146 that this is transported to the signal that ground is used to analyze.
Can carry out conversion to utilizing gamma ray detector to obtain measuring amount according to following scheme, detector can be written as follows for the response of the gamma-ray flux that is come by secondary source in this scheme:
N OX=CN Se -aXnP Oxe -bXc-cXpp(1) wherein: C=calibrates constant, N S=neutron source strength, e -aXnThe decay of=fast neutron; P Ox=rock stratum oxygen concentration, e -bXc-cXppThe decay of=gamma-rays.
Equation (1) is supposed fixed position of detector and is not comprised the solid angle effect.By in the calibration constant C, comprising them it is paid attention to.Neutron source strength N sIt is output level in the neutron source (Minitron) of neutron/second.
The fast neutron damping capacity depends on the fast neutron cross section Xn that determines by around the composition of boring/rock stratum environment.This fast neutron cross section is all various reactions (comprising elastic scattering, inelastic scattering and the charged particle generates) sum that influences the fast neutron motion.Certainly, the elastic scattering that is caused by hydrogen is most important.Therefore, the moderation length of boring/rock stratum environment is depended in the fast neutron motion strongly, and its mode is quite similar to be measured in the thermal neutron voidage, but has much smaller dynamic range.Because this reason, any detection signal that presents such correlativity can be used as the correction signal of this density measure.Correction signal can be the correction signal of fast neutron detector, thermal neutron detector, FS, or from for example non-resilient ion of non-resilient measuring amount itself or crystal background signal.
Because propose to utilize energetic gamma rays to realize this density measure by oxygen as secondary source, detected gamma-ray intensity will depend on the concentration of oxygen atoms in boring and rock stratum.Usually, oxygen concentration is unknown, but for great majority carrying deposition rock (sandstone, lime stone, rauhkalk, chlorite, muriacite, black mica, siderite and garnet) fluid be the (see figure 10) that can represent, the correlationship of oxygen concentration and rock density can utilize following simple linear relationship formula to represent:
P Ox=d+eP e(2) wherein d and e are constants, P eIt is the electron density index of rock.
The gamma-rays attenuation term has been represented the correlativity that the generation of non-resilient oxygen counting rate and Compton scattering and electron pair absorbs.Counting rate depends on generation (Xpp) cross section of Compton (Xc) and electron pair by exponential relationship.In pairs the product cross section depend on the rock stratum average atomic number Z square.Low ratio with the high-energy window is next measures rock stratum Pe to measure identical mode with standard density/lithology by utilizing, and average rock stratum Z can be derived out by non-resilient gamma-rays frequency spectrum.Therefore, can realize that Pe measures, and provides for the required correction estimated value of the generation assimilation effect of the electron pair in the equation (1).
It is every to remap, and equation (1) can be written as:
N Ox=K Poxe -bXc(3) wherein
K=CN se -aXne -cXpp(4) generation that comprises normalized constant, neutron source strength, neutron transport item and electron pair now absorbs.Slope in equation (2) reaches good approximation like this much smaller than 1.
P Ox=fe Gpe(5) with equation (5) substitution equation (3),
N ox＝Ke -bXcfe gpe
Electron density index Pe in Compton cross section Xc and the rock stratum is proportional.
Xc=hp eAnd new normalized constant can be determined
K s=Kf and
I=bh like this
N ox＝K se -(i-g)pe (6)
By equation (6) as can be seen, the oxygen concentration item is integrated in the density relations in the equation (1), only is used to reduce the sensitivity of non-resilient gamma-rays density measure.
Determine new sensitivity constant
k＝i-g
Obtain
N Ox=K se -kpe(7) or
N Ox/ K s=e -kpe(8) it is with identical about the response equation of chemical source density measure.Importantly to point out the oxygen counting rate N of correction by equation (8) Ox/ K sShow electron density by exponential damping rather than simply by N OxDecay.Utilize the left side of equation (4) EXPANSION EQUATION FOR STEEL (8),
N Ox/ K s=N Ox/ (CN se -aXne -cXpp) (9) wherein carry out the oxygen counting rate according to generation, neutron transport neutron source strength and the normaliztion constant of electron pair and proofread and correct, usually, neutron source strength is not a constant and must be to its monitoring and correction.
Can carry out Monte Carlo (Monte Carlo) simulation to check the validity of equation (7).A kind of 8.5 " Minitron in the fresh water boring for the basis 6.5 " model of LWD downhole cartridge is used for calculating from downhole cartridge the non-resilient gamma-ray intensity of boring and rock stratum.Get it right in the gamma-rays frequency spectrum of each element for each example studied and fast neutron spectrometer.The known average Z in fast neutron signal and rock stratum has been used to calculate the Ks of each example.N draws in figure (2) Ox/ K sLogarithm for the relation of the electron density Pe of each layer.
Can consult Figure 11 for sandstone, lime stone, rauhkalk and the clay of water and gassiness and the calculating of evaporitic rock.Can clearly be seen that by this figure non-resilient gamma-rays density measure can substitute the density measure based on chemical source effectively.Have only the data point that does not drop on the response curve to belong to evaporitic rock, it does not drop on the reflection oxygen concentration on the curve among Figure 10 of rock stratum electron density relation.In these examples, to compare with the sedimentogeneous rock that contains liquid, oxygen concentration is low, even density is high.This just forms low non-resilient oxygen counting rate and non-natural high density reading.In fact, by utilizing spectrum analysis, with non-resilient spectral decomposition for its elemental composition and then this information flag evaporitic rock or other do not satisfy the well-logging of the rock stratum type of equation (2), can differentiate these examples.
Need be to owing to change the non-resilient gamma-rays density value of the influence of borehole environment and proofread and correct based on the extensive employing of the drilling fluid of water, this is because the oxygen concentration that comprises based on the drilling fluid of water is very big.Can be according to carrying out bore hole compensated with the same way as that in the chemical source density measure, is adopted.Second detector that promptly comprises more near neutron source will provide method, with measure the downhole cartridge gap, influence is washed away in rugosity and boring.Utilize any scheme of advantage of difference of the radial sensitivity of two detectors can realize the correction of density logging record.In order to proofread and correct accurately, may need the information of common available soil profile.

Claims (22)

1, a kind of method that is used for definite around the underground earth stratum density of holing comprises:
A) by source irradiates rock stratum in boring inside;
B) detect because neutron and the gamma-rays that irradiation forms; And
C) gamma-rays of the neutron of analyzing and testing and detection is to determine the stratum density around described boring.
2, the method for claim 1, wherein said analytical procedure comprises the application inversion technique.
3, the method for claim 1, the step of wherein shining the rock stratum comprise utilizes the pulse neutron source irradiation.
4, the method for claim 1 wherein detects gamma-ray step and comprises the gamma-rays that detection is formed by the neutron scattering of the atom in the rock stratum.
5, method as claimed in claim 4 also comprises gamma-rays is carried out spectrum measurement and differentiates the gamma-rays that the neutron scattering by the atom in the rock stratum forms.
6, method as claimed in claim 5, wherein spectrum measurement is used to differentiate the lithology of rock stratum, this lithology is used for the density of correcting determination.
7, method as claimed in claim 5 also comprises the neutron attenuation of measurement in boring and rock stratum, and the gamma-rays that utilizes the attenuation analysis detection that detects.
8, the gamma-rays that the method for claim 1, the step that also comprises have the decay of the neutron in boring of being determined at and the rock stratum and utilize the attenuation analysis detection of measuring.
9, the method for claim 1, wherein the gamma-ray step of analyzing and testing comprises the oxygen concentration that is determined in the rock stratum and by oxygen concentration determination gamma-rays signal.
10, method as claimed in claim 9, the step that also comprises have the electron density index of measuring the rock stratum and utilize this assessment of indices density.
11, method as claimed in claim 10, wherein said detection to neutron be by:
Adorn first neutron detector at first interval apart from described source, the output of described first neutron detector is proportional with the neutron flux of described neutron source basically;
Adorn second neutron detector at second interval far away apart from described source, described second detector is sensitive to epithermal neutron, and its output is basically in response to the hydrogen concentration in the earth formation on every side, and just quadratic response in around the density of earth formation; And
Is being that the 3rd neutron detector is adorned at farther interval apart from described source, the output of described the 3rd detector is compared multiple response in the density of earth formation on every side with described second detector, and is less in response to the hydrogen concentration in the earth formation on every side.
12, method as claimed in claim 11 is wherein measured the signal that is produced by described detected neutron by the output of comprehensive described first, second and the 3rd detector.
13, method as claimed in claim 12, wherein said comprehensive step comprises by according to the output normalization of first detector output to the described second and the 3rd detector, and is comprehensive with this output with described first detector output and described second detector and the 3rd detector.
14, method as claimed in claim 13, wherein said comprehensive step further comprise describe the described second and the 3rd detector through normalized output X plot.
15, method as claimed in claim 14, wherein through normalized, by described to hand over the output of drawing be inverting through normalized output.
16, method as claimed in claim 13, wherein said comprehensive step is exported the numerical value that draws hydrogen index according to the first predetermined empirical relationship curve by normalized second detector, and the numerical value that is drawn moderation of neutrons length according to the second predetermined empirical relationship curve by the numerical value of normalized the 3rd detector output and described hydrogen index.
17, method as claimed in claim 12, wherein:
The output of the first and the 3rd detector is comprehensive so that measure high-energy neutron moderation length (L h) and low energy neutron moderation length (Lepi) at least one;
Interval longitudinally between second detector and source is essentially 2 times of low energy neutron moderation length (Lepi);
The output of first and second detectors is comprehensive, so that draw the measured value of hydrogen index; And
Describe described at least one L hThe X plot of measured value or Lepi measured value and described hydrogen index measured value is so that the voidage of the earth formation around obtaining and at least one in these two information of lithology.
18, method as claimed in claim 12, wherein:
Between described second detector and described source is the twice of low energy neutron moderation length Lepi longitudinally at interval basically;
Utilize the output normalization of the output of first detector to the second and the 3rd detector; And
Describe the X plot of the normalized output of the second and the 3rd detector, so that provide voidage, lithology and about there being at least one in these three information of gas in the earth formation around.
19, method as claimed in claim 12, comprehensive step wherein comprises:
The normalized output of the described second and the 3rd detector is comprehensive so that draw the hydrogen index and the high-energy neutron moderation length (L of earth formation on every side h) or the numerical value of low energy neutron moderation length (Lepi);
According to a predetermined relationship curve, with hydrogen index and L hOr the described numerical value of Lepi is comprehensive, and described this predetermined relationship curve is with L hOr the measurement numerical value change of Lepi changes with effective density for the demarcation rock stratum of known effective density, hydrogen index and elemental composition, so that obtain about the information of the effective density of earth formation on every side.
20, method as claimed in claim 12, comprehensive step wherein comprises:
The hydrogen index and the moderation of neutrons length of earth formation around measuring;
Be determined at poor between the described moderation length of the demarcation rock stratum that has identical hydrogen index and known effective density basically and the moderation of neutrons length; And
Will be mutually comprehensive with density one moderation length sensitivity ratio for the described moderation of neutrons length difference of demarcating the rock stratum, so that obtain and the relevant measured value of effective density of earth formation on every side.
21, the method for claim 1, wherein detect described neutron and be by:
Separate, install at least one radiation detector with described source, be used to detect the radiation that the described neutron irradiation by earth formation forms and be used for producing output in response to the radiation of described detection, this density that is arranged so that the rock stratum at interval can influence the radiation that is formed by described neutron irradiation; And
Will be as at least one the output record of described at least one detector of function in drilling depth and the orientation in boring.
22, a kind of method of measuring around the subterranean strata density of boring comprises
A) by source irradiates rock stratum in boring inside;
B) be formed on gamma ray projector in the rock stratum by the neutron of described radiation;
C) detect because neutron and the gamma-rays that radiation forms in boring; And
D) gamma-rays of the neutron of analyzing and testing and detection is so that mensuration is around the density of the rock stratum of described boring.
CN 98108288 1997-03-04 1998-03-04 Method for measuring earth stratum density Pending CN1206837A (en)

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