CN114647912B - Through-casing cement invasion model establishing method and through-casing stratum three-porosity measuring method - Google Patents
Through-casing cement invasion model establishing method and through-casing stratum three-porosity measuring method Download PDFInfo
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Abstract
The invention belongs to the technical field of well logging, and particularly relates to a through-casing stratum measurement cement invasion model establishing method and a through-casing stratum measurement method, which are designed aiming at cement uncertainty during through-casing stratum measurement. And based on the physical quantity influencing the three-porosity measurement, converting the physical quantity into the problem of the change relation between the density and the components of the solid cement, including the change of the migration length, establishing a cement intrusion model according to the change relation between the physical quantity and the components to determine the constraint setting corresponding to the measured physical quantity, and realizing the physical layer constraint of the problem of uncertainty of the quality of the solid cement caused by fluid intrusion into the solid cement. According to the stratum measurement method, the cement invasion model provided by the invention is added in the measurement process, the problems of low measurement accuracy and the like caused by the uncertainty problem of cement are reduced by utilizing the physical constraint of the cement invasion model, and the measurement accuracy after sleeving is improved.
Description
Technical Field
The invention belongs to the technical field of well logging, and particularly relates to a through casing cement invasion model establishing method and a through casing stratum three-porosity measuring method which are designed aiming at cement uncertainty during through casing stratum measurement.
Background
The development of the logging technology provides important parameters such as porosity, permeability, oil-gas saturation and the like for reservoir evaluation, and has important significance for the exploitation of oil-gas reservoir resources. In recent years, with the increase of the complexity of oil exploration depth and environment, deep wells are more and more, the difficulty of downhole operation is increased year by year, and in the face of complex well conditions, two lines (gamma resistivity) while drilling cannot meet the oil reservoir evaluation requirement, so that the operation risk of a conventional open hole well cannot be effectively controlled, and finally the risk coefficient of radioactive source measurement in the downhole is increased. The measurement after sleeving can avoid some possible engineering risks, shorten the construction period, and meanwhile, the measurement after sleeving can reevaluate the old well, so that the management of known oil and gas resources is improved.
The post-nesting technique is currently in the preliminary stage. Compared with an open hole well, the cased well measurement difficulty is higher, because a metal casing and a cement layer for well cementation are added in the cased well, the cased well is inevitably influenced by the casing and the cement during the casing passing measurement, and the uncertainty (such as mud invasion or cement shrinkage) existing in the well cementation process makes the process of instrument detection and signal acquisition more difficult to carry out system correction and quantitative evaluation. In contrast, the scholars at home and abroad make a great deal of research on the aspects of cement bond formation factor, well cementation evaluation and the like, and provide schemes such as acoustic amplitude cement bond logging (CBL-VDL), sector cement bond logging (SBT), ultrasonic cement evaluation and the like; in practical application, however, the quantitative evaluation of cement is difficult to implement, and the uncertainty of environmental parameters after the quantitative evaluation of cement can cause great interference to the acquisition of underground detection signals, so that the measurement result of the scheme is inaccurate. In order to solve the problem of cement uncertainty in the measurement of the through-casing stratum, a cement invasion model suitable for the through-casing stratum needs to be researched.
Disclosure of Invention
The invention aims to solve the technical problems that the existing after-casing measurement technology is influenced by cement uncertainty, has high correction difficulty and low measurement accuracy, provides a through-casing cement invasion model establishing method and a through-casing stratum three-porosity measurement method, and can convert the cement uncertainty problem during casing measurement into the problem of the change relation between cement density and components by using the cement invasion model, so that the problems of low measurement accuracy and the like caused by cement uncertainty are reduced, and the after-casing measurement accuracy is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a through-casing cement invasion model building method comprises the following steps:
step 1, setting solid cement containing invaded substances as a homogeneous medium, namely uniformly mixing the invaded substances with the solid cement, and setting the type of the invaded substances as m; the problem of influencing logging is determined according to the three-porosity measurement principle after the well is sleeved: migration length, solid cement density and composition change, wherein the composition change refers to the proportion of invasion cement substances in the solid cement; establishing a relation (1) among the density of the solid cement, the density of a substance invading into the solid cement and the density of the solid cement after mixing the invading substance so as to convert the cement uncertainty problem into a change relation problem of the density and the components of the solid cement;
ρ c ＝q·ρ fluid +(1-q)·ρ solid (1)
in the formula (1), ρ c The density of the solid cement after mixing of the invader, q is the invader volume ratio, ρ fluid For invasion of material density, ρ solid The density of the solid cement is the density of the solid cement; meanwhile, the formula of the composition change of the solid cement can be obtained based on the proportion of the invaded substance is as follows:
in the formula (2), q i 、ρ i The volume ratio and density of the i-th invasive substance respectively; q. q of cem 、ρ cem Solid cement proportion and density respectively; m is a unit of i_e 、m cem_e The mass ratio of the representative element 'e' in the i-th invading substance and the solid cement, and the specific element is determined by the specific material components;
step 2, according to the density range of the conventional solid cement of 1.3-1.9 g/cm 3 Setting the density of solid cement in the well logging after sleeving, and setting the elements and density of the invaded substance according to the analysis result of the reason for generating cement cementation by the invaded cement after sleeving; mixing the set cement with different solid densities and various invasion substances according to different proportions to obtain a cement invasion model database;
step 3, according to actual requirements, selecting corresponding data from the database obtained in the step 2 to substitute the formula (1) and the formula (2), and obtaining a cement invasion model; it should be noted that: the actual requirement for neutron porosity measurement further includes calculating the increased migration length based on the set composition in the database. The model is used for carrying out constraint setting on the measured physical quantity and realizing the constraint of the uncertain problem in the three-porosity measurement of the physical layer surface.
Further, in order to further improve the logging accuracy, the cement invasion model database also includes a variation relation between different well diameters and cement areas under the condition that the set casing outer diameter is not changed; and then mixing the invasion substances with cement according to different proportions according to different well diameters to obtain cement invasion model data.
The method for measuring the three-porosity of the through-casing stratum by using the cement invasion model obtained by the method comprises the following steps:
step A, obtaining logging curves with multiple dimensions according to actual logging requirements, and naturally layering a measuring depth section by combining the logging curves with the multiple dimensions through a logging curve natural layering algorithm to obtain stratum parameters of each layer; selecting a corresponding cement invasion model from the cement invasion models obtained by the method according to the layering result;
step B, establishing a detector forward model under corresponding environmental parameters corresponding to the cement invasion model selected in the step 1, wherein the detector forward model refers to a response model obtained according to the environmental parameters corresponding to the selected cement invasion model, and can be understood as a mathematical relationship between the environmental parameters and the detector response parameters; in the detection forward modeling, environmental parameters are determined by the measured physical quantity, and corresponding parameters of the detector are obtained from simulation or experimental data;
and 3, establishing a stratum inversion model by using the detector forward model established in the step B, and solving the stratum inversion model to obtain the measured stratum parameters and the cement reference curve.
Further, in the step a, a logging curve natural layering algorithm is adopted to naturally layer the multidimensional curve, and the detailed process is as follows:
step A-1, determining the weight of each curve based on the correlation of each logging curve, wherein the higher the correlation is, the larger the weight is;
and step A-2, determining the use sequence of each curve in layering according to the weight determined in the step A-1, wherein the larger the weight is, the more dominant the use is.
And step A-3, finishing layering by progressive judgment according to the sequencing result of the step A-to obtain stratum parameters of each layer.
Furthermore, the detector model established in the step B is a forward model under the condition of a single invading substance, so that the concrete invading model is favorably refined, the forward model parameters are reduced, and the forward model precision is improved.
The invention provides a method for establishing a through-casing cement invasion model, which is used for converting a problem of uncertainty of quality of well cementation cement caused by invasion of slurry or formation fluid into solid cement during cement cementing into a problem of change relation between density and components of the solid cement based on physical quantities influencing three-porosity measurement, including change of migration length, and establishing a cement invasion model according to the change relation between the physical quantities to determine constraint setting corresponding to the measured physical quantities, so as to realize physical layer constraint on the problem of uncertainty of quality of the solid cement caused by invasion of the slurry or the formation fluid into the solid cement. Aiming at the cement invasion model, the invention also provides a method for measuring the three-porosity of the through-casing stratum by using the cement invasion model, wherein in the measuring process, a logging curve with multiple dimensions is obtained according to the actual requirement, and the logging curve natural layering algorithm is adopted to carry out natural layering on the multi-dimensional curve so as to obtain stratum parameters of each layer; then, selecting a proper cement intrusion model to establish a detector forward model under corresponding environmental parameters based on stratum parameters obtained by natural layering; and finally, establishing a stratum inversion model based on the detector forward model, and solving the stratum inversion model to obtain the measured stratum parameters and the cement reference curve. The physical constraint of the cement invasion model is utilized in the logging process, so that the problems of low measurement accuracy and the like caused by cement uncertainty are solved, and the measurement accuracy after sleeving is improved.
Compared with the prior art, the invention designs various cement models from the actual well cementation angle, can realize the measurement of the three-hole degree after the casing under the condition of cement uncertainty, and can provide reference basis for well cementation cement, thereby improving the accuracy of the measurement after the casing.
Drawings
FIG. 1 is a flow chart of a cement uncertainty analysis model for through-casing formation evaluation provided by the present invention;
FIG. 2 is a flow chart of an algorithm for achieving automatic well stratification using a log according to the present invention;
FIG. 3 is a flow chart of logging using a selected cement invasion model in an embodiment;
FIG. 4 is a schematic diagram of an ideal cement homogeneous mixing model;
FIG. 5 cement intrusion model example;
FIG. 6 is a schematic view of a through casing measurement;
FIG. 7 is a flow chart of an embodiment of a log natural layering algorithm for natural layering of curves in multiple dimensions;
FIG. 8 is a schematic of a three-porosity measurement after applying a cement uncertainty analysis model.
Detailed Description
For a better understanding of the objects and advantages of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
Before the description, the three logging modes involved in the three-gap measurement, namely gamma density logging, neutron porosity logging and sonic moveout logging, are analyzed in detail:
gamma density log
Gamma density logs are typically cesium-137, emitting gamma rays with an energy of 0.662 MeV; the gamma rays enter the formation after being attenuated by the casing and cement and compton scatter by interacting with electrons in the atoms that make up the formation. Compton scattering reduces the energy of the gamma rays in a step-wise manner and scatters the gamma rays in all directions. When the energy of gamma rays is less than 0.5MeV, they may undergo photoelectric absorption through interaction with atomic electrons. Thus, the gamma ray flux reaching the detector is attenuated by the casing, cement and formation by an amount that depends on the density of the gamma ray through the medium.
The gamma-nested post-measurement problem can be classified as a particle transport and deep penetration type problem, which can be described as follows using boltzmann transport equation (using a spherical coordinate system r = r (r, z, θ) in a three-dimensional environment):
where r is the spatial coordinate, E is the energy, Ω is the direction, μ to (r, E) is the total linear attenuation coefficient, [ integral ] dE '[ integral ] d Ω' μ (r, E '→ E, Ω' → Ω) Φ (r, E ', Ω') is the collisional term, and S (r, E, Ω) is the gamma ray source density.
The non-collision point nuclear model assumes no contribution of scattered or secondary gamma rays, i.e. in the equation, the collision term is set to zero:
in space r s Monoenergetic, isotropic source S of 0 Solving the above equation in homogeneous media yields:
however, scattered or secondary radiation may cause flux to accumulate in the formation. To account for the cumulative introduction of the flux by the accumulation factor B, the gamma point kernel integral can then be written approximately as:
wherein
The gamma point kernel integral can therefore ultimately be written as:
wherein A is 1 Alpha is related to gamma energy, atomic number of the attenuating medium, and medium density. Namely fromThe point-kernel integration of the horse decay shows that the gamma decay is related to the atomic number and density of the medium. To express more intuition, further derivation is made below assuming the detector is isotropic with a source-to-source distance r 0 Then its count can be written as:
N′ 0 for counts after attenuation by the cannula, μ 1 、μ 2 The attenuation coefficients (related to gamma energy and atomic number of attenuation medium) of particles in cement and stratum respectively are rho c Is cement density, p f Is the formation density. That is, the sonde is affected by the cement, formation composition and density as the through-casing measurement, i.e., the uncertainty of the cement affects the formation density measurement.
Neutron porosity log
Similar situations exist for cased neutron logging. Casing neutron logging is commonly used 241 An Am-Be neutron source; neutrons enter the formation after being attenuated by the casing and the cement and then return to the detector again. The fast neutrons emitted in the process are elastically scattered and inelastically scattered to lose energy and change into thermal neutrons, and part of the thermal neutrons also undergo a capture reaction to fall back to a ground state. Thus, the thermal neutron count arriving at the detector will vary with casing, cement, and formation, with the amount of variation depending primarily on the length of deceleration, diffusion, etc. of the neutrons through the medium.
The neutron after-sheath measurement problem is similar to the gamma after-sheath measurement problem, belongs to the particle transport problem, and can use the boltzmann transport equation. In the case of neutrons, formula (3) can be written as
In the formula (I), the compound is shown in the specification,
in which leakage occurs per unit time and unit volumeSub-number, or>
Is laplace operator, Φ is neutron flux, D represents diffusion coefficient for flux;
Σ a phi is the number of neutrons absorbed per unit volume of time, sigma a Is a macroscopic trapping cross-section of the medium;
s is the rate at which neutrons are produced per unit volume of time (neutron source).
If a neutron source is arranged in an infinite medium, a spherical coordinate system is selected, and the origin is arranged on the coordinates of the point source, namely the neutron source is located at r =0. Setting a boundary condition: (1) Φ is finite except at r = 0; (2) at r → 0, passes through the sphere of a small radius (4 π r) per second 2 ) Must be equal to the neutron source intensity S. The above formula is solved to obtain:
based on the principle of double-group diffusion, the method can be obtained according to the formula:
Φ t (r) represents the flux of thermal neutrons in a uniform infinite medium from a source r, L f For the deceleration length, L, of the fast neutron t Is thermal neutron diffusion length and D t Is the thermal neutron diffusion coefficient.
Migration length L m Is a composite effect showing the neutrons in deceleration and capture, and comprises:
generally, the deceleration length is much greater than the diffusion length, so there is a simplified form of the detector count ratio R:
from the above formula, the detector count ratio and the source distance r 1 、r 2 And L m It is related. The source-to-source distance of the instrument is generally fixed, and therefore, the ratio is mainly related to the migration length. In a cased logging environment, the migration length of the casing layer is relatively fixed. The migration length of the cement layer is changed by the density of the solid cement and the change of the invasion substance. For example, when the density of the solid cement is unchanged, the migration length of the solid cement is increased along with the increase of the water intrusion ratio, so that the counting ratio of the detector is influenced, and the final porosity prediction result is influenced.
Sonic time difference logging
The acoustic velocity logging, also called acoustic time difference logging, is the reciprocal of the acoustic longitudinal wave velocity of a measured well profile, i.e. the time required for the acoustic longitudinal wave to propagate in a 1m formation. The full wave waveform in the open hole well is the following waves such as longitudinal wave, transverse wave, stoneley wave and the like, while the casing wave appears before the longitudinal wave in the casing well, the amplitude is very small when the cement cementation quality is good, and the propagation time of the whole well section is basically unchanged. Therefore, whether longitudinal waves can be extracted in the through-casing full-wave data depends on the cement cementation condition, when no cement exists outside the casing and only the mud exists, most of sound wave energy is transmitted along the casing and the minimum part of the sound wave energy is transmitted to the stratum due to the fact that the acoustic impedance difference between the casing and the mud is too large and the acoustic coupling is not good, the amplitude of the casing waves is large, the amplitude of the longitudinal waves is small, and even the longitudinal waves cannot be seen; similarly, gas invading substances will also have similar effects. When the cement is well cemented with the casing and the formation, the acoustic coupling is good, a considerable part of the acoustic energy is transmitted to the formation, and at the moment, the amplitude of the casing wave is small, and the amplitude of the longitudinal wave is large. The calculation formula of the acoustic impedance is as follows:
Z＝ρc (15)
where Z is acoustic impedance, ρ is medium density, and c is acoustic velocity.
Wherein the propagation speeds of longitudinal wave and transverse wave are as follows:
wherein: rho is the density of the medium (namely cement and stratum), mu shear modulus, lambda Laume elastic constant, E Young modulus and sigma Poisson ratio; i.e. longitudinal and transverse waves, are measured by the density of the medium. That is, the through-casing measurement of longitudinal and transverse waves is affected by the cement density.
It is readily apparent from the above that gamma density, neutron porosity and sonic measurements through the casing are affected by the cement density or composition.
Example 1
Taking gamma density logging as an example, the method for establishing the through-casing cement invasion model according to the invention establishes the cement invasion model, and comprises the following steps:
step 1, setting solid cement containing invaded substances as a uniform medium, namely uniformly mixing the invaded solid cement with the solid cement (as shown in figure 4, considering that cement completely fills a gap between a casing and a well wall), and setting the type of the invaded substances as m; determining factors influencing logging according to the three-porosity measurement principle after casing: migration length, solid cement density and composition change, wherein the composition change refers to the proportion of invasion cement substances in the solid cement; and establishing a relation (1) between the density of the solid cement, the density of a substance intruding into the solid cement, and the density of the solid cement after mixing the intruding substance to convert the cement uncertainty problem into the change of the density and the composition of the solid cement;
ρ c ＝q·ρ fluid +(1-q)·ρ solid (18)
in the formula (18), p c The density of the solid cement after mixing the invader, q is the invader volume ratio, ρ fluid For invasion of material density, ρ solid The density of the solid cement is; while obtaining solid cement on the basis of the proportion of invading substancesThe expression for the change in composition is:
in the formula (19), q i 、ρ i The volume ratio and density of the i-th invasive substance respectively; q. q.s cem 、ρ cem Solid cement proportion and density respectively; m is i_e 、m cem_e The mass ratio of the representative element 'e' in the i-th invading substance and the solid cement, and the specific element is determined by the specific material components;
step 2, according to the conventional density range of the solid cement, 1.3-1.9 g/cm 3 The solid cement density in the cased log is set. In this example, the densities of the solid cement were set to 1.3, 1.6 and 1.9g/cm 3 . Three downhole common invaded substances of methane, fresh water and mud are set as invaded substances in the embodiment according to the analysis result of the cause of poor cement cementation during measurement after the casing, and the densities of the three substances are respectively set as follows: methane (0.2 g/cm) 3 ) Water (1.0 g/cm) 3 ) Slurry (1.3 g/cm) 3 ). Considering the influence caused by the change of the well diameter, under the condition that the outer diameter of the casing is 244.5mm, three well diameters of 311mm,336mm and 363mm are set, and cement completely fills the interval between the casing and the well wall. Mixing the invasion substances with cement according to different proportions under different well diameters to obtain a cement invasion model database;
and 3, according to actual requirements, selecting corresponding data from the database obtained in the step 2 to substitute in formulas (19) and (19) to obtain a mixed density calculation formula (20), wherein the formula is a cement invasion model.
ρ c ＝q gas ·0.2+q mud ·1.3+q water ·1.0+(100-q gas -q mud -q water )·ρ solid (20)
FIG. 5 shows 1.6g/cm 3 An example of a model mixed with three invaded substances, namely water, mud and methane, wherein each axis represents the invasion of a single invaded substance into cement, the starting point of the axis is uncontaminated cement, and the axis is emphasizedThe surface cement is completely replaced by the invaded material; the axis contains the variation in cement density and migration length. Therefore, the cement invasion model provided by the embodiment can be used for carrying out constraint setting on the measured physical quantity, and the constraint of the physical layer to the uncertain problem in the three-porosity measurement is realized.
In order to improve the application range of the model, the embodiment further provides the following constraint modes for the problems which may occur in use:
1) If the broadest constraints are chosen to cover the full possible range of various cement densities without any a priori information (e.g. solid cement density or solid-liquid-gas curves, etc.): rho gas ～ρ solid_max (i.e., 0.2 to 1.9 g/cm) 3 )
2) If well cementation evaluation information is available, such as solid liquid gas imaging, the restriction condition may be determined from the volume fraction of the invading fluid: (1-q). Rho solid_min +q·ρ gas ～(1-q)·ρ solid_max +q·ρ mud
3) If the solid cement density is known, but there is no bond evaluation data, then the constraint is defined as: ρ is a unit of a gradient gas ～max{ρ solid ,ρ mud }
4) If both the cement bond information and the solid cement density are known, then the constraints are defined as: q · ρ solid +(1-q)·ρ gas ～q·ρ solid +(1-q)·ρ mud
For the cement invasion model, the embodiment also provides a method for measuring the three-porosity of the through-casing stratum by using the cement invasion model, as shown in fig. 1, the method comprises the following steps:
a, obtaining logging curves with multiple dimensions according to actual logging requirements, and naturally layering the curves with multiple dimensions by adopting a logging curve natural layering algorithm to obtain stratum parameters of each layer; and selecting a corresponding cement invasion model from the cement invasion models obtained by the method according to the layering result. In this embodiment, a detailed process of performing natural layering on a multidimensional curve by using a log natural layering algorithm is performed as the flow shown in fig. 7:
step A-1, determining the weight of each curve based on the correlation of each logging curve, wherein the higher the correlation is, the larger the weight is;
and step A-2, determining the use sequence of each curve in layering according to the weight determined in the step A-1, wherein the larger the weight is, the more dominant the use is.
And step A-3, finishing layering according to the sequencing result of the step A-1 by progressive judgment to obtain stratum parameters of each layer.
Step B, as shown in figure 3,
step B, establishing a detector forward model under corresponding environmental parameters corresponding to the cement invasion model selected in the step 1, wherein the detector forward model refers to a response model obtained according to the environmental parameters corresponding to the selected cement invasion model and can be understood as a mathematical relationship between the environmental parameters and the detector response parameters; in the detection forward model, the environmental parameters are determined by the measured physical quantity, and the corresponding parameters of the detector in the embodiment are obtained from simulation data. The conditions of the permutation and combination of different substances invading the cement are many and cannot be considered completely, so that the forward model is favorable for refining the cement invasion model under the condition of considering the boundary condition of the problem and independently establishing a single invading substance, and simultaneously, the forward model parameters are reduced, and the forward model precision is improved. The concrete invasion model selected in the corresponding step 1 of the implementation establishes a detector forward model under corresponding environmental parameters as follows:
DM＝DM(ρ c ,ρ f ) (21)
where ρ is f Is the formation density, rho c The density of the cement.
Step 3, establishing a detector forward model by utilizing the step 2 to establish a stratum inversion model, wherein the stratum inversion model FM (format model) can be written as follows:
wherein R is the actual measurement response of the instrument, i represents the detector, and n represents the number of the instrument detectors; the solution of the stratum inversion model is the measured stratum density and the cement density (wherein the measured stratum density is realThe cement area, s, can be determined substantially according to the hole diameter curve or the size of the drill bit during logging c I.e., a known amount).
And solving a Formation inversion model FM (Formation model), thus obtaining the measured Formation parameters and the cement reference curve. In practical application, because the invaded substance is not a single substance, a plurality of groups of forward and backward models can be obtained according to the steps; and solving the inversion model to obtain different stratum densities and cement densities when different models are selected based on the instrument response R. Therefore, under different conditions, a proper forward and backward modeling model is selected, and more accurate stratum parameters can be obtained by limiting sampling. The invasion model comprises three invasion substances of water, mud and methane, and comprises physical quantities (density and composition change) influencing formation density measurement. The method has the advantages that the proper cement invasion model is selected, reasonable constraint conditions are set in the database of the model, and the problems of low measurement accuracy and the like caused by cement uncertainty can be effectively reduced. Taking density measurement as an example, the specific selection method is as follows (gas density ρ) gas Density of mud ρ mud Density of solid cement rho solid Maximum density ρ of solid cement in the set model solid_max Minimum density ρ solid_min )：
1) The broadest constraints are chosen to cover the full possible range of various cement densities if there is no a priori information: rho gas ～ρ solid_max (i.e., 0.2 to 1.9 g/cm) 3 ) And according to the automatic layering result, determining the cement invasion model selected by each section under the constraint environment of the cement solid density change and the invasion material change, so as to obtain reasonable stratum density under the physical constraint.
2) If the solid cement density is known, the constraint is defined as: rho gas ～max{ρ solid ,ρ mud And determining the selected cement invasion model of each section under the constraint environment of invasion material change according to the automatic layering result, so as to obtain reasonable stratum density under physical constraint.
3) If well cementation evaluation information (e.g., solid-liquid-gas imaging) is available, but no solid cement density, then the fluid invasion can be based onVolume fraction to determine the limiting condition: (1-q). Rho solid_min +q·ρ gas ～(1-q)·ρ solid_max +q·ρ mud And determining the selected cement invasion model of each section under the constraint environment of the change of the cement solid density so as to obtain reasonable stratum density under the physical constraint. .
4) If both cement bond information and solid cement density are known, then the constraint is defined as: (1-q). Rho solid +q·ρ gas ～(1-q)·ρ solid +q·ρ mud And determining the cement invasion model of each section according to the solid-liquid-gas ratio.
5) After the logging curve is output based on the density measurement 1) -4), the output result can be confirmed by combining the three porosities. Supplementary explanation: when the actual output curve is selected, an intersection graph of curves obtained after the cement invasion model is restrained and neutrons can be drawn, and a cement-gas model is selected when any one curve is intersected.
For acoustic moveout logging, the following specific choices are made:
1) 4) procedure same as Density logging
5) And after the logging curves are output based on the acoustic wave time difference logging 1) -4), the output result can be confirmed by combining the three porosities. Supplementary notes: the acoustic time difference curve has cycle skip at the gas-containing part of the stratum, and a cement-gas model is selected at the part.
Taking neutron porosity measurement as an example, the specific selection method is as follows:
1) The broadest constraints were chosen to cover the full range of possible migration lengths for various cements without any prior information: l is m-mud ～L m-gas (i.e., 7.4-19cm m-mud 、L m-gas Indicating the migration length of the slurry and gas, respectively). And according to the automatic layering result, determining the selected cement invasion model of each section under the constraint environment of cement solid migration length change and invasion substance change, thereby obtaining reasonable formation porosity under physical constraint.
2) If the density of the solid cement is known, the constraint condition is still the same as (1) because of the related cementing data without solid liquid gas: l is m-mud ～L m-gas . And according to the automatic layering result, determining the selected cement invasion model of each section under the constraint environment of invasion material change so as to obtain reasonable formation porosity under physical constraint.
3) If well cementation evaluation information (e.g., solid liquid gas imaging) is available, but no solid cement density, the restriction condition may be determined from the volume fraction of the invading fluid. Assuming that the volume fraction of the invader is q and the invader is gas, the corresponding migration length values at the minimum and maximum cement densities, respectively, are L m-gas_solidmin And L m-gas_solidmax (ii) a If the invaded material is slurry, then there is L m-mud_solidmin And L m-mud_solidmax . Assuming that the maximum and minimum solid cement correspond to a migration length L m-solidmax And L m-solidmin . The total constraint conditions available are: l is a radical of an alcohol m-mud_solidmax ～L m-gas_solidmin (ii) a If the invading species is methane only, then the constraints can be updated as: l is m-solidmax ～L m-gas_solidmin (ii) a If the invading material is mud only, then the constraints can be updated as: l is m-mud_solidmax ～L m-solidmin . And determining the selected cement invasion model of each section under the constraint environment of the change of the cement solid migration length so as to obtain reasonable formation porosity under the physical constraint.
4) If the cement bond information and the density of the solid cement are both known, the migration length value L of the density of the solid cement can be directly calculated m-solid . Then the total constraint is: l is m-mud ～L m-gas (ii) a If the invading species is methane alone, the constraints can be updated as: l is m-solid ～L m-gas_solidmin (ii) a If the invading material is mud only, then the constraints can be updated as: l is m-mud_solidmax ～L m-solid . And determining a cement invasion model of each section according to the solid-liquid-gas ratio.
5) After the logging curve is output based on the neutron porosity measurement 1) -4), the output result can be confirmed by combining the three-porosity. Supplementary explanation: when the actual output curve is selected, an intersection graph of curves obtained after constraint of the cement invasion models and the density can be drawn, and if any one curve is intersected, the cement-gas model is selected.
The above description is only one example of the present invention, and should not be taken as limiting the invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A through-casing cement invasion model building method is characterized by comprising the following steps: the method comprises the following steps:
step 1, setting solid cement containing invaded substances as a uniform medium, namely uniformly mixing the invaded substances with the solid cement, and setting the type of the invaded substances as m; the problem of influencing logging is determined according to the three-porosity measurement principle after the well is sleeved: migration length, solid cement density and composition change, wherein the composition change refers to the proportion of invasion cement substances in the solid cement; establishing a relational expression (1) among the density of the solid cement, the density of a substance intruding into the solid cement and the density of the solid cement after mixing the intruding substance so as to convert the problem of cement uncertainty into the problem of the variation relation between the density of the solid cement and components;
ρ c ＝q·ρ fluid +(1-q)·ρ solid (1)
in the formula (1) (. Rho) c The density of the solid cement after mixing the invader, q is the invader volume ratio, ρ fluid For invasion of material density, ρ solid The density of the solid cement is; meanwhile, the formula of the composition change of the solid cement can be obtained based on the proportion of the invaded substance is as follows:
in the formula (2), q i 、ρ i The volume ratio and density of the i-th invading substance are respectively; q. q.s cem 、ρ cem Solid cement proportion and density respectively; m is i_e 、m cem_e The mass ratio of the representative element 'e' in the i-th invading substance and the solid cement, and the specific element is determined by the specific material components;
step 2, according to the density range of the conventional solid cement of 1.3-1.9 g/cm 3 Setting the density of solid cement in the well logging after sleeving, and setting the elements and density of the invaded substance according to the analysis result of the reason for generating cement cementation by the invaded cement after sleeving; mixing the set cement with different solid densities and various invasion substances according to different proportions to obtain a cement invasion model database;
step 3, according to actual requirements, selecting corresponding data from the database obtained in the step 2 to substitute the formula (1) and the formula (2), and obtaining a cement invasion model; the actual demand is a neutron porosity measurement and the method further comprises calculating an incremental migration length from the set components in the database.
2. The through-casing cement invasion model building method according to claim 1, wherein: the cement invasion model database also comprises a change relation between different hole diameters and cement areas under the condition that the set casing outer diameter is not changed; and then mixing the invasion substances with cement according to different proportions according to different well diameters to obtain cement invasion model data.
3. A method for measuring the through-the-casing formation three-porosity using the cement invasion model obtained in claim 1, comprising the steps of:
a, obtaining logging curves with multiple dimensions according to actual logging requirements, and naturally layering a measurement depth section by combining the logging curves with the curves with multiple dimensions by adopting a logging curve natural layering algorithm to obtain stratum parameters of each layer; selecting a corresponding cement invasion model from the cement invasion models obtained by the method according to the layering result;
step B, establishing a detector forward model under corresponding environmental parameters corresponding to the cement invasion model selected in the step 1, wherein the detector forward model is a response model obtained according to the environmental parameters corresponding to the selected cement invasion model; in the detection forward modeling, environmental parameters are determined by the measured physical quantity, and corresponding parameters of the detector are obtained from simulation or experimental data;
and 3, establishing a stratum inversion model by using the detector forward model established in the step B, and solving the stratum inversion model to obtain the measured stratum parameters and the cement reference curve.
4. The method of claim 3 for making a through-the-casing formation three-porosity measurement using the cement invasion model obtained in claim 1, wherein: in the step A, a logging curve natural layering algorithm is adopted to carry out natural layering on the multidimensional curve, and the detailed process is as follows:
a-1, determining the weight of each curve based on the correlation of each logging curve, wherein the higher the correlation is, the larger the weight is;
step A-2, determining the use sequence of each curve in layering according to the weight determined in the step A-1, wherein the larger the weight is, the more dominant the use is;
and step A-3, finishing layering by progressive judgment according to the sequencing result of the step A-to obtain stratum parameters of each layer.
5. The method of claim 3 for making a through-the-casing formation three-porosity measurement using the cement invasion model obtained in claim 1, wherein: the detector model established in the step B is a forward model under the condition of a single invading substance, so that the cement invading model can be refined, the forward model parameters can be reduced, and the forward model precision can be improved.
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