CN115680638A - Method for identifying overpressure top seal layer by utilizing pressure attenuation gradient - Google Patents
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Abstract
The invention belongs to the technical field of oil and gas field exploration, and particularly relates to a method for identifying an overpressure top seal layer by utilizing a pressure attenuation gradient. The method comprises the steps of calculating single-well pressure prediction by utilizing sound wave time difference data, actually measured pressure data and formation lithology data, correcting predicted pressure by utilizing the actually measured pressure data, and dividing and rarefying a pressure structure; and calculating the pressure attenuation gradient based on the division of the pressure structure, and identifying the overpressure top seal layer according to the pressure attenuation gradient change value. The method provided by the invention fully considers the particularity of the overpressure top seal layer pressure attenuation gradient, combines the pressure structure change rule and lithology combination characteristics, can accurately identify the development range of the overpressure top seal layer, and provides a research basis for next overpressure seal storage box division and understanding of the accumulation relationship between the overpressure seal storage box and oil gas.
Description
Technical Field
The invention belongs to the technical field of oil and gas field exploration, and particularly relates to a method for identifying an overpressure top seal layer by utilizing a pressure attenuation gradient.
Background
Overpressure sealing layers have important significance for the preservation of overpressure fluid, and the sealing layers can be divided into 4 types according to the occurrence relation of the overpressure sealing layers and permeability overpressure reservoirs: the sealing device comprises a vertical sealing layer, a lateral sealing layer, a top sealing layer and an upward-inclined sealing layer. The overpressure top sealing layer belongs to a top overpressure sealing layer, is a rock zone capable of preventing overpressure fluid from flowing upwards in a relatively long geological period, is not controlled by lithologic thickness, stratum distribution and structural boundaries, and is structurally represented to have a high pressure gradient.
The overpressure top seal layer divides the overpressure body into a plurality of sealed storage boxes with independent pressure systems, which is not only beneficial to the storage of oil gas, but also controls the migration of the oil gas in the overpressure oil-gas-containing basin and the distribution of oil gas reservoirs. The identification method of the predecessor for the overpressure top-sealing layer mainly comprises pressure structure identification, drilling identification and diagenetic identification. Considering the pressure transition zone as an overpressure sealing layer from the perspective of a pressure structure; in the aspect of well drilling, the drilling speed is generally considered to be sharply reduced after the drilling is carried out on the overpressure top seal layer in the well drilling process; from the diagenesis perspective, the overpressure capping layer shows that the content of carbonate cement is abnormally high and the composition of clay mineral is changed sharply, for example, the content of an illite-montmorillonite mixed layer is sharply reduced and the content of kaolinite is sharply increased. However, a plurality of pressure transition zones exist in the vertical direction in the actual pressure structure, and not all the pressure transition zones play a role in sealing the overpressure body; the drilling speed is sharply reduced in the drilling process, so that complete coring is difficult to obtain, and certain difficulty is brought to identification of an overpressure top seal layer; in the aspect of diagenetic mineral change, a stratum with a high carbonate cement content value does not completely play a role in closing upwelling of lower overpressure fluid, a part of a high-development-value area of the carbonate cement is generally filled with oil gas, the overpressure fluid is not blocked, and the high-development-value area cannot be used as an overpressure top sealing layer identification parameter in a strict sense.
The overpressure transition zone is a pressure zone in which the overpressure development highest value in the overpressure sealing storage box is slowly reduced to the top pressure of the sealing storage box, generally has a large development range, indicates an overpressure slow release process, and is a set of semi-open-semi-closed stratum instead of completely blocking the developed overpressure. The development position of the overpressure sealing layer is judged by the variation amplitude of common pressure and the content of carbonate cement whether an overpressure transition zone or an overpressure mutation zone is considered by the predecessor, and the overpressure top sealing layer is considered to be a set of stratum with the permeability approximate to zero actually, so that the overpressure can be sealed well.
The overpressure top seal layer is different from an overpressure transition zone and an overpressure sudden change zone to a certain extent, multiple relations exist among the overpressure top seal layer, the overpressure transition zone and the overpressure sudden change zone, and when the overpressure transition zone is in a mutant form, the overpressure sudden change zone or a set of rock cream near the overpressure sudden change zone is the overpressure top seal layer; when the overpressure transition zone is in a gradual change type, the local compact lithology in the overpressure transition zone is combined into an overpressure top seal layer. The overpressure top seal layer does not generally consider thickness, the only consideration factor is that the rock stratum permeability is extremely low, the rock stratum permeability can be an impermeable stratum such as a permafrost layer and a rock cream, and can also be a set of compact stratum formed under the action of diagenesis, the drilling speed is sharply reduced after the drilling is carried out on the overpressure top seal layer in the general drilling process, and coring is difficult to obtain.
In the 'difference of depression overpressure structure of Jinyang depression and control factors thereof', wang Yongshi, qin mussels divide overpressure systems of Dongying depressions, vehicle-town depressions, depression of Zhan and depressions of Huimin into 3 types by researching actual measurement stratum pressure statistics, mud-rock overpressure logging response and overpressure profile development characteristics of depressions in Jinyang depression: single-strong overpressure systems, composite overpressure systems, and single-weak overpressure systems. And gives: the formation and distribution of overpressure are controlled by the distribution and evolution of hydrocarbon source rocks, the overpressure top-bottom interface is controlled by a pressure sealing layer, and the internal and external transverse boundaries of an overpressure system are controlled by deep fracture (1 Wang Yongshi, qin mytilus, wang, and the like.
Wang Xudong et al analyzed the distribution of the seal in the longitudinal direction based on the log response characteristics of mudstone in the overpressured zone in the Dongying pit ancient and near system overpressure seal characteristics and seal capability research, and carried out systematic research on the petrology characteristics and seal capability thereof on the basis of the log response characteristics of mudstone in the overpressure zone (1 Wang Xudong, final, qujiang Xiu, et al, dongying pit ancient and near system overpressure seal characteristics and seal capability research [ J ] lithologic hydrocarbon reservoir, 2012,24 (005): 76-82.).
Hanyuan Jia et al studied the relationship between the development of carbonate mineralization in the overpressured seal and the sandstone near it under the influence of the deep overpressured fluid in "the cause of carbonate cement in the Dongying depressed overpressured seal and sandstone near it". After mathematical statistics is carried out on the component data of the 101-carbon carbonate cement in-situ micro-area electronic probe of 53 sandstone samples, the carbonate minerals can be mainly divided into 3 types of quasi-syngeneic dolomite, calcite and iron dolomite, and the diagenetic sequence of the carbonate minerals is judged to be the quasi-syngeneic dolomite → the calcite → the iron dolomite by combining X-diffraction, cathodoluminescence and the like. According to the observation result of the carbonate cement diagenetic fluid inclusion, the precipitation of the carbonate cement in the overpressure top seal layer and the sandstone nearby the overpressure top seal layer is accompanied by an overpressure fluid environment, the minimum ancient pressure coefficient is 1.29-1.62, the precipitation temperature is obviously higher than the background temperature value, and the indication is related to the invasion of overpressure hot fluid.
From the above analysis, the existing research on identification technology of the overpressure top seal layer is still weak, and especially the research on effective identification of the overpressure top seal layer is weak. At present, no patent technology for accurately identifying the overpressure top seal layer exists.
Disclosure of Invention
The method can accurately identify the distribution range of the overpressure top seal layer, and can directly divide the top plate of the overpressure seal storage box, so that the method is used for analyzing the distribution range of the overpressure seal storage box and is beneficial to oil-gas exploration and research of an oil-gas-containing overpressure basin.
In order to realize the purpose, the invention adopts the following technical scheme:
the invention provides a method for identifying an overpressure top-sealing layer by using a pressure attenuation gradient, which comprises the following steps of:
and 5, dividing the overpressure top seal layer according to the positive and negative values of the pressure attenuation gradient change and the lithologic combination rule.
Further, in step 1, collecting logging data, logging data and actual measurement pressure data of the research area, predicting single well pressure of the research area by using an Eaton pressure prediction model and an equivalent depth pressure prediction model, and correcting by using the actual measurement pressure.
Further, the Eaton pressure prediction model is used for calculating the overpressure of the hydrocarbon producing area, namely the pore pressure P E Obtained by the following formula:
P E ＝σ v -(σ v -P h )(Δt norm /Δt) x (1)
wherein x is an index, σ v Is vertical pressure, P h Is hydrostatic pressure,. DELTA.t norm And the acoustic time difference is normal compaction acoustic time difference, and delta t is acoustic time difference in acoustic time difference logging data.
Furthermore, the equivalent depth pressure prediction model is used for calculating the formation pressure of the under-compacted and supercharged area and the pore pressure P U Obtained by the following formula:
P U ＝P U’ +(P LU -P LU’ )＝1/10*ρ w *H U’ +1/10*ρ l *(H U -H U’ )(2)
in the formula, P U’ Is the formation pressure value, unit: MPa; p LU 、P LU’ The static rock pressure of U and U' points is respectively as follows: MPa; ρ is a unit of a gradient w And rhol is a stratum water density numerical value and a rock average density numerical value respectively, and the unit is as follows: g/cm 3 ；H U 、H U’ Respectively, U and U' points buried depth, unit: and km.
Further, in step 3, an integral multiple 0.125n of the sound wave time difference data depth interval 0.125m is selected, wherein n =1,2,3 \8230iis used as a step length, a difference value delta P between an average value Pn of pressure in the step length 0.125n and a depth pressure value Pi corresponding to a step length median step length is obtained, a variance of the delta P is calculated, and a step length X when the variance is the minimum value of a first descending section is selected min With X min And performing thinning on the pressure structure for the step length.
Further, the average value P of the pressures in the step is obtained by the following formula n ：
In the above formula, pn is the average value of pressure in steps of integral multiple n of interval 0.125m, and n is the integral multiple value of 0.125 m;
obtaining a depth pressure value Pi corresponding to the step length median step length, obtaining a difference value delta P between Pn and Pi by using a formula (3), and calculating a variance S of the delta P △P Namely:
in the above formula, pi is the pressure value of depth corresponding to the step length of integral multiple n of interval 0.125m, S ΔP Is the variance of the difference Δ P between Pn and Pi.
Further, in step 5, the pressure attenuation gradient change curve is mapped to the pressure structure curve, and from the bottom of the pressure attenuation gradient change curve, the range from the zero value corresponding depth of the first pressure attenuation gradient at the upper part of the negative pressure attenuation gradient to the maximum value corresponding depth of the first pressure attenuation gradient at the upper part of the negative pressure attenuation gradient is the development range of the development overpressured capping layer.
Compared with the prior art, the invention has the following beneficial effects:
the method provided by the invention fully considers the particularity of the pressure attenuation gradient of the overpressure top seal layer, combines the pressure structure change rule and lithology combination characteristics, can accurately identify the development range of the overpressure top seal layer, and provides a research basis for next overpressure seal storage box division and understanding of the accumulation relationship between the overpressure seal storage box and oil gas.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a flow chart of a method for identifying an overpressure top seal using a pressure decay gradient according to example 1 of the present invention;
FIG. 2 is a data map of a study area according to example 2 of the present invention;
FIG. 3 is a schematic view of the identification of the overpressure transition zone of the research area according to example 2 of the present invention;
FIG. 4 is a schematic diagram illustrating the identification of lithology of an overpressure transition zone in a research area according to example 2 of the present invention;
FIG. 5 is a schematic view of the identification under the mirror of the overpressure transition zone of the research area according to embodiment 2 of the present invention;
FIG. 6 is a schematic diagram of the division of the overpressure top seal layer in the research area according to embodiment 2 of the present invention;
fig. 7 is a diagram illustrating an identification result of the ultra-high pressure capping layer according to embodiment 2 of the present invention.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.
In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.
Example 1
As shown in fig. 1, the method for identifying an overpressure top-sealing layer by using a pressure decay gradient comprises the following steps:
in the embodiment of the present invention, the logging data, and the actually measured pressure data mainly include: stratum layering data, lithology change data, stratum water density data, rock density data, acoustic time difference logging data, density logging data and actual measurement pressure data. In the step, the lithology change data, the acoustic wave time difference data and the density data are combined with an Eaton pressure prediction model and an equivalent depth pressure prediction model to predict the pressures of different layers of a research area, and the actually measured pressures are used for correcting.
Specifically, the Eaton pressure prediction model is used for calculating the overpressure of the hydrocarbon-producing zone, the pore pressure P E Obtained by the following formula:
P E ＝σ v -(σ v -P h )(Δt norm /Δt) x (1)
wherein x is an index, σ v Is vertical pressure, P h Is hydrostatic pressure,. DELTA.t norm And in order to normally compact the acoustic time difference, delta t is the acoustic time difference in the acoustic time difference logging data.
The equivalent depth pressure prediction model is used for calculating the pressure of the formation in the undercompression pressurization area and the pore pressure P U Obtained by the following formula:
P U ＝P U’ +(P LU -P LU’ )＝1/10*ρ w *H U’ +1/10*ρ l *(H U -H U’ ) (2)
in the formula, P U’ Is the formation pressure value, unit: MPa; p LU 、P LU’ The static rock pressure of U and U' points is respectively as follows: MPa; rho w 、ρ l The water density value of the stratum and the average density value of the rock are respectively as follows: g/cm 3 ；H U 、H U’ Respectively, U and U' points buried depth, unit: and km.
By establishing the relation between the acoustic time difference logging and the burial depth and judging the supercharging mechanism, the formation pressure is predicted by respectively using a formula (1) and a formula (2), and the predicted pressure error is ensured to be within 5 percent by correcting the actually measured pressure.
And 2, dividing a pressure structure curve by utilizing a trend line which is formed on the pressure prediction result in the step 1 and represents the vertical change of the pressure.
specifically, with the collected single-well acoustic time difference data, taking an integral multiple (n, n =1,2,3 \8230;) of the standard acoustic time difference data interval of 0.125m as a step length, the average value Pn of the pressure in the step length of 0.125n is obtained, namely:
in the above formula, pn is the average value of the pressure in steps spaced by an integer multiple n of 0.125m, and n is an integer multiple of 0.125 m.
At the same time, the depth pressure value (Pi) corresponding to the step length median step length is obtained, the difference value DeltaP between (Pn) and (Pi) is obtained by using the formula (3), and the variance S of the DeltaP is calculated △P Namely:
in the above formula, pi is a pressure value of depth corresponding to a step length of integral multiple n of 0.125m, S △P The variance of the difference Delta P between Pn and Pi;
selecting variance S according to formula (4) △P And (4) calculating the pressure value corresponding to the step length when the step length of the first descending section is 0.125n, wherein the vertical variation rule of the pressure value represents the development characteristic of the single-well vertical pressure system.
in the embodiment of the present invention, the pressure decay gradient GP of the depth corresponding to the step length Xmin is calculated, that is:
GP＝(P Bn -P Tn )/0.125n (5)
in the above formula, P Bn 、P Tn Bottom and top formation pressure values in units: MPa;0.125n is the interval step size of the stratum, unit: and m is selected.
And (5) drawing a vertical pressure attenuation gradient change curve according to the pressure attenuation gradient obtained in the formula (5).
And 5, corresponding the pressure attenuation gradient change curve to the pressure structure curve, wherein the range from the bottom of the pressure attenuation gradient change curve to the depth corresponding to the first pressure attenuation gradient zero value at the upper part of the negative pressure attenuation gradient to the depth corresponding to the first pressure attenuation gradient maximum value at the upper part is the development range of the development overpressure capping layer.
Example 2
The method for identifying the overpressure capping layer by using the pressure attenuation gradient selects an overpressure layer section in a Bohai Bay Dongyng sunken oregano sunken region as a research area, and comprises the following specific steps of:
step one, data collection, arrangement and pressure prediction:
geological data of overpressure layer sections of east-camp sunken bozhuan cave regions in Bohai Bay basin are collected and sorted, and the geological data comprise stratum layering data, lithology data, stratum water density data, rock density data, acoustic wave time difference logging data, density logging data and actually measured pressure data (shown in figure 2). And (3) respectively carrying out pressure prediction on the stratum with the number of 96 single-well sand and the number of four-sand sections in the depressed area of the Bozhuang by using the formula (1) and the formula (2), carrying out prediction pressure correction by using the actually measured pressure, wherein the error rates are below 5%, and the calculation results are shown in a table 1.
TABLE 1
Step two, pressure structure division:
and dividing the pressure structure according to a trend line which is formed on the vertical direction of the pressure prediction result and represents the vertical change of the pressure. Taking the main hollow center king 550 well as an example, the pressure structure division result is shown in fig. 3.
Step three, pressure structure rarefying;
taking a main hollow center king 550 well as an example, selecting integral multiples (n, n =1,2,3 \8230; 18800) of the single-well acoustic time difference depth interval of 0.125m as step lengths, and solving pressure in different step lengths according to a formula (3)The depth pressure value Pi corresponding to the step length median step length is simultaneously obtained, the difference value between the two pressure values is calculated, and the variance S of the difference value is calculated by using the formula (4) ΔP Selecting variance S ΔP The minimum value of the first descending section corresponds to the step length (fig. 4), at this time, when n =320 and the step length is 0.125n =40m, the variance value is at the minimum value at the first descending section, so n =320 is selected, the pressure value corresponding to the step length of 40m is obtained, at this time, the vertical variation law of the pressure value can relatively accurately represent the development characteristics of the single-well vertical pressure system, and therefore, the pressure structure is used for rarefaction, and the rarefaction result of the pressure structure is shown in fig. 5.
Step four, calculating the pressure attenuation gradient;
and calculating the pressure attenuation gradient corresponding to each depth when the step length is 40m, and drawing a vertical pressure attenuation gradient change curve according to the calculated pressure attenuation gradient, wherein the result is shown in figure 6.
Identifying an overpressure top seal layer;
and (3) corresponding the pressure attenuation gradient change curve to the pressure structure curve, wherein from the bottom of the pressure attenuation gradient change curve, the range from the depth corresponding to the first pressure attenuation gradient zero value at the upper part of the negative pressure attenuation gradient to the depth corresponding to the first pressure attenuation gradient maximum value at the upper part is the development range of the development overpressure top seal layer, and the identification result of the overpressure top seal layer is shown in figure 7.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (7)
1. A method of identifying an overbalanced capping layer using a pressure decay gradient, comprising the steps of:
step 1, predicting the single-well pressure of a research area;
step 2, drawing a pressure structure curve, and dividing the curve;
step 3, performing rarefaction on the pressure structure;
step 4, calculating the pressure attenuation gradient, and drawing a vertical pressure attenuation gradient change curve;
and 5, dividing the overpressure top seal layer according to the positive and negative values of the pressure attenuation gradient change and the lithologic combination rule.
2. The method of claim 1, wherein in step 1, logging data and measured pressure data of the research area are collected, the Eaton pressure prediction model and the equivalent depth pressure prediction model are used to predict the single well pressure of the research area, and the measured pressure is used to perform correction.
3. The method of claim 2, wherein the Eaton pressure prediction model is used to calculate the overpressure in the hydrocarbon producing zone, pore pressure P E Obtained by the following formula:
P E ＝σ v -(σ v -P h )(Δt norm /Δt) x (1)
wherein x is an index, σ v Is vertical pressure, P h Is hydrostatic pressure,. DELTA.t norm And in order to normally compact the acoustic time difference, delta t is the acoustic time difference in the acoustic time difference logging data.
4. The method of claim 2, wherein the equivalent depth pressure prediction model is used for calculating the formation pressure in the undercompression boost region, and the pore pressure P U Obtained by the following formula:
P U ＝P U’ +(P LU -P LU’ )＝1/10*ρ w *H U’ +1/10*ρ l *(H U -H U’ ) (2)
in the formula, P U’ Is the formation pressure value, unit: MPa; p is LU 、P LU’ The static rock pressure of U and U' points is respectively as follows: MPa; ρ is a unit of a gradient w 、ρ l The water density value of the stratum and the average density value of the rock are respectively as follows: g/cm 3 ；H U 、H U’ Respectively, U and U' points buried depth, unit: and km.
5. The method as claimed in claim 1, wherein in step 3, an integral multiple 0.125n of the sound wave time difference data depth interval 0.125m is selected, wherein n =1,2,3 \8230i, i is a step length, a difference Δ P between an average value Pn of pressure in the step length 0.125n and a depth pressure value Pi corresponding to a median step length of the step length is obtained, a variance of Δ P is calculated, and a step length X at the time of a first descending section minimum value of the variance is selected min With X min And performing thinning on the pressure structure for the step length.
6. A method according to claim 5, characterized in that the mean value P of the pressure in the step is determined by the following formula n ：
In the above formula, pn is the average value of pressure in steps of integral multiple n of interval 0.125m, and n is the integral multiple value of 0.125 m;
obtaining a depth pressure value Pi corresponding to the step length median step length, obtaining a difference value delta P between Pn and Pi by using a formula (3), and calculating a variance S of the delta P △P Namely:
in the above formula, pi is a pressure value of depth corresponding to a step length of integral multiple n of 0.125m, S ΔP Is the variance of the difference Δ P between Pn and Pi.
7. The method as claimed in claim 1, wherein in step 5, the pressure-decreasing gradient change curve is mapped to the pressure structure curve, and from the bottom of the pressure-decreasing gradient change curve, the depth range from the upper first pressure-decreasing gradient zero value to the upper first pressure-decreasing gradient maximum value on the negative pressure-decreasing gradient is the development range of the development super-pressure capping layer.
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