CN107605469B - Method for predicting formation pore pressure - Google Patents
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- CN107605469B CN107605469B CN201610548005.7A CN201610548005A CN107605469B CN 107605469 B CN107605469 B CN 107605469B CN 201610548005 A CN201610548005 A CN 201610548005A CN 107605469 B CN107605469 B CN 107605469B
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Abstract
The invention relates to the field of seismic data interpretation, and particularly discloses a method for predicting formation pore pressure. The method comprises the following steps: obtaining seismic interval velocity v in a work area and obtaining an Eton index n at a plurality of positions based on well logging datai(ii) a Based on making E2Determining the relation n ═ p (v) between the Eton index n and the seismic interval velocity v in the work area according to the minimum principle; in a work area, obtaining an Eton index n in the work area range based on the seismic interval velocity v and the determined functional relation n ═ p (v); thereby predicting the formation pore pressure P in the work areap. By applying the method and the device, the accuracy of predicting the formation pore pressure can be greatly improved.
Description
Technical Field
The invention relates to the field of seismic data interpretation, in particular to a method for predicting formation pore pressure.
Background
Formation pore pressure refers to the pressure that the fluid has in the formation pores or fractures. The method is the basis for reasonably determining the casing program and is also the key for reasonably selecting the mud density to realize safe and efficient drilling. Meanwhile, the formation pore pressure is one of the main control factors of oil and gas reservoir formation and distribution and is the basis of the oil and gas reservoir formation fluid dynamics research.
The pore pressure of the formation has been studied for over 40 years, but has not been completely solved to date strictly speaking. Since the century, the prediction of formation pore pressure has become a research hotspot in the fields of geology, well drilling, well logging, geophysical prospecting and the like in western countries. The specific prediction method includes seismic interval velocity prediction, well logging data interpretation (detection), well drilling data interpretation (detection), actual measurement and the like.
These conventional methods are empirical semi-empirical methods based on normal compaction trend lines, and generally suffer from the common disadvantage of being only applicable to the situation of high pressure of formations under-compacted caused by an unbalanced compaction process; most of the methods are limited to use in pure shale; establishing a normal compaction trend line, and assuming that a semi-logarithmic coordinate system is a straight line; because the pressure for establishing the experience chart comes from a permeable stratum, the result is often lower when a mudstone stratum is predicted in return; it is an empirical and semi-empirical method in quantification, and lacks a theoretical basis.
The theoretical basis for formation pore pressure prediction is the effective stress theorem. According to this theorem, the formation pore pressure is equal to the difference between overburden pressure and vertical effective stress. Overburden pressure can be determined in a variety of ways, such as by apparent density log data of the drilled well, so that formation pore pressure can be determined by simply determining the vertical effective stress. The effective stress of a saturated porous medium is a parameter that cannot be directly measured physically, and its value is calculated indirectly by measuring the result it produces (e.g., change in porosity). Typical examples of the searched domestic and foreign documents include the Foster & Whalen method, Eaton method, Fan simplified method, and petrophysical method, which are methods for determining pore pressure using seismic velocity data based on the effective stress theorem. The Foster & Whalen method is a regional semi-empirical method, the Fan simple method is more suitable for under-compacted strata, and the method based on rock physics mainly aims at a sand shale section and is complex in calculation. The Eaton method is therefore preferred for formation pore pressure prediction. The important parameter Eaton index n in the Eaton formula is usually determined empirically, and because the conditions of different work areas are different, the Eaton index n determined empirically often cannot be well adapted to the actual conditions of the work areas, thereby seriously affecting the pore pressure prediction accuracy.
Disclosure of Invention
The invention aims to obtain a method for accurately predicting pore pressure by using an Eaton method, which can overcome the defects.
In order to achieve the above object, the present invention provides a method of predicting formation pore pressure, the method comprising: obtaining seismic interval velocity v in a work area and obtaining an Eton index n at a plurality of positions based on well logging dataiA subscript i denotes a number of each position, i 1, 2., N denotes the number of the positions included in the plurality of positions; based on the following formula E2Determining the relation n ═ p (v) between the Eton index n and the seismic interval velocity v in the work area according to the minimum principle:
wherein v isiRepresenting the seismic interval velocity at the corresponding position, n ═ p (v) selected from a preset set of functions; in a work area, obtaining an Eton index n in the work area range based on the seismic interval velocity v and the determined functional relation n ═ p (v); predicting formation pore pressure P in a work zone based on the formulap：Pp＝Sv-(Sv-Ph)(v/vnorm) Wherein S isvFor overburden pressure, Ph is hydrostatic pressure, vnormIs the ply speed under normal compaction conditions.
In the invention, firstly, an Eaton formula method is preferably selected as an effective method for predicting the formation pore pressure based on an effective stress theory; then, aiming at the actual stratum complexity of unconventional reservoirs such as shale gas and the like, the influence of the anisotropic stratum on key parameters in a pore pressure prediction formula is fully considered, so that the prediction precision is greatly improved.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts throughout.
FIG. 1 shows a flow diagram of a method of predicting formation pore pressure according to one embodiment of the invention.
FIG. 2 shows a schematic of a pore pressure prediction pre-seismic velocity refinement process, inversion technique, according to the present invention.
FIG. 3 shows a schematic of velocity and therefore overburden pressure using the Gardner equation in accordance with the present invention.
FIG. 4 shows a schematic of the error rate of the Eaton index determined according to the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While the preferred embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein.
FIG. 1 illustrates a method of predicting formation pore pressure, the method comprising:
103, in a work area, obtaining an Eton index n in the work area based on the seismic interval velocity v and the determined functional relation n ═ p (v);
Pp＝Sv-(Sv-Ph)(v/vnorm) Wherein S isvFor overburden pressure, Ph is hydrostatic pressure, vnormIs the ply speed under normal compaction conditions.
In the embodiment, the formation pore pressure is predicted by means of the Eaton formula, the influence of the anisotropic formation on key parameters (such as Eaton indexes) in the pore pressure prediction formula is fully considered, and the prediction precision is greatly improved.
In one embodiment, the preset function set may include some or all of the following: linear fitting functions, quadratic functions, exponential functions, power functions, logarithmic functions. The functional form contained in the function set can be set by a person skilled in the art based on experience and practical circumstances.
In one embodiment, the relationship n ═ p (v) between the eaton index n and the seismic interval velocity v in the work area may be determined using a least squares method.
In one embodiment, the seismic interval velocity v may be obtained by: carrying out velocity spectrum processing and adjustment interpretation; performing residual speed analysis; carrying out constraint velocity inversion; and correcting the interval velocity to obtain the seismic interval velocity v.
In one embodiment, the overburden pressure SvCan be obtained by the following method: fitting to obtain a Gardner coefficient based on the logging data; obtaining a density within a work area based on the seismic interval velocities and using a Gardner formula; deriving the overburden pressure S based on the densityv。
Examples of the applications
FIG. 2 shows a schematic of a pore pressure prediction pre-seismic velocity refinement process, inversion technique, according to the present invention. FIG. 3 shows a schematic of velocity and therefore overburden pressure using the Gardner equation in accordance with the present invention. FIG. 4 shows a schematic of the error rate of the Eaton index determined according to the present invention.
The present invention may be a system, method and/or computer program product. The computer program product may include a computer-readable storage medium having computer-readable program instructions embodied therewith for causing a processor to implement various aspects of the present invention.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.
Claims (4)
1. A method of predicting formation pore pressure, the method comprising:
obtaining seismic interval velocity v in a work area and obtaining an Eton index n at a plurality of positions based on well logging dataiA subscript i denotes a number of each position, i 1, 2., N denotes the number of the positions included in the plurality of positions;
based on the following formula E2Determining the relation n ═ p (v) between the Eton index n and the seismic interval velocity v in the work area according to the minimum principle:
in a work area, obtaining an Eton index n in the work area range based on the seismic interval velocity v and the determined functional relation n ═ p (v);
predicting formation pore pressure P in a work zone based on the formulap：
Pp＝Sv-(Sv-Ph)(v/vnorm)nWherein S isvFor overburden pressure, Ph is hydrostatic pressure, vnormThe bed velocity under normal compaction, n is the Eton index;
and determining the relation n between the Eton index n and the seismic interval velocity v in the work area as p (v) by adopting a least square method.
2. The method of claim 1, wherein the preset set of functions includes some or all of the following: linear fitting functions, quadratic functions, exponential functions, power functions, logarithmic functions.
3. The method of claim 1, wherein the seismic interval velocity v is obtained by:
carrying out velocity spectrum processing and adjustment interpretation;
performing residual speed analysis;
carrying out constraint velocity inversion;
and correcting the interval velocity to obtain the seismic interval velocity v.
4. The method of claim 1 wherein the overburden pressure SvIs obtained by the following method:
fitting to obtain a Gardner coefficient based on the logging data;
obtaining a density v in a work area based on the seismic interval velocity v and by using a Gardner formula;
deriving the overburden pressure S based on the densityv。
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| CN108562938B (en) | 2018-03-23 | 2019-09-06 | 中国石油天然气股份有限公司 | A kind of method, apparatus and system for eliminating frequency dispersion effect |
| CN108594305A (en) * | 2018-08-13 | 2018-09-28 | 中国石油化工股份有限公司江汉油田分公司勘探开发研究院 | Shale reservoir gas-bearing property analysis method and device |
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| CN105134189A (en) * | 2015-08-24 | 2015-12-09 | 西南石油大学 | Logging GeoMechanics Identify Reservoir (LogGMIR) method |
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| US10385678B2 (en) * | 2014-03-21 | 2019-08-20 | Conocophillips Company | Method for analysing pore pressure in shale formations |
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| CN105134189A (en) * | 2015-08-24 | 2015-12-09 | 西南石油大学 | Logging GeoMechanics Identify Reservoir (LogGMIR) method |
| CN105445791A (en) * | 2015-11-25 | 2016-03-30 | 成都理工大学 | Stratum aperture pressure prediction method based on variety earthquake attributes |
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