CN105804737A - Method for solving formation porosity on basis of iterative algorithm - Google Patents

Method for solving formation porosity on basis of iterative algorithm Download PDF

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Publication number
CN105804737A
CN105804737A CN201610325221.5A CN201610325221A CN105804737A CN 105804737 A CN105804737 A CN 105804737A CN 201610325221 A CN201610325221 A CN 201610325221A CN 105804737 A CN105804737 A CN 105804737A
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China
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porosity
density
model
physical model
reservoir
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CN201610325221.5A
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Chinese (zh)
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赵军
武延亮
何胜林
王迪
唐深华
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Southwest Petroleum University
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Southwest Petroleum University
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Priority to CN201610325221.5A priority Critical patent/CN105804737A/en
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells

Abstract

The invention relates to a method for solving a formation porosity on basis of an iterative algorithm, and belongs to the field of geophysical exploration. The method disclosed by the invention comprises the following steps of: 1, establishing a density-based volume physical model, i.e. firstly, accurately determining a skeleton density and a fluid density and then establishing the volume physical model for calculating the porosity by density logging; 2, establishing a reservoir porosity model based on an Archie formula, i.e. applying the Archie formula to derive out the model for calculating a reservoir porosity; 3, combining the volume physical model and the Archie porosity model, carrying out simultaneous processing on porosity calculation formulas obtained in the first two steps, and adopting the iterative algorithm to simultaneously solve two unknown parameters of a total porosity and a water-filled porosity; 4, checking algorithm accuracy, i.e. comparing a core testing porosity subjected to overburden pressure correction with the porosities calculated by the method disclosed by the invention to check accuracy of calculation. According to the method disclosed by the invention, the porosity of a gas-bearing reservoir is solved by combining the volume physical model and the Archie porosity model and adopting the iterative algorithm; the models are high in accuracy; the method is high in practicality, has very high popularization and application value, and provides a new technology for calculation of the reservoir logging porosity.

Description

A kind of method solving formation porosity based on iterative algorithm
Technical field
A kind of method solving formation porosity based on iterative algorithm of the present invention, associating volume physical model and Archie formula is utilized to adopt iterative algorithm to solve gas-bearing reservoir porosity, there is provided a kind of new technology for calculating of reservoir well logging porosity, belong to field of geophysical exploration.
Background technology
Along with deepening continuously of oil-gas exploration and development degree, current Exploration Domain turns to unconventional reservoir from conventional reservoir gradually.The exploration and development that unconventionaloil pool is hidden increasingly comes into one's own；But the logging evaluation of unconventional reservoir is always up the heavy difficult point of evaluating reservoir.The evaluation of reservoir porosity, to describe be wherein one of most critical, most crucial technical problem, unconventional characteristic makes reservoir fluid change greatly for the contribution of log response, in addition the environmental effect such as well is bigger, make part well log information for the reflection distortion on stratum so that unconventional reservoir well logging fluid is known and evaluates more difficult.
Reservoir pore space is one of important parameter of oil-gas exploration and development, its accurate key being not only refined reservoir evaluation that calculates, and is the key of the resources and reserves estimation such as oil, natural gas, has great significance for look for oil and gas reservoir.The current method calculating reservoir porosity is a lot, mainly has three hole theoretical response equation methods, cross-plot, single factor test (interval transit time, density, neutron) fitting process etc. based on core analyzing data.
When utilizing conventional logging to calculate reservoir porosity, for conventional stratum, when in reservoir pore space containing only when having water-oil phase, consider that density and the compressional wave time difference value difference of oil and water are not little, therefore drilling core graduation method can be adopted, namely set up density or the compressional wave time difference value corresponding relation with core analysis porosity to ask for reservoir porosity.But for unconventional gas-bearing reservoir, owing to natural gas is bigger with the density of water and compressional wave time difference difference, it is impossible to regard fluid as single fluid in density and compressional wave time difference, if being continuing with the porosity deviation true hole porosity that drilling core graduation rule is likely to make to obtain.For this problem, invention herein proposes to utilize the rock volume physical model considering fluid composition, then combines saturation computation classical formulas Archie formula, jointly solves gas-bearing reservoir porosity.
In order to improve the exploration and development efficiency of unconventional gas reservoir, ask for reservoir porosity exactly and be particularly important.To this, first the impact of gaseous exchange body density and formation water resistivity has been analyzed by the present invention, then resettles corresponding porosity calculation model.The porosity logging means of interpretation of this optimization, improves the precision of existing UNCONVENTIONAL GAS Reservoir Logging Interpretation Model, obtains good utilization in study area.
Summary of the invention
The invention aims to efficiently against UNCONVENTIONAL GAS reservoir in well logging porosity calculating process, difference due to gas and water character, if asking for reservoir porosity by drilling core graduation method, can cause that the porosity value calculated can not reflect stratum truth, to this, it is proposed to the method for associating volume physical model and Archie formula solves the porosity of UNCONVENTIONAL GAS reservoir.Application shows, it is relatively succinct that this combines the method solving porosity, and explanation results is coincide better with the core porosity after overburden pressure correction, meets the requirement of UNCONVENTIONAL GAS evaluating reservoir, illustrates that the method is reliable, effective.The method can calculate for UNCONVENTIONAL GAS reservoir well logging porosity and provide a kind of new technology.
For achieving the above object, the technical scheme is that
A kind of method solving formation porosity based on iterative algorithm of the present invention, has first analyzed the impact of gaseous exchange body density contained by reservoir and formation water resistivity, has then resettled corresponding porosity calculation model.The porosity logging means of interpretation of this optimization, improves the precision of existing UNCONVENTIONAL GAS Reservoir Logging Interpretation Model, obtains good utilization in real data processes.Method comprises the following steps:
1. setting up the volume physical model of density based: owing to being affected by gas-bearing formation, there is cycle skipping phenomenon in acoustic logging, causes that porosity and acoustic logging value dependency are poor；Owing to the middle subvalue of skeleton and fluid is difficult to accurate acquisition, and neutron well logging value is affected relatively big by the excavation effect of natural gas, therefore the present invention selects density log to set up rock volume physical model.
Volume physical model is set up it may first have to will accurately determine skeletal density and fluid density by density log value.
1. the determination of matrix density: the sheet data of study area is analyzed, the content of statistics wherein various mineralogical compositions, use the method for volume physical model to ask for matrix density, computing formula is as follows:
B = Σ i = 1 n B i · V i - - - ( 1 )
B, B in formulaiThe each ingredient density of skeletal density, skeleton；
ViThe each ingredient of skeleton accounts for skeleton cumulative volume ratio.
2. the determination of rock stream body density: the density obtaining single fluid or multiple fluid-mixing and other parameter values can be measured and be calculated to fluid density either directly through experimental simulation stratum Temperature-pressure Conditions,.The present invention selects the method for volume physical model to calculate rock stream body density equally.
3. the volume physical model of density based log value is set up: according to the rock volume physical model of gas-bearing formation, the response equation of its density log is
Can obtain after transformed:
ρ in formulama、ρg、ρwAnd ρshThe respectively density of clean sandstone skeleton, gas, formation water and shale；
WithTotal porosity and moisture volume；
SwWater saturation；
VshShale content.
Formula has total porosity in (3)With moisture volumeTwo unknown parameters, only cannot all solve with a volume physical equation.But it should be noted that total porosityWith moisture volumeBetween exist a water saturation SwRelation, therefore, it can simultaneous Archie formula, obtain above-mentioned two unknown parameter simultaneously.
2. based on the porosity model of Archie formula: the present invention proposes application Archie formula and calculates reservoir porosity.Utilization Archie formula asks for the expression formula of water saturation:
Take the logarithm simultaneously and can obtain in both sides:
By SwCan obtain after converting:
The value of four litho-electric parameters a, b, m, n can be obtained by rock-electric test, and formation water resistivity R can be obtained by formation water analysis of dataw.Therefore, same containing total porosity in formula (6)With moisture volumeTwo unknown parameters, it is possible to associating above formula (3) solves two unknown parameters jointly.
3. associating volume physical model A Erqi porosity model, adopts iterative algorithm to calculate porosity: from the foregoing, after simultaneous formula (3) and (6) two equations of formula, can solve total porosity simultaneouslyWith moisture volumeTwo unknown parameters.Additionally, due to formula (6) exists logarithm, therefore the two unknown number cannot be solved simply.Therefore, the present invention adopts and composes initial value and with the principle of a fixed step size circulation, the two unknown number carried out discretization numerical solution, comprises the concrete steps that:
(1) total porosity is composed initial value
(2) moisture volume is composed initial valueThen with 0.1 for the sampling interval, water-filled porosity being scanned value, the maximum of water-filled porosity isThen pass through Automatic Program and determine that one group makes equation (3) and the minimum solution of (6) error, as thisNumerical value optimal solution；
(3)WhenLoop ends；Otherwise repeat the above steps is 2.；
(4) from 2., extract often group make equation (3) and the minimum solution of (6) errorPreferably go out one group of solution that error is minimumAs moisture volume hereinAnd total porosityNumerical value optimal solution.
The mean error calculated between porosity that instrument connection porosity after the overburden pressure correction of all sidewall corings of certain study area and the present invention are logged well is 5.81%, as shown in Figure 1.It is confirmed that, the porosity calculation method proposed based on the present invention disclosure satisfy that the requirement that this district's evaluating reservoir and reserves calculate.
Advantages of the present invention: 1, the basic data that this method utilizes is entirely from scene, and the acquisition of data is convenient, it is easy to；2, utilizing associating volume physical model and Archie formula to adopt iterative algorithm to solve gas-bearing reservoir porosity, existing certain theoretical foundation, having again the statistical law that real data draws, thus improve the precision of calculating；3, the method is simple to operate, and practicality is relatively strong, and has good application value.4, efficiently against UNCONVENTIONAL GAS reservoir in logging evaluation porosity calculation process, owing to the difference of gas and water character causes that the porosity value calculated can not reflect stratum truth, the precision that UNCONVENTIONAL GAS reservoir well logging porosity calculates can be improve.
Accompanying drawing explanation
Fig. 1 present invention log well calculating porosity and rock core overburden pressure correction after porosity cross plot
Detailed description of the invention
A kind of method solving formation porosity based on iterative algorithm of the present invention, its method is embodied as comprising the following steps:
1. set up the volume physical model of density based: it is first necessary to accurately to determine skeletal density and fluid density, by the sheet data of study area is analyzed, the content of statistics wherein various mineralogical compositions, the method using volume physical model asks for matrix density, matrix density computing formula such as formula (1)；The Temperature-pressure Conditions of simulated formation by experiment, measures and calculates the density obtaining single fluid or multiple fluid-mixing and other parameter values, and the same method selecting volume physical model calculates rock stream body density.Then according to the rock volume physical model of gas-bearing formation, density log rock volume physical model, the response equation of its density log such as formula (2) are set up.
2. based on the porosity model of Archie formula: use Archie formula to ask for the expression formula such as formula (4) of water saturation, are taken the logarithm in formula (4) both sides and can obtain formula (5), just the S in formula (5) simultaneouslywFormula (6) can be obtained after converting.The value of four litho-electric parameters a, b, m, n in formula (6) is obtained by rock-electric test, formation water resistivity RwObtained by formation water analysis of data.
3. associating volume physical model A Erqi porosity model, adopts iterative algorithm to calculate porosity: by step 1 and 2 it can be seen that after simultaneous formula (3) and (6) two equations of formula, can solve total porosity simultaneouslyWith moisture volumeTwo unknown parameters.Owing to there is logarithm in formula (6), therefore cannot solving the two unknown number simply, therefore, the present invention adopts and composes initial value and with the principle of a fixed step size circulation, the two unknown number carried out discretization numerical solution.

Claims (1)

1. the method solving formation porosity based on iterative algorithm, it is characterised in that utilizing associating volume physical model and A Erqi porosity model to adopt iterative algorithm to solve gas-bearing reservoir porosity, method comprises the following steps:
(1) set up the volume physical model of density based: accurately determining on the basis of skeletal density and fluid density, set up density log and calculate the volume physical model of porosity:
(2) porosity model based on Archie formula is set up:
(3) joint density volume physical model A Erqi porosity model, adopts iterative algorithm to calculate porosity:
1. total porosity is composed initial value
2. moisture volume is composed initial valueThen with 0.1 for the sampling interval, water-filled porosity being scanned value, the maximum of water-filled porosity isThen pass through Automatic Program and determine that one group makes equation (3) and the minimum solution of (6) error, as thisNumerical value optimal solution；
③WhenLoop ends；Otherwise repeat the above steps is 2.；
4. from 2., extract often group make equation (3) and the minimum solution of (6) errorPreferably go out one group of solution that error is minimumAs moisture volume hereinAnd total porosityNumerical value optimal solution.
CN201610325221.5A 2016-05-17 2016-05-17 Method for solving formation porosity on basis of iterative algorithm Pending CN105804737A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107923240A (en) * 2015-09-16 2018-04-17 因格瑞恩股份有限公司 Method for determining the porosity associated with the organic matter in well or stratum
CN109033575A (en) * 2018-07-10 2018-12-18 中国海洋石油集团有限公司 A kind of water saturation calculation method of Complicated Pore Structures reservoir
CN112761631A (en) * 2021-01-12 2021-05-07 中国海洋石油集团有限公司 Method for determining density, sampling method and pollution rate of pure formation water
CN113187463A (en) * 2021-04-14 2021-07-30 中海石油(中国)有限公司海南分公司 Pore pressure while drilling prediction method based on stratum overpressure single-cause contribution rate
CN116291415A (en) * 2023-04-12 2023-06-23 西南石油大学 Method and system for calculating porosity of gas-bearing stratum

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107923240A (en) * 2015-09-16 2018-04-17 因格瑞恩股份有限公司 Method for determining the porosity associated with the organic matter in well or stratum
CN107923240B (en) * 2015-09-16 2021-02-26 因格瑞恩股份有限公司 Method for determining porosity associated with organic matter in a well or formation
CN109033575A (en) * 2018-07-10 2018-12-18 中国海洋石油集团有限公司 A kind of water saturation calculation method of Complicated Pore Structures reservoir
CN109033575B (en) * 2018-07-10 2023-04-07 中国海洋石油集团有限公司 Water saturation calculation method for reservoir with complex pore structure
CN112761631A (en) * 2021-01-12 2021-05-07 中国海洋石油集团有限公司 Method for determining density, sampling method and pollution rate of pure formation water
CN112761631B (en) * 2021-01-12 2023-08-11 中国海洋石油集团有限公司 Density determination method, sampling method and pollution rate determination method for pure formation water
CN113187463A (en) * 2021-04-14 2021-07-30 中海石油(中国)有限公司海南分公司 Pore pressure while drilling prediction method based on stratum overpressure single-cause contribution rate
CN113187463B (en) * 2021-04-14 2022-08-02 中海石油(中国)有限公司海南分公司 Pore pressure while drilling prediction method based on stratum overpressure single-cause contribution rate
CN116291415A (en) * 2023-04-12 2023-06-23 西南石油大学 Method and system for calculating porosity of gas-bearing stratum
CN116291415B (en) * 2023-04-12 2023-11-24 西南石油大学 Method and system for calculating porosity of gas-bearing stratum

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