CN103592687B - The quantitative calculation method of coal petrography adsorbed gas content - Google Patents

Abstract

The invention discloses a kind of quantitative calculation method of coal petrography adsorbed gas content, first, pre-service is carried out to well-log information; Then, calculate fixed carbon content, reservoir pressure, set up the quantitative relationship chart board of coal petrography adsorbed gas content and coal rank, buried depth, temperature, pressure, the regression coefficient of acquisition vitrinite reflectance function, factor of influence and Lan Shi pressure; Finally, based on the Dynamic Adsorption computation model of Lan Shi establishing equation coal petrography adsorbed gas content, and calculate in log data and above-mentioned parameter introducing Dynamic Adsorption model, obtain coal petrography adsorbed gas content; Coal petrography gassiness characteristic is evaluated according to the coal petrography adsorbed gas content calculated.Under these computing method fully have studied formation condition, many factors is to the quantitative effect of coal petrography adsorbed gas content, utilize experimental data scale to the well-log information of conditions down-hole, establish the Dynamic Adsorption computation model of the coal petrography adsorbed gas content based on well-log information, improve the computational accuracy of absorption tolerance.

Description

The quantitative calculation method of coal petrography adsorbed gas content

Technical field

The invention belongs to cbm exploration technical field, particularly relate to a kind of quantitative calculation method of coal petrography adsorbed gas content.

Background technology

The quantitative calculation method of coal petrography adsorbed gas content is key and the main difficult technical of coalbed methane reservoir evaluation, and utilizing well-log information to calculate its content becomes important channel, and its computational accuracy directly has influence on the exploratory development decision-making of coal-seam gas.For this reason, carried out the Research on Calculation of coal petrography absorption tolerance both at home and abroad and established some computation models, having comprised Langmuir model (Lan Shi equation), Freundlich empirical model, neutron incremental model, BP neural network model etc.

Wherein Lan Shi equation is most widely used general, and its formula is as follows:

$V=\frac{V_{L}P}{P+P_L}$

Wherein:

V: coal petrography adsorbed gas content, represents specific coal petrography adsorbed gas volume under a certain pressure, unit m ³/ t;

V _l: Lan Shi volume, represents the adsorbed gas volume that coal petrography is maximum, unit m ³/ t;

P _l: be Lan Shi pressure;

P: reservoir pressure.

Three parameters on the right of this model all need by obtaining the experiment of particular type coal petrography, and the model of foundation is also be suitable under experiment condition.

The limitation of this equation is: under the formation condition of reality, characterizes the V of coal petrography maximum adsorption ability _llan Shi volume is not fixing, and it is subject to the impact of the multiple changing factors such as coal rank, buried depth of strata, temperature, pressure, the V of measuring _lonly reflect the coal petrography adsorptive power under experiment condition; P _llan Shi pressure is subject to similar impact.Gaseous tension P during adsorption equilibrium is mainly subject to the reservoir pressure impact of different buried depth coal petrography, and the reservoir pressure of dynamic change cannot be determined in laboratory.Therefore, if directly use experimental data to calculate, accurately cannot obtain the coal petrography adsorbed gas content under Different Strata condition, its error calculated is very large.

Other models are all generally the coal petrographys based on experimental analysis particular type, obtain the parameters such as coal petrography component content, adsorbed gas content, set up based on the coal petrography adsorbed gas content computation model under experiment condition.All there is larger application limitation in these models, be first the actual formation condition that laboratory condition is different from coal petrography and buries, model is not exclusively applicable to the mode of occurence of dynamic change; Next factor being existing model is considered is less, more accurately can not describe the impact of the multiple objective factor in underground on coal petrography absorption tolerance.Therefore, the applicable elements of existing model is comparatively harsh, and the influence factor that model is considered is comparatively simple, and during coal petrography adsorbed gas content under the formation condition evaluating dynamic change, its error of calculation is larger.

Summary of the invention

Object of the present invention is just to provide a kind of quantitative calculation method of coal petrography adsorbed gas content, comprehensive considering various effects, utilize log data to calculate the dynamic change section obtaining longitudinal continuous print coal petrography adsorbed gas content, calculate more accurate, thus solve the problem completely.

Object of the present invention is realized by following technical proposals:

A quantitative calculation method for coal petrography adsorbed gas content, comprises the following steps:

Step 1, carries out pre-service to well-log information;

Step 2, utilizes volume-based model or probability statistics model to calculate fixed carbon content;

Step 3, utilizes coal heart scale to log well, and sets up the quantitative relationship chart board of coal petrography adsorbed gas content and coal rank, buried depth, temperature, pressure;

Step 4, utilizes the coal heart to analyze the well logging of data scale, obtains the regression coefficient of vitrinite reflectance function, factor of influence and Lan Shi pressure;

Step 5, base area layer depth and log parameter fitting process, calculate the reservoir pressure obtaining coal seam;

Step 6, based on the Dynamic Adsorption computation model of Lan Shi establishing equation coal petrography adsorbed gas content, and calculates in log data and above-mentioned parameter introducing Dynamic Adsorption model, obtains coal petrography adsorbed gas content;

The Dynamic Adsorption computation model of this coal petrography adsorbed gas content is:

$V=V_{\mathrm{FC}}\frac{F\left(R_O\right)\×P}{P+m\×\mathrm{Temp}+n},$ Wherein:

V-coal petrography adsorbed gas content; V _fC-fixed carbon content; F (R _o)-vitrinite reflectance function; P-reservoir pressure; Temp-temperature; The regression coefficient of m, n-factor of influence (temperature or vertical depth) and Lan Shi pressure;

Step 7, evaluates coal petrography gassiness characteristic according to the coal petrography adsorbed gas content calculated.

Further, in step 1, well-log information pre-service comprises curvature correction and standardization.

Further, in step 4, vitrinite reflectance function is:

$F\left(R_O\right)=-76.236\×R_O^2+331.97\×R_O-324.08,$ Wherein:

R _O＝0.000678859×Depth+0.000425572×AC-0.01059×CNL+0.48888×DEN；

+0.000278356×GR+0.000524556×RD-0.000547578×RS+1.29068

R _o-vitrinite reflectance; The Depth-degree of depth; AC-interval transit time; CNL-neutron porosity; DEN-volume density; GR-natural gamma; RD-deep lateral resistivity; The shallow side direction resistivity of RS-.

Further, in step 5, method of Eaton is adopted to calculate reservoir pressure on non-coal stratum:

$P={\mathrm{\σ}}_V-({\mathrm{\σ}}_V-{\mathrm{\σ}}_W)\×{\left(\frac{{\mathrm{\Δt}}_n}{\mathrm{\Δt}}\right)}^c,$ Wherein:

σ _v-vertical stress; σ _w-local water liquid column hydrostatic pressure; C compactability index; Δ t-surveys sound wave; Δ t _nsound wave on-compaction trend line;

Reservoir pressure is calculated adopting following relational expression containing coal bearing seams:

P=0.016895 × Depth-1.078 × DEN-8.9147, wherein:

The Depth-degree of depth; DEN-volume density.

Compared with prior art, beneficial effect of the present invention is: under these computing method fully have studied formation condition, many factors is to the quantitative effect of coal petrography adsorbed gas content, utilize experimental data scale to the well-log information of conditions down-hole, establish the Dynamic Adsorption computation model of the coal petrography adsorbed gas content based on well-log information, improve the computational accuracy of absorption tolerance, remarkable at regional effects such as south, Yanchuan.

Accompanying drawing explanation

Fig. 1 is blue co-volume and coal rank graph of a relation in the present invention;

Fig. 2 is the graph of a relation of Lan Shi volume and buried depth in the present invention;

Fig. 3 is the graph of a relation of Lan Shi volume and temperature in the present invention;

Fig. 4 is the graph of a relation of Lan Shi volume and pressure in the present invention;

Fig. 5 is the graph of a relation of buried depth in the present invention, volume density and pressure;

Fig. 6 is method flow diagram of the present invention;

Fig. 7 is the coal petrography adsorbed gas content result map that the present invention implements at a bite well;

Fig. 8 is the coal petrography adsorbed gas content result map that the present invention implements at another mouthful of well.

Embodiment

Below in conjunction with specific embodiments and the drawings, the present invention is further illustrated.

Shown in Fig. 5 and Fig. 6, a kind of quantitative calculation method of coal petrography adsorbed gas content, comprises the following steps:

Step 1, carries out pre-service to well-log information, comprises curvature correction and standardization;

Step 2, utilizes volume-based model or probability statistics model to calculate fixed carbon content V _fC;

Step 3, utilizes coal heart scale to log well, and sets up the quantitative relationship chart board of coal petrography adsorbed gas content and coal rank, buried depth, temperature, pressure;

Step 4, utilizes the coal heart to analyze the well logging of data scale, obtains the regression coefficient of vitrinite reflectance function, factor of influence and Lan Shi pressure;

Vitrinite reflectance function is:

$F\left(R_O\right)=-76.236\×R_O^2+331.97\×R_O-324.08$ (related coefficient=0.86), wherein:

R _O＝0.000678859×Depth+0.000425572×AC-0.01059×CNL+0.48888×DEN；

+0.000278356×GR+0.000524556×RD-0.000547578×RS+1.29068

R _o-vitrinite reflectance, %; The Depth-degree of depth, m; AC-interval transit time, us/ft; CNL-neutron porosity, %; DEN-volume density, g/m ³; GR-natural gamma, API; RD-deep lateral resistivity, Ω m; The shallow side direction resistivity of RS-, Ω m;

Step 5, base area layer depth and log parameter fitting process, calculate the reservoir pressure P obtaining coal seam;

Method of Eaton is adopted to calculate reservoir pressure on non-coal stratum:

$P={\mathrm{\σ}}_V-({\mathrm{\σ}}_V-{\mathrm{\σ}}_W)\×{\left(\frac{{\mathrm{\Δt}}_n}{\mathrm{\Δt}}\right)}^c,$ Wherein:

σ _v-vertical stress, Mpa; σ _w-local water liquid column hydrostatic pressure, Mpa; C compactability index; Δ t-surveys sound wave, us/ft; Δ t _nsound wave on-compaction trend line, us/ft;

Reservoir pressure is calculated adopting following relational expression containing coal bearing seams:

P=0.016895 × Depth-1.078 × DEN-8.9147 (related coefficient=0.99), wherein:

The Depth-degree of depth, m; DEN-volume density, g/m ³.

Step 6, based on the Dynamic Adsorption computation model of Lan Shi establishing equation coal petrography adsorbed gas content, and calculates in log data and above-mentioned parameter introducing Dynamic Adsorption model, obtains coal petrography adsorbed gas content V;

The Dynamic Adsorption computation model of this coal petrography adsorbed gas content is:

$V=V_{\mathrm{FC}}\frac{F\left(R_O\right)\×P}{P+m\×\mathrm{Temp}+n},$ Wherein:

V-coal petrography adsorbed gas content, m ³/ t; V _fC-fixed carbon content, %; F (R _o)-vitrinite reflectance function; P-reservoir pressure, Mpa; Temp-temperature; The regression coefficient of m, n-factor of influence (temperature or vertical depth) and Lan Shi pressure;

Step 7, evaluates coal petrography gassiness characteristic according to the coal petrography adsorbed gas content calculated.

Based on Lan Shi equation analysis coal rank, buried depth, temperature, pressure on the impact of coal petrography adsorbed gas content:

A () coal rank affect

See Fig. 1, coal rank are one of principal elements affecting coal adsorptive power, and different rank coal-seam gas adsorption/desorption ability has difference.Usually, coal petrography adsorbed gas content increases along with the increase on coal rank; But to a certain extent, under same temperature and pressure condition, high-rank coals adsorbed methane ability is apparently higher than the adsorptive power of low coal rank.In coal petrography combustible basis, Lan Shi volume V _lwith the vitrinite reflectance R on reflection coal rank _oin " U " relation; At R _oabout=2.18, V _lvalue reaches peak.

B () buried depth affects

See Fig. 2, in the good situation of Seal Condition, along with the increasing of buried depth Depth, Lan Shi volume V _lthere is the trend reduced gradually.

(c) influence of temperature change

See Fig. 3, Lan Shi volume V _lincrease with temperature Temp and decline gradually, the two is good linear relationship, basically identical to coal petrography adsorbed gas content influence factor with buried depth.

(d) pressure variations influence

See Fig. 4, under isothermy, coal is to the adsorbance V of methane gas _lpositive correlation is become with reservoir pressure P.Interval at different pressures, gathering way of its adsorbance is not quite similar, and in the interval of 0 ~ 6MPa, adsorbance sharply rises, and becomes approximately linear to increase; In the interval of 6 ~ 8MPa, adsorbance gathers way and slows down, and starts to tend towards stability, and the now absorption of coal petrography to methane reaches capacity state.After pressure is more than 8Mpa, the adsorbed gas content impact increased that is stressed is less, but by temperature, buried depth, R _othe impact increased is more obvious, therefore starts to occur slightly declining.

These computing method are compared to classical Lan Shi equation, the Dynamic Adsorption model of coal petrography adsorbed gas content quantitatively considers more influence factors, comprise coal seam vertical depth (temperature), reservoir pressure, vitrinite reflectance etc., introduce log data in a model, establish the coal petrography air content Dynamic Adsorption model mated with conditions down-hole.In error of calculation evaluation: when selecting resolution gas content to evaluate model accuracy, adopt relative error analysis; When the coal-bed gas content selecting laboratory isothermal adsorption theory to calculate is evaluated model accuracy, adopt absolute difference analysis.

Adopt multiple coal petrography adsorbed gas content computation model, the coal petrography adsorbed gas content prolonging southern Sichuan more than 10 mouthful of well is calculated.Because resolution gas content sample point is relatively many, therefore the main relative error computing method that adopt are analyzed model error.From statistics, the error of calculation of the Dynamic Adsorption model of the application is minimum, has higher precision in actual computation, and effect is better, as shown in table 1 and accompanying drawing 7 and accompanying drawing 8.

Table 1, prolongs southern Sichuan coal petrography adsorbed gas content multi-model error of calculation comparison sheet (for Tong Koujing, same coal seam)

From above-mentioned table 1, we clearly can find out that employing computing method of the present invention have higher precision, and the error of calculation is minimum.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. quantitatively determine a method for coal petrography adsorbed gas content, it is characterized in that, comprise the following steps:

Step 1, carries out pre-service to well-log information, comprises curvature correction and standardization;

Step 2, utilizes volume-based model or probability statistics model to calculate fixed carbon content;

Step 3, utilizes coal heart scale to log well, and sets up the quantitative relationship chart board of coal petrography adsorbed gas content and coal rank, buried depth, temperature, pressure;

Step 4, utilize the coal heart to analyze the well logging of data scale, obtain the regression coefficient of vitrinite reflectance function, factor of influence and Lan Shi pressure, vitrinite reflectance function is:

, wherein:

；

-vitrinite reflectance; The Depth-degree of depth; AC-interval transit time; CNL-neutron porosity; DEN-volume density; GR-natural gamma; RD-deep lateral resistivity; The shallow side direction resistivity of RS-;

Step 5, base area layer depth and log parameter fitting process, calculate the reservoir pressure obtaining coal seam;

Step 6, based on the Dynamic Adsorption computation model of Lan Shi establishing equation coal petrography adsorbed gas content, and calculates in log data and above-mentioned parameter introducing Dynamic Adsorption model, obtains coal petrography adsorbed gas content;

The Dynamic Adsorption computation model of this coal petrography adsorbed gas content is:

, wherein:

V-coal petrography adsorbed gas content; -fixed carbon content; -vitrinite reflectance function; P-reservoir pressure; Temp-temperature; The regression coefficient of m, n-factor of influence (temperature or vertical depth) and Lan Shi pressure;

Step 7, evaluates coal petrography gassiness characteristic according to the coal petrography adsorbed gas content calculated.

2. a kind of method quantitatively determining coal petrography adsorbed gas content according to claim 1, is characterized in that: in step 5, adopts method of Eaton to calculate reservoir pressure on non-coal stratum:

, wherein:

-vertical stress; -local water liquid column hydrostatic pressure; C compactability index; -actual measurement sound wave; sound wave on-compaction trend line;

Reservoir pressure is calculated adopting following relational expression containing coal bearing seams:

, wherein:

The Depth-degree of depth; DEN-volume density.