CN105350959A - Method for determining gas saturation of shale gas reservoir through well-logging lithologic density - Google Patents

Abstract

The invention relates to a method for determining gas saturation of shale gas reservoir through well-logging lithologic density. The method comprises following steps: obtaining gas saturation of core test analyses, core volume and density and well-logging natural gamma at the corresponding depth and utilizing a least square method to determine model coefficients of a first model and a second model in order to ultimately determine an optimal model; acquiring natural gamma and lithologic density of a well to be interpreted, acquiring total hydrocarbon and methane content of the well to be interpreted through gas-logging resources and acquiring lithic fragments, cores, lithology of geological logging to be explained through geological-logging resources; dividing the shale gas reservoir through acquired gas-logging and mud-logging resources; calculating gas saturation Sg of the reservoir of the well to be interpreted through the determined optimal model and well-logging resources; and outputting a calculation result.The method for determining gas saturation of the shale gas reservoir through well-logging lithologic density has following beneficial effects: the method is easy and convenient and is extensively applied and is ready to use in 120 wells of shale gas; and calculated gas saturation of the shale gas reservoir is approximate to gas saturation of the shale gas reservoir, with the average error less than 10%.

Description

Method for determining gas saturation of shale gas reservoirs from logging lithology density

technical field

The invention relates to a method for determining the gas saturation of shale gas reservoirs by logging lithology density

Background technique

The successful development of shale gas has brought a new energy revolution to the world. The utilization of shale gas is of great significance to environmental protection and energy saving. People pay more and more attention to the search and discovery of shale gas layers. Rock gas has become a new normal in mineral development. Shale gas gas saturation is an indispensable key parameter in the evaluation of shale gas reservoirs, shale gas pools and shale gas area selection.

The traditional method for determining the gas saturation of shale gas reservoirs is to use the ECS element capture logging method or the Archie method to obtain it. At present, ECS element capture logging can only rely on the services of foreign logging companies, and the cost is very high. The Archie method is used to calculate the gas saturation of shale gas reservoirs, mainly using the logging resistivity, porosity and other data of shale gas reservoirs. The prerequisite for calculating the gas saturation of shale gas reservoirs by the Archie method is that only the formation water conducts electricity, and the mineral components constituting the formation framework do not conduct electricity. However, conductive minerals such as pyrite often exist in shale gas reservoirs, which makes the resistivity of shale gas reservoirs abnormally small, and the calculated gas saturation has low accuracy and large errors. This method has Certain limitations.

Contents of the invention

The purpose of the present invention is to aim at the present technical situation mentioned above, aiming at providing a kind of calculation model of determining the gas saturation of shale gas reservoir by lithological density logging data, which can improve the shale gas under the condition of low resistivity interlayer. A method for the accuracy of gas saturation in gas reservoirs.

The realization mode of the object of the present invention is, the method for determining gas saturation of shale gas reservoir by logging lithology density, concrete steps are:

1) Obtain core samples from known wells in the work area, test and analyze the gas saturation Sg, core bulk density ρb, and log natural gamma ray GR at the corresponding depth; the selected samples must be from the same work area and the same layer series, and the number should not be less than 12 block, the number of wells is not limited; then use the least squares method to determine the model coefficients of model one Sg1=a/ρb+b, model two Sg2=a·ρb+b·GR+c, and finally determine the best model;

In the formula, the dimension of core bulk density ρb is g/cm ³ ,

The dimension of natural gamma GR is API,

The dimension of gas saturation Sg is %;

2) Obtain the natural gamma ray and lithology density DEN of the well to be interpreted through the logging data, obtain the total hydrocarbon and methane content of the well to be interpreted through the gas logging data, and obtain the geological logging data of the well to be interpreted through the geological logging data. Cuttings, core lithology; lithology density DEN dimension is g/cm ³ ;

3) dividing the shale gas reservoir by the logging and mud logging data obtained in step 2);

4) Replace step 1) core bulk density (ρb) with step 2) logging lithology density (DEN) of the well to be interpreted, and calculate the reservoir gas saturation Sg of the well to be interpreted through the determined optimal model and logging data;

5) Output calculation results.

The invention provides a solution for calculating the formation gas saturation of low-resistivity shale reservoirs, which is simpler and has a wider application range than the Archie method for determining the gas saturation of shale reservoirs.

The present invention has been used in 120 wells in a certain shale gas field, and the calculated gas saturation of shale gas reservoirs is close to the gas saturation of shale gas layers obtained by core testing, with an average error of no more than 10%, which can satisfy Field logging reservoir evaluation and the need to calculate the gas saturation of shale gas.

Description of drawings

Fig. 1 is the workflow block diagram of the present invention,

Fig. 2 is the intersecting diagram of model one inverse calculation saturation and rock core saturation of the present invention,

Fig. 3 is the intersecting diagram of the inverse calculation saturation and the core saturation of the second model of the present invention,

Fig. 4 is an application example diagram of well S in J shale gas field of the present invention.

detailed description

Through shale gas reservoir core experiments, the applicant found that there is an obvious quantitative relationship between the shale gas reservoir core volume density (ρb) and its gas saturation (Sg), and this relationship is expressed as the gas saturation and core volume The reciprocal of the density is positively correlated, and the gas saturation is also linearly related to the core bulk density and the corresponding log natural gamma ray. The log lithology density (DEN) is numerically equal to the core bulk density, but the measurement method is different. Therefore, the above-mentioned quantitative relationship exists between the logging lithology density and the gas saturation of shale gas reservoirs, and the gas saturation (Sg) of shale gas reservoirs can be quantitatively determined by using the logging density and natural gamma ray (GR) data. . Calculation based on core data, use model one Sg=a1/ρb+b1, calculation model two Sg=a2·ρb+b2·GR+c2; calculation based on logging data, model one Sg=a1/DEN+b1, calculation Model 2 Sg=a2·DEN+b2·GR+c2.

In the formula, a1, b1, a2, b2, c2 are equation coefficients.

The present invention will be described in detail below with reference to the accompanying drawings.

With reference to Fig. 1, concrete steps of the present invention are:

1) Obtain core samples from known wells in the work area, test and analyze the gas saturation Sg, core bulk density ρb, and log natural gamma ray GR at the corresponding depth; the selected samples must be from the same work area and the same layer series, and the number should not be less than 12 block, and the number of wells is not limited; then use the least squares method to determine the model coefficients of model 1 Sg1=a/ρb+b and model 2 Sg2=a·ρb+b·GR+c, and then use the model back calculation to obtain the gas-bearing Regression between saturation and core test saturation, the model with the highest correlation coefficient is the best model.

2) Obtain the natural gamma ray and lithology density DEN of the well to be interpreted through the logging data, obtain the total hydrocarbon and methane content of the well to be interpreted through the gas logging data, and obtain the geological logging data of the well to be interpreted through the geological logging data. Cuttings, core lithology;

The depth interval of natural gamma ray GR and lithology density DEN data of wells to be interpreted is 0.1m to 1.0m, saved in wis or txt format; the depth interval of gas logging full hydrocarbon and methane content is 1m or 0.5m, saved as wis or txt format; the lithology data of geological cuttings and cores are saved in excel or txt format.

3) dividing the shale gas reservoir by the logging and mud logging data obtained in step 2);

Shale gas reservoirs are classified based on: lithology is shale or argillaceous rock; there are obvious anomalies in all hydrocarbons and methane, and no heavy hydrocarbon components; high natural gamma ray and low density.

4) Replace step 1) core bulk density (ρb) with step 2) logging lithology density (DEN) of the well to be interpreted, and calculate the reservoir gas saturation Sg of the well to be interpreted through the determined optimal model and logging data;

5) Output the calculation results, usually, the gas saturation Sg of the shale gas layer is not less than 0.5.

The present invention will be described in detail below with specific examples of the S well in the J shale gas field.

1) The gas saturation (Sg) and core bulk density (ρb) of 82 shale cores from 4 shale wells were obtained through the core test analysis of the J shale gas field, and the natural gamma ray (GR ), then 82 pieces of shale core Sg, ρb and GR, according to the model one Sg=a1/ρb+b1 and the model two Sg=a2·ρb+b2·GR+c2 to do least squares regression processing, to obtain the model coefficient a1 =1610.600, b1=567.240, a2=-262.896, b2=0.183, c2=768.147, that is, model one Sg=1610.6/ρb+567.24, model two Sg=-262.896·ρb-0.183·GR+768.147, and then use model one The inversely calculated gas saturation is used as the Y axis, and the core test gas saturation is used as the X axis for fitting. The correlation coefficient R is 0.79 (see Figure 2); the inversely calculated gas saturation of Model 2 is used as the Y axis, and the core saturation Perform regression on the X axis, and the correlation coefficient R is 0.81 (see Figure 3). Comparing the correlation coefficients of model 1 and model 2, the correlation coefficient of model 2 is higher than that of model 1, and model 2 is the best model, so choose model 2.

2) Obtain natural gamma ray and lithology density DEN of well S to be interpreted through well logging data, obtain total hydrocarbon and methane content of well S to be interpreted through gas logging data, and obtain geological Cuttings and core lithology of mud logging;

3) According to the natural gamma ray, lithology density, total hydrocarbon, methane and cuttings core lithology of Well S obtained in step 2), the shale gas reservoir of Well S is divided, and the shale gas of Well S mainly shows intervals at 2170.0 ~2220.0m;

4) Calculate the reservoir gas saturation Sg of Well S by using the best model Sg=-262.896 ρb+0.183 GR+768.147 and the density and natural gamma data of Well S in step 2;

5) Output the calculation results. The main range of calculated gas saturation in the 2170.0-2220.0m section of Well S is 50.0%-80.0% (see Fig. 4). Compared with the core saturation test results of this well, the average error is less than 10%. Meet the needs of shale gas reservoirs and shale gas reservoir evaluation.

Claims (4)

1. The method for determining the gas saturation of shale gas reservoirs by logging lithology density is characterized in that the specific steps are: 1) Obtain core samples from known wells in the work area, test and analyze the gas saturation Sg, core bulk density ρb, and log natural gamma ray GR at the corresponding depth; the selected samples must be from the same work area and the same layer series, and the number should not be less than 12 block, the number of wells is not limited; then use the least squares method to determine the model coefficients of model one Sg1=a/ρb+b, model two Sg2=a·ρb+b·GR+c, and finally determine the best model; In the formula, the dimension of core bulk density ρb is g/cm ³ , The dimension of natural gamma GR is API, The dimension of gas saturation Sg is %; 2) Obtain the natural gamma ray and lithology density DEN of the well to be interpreted through the logging data, obtain the total hydrocarbon and methane content of the well to be interpreted through the gas logging data, and obtain the geological logging data of the well to be interpreted through the geological logging data. Cuttings, core lithology; lithology density DEN dimension is g/cm ³ ; 3) dividing the shale gas reservoir by the logging and mud logging data obtained in step 2); 4) Replace step 1) core bulk density (ρb) with step 2) logging lithology density (DEN) of the well to be interpreted, and calculate the reservoir gas saturation Sg of the well to be interpreted through the determined optimal model and logging data; 5) Output calculation results. 2. the method for determining the gas saturation of shale gas reservoirs by the logging lithology density according to claim 1, is characterized in that in step 1) utilizes the gas saturation and the core test saturation obtained by model inverse calculation For regression, the model with the highest correlation coefficient is the best model. 3. the method for determining shale gas reservoir gas saturation by logging lithology density according to claim 1, is characterized in that the natural gamma GR, lithology density DEN data depth of the well to be interpreted in step 2) The interval is 0.1m～1.0m; the depth interval of gas logging full hydrocarbon and methane content is 1m or 0.5m. 4. the method for determining gas saturation of shale gas reservoirs by logging lithology density according to claim 1, characterized in that step 3) shale gas reservoirs are divided according to: lithology is shale or mud Rock type; there are obvious anomalies in all hydrocarbons and methane, and no heavy hydrocarbon components; high natural gamma ray and low density.