Chloride ion concentration-based tight gas layer gas-water ratio parameter prediction method and system

Abstract

The invention discloses a tight gas reservoir gas-water ratio parameter prediction method and system based on chloride ion concentration, and the method comprises the steps: obtaining a tight gas reservoir test produced water sample, and carrying out the water sample chloride ion concentration data collection, and obtaining a formation water sample chloride ion concentration parameter; selecting a regional gas-water ratio calculation model coefficient, and constructing a gas-water ratio parameter prediction model; and performing gas-water ratio prediction treatment on the chloride ion concentration parameter of the formation water sample based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer. According to the embodiment of the invention, the gas-water ratio parameter calculation model can be constructed by combining the chloride ion concentration parameter of the formation water, and the prediction precision of the gas-water ratio parameter in the tight gas production process is improved. The method can be widely applied to the technical field of gas-water ratio prediction of tight gas reservoirs.

Description

Technical Field

[0001] The present application relates to the technical field of tight gas reservoir gas-water ratio prediction, and in particular to a tight gas reservoir gas-water ratio parameter prediction method and system based on chloride ion concentration. Background Art

[0002] Tight gas reservoirs have complex gas-water relationships, well-developed micropores, high immobile water saturation, small differences in logging response characteristics between oil and gas layers and water layers, industrial production layers and low-yield layers, low contrast, and great difficulty in logging identification. In order to increase the gas production of tight gas, fracturing is currently used to transform tight gas reservoirs to generate more microcracks to communicate the gas production channels between the reservoir and the wellbore. However, the fracturing process often easily converts bound water in tight gas reservoirs into movable water, so the tight gas production process is mostly in a state of gas and water co-production. For this reason, oilfield technicians need to accurately evaluate the gas-water ratio parameters of the tight gas production process through various geological data to formulate the optimal tight gas reservoir development implementation plan and production allocation plan. The existing plans include trial production method and logging prediction method. Among them, the logging prediction method has high time efficiency, but it relies on rich logging data and core test analysis results. The prediction model parameter determination process cycle is long, which makes the prediction model accuracy poor. The trial production method is expensive and has a long operation cycle, which cannot meet the evaluation needs of tight gas reservoirs.

[0003] In summary, the technical problems existing in the relevant technologies need to be improved. Summary of the invention

[0004] The main purpose of the embodiments of the present application is to propose a method and system for predicting the gas-water ratio parameters of tight gas layers based on chloride ion concentration, which can construct a gas-water ratio parameter calculation model by combining the formation water chloride ion concentration parameters, thereby improving the prediction accuracy of the gas-water ratio parameters in the tight gas production process.

[0005] To achieve the above object, one aspect of an embodiment of the present application proposes a method for predicting gas-water ratio parameters of a tight gas layer based on chloride ion concentration, the method comprising:

[0006] Obtain water production samples from tight gas formations and collect chloride ion concentration data of water samples to obtain chloride ion concentration parameters of formation water samples;

[0007] Select the regional gas-water ratio calculation model coefficients and build a gas-water ratio parameter prediction model;

[0008] Based on the gas-water ratio parameter prediction model, the chloride ion concentration parameter of the formation water sample is processed for gas-water ratio prediction to obtain the gas-water ratio parameter of the tight gas layer.

[0009] In some embodiments, the method of obtaining a water production sample for a tight gas formation test and collecting chloride ion concentration data of the water sample to obtain a chloride ion concentration parameter of the formation water sample includes:

[0010] Obtaining the water production sample for testing the tight gas layer by using a downhole formation water in-situ sampler;

[0011] The chloride ion concentration data of the water samples tested in the tight gas layer is collected to obtain the chloride ion concentration parameters of the formation water samples.

[0012] In some embodiments, the step of obtaining the water production sample for testing the tight gas formation by using a downhole formation water in-situ sampler comprises:

[0013] Identify the area to be studied;

[0014] The downhole formation water in-situ sampler is lowered to the depth of the production layer section of the area to be studied to extract and process, so as to obtain a preliminary tight gas layer test water production sample;

[0015] The preliminary dense gas layer test water production sample is transported and processed through a heat-insulating and pressure-maintaining sample tube to obtain the dense gas layer test water production sample.

[0016] In some embodiments, the step of collecting chloride ion concentration data of water samples from a tight gas formation test to obtain chloride ion concentration parameters of formation water samples includes:

[0017] Performing sedimentation and filtration treatment on the dense gas layer test water production sample to obtain a filtered dense gas layer test water production sample;

[0018] Based on the preset ambient temperature, the chloride ion sensor is used to collect data on the water production sample of the filtered dense gas layer test to obtain preliminary chloride ion concentration parameters;

[0019] Based on the preset ambient temperature, data of the filtered dense gas layer test water production sample is collected by a conductivity sensor to obtain conductivity parameters;

[0020] The preliminary chloride ion concentration parameter and the conductivity parameter are integrated to determine the chloride ion concentration parameter of the formation water sample.

[0021] In some embodiments, the selecting of regional gas-water ratio calculation model coefficients and constructing a gas-water ratio parameter prediction model includes:

[0022] Select the regional gas-water ratio to calculate the model coefficients;

[0023] Obtain tight gas production data of several layers of tight gas reservoirs and determine the gas-water ratio parameters of the layers;

[0024] Obtain tight gas formation water samples from several layers of tight gas reservoirs and determine the chloride ion concentration data of the formation water;

[0025] The gas-water ratio parameter of the layer is used as the horizontal coordinate, and the chloride ion concentration data of the formation water of the layer is used as the vertical coordinate to construct a relationship diagram between the gas-water ratio and the chloride ion concentration value of the test water production;

[0026] Based on the relationship diagram between the gas-water ratio and the test produced water chloride ion concentration value, the regional gas-water ratio calculation model coefficient is introduced to construct the gas-water ratio parameter prediction model.

[0027] In some embodiments, the regional gas-water ratio calculation model coefficient includes a first control index parameter and a second control index parameter, and the regional gas-water ratio calculation model coefficient is determined by a regional tight gas test.

[0028] In some embodiments, the expression of the gas-water ratio parameter prediction model is specifically as follows:

[0029] GW=a×e (b×CL)

[0030] In the above formula, GW represents the gas-water ratio parameter, a and b represent the regional gas-water ratio calculation model coefficients, e represents the natural base, and CL represents the chloride ion concentration parameter of the formation water sample.

[0031] In some embodiments, the gas-water ratio prediction processing of the formation water sample chloride ion concentration parameter based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer includes:

[0032] Inputting the chloride ion concentration parameter of the formation water sample into the gas-water ratio parameter prediction model;

[0033] The chloride ion concentration parameter of the formation water sample is subjected to exponential calculation and prediction processing to obtain the gas-water ratio parameter of the tight gas layer.

[0034] In some embodiments, the method further includes storing the gas-water ratio parameters of the tight gas layer for use in tight gas reservoir reserve evaluation and preparation of tight gas layer well development implementation plans.

[0035] To achieve the above object, another aspect of the embodiment of the present application provides a dense gas layer gas-water ratio parameter prediction system based on chloride ion concentration, the system comprising:

[0036] The first module is used to obtain water production samples for testing of tight gas formations and collect chloride ion concentration data of water samples to obtain chloride ion concentration parameters of formation water samples;

[0037] The second module is used to select the regional gas-water ratio calculation model coefficients and build a gas-water ratio parameter prediction model;

[0038] The third module is used to perform gas-water ratio prediction processing on the chloride ion concentration parameter of the formation water sample based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer.

[0039] The embodiments of the present application include at least the following beneficial effects: The present application provides a method and system for predicting the gas-water ratio parameters of tight gas layers based on chloride ion concentration. The scheme obtains a water production sample for a tight gas layer test and collects chloride ion concentration data of the water sample to obtain the chloride ion concentration parameters of the formation water sample, and then selects the regional gas-water ratio calculation model coefficient to construct a gas-water ratio parameter prediction model. Finally, based on the gas-water ratio parameter prediction model, the chloride ion concentration parameters of the formation water sample are subjected to gas-water ratio prediction processing. There is no need to collect additional geological basic data, and no data collection operation fees are incurred. The gas-water ratio parameter calculation can be realized by processing and mining the existing geological data. The gas-water ratio parameter calculation model can be constructed by combining the formation water chloride ion concentration parameters, thereby improving the prediction accuracy of the gas-water ratio parameters in the tight gas production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of a method for predicting gas-water ratio parameters of a tight gas layer based on chloride ion concentration provided in an embodiment of the present application;

[0041] Figure 2 It is a structural schematic diagram of a dense gas layer gas-water ratio parameter prediction system based on chloride ion concentration provided in an embodiment of the present application;

[0042] Figure 3 Schematic diagram of the relationship between the gas-water ratio and the chloride ion concentration of the test water produced provided in the embodiment of the present application;

[0043] Figure 4 It is a schematic diagram of a tight gas layer well provided in an embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the embodiments of the present application. They are only examples of systems and methods consistent with some aspects of the embodiments of the present application as detailed in the attached claims.

[0045] It is understood that the terms "first", "second", etc. used in this application can be used to describe various concepts in this article, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another concept. For example, without departing from the scope of the embodiment of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if" and "if" as used herein can be interpreted as "at the time of" or "when" or "in response to determination".

[0046] The terms "at least one", "multiple", "each", "any", etc. used in this application, at least one includes one, two or more, multiple includes two or more, each refers to each of the corresponding multiple, and any refers to any one of the multiple.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0048] Reference Figure 1 , Figure 1 A flow chart of a method for predicting gas-water ratio parameters of a dense gas layer based on chloride ion concentration provided by an embodiment of the present invention, referring to Figure 1 , the method comprises the following steps:

[0049] S100, obtaining a water production sample for a tight gas layer test and collecting chloride ion concentration data of the water sample to obtain a chloride ion concentration parameter of the formation water sample;

[0050] It should be noted that, in some embodiments, step S100 may include: S110, obtaining a tight gas layer test water production sample through a downhole formation water in-situ sampler; S120, collecting water sample chloride ion concentration data for the tight gas layer test water production sample to obtain the formation water sample chloride ion concentration parameter.

[0051] It should be further explained that, in some embodiments, step S110 may include: S111, determining the area to be studied; S112, lowering the downhole formation water in-situ sampler to the depth of the production layer section in the area to be studied to extract and process, and obtain a preliminary tight gas layer test water production sample; S113, transporting and processing the preliminary tight gas layer test water production sample through an insulated and pressure-maintaining sample tube to obtain a tight gas layer test water production sample.

[0052] In this embodiment, the downhole formation water in-situ sampling instrument is lowered to the depth of the production layer to sample the water produced in the tight gas reservoir test production section. The downhole sampling samples are placed in an insulated and pressure-maintaining sample tube to avoid contamination of the water samples by the wellbore fluid and ensure that the samples are representative.

[0053] It should be noted that, in some embodiments, step S120 may include: S121, performing sedimentation and filtration treatment on the dense gas layer test water production sample to obtain a filtered dense gas layer test water production sample; S122, based on a preset ambient temperature, collecting data on the filtered dense gas layer test water production sample through a chloride ion sensor to obtain a preliminary chloride ion concentration parameter; S123, based on a preset ambient temperature, collecting data on the filtered dense gas layer test water production sample through a conductivity sensor to obtain a conductivity parameter; S124, integrating the preliminary chloride ion concentration parameter with the conductivity parameter to determine the chloride ion concentration parameter of the formation water sample.

[0054] In this embodiment, the formation water sample in the heat-insulating and pressure-maintaining sample tube is placed in a laboratory vessel, and then the vessel containing the formation water sample is placed for 24 hours. The principle of sedimentation is used to separate some impurities such as mud, oil and other impurities in the sample to ensure the purity of the formation water; 200 mL of formation water is taken out from the vessel, and air conditioning is used to ensure that the laboratory measurement environment temperature is stable at 26 degrees. The chloride ion sensor and the conductivity sensor are used to collect data simultaneously. The chloride ion sensor can directly obtain the chloride ion concentration parameter, and the conductivity sensor can obtain the conductivity parameter of the formation water sample to be tested. The chloride ion concentration can also be obtained by conversion. The data measured by the dual sensors are calibrated with each other to ensure that the chloride ion concentration parameter is accurate and reliable.

[0055] S200, selecting regional gas-water ratio calculation model coefficients and constructing a gas-water ratio parameter prediction model;

[0056] It should be noted that, in some embodiments, step S200 may include: S210, selecting regional gas-water ratio calculation model coefficients; S220, obtaining tight gas production data of several layers of tight gas reservoirs, and determining the layer gas-water ratio parameters; S230, obtaining tight gas formation water samples of several layers of tight gas reservoirs, and determining the layer formation water chloride ion concentration data; S240, using the layer gas-water ratio parameters as the horizontal coordinate and the layer formation water chloride ion concentration data as the vertical coordinate to construct a relationship graph between the gas-water ratio and the test water production chloride ion concentration value; S250, based on the relationship graph between the gas-water ratio and the test water production chloride ion concentration value, introducing the regional gas-water ratio calculation model coefficients, and constructing a gas-water ratio parameter prediction model.

[0057] Among them, the regional gas-water ratio calculation model coefficient includes a first control index parameter and a second control index parameter, and the regional gas-water ratio calculation model coefficient is determined by regional tight gas testing.

[0058] In some specific embodiments, the coefficients a and b of the regional gas-water ratio calculation model are selected, and their values ​​are related to the sedimentary environmental factors. When the sedimentary environment is marine, the method for taking the values ​​of a and b described in the embodiment of the present invention is consistent, and can be determined by regional production data.

[0059] Specifically, Figure 3 As shown in the figure, the existing tight gas production data of 10 layers in a tight gas reservoir can be obtained through the production data. The gas-water ratio parameters of the layer can be obtained. At the same time, the formation water samples of the layer section can be obtained through sampling equipment. The formation water chloride ion concentration data of the corresponding layer section can be obtained through chemical analysis. The relationship between the gas-water ratio and the chloride ion concentration value of the test water production is plotted. It can be seen from the figure that the area a=2.5×10 9 , b=-0.0032.

[0060] Therefore, the expression of the gas-water ratio parameter prediction model of the embodiment of the present invention is specifically as follows:

[0061] GW=a×e (b×CL)

[0062] In the above formula, GW represents the gas-water ratio parameter, a and b represent the regional gas-water ratio calculation model coefficients, e represents the natural base, and CL represents the chloride ion concentration parameter of the formation water sample.

[0063] S300, performing gas-water ratio prediction processing on the chloride ion concentration parameter of the formation water sample based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer;

[0064] It should be noted that, in some embodiments, step S300 may include: S310, inputting the chloride ion concentration parameter of the formation water sample into the gas-water ratio parameter prediction model; S320, performing exponential calculation and prediction processing on the chloride ion concentration parameter of the formation water sample to obtain the gas-water ratio parameter of the tight gas layer.

[0065] In some specific embodiments, several sample data of the tight gas layer section for which the gas-water ratio parameters are to be determined are obtained; the sample data include the chloride ion concentration of formation water; the chloride ion concentration data is input into the gas-water ratio parameter prediction model, and the regional gas-water ratio prediction model coefficients a and b values ​​are substituted into the gas-water ratio parameter prediction model to calculate the gas-water ratio parameters of the tight gas layer section. Finally, the gas-water ratio prediction results are output and stored for use by users in evaluating the reserves of tight gas reservoirs and formulating development implementation plans.

[0066] Further, the embodiments of the present invention are described by experiments. Figure 4As shown, it is a tight gas layer well, the reservoir section porosity is 8%, the permeability is 0.05mD, the well logging interpretation is a tight gas layer, the drill pipe test is carried out in the 4100-4175m gas layer section, and the gas layer section produces formation water after perforation. Due to the water lock effect, the formation gas production is not high. If the gas and water production are used to calculate the gas-water ratio parameters, the gas-water ratio parameters will inevitably be inaccurate. By sampling and analyzing the formation water as in the above step S100, the formation water chloride concentration is obtained to be 5000ppm, and the gas-water ratio parameter prediction model GW=a×e is substituted. (b×CL) The calculated gas-water ratio is 281.3m 3 / m 3 Tight gas development generally adopts fracturing to make the formation permeability better in order to produce more natural gas, which will also produce more water. Since the water produced by the formation has a high mineralization, it cannot be discharged directly. Special water treatment equipment is required to treat the produced water to meet the indicators before discharge. Therefore, the gas-water ratio parameters of the tight gas layer must be clearly defined in the development plan. The daily gas and water production are evaluated through reserves. These two indicators serve as control indicator parameters for the scale of some devices in the tight gas layer development process. Therefore, the gas-water ratio parameter is one of the core parameters in the design of the tight gas layer development plan.

[0067] In summary, the prediction of gas-water ratio parameters in the test process of tight gas reservoirs provided by the embodiment of the present invention is based on the chloride ion concentration data of water produced by wellbore test, and provides a fast and reliable method for calculating gas-water ratio parameters in the test process for tight gas reservoir exploitation. Compared with related methods, the method for calculating gas-water ratio parameters in the test process of tight gas reservoirs provided by the embodiment of the present invention has the following advantages:

[0068] 1) High prediction accuracy: The accuracy of the calculation results depends on the abundance of regional production data. A large amount of test oil data can improve the accuracy of the a and b values ​​of the gas-water ratio calculation model parameters. Compared with predictions based on well logging data, the calculation results of this method are more accurate.

[0069] 2) Low cost: The production unit does not need to collect additional geological basic data, and does not incur data collection operation fees. It only needs to process and mine the existing geological data to realize the calculation of gas-water ratio parameters. Compared with the prediction through the trial production method, the cost of this method is lower.

[0070] See also Figure 2 The embodiment of the present application also provides a system for predicting gas-water ratio parameters of a dense gas layer based on chloride ion concentration, which can implement the above-mentioned method for predicting gas-water ratio parameters of a dense gas layer based on chloride ion concentration. The system includes:

[0071] The first module 201 is used to obtain a water production sample for a tight gas layer test and collect chloride ion concentration data of the water sample to obtain a chloride ion concentration parameter of the formation water sample;

[0072] The second module 202 is used to select the regional gas-water ratio calculation model coefficients and construct the gas-water ratio parameter prediction model;

[0073] The third module 203 is used to perform gas-water ratio prediction processing on the chloride ion concentration parameter of the formation water sample based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer.

[0074] It can be understood that the contents of the above method embodiments are all applicable to the present system embodiments, the functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0075] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the rights of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present invention should be within the scope of the rights of the present invention.

Claims

1. A method for predicting gas-water ratio parameters of tight gas layers based on chloride ion concentration, characterized in that: The method comprises the following steps: Obtain water production samples from tight gas formations and collect chloride ion concentration data of water samples to obtain chloride ion concentration parameters of formation water samples; Select the regional gas-water ratio calculation model coefficients and build a gas-water ratio parameter prediction model; Based on the gas-water ratio parameter prediction model, the chloride ion concentration parameter of the formation water sample is processed for gas-water ratio prediction to obtain the gas-water ratio parameter of the tight gas layer.

2. The method according to claim 1, characterized in that: The method of obtaining a water production sample for testing a tight gas layer and collecting chloride ion concentration data of the water sample to obtain chloride ion concentration parameters of the formation water sample includes: Obtaining the water production sample for testing the tight gas layer by using a downhole formation water in-situ sampler; The chloride ion concentration data of the water samples tested in the tight gas layer is collected to obtain the chloride ion concentration parameters of the formation water samples.

3. The method according to claim 2, characterized in that The method of obtaining the water production sample for testing the tight gas layer by using a downhole formation water in-situ sampler comprises: Identify the area to be studied; The downhole formation water in-situ sampler is lowered to the depth of the production layer section of the area to be studied to extract and process, so as to obtain a preliminary tight gas layer test water production sample; The preliminary dense gas layer test water production sample is transported and processed through a heat-insulating and pressure-maintaining sample tube to obtain the dense gas layer test water production sample.

4. The method according to claim 2, characterized in that: The method of collecting chloride ion concentration data of water samples from the tight gas formation test water production sample to obtain the chloride ion concentration parameters of the formation water sample includes: Performing sedimentation and filtration treatment on the dense gas layer test water production sample to obtain a filtered dense gas layer test water production sample; Based on the preset ambient temperature, the chloride ion sensor is used to collect data on the water production sample of the filtered dense gas layer test to obtain preliminary chloride ion concentration parameters; Based on the preset ambient temperature, data of the filtered dense gas layer test water production sample is collected by a conductivity sensor to obtain conductivity parameters; The preliminary chloride ion concentration parameter and the conductivity parameter are integrated to determine the chloride ion concentration parameter of the formation water sample.

5. The method according to claim 1, characterized in that The method of selecting a regional gas-water ratio calculation model coefficient and constructing a gas-water ratio parameter prediction model comprises: Select the regional gas-water ratio to calculate the model coefficients; Obtain tight gas production data of several layers of tight gas reservoirs and determine the gas-water ratio parameters of the layers; Obtain tight gas formation water samples from several layers of tight gas reservoirs and determine the chloride ion concentration data of the formation water; The gas-water ratio parameter of the layer is used as the horizontal coordinate, and the chloride ion concentration data of the formation water of the layer is used as the vertical coordinate to construct a relationship diagram between the gas-water ratio and the chloride ion concentration value of the test water production; Based on the relationship diagram between the gas-water ratio and the test produced water chloride ion concentration value, the regional gas-water ratio calculation model coefficient is introduced to construct the gas-water ratio parameter prediction model.

6. The method according to claim 5, characterized in that The regional gas-water ratio calculation model coefficient includes a first control index parameter and a second control index parameter, and the regional gas-water ratio calculation model coefficient is determined by regional tight gas testing.

7. The method according to claim 5, characterized in that The expression of the gas-water ratio parameter prediction model is specifically as follows: GW=a×e (b×CL) In the above formula, GW represents the gas-water ratio parameter, a and b represent the regional gas-water ratio calculation model coefficients, e represents the natural base, and CL represents the chloride ion concentration parameter of the formation water sample.

8. The method according to claim 1, characterized in that: The gas-water ratio prediction processing is performed on the chloride ion concentration parameter of the formation water sample based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer, including: Inputting the chloride ion concentration parameter of the formation water sample into the gas-water ratio parameter prediction model; The chloride ion concentration parameter of the formation water sample is subjected to exponential calculation and prediction processing to obtain the gas-water ratio parameter of the tight gas layer.

9. The method according to claim 1, characterized in that: The method also includes storing the gas-water ratio parameters of the tight gas layer for use in tight gas reservoir reserve evaluation and preparation of tight gas layer well development implementation plans.

10. A dense gas layer gas-water ratio parameter prediction system based on chloride ion concentration, characterized in that: The system comprises: The first module is used to obtain water production samples for testing of tight gas formations and collect data on chloride ion concentration of water samples to obtain chloride ion concentration parameters of formation water samples; The second module is used to select the regional gas-water ratio calculation model coefficients and build a gas-water ratio parameter prediction model; The third module is used to perform gas-water ratio prediction processing on the chloride ion concentration parameter of the formation water sample based on the gas-water ratio parameter prediction model to obtain the gas-water ratio parameter of the tight gas layer.

Images