Method for evaluating water content of gas layer based on ion chromatographic analysis

Abstract

The invention discloses a gas reservoir water-containing property evaluation method based on ion chromatographic analysis. The method comprises the following steps: establishing a gas reservoir water saturation quantitative characterization model based on ion chromatographic analysis; drilling operation data and rock breaking volume related data are obtained and recorded; determining the water saturation of the gas reservoir by using the quantitative characterization model of the water saturation of the gas reservoir, the operation data and the rock breaking volume related data; and evaluating the water content of the gas reservoir according to the water saturation of the gas reservoir. By means of the scheme, effective evaluation of the tight sandstone and carbonate rock water layers can be achieved, and assistance is provided for further deepening the exploration and development potential of tight sandstone and carbonate rock gas reservoirs and efficiently increasing storage and building production.

Description

Technical Field

[0001] The present invention relates to the exploration and development fields of tight sandstone gas and carbonate gas, and particularly relates to a method for evaluating water content in gas layers based on ion chromatography analysis. Background Art

[0002] With the continuous increase in the utilization rate of natural gas energy and the fact that natural gas fields have become the focus of global exploration and development, the sources of natural gas include tight sandstone gas, carbonate gas, shale gas, coalbed methane, condensate gas, etc. At present, the main sources and production of natural gas in China are tight sandstone gas and carbonate gas, and the largest tight sandstone gas field and carbonate gas field are distributed in the Ordos Basin. The Ordos Basin is the second largest sedimentary basin in China, with tectonic characteristics of stability within the basin, activity at the basin margin, uplift in the north and south, and westward thrust and eastward uplift. Due to the characteristics of poor reservoir physical properties, strong heterogeneity, and complex gas-water relationship in the Ordos Basin, there is a lack of effective water layer identification means during the exploration and development process, resulting in a sharp increase in water content after fracturing, the occurrence of the "water lock" phenomenon in gas wells, and a series of adverse effects such as shortening the production cycle of gas wells and reducing the gas production of gas wells.

[0003] Currently, there are mainly three methods for calculating the water saturation of gas layers: logging data analysis method, nuclear magnetic resonance analysis method, and ion chromatography method. For loose lithology, logging data can better reflect the pore structure and fluid characteristics in the formation. Therefore, the logging data analysis method has advantages in the evaluation of oil-gas-water layers in conventional reservoirs. However, due to the limitations and errors of logging technology in unconventional reservoirs, the accuracy of calculating water saturation using logging data in the Ordos Basin is relatively low; nuclear magnetic resonance analysis mainly focuses on the evaluation of movable fluids and pore structures in cores. This method has the highest accuracy, but it is only applicable during the core sampling process and cannot be widely promoted and applied; through large-scale experiments and on-site implementations in tight sandstone and carbonate reservoirs in recent years, the ion chromatography method has only achieved qualitative evaluation in the field of core ion chromatography analysis, forming a water content evaluation standard and chart, and partial parameter research has been carried out in the drilling fluid field, but no effective evaluation means have been formed. Summary of the Invention

[0004] The present invention provides a method for evaluating water content in gas layers based on ion chromatography analysis to achieve effective evaluation of water layers in tight sandstone and carbonate rocks.

[0005] For this purpose, the present invention provides the following technical solutions:

[0006] A method for evaluating water content in gas layers based on ion chromatography analysis, the method comprising:

[0007] Establishing a quantitative characterization model for water saturation in gas layers based on ion chromatography analysis;

[0008] Obtain and record the drilling operation data and the data related to the rock-breaking volume;

[0009] Utilize the gas reservoir water saturation quantitative characterization model, the operation data, and the data related to the rock-breaking volume to determine the gas reservoir water saturation;

[0010] Evaluate the water content of the gas reservoir according to the gas reservoir water saturation.

[0011] Optionally, the operation data includes any one or more of the following: bit diameter, gas reservoir thickness.

[0012] Optionally, the data related to the rock-breaking volume includes: porosity φ, formation water salinity TDS1, total salinity of the drilling fluid outlet TDS2, total salinity of the drilling fluid inlet TDS3, and volume of the drilling fluid outlet sample V2.

[0013] Optionally, the establishment of the gas reservoir water saturation quantitative characterization model based on ion chromatography analysis includes:

[0014] Establish a gas reservoir salt content calculation model M1;

[0015] Based on the data related to the rock-breaking volume, determine the salt content of the drilling fluid M2 based on ion chromatography analysis;

[0016] Establish a gas reservoir water saturation quantitative characterization model according to the gas reservoir salt content calculation model M1 and the salt content of the drilling fluid M2.

[0017] Optionally, the establishment of the gas reservoir salt content calculation model M1 includes:

[0018] Establish a gas reservoir salt content calculation model M1 according to the rock-breaking volume V1 during drilling and the total salinity A of water in the rock-breaking volume: M1 = V1·A;

[0019] Wherein, A = φ×S w ×TDS1×10 -4 , S w is the gas reservoir water saturation.

[0020] Optionally, the rock-breaking volume V1 is represented by the volume of a cylinder,

[0021] Optionally, the determination of the salt content of the drilling fluid based on the data related to the rock-breaking volume and ion chromatography analysis includes: calculating the salt content of the drilling fluid M2 according to the following formula: M2 = (TDS2 - TDS3)×V2.

[0022] Optionally, according to the gas reservoir salt content calculation model M1 and the salt content of the drilling fluid M2, the established gas reservoir water saturation quantitative characterization model is:

[0023]

[0024] Among them, S w is the water saturation of the gas layer.

[0025] Optionally, the evaluation of the water content of the gas layer according to the water saturation of the drilling fluid includes: determining the gas layer type according to the water saturation of the drilling fluid.

[0026] Optionally, the gas layer types include: gas-bearing water layer, gas-water coexistence layer, and gas layer.

[0027] Optionally, the method further includes: generating a development suggestion according to the gas layer type.

[0028] The method for evaluating the water content of the gas layer based on ion chromatography analysis provided by the present invention establishes a quantitative characterization model of the water saturation of the gas layer based on ion chromatography analysis. During the drilling process, drilling operation data and data related to the rock-breaking volume are obtained and recorded. Using the quantitative characterization model of the water saturation of the gas layer, the operation data, and the data related to the rock-breaking volume, the water saturation of the gas layer is determined. Furthermore, the water content of the gas layer is evaluated according to the water saturation of the gas layer, realizing the transformation of the evaluation of the water content of the gas layer from qualitative to quantitative.

[0029] In the process of evaluating the water content of the present invention, through the comprehensive application of ion chromatography technology, a quantitative calculation method for water saturation is formed. During the process of selecting gas layers for a gas well, layers with lower water saturation are selected for fracturing development, delaying the water production time of the gas well, increasing the gas production cycle of the gas well, realizing the optimization of the fracturing development layer system of the gas well, and providing reliable support for the high and stable production of the gas well. Description of the Drawings

[0030] Figure 1 is a schematic diagram of the rock-breaking process during drilling;

[0031] Figure 2 is a flow chart of a method for evaluating the water content of the gas layer based on ion chromatography analysis of the present invention;

[0032] Figure 3 is the comprehensive ion chromatography diagram of Well S49-72. Detailed Embodiments

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments cannot be elaborated one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0035] Due to the great difficulty in identifying tight sandstone and carbonate aquifers, which cannot effectively guide the selection of layers for fracturing development, a complete interpretation and evaluation technology system has not been formed yet. Therefore, the gas-bearing water evaluation method based on ion chromatography analysis provided by the present invention establishes a quantitative characterization model for the water saturation of the gas layer based on ion chromatography analysis. During the drilling process, drilling operation data and data related to the rock-breaking volume are obtained and recorded. Using the quantitative characterization model of the water saturation of the gas layer, the operation data and the data related to the rock-breaking volume, the water saturation of the gas layer is determined, and then the gas-bearing water evaluation is carried out according to the water saturation of the gas layer.

[0036] First, a brief description will be given to the basic principle of the calculation formula for the water saturation of the gas layer.

[0037] Refer to Figure 1 , Figure 1 is a schematic diagram of the rock-breaking process during drilling.

[0038] In the wellbore structure 11, the rock is broken by the drill bit 14 fixed on the drill pipe 12, and the drilling fluid 13 is led out through the drill pipe 12. In the rock layer, there are not only rock particles 15, but also water in the rock pores, and the water is divided into bound water 16 and mobile water 17. The bound water 16 refers to the formation water that cannot flow in the formation pores under a certain pressure difference; the mobile water 17 refers to the formation water that can flow in the formation pores under a certain pressure difference.

[0039] According to the law of conservation of mass, it can be known that the salt content in the gas layer during the drilling process is equal to the salt content analyzed by ion chromatography of the drilling fluid. Since overbalanced and near-balanced drilling is generally adopted during the drilling process in the Ordos Basin area, the liquid column pressure is greater than the formation pressure. Therefore, the formation water outside the wellbore generally does not flow into the wellbore, and the formation water contained in the drilling fluid is all the formation water in the reservoir rock pores during the rock-breaking process. The circulation time of the drilling fluid is short. It generally takes about 1 hour from the time when the formation water invades the drilling fluid to its return. Moreover, the gas layer thickness in the Ordos Basin is small, and the corresponding volume of the drilling fluid is small. Therefore, the diffusion effect of various ions of the formation water in the drilling fluid system can be ignored. After the drilling fluid returns, continuous sampling is carried out in the elevated trough. After the pressure filtration is completed, ion chromatography analysis is carried out. Using the results of the ion chromatography analysis and combining parameters such as the gas layer thickness, the original formation water salinity, the porosity, and the drill bit diameter, the water saturation of the gas layer is inversely calculated.

[0040] During the drilling process, the total salinity data in the drilling fluid is affected by many factors. Some are the influences of drilling engineering parameters, such as additives and lag time, and the other part is the influence of formation factors, such as porosity, water saturation, and formation water salinity. These factors will affect the accuracy of the calculation results of water saturation in the drilling fluid. Therefore, the solution of the present invention can further analyze the principles of different influencing factors, determine the magnitude of the influence of each factor on the total salinity data, and eliminate and reduce the influence of these factors through sampling, experimental analysis, calculation, etc., to improve the accuracy of the calculation results.

[0041] The following briefly analyzes the influences of various different factors.

[0042] (1) Drilling fluid additives

[0043] Different types of additives have different effects on the total salinity in the drilling fluid. Some water-soluble additives such as potassium salts, whose main component is KCl (potassium chloride), are extremely soluble in water, while barite that is insoluble in water, whose main component is BaSO4 (barium sulfate). Generally, there are many additives in the drilling fluid, so the drilling fluid additives have a greater impact on the total salinity. However, regardless of whether the additive is soluble in water or not, when taking the sample at the outlet of the drilling fluid, take the sample at the inlet of the drilling fluid (corresponding to the lag time) at the same time, and the influence of the drilling fluid additives can be completely eliminated by using differential spectrum analysis.

[0044] For example: Take a sample at the outlet of the 4000m drilling fluid. Assume that the lag time at a well depth of 4000m is 1h. By backtracking the drilling time by 1h, the well depth reached is 3990m. Then the inlet of the 3990m drilling fluid is the corresponding sample of the 4000m drilling fluid outlet.

[0045] (2) Lag time

[0046] It takes some time for the drilling fluid to return from the bottom of the well to the ground. This time is called the lag time. As the well depth continues to increase, the lag time also continues to increase. The lag time affects the sampling accuracy at the outlet of the drilling fluid, so it has a greater impact on the analysis results of the total salinity. By using the method of calibrating the lag time and calculating the accurate lag time, the influence of the lag time on the analysis results of the total salinity can be completely eliminated.

[0047] The lag time can be determined by calibration. For example: At every 50m interval of the well depth, when stopping the pump to connect a single joint, put a marker, record the time t1 after starting the pump, and record the time when the marker appears in the elevated tank or shaker. This time is t2. Then t2 - t1 is the accurate lag time.

[0048] (3) Porosity and water saturation

[0049] All the mobile water in the formation is stored in the pore volume of the rock. The larger the porosity, the larger the pore volume; the smaller the porosity, the smaller the pore volume. The water saturation is divided into mobile water saturation and irreducible water saturation, which reflects the water content in the pore volume. The higher the water saturation, the more water in the pore volume; the lower the water saturation, the less water in the pore volume. Therefore, porosity mainly affects the pore volume, water saturation mainly affects the water content, and porosity and water saturation jointly affect the total salinity data in the drilling fluid.

[0050] (4) Formation water salinity

[0051] The formation water salinity is the sum of cations and anions in the formation water. For example, the formation water salinity in the Ordos Basin has a wide range of values. The formation water salinity in the Mesozoic strata is about 10,000 - 20,000, and the formation water salinity in the Paleozoic strata is about 50,000 - 100,000. Therefore, the formation water salinity is the main factor affecting the total salinity data in the drilling fluid.

[0052] Based on the above analysis, since the drilling fluid additives and lag time can be eliminated during sampling and analysis, the total salinity data of the drilling fluid is only related to porosity, water saturation, and formation water salinity. To obtain the water saturation value, porosity and formation water salinity are taken as invariants and calculated through formulas.

[0053] As Figure 2 shown, it is a flowchart of a method for evaluating the water content in a gas layer based on ion chromatography analysis provided by the present invention, including the following steps:

[0054] Step 201, establish a quantitative characterization model for the water saturation in the gas layer based on ion chromatography analysis.

[0055] According to the previous analysis, the quantitative characterization model for the water saturation in the gas layer can be established in the following way:

[0056] First, establish a calculation model M1 for the salt content in the gas layer, and determine the salt content M2 of the drilling fluid based on ion chromatography analysis according to the relevant data of the rock-breaking volume; where:

[0057] M1 = V1 × A; (1)

[0058] A = φ × S w × TDS1 × 10 -4 (2)

[0059]

[0060] The meanings of the parameters in the above formulas are as follows:

[0061] V1 - the rock-breaking volume, in L;

[0062] d——bit diameter, unit: cm;

[0063] h——thickness of gas layer, unit: cm;

[0064] A——the meanings of each parameter of formation water in the rock-breaking volume are as follows: total salinity, unit: mg / L;

[0065] φ——porosity, unit: %;

[0066] S w ——water saturation of gas layer, unit: %;

[0067] TDS1——formation water salinity, unit: mg / L;

[0068] M1——salt content in the gas layer, unit: mg.

[0069] The calculation formula for determining the salt content M2 of drilling fluid based on ion chromatography analysis is as follows:

[0070] M2 = (TDS2 - TDS3) × V2 (4)

[0071] The meanings of each parameter in the formula are as follows:

[0072] M2——salt content determined by ion chromatography analysis, unit: mg;

[0073] TDS2——total salinity of drilling fluid at the outlet, unit: mg / L;

[0074] TDS3——total salinity of drilling fluid at the inlet, unit: mg / L;

[0075] V2——volume of drilling fluid outlet sample, unit: L.

[0076] According to the law of conservation of mass, it can be known that M1 = M2. Therefore, based on the gas layer salt content calculation model M1 and the drilling fluid salt content M2, a quantitative characterization model of gas layer water saturation is established.

[0077] According to the above calculation formulas of M1 and M2, the following equation is obtained:

[0078]

[0079] According to the above equation, the water saturation S of the gas layer can be obtained w The calculation formula is:

[0080]

[0081] The above calculation formula of the water saturation S of the gas layer w is the quantitative characterization model of the water saturation of the gas layer.

[0082] Step 202: Obtain and record the drilling operation data and the data related to the rock-breaking volume.

[0083] The operation data includes any one or more of the following: bit diameter, gas layer thickness; the data related to the rock-breaking volume includes: porosity formation water salinity TDS1, total salinity of the drilling fluid at the outlet TDS2, total salinity of the drilling fluid at the inlet TDS3, volume of the drilling fluid outlet sample V2.

[0084] Step 203: Determine the water saturation of the gas layer by using the gas layer water saturation quantification and characterization model, the operation data, and the data related to the rock-breaking volume.

[0085] Input the drilling operation data and the data related to the rock-breaking volume obtained in the above step 202 into the above gas layer water saturation quantification and characterization model, and the corresponding gas layer water saturation S w value can be calculated.

[0086] Step 204: Evaluate the water content of the gas layer according to the water saturation of the gas layer.

[0087] Specifically, the gas layer type can be determined according to the water saturation of the drilling fluid. Further, development suggestions can also be generated according to the gas layer type.

[0088] Assume that the formation conditions and fracturing parameters are the same. When the movable water saturation is greater than the irreducible water saturation (generally the regional experience data or measured by the nuclear magnetic resonance experiment of the core in the same horizon of this area), water breakthrough occurs in the early stage of gas layer exploitation. According to this principle, combined with the regional irreducible water saturation or the nuclear magnetic irreducible water saturation value, using the calculated water saturation value, determine the gas layer evaluation criteria, providing a reference for gas well layer selection for development and well testing and fracturing.

[0089] For example, in a non-limiting embodiment, the gas layer type can be divided into: gas-bearing water layer, gas-water coexisting layer, gas layer.

[0090] Correspondingly, the gas layer evaluation criteria shown in Table 1 below can be set.

[0091] Table 1

[0092]

[0093] By comparing the calculated gas layer water saturation value with the irreducible water saturation values of different reservoir lithologies, the reservoir evaluation criteria are formed, and the application effect in the Paleozoic strata of Ordos is good, providing technical support and guarantee for the large-scale development and production of the gas field.

[0094] The method for evaluating the water content in gas-bearing formations based on ion chromatography analysis provided by the present invention studies the calculation method of water saturation in ion chromatography logging. By using the total salinity parameter in drilling fluid and combining data such as porosity and engineering parameters, a quantitative characterization model of water saturation in gas-bearing formations is established, realizing the transformation of the evaluation of water content in gas-bearing formations from qualitative to quantitative, and can provide reliable support for the high and stable production of gas wells.

[0095] The following examples further illustrate the evaluation process of different geological formations using the solution of the present invention during the drilling process.

[0096] Taking Well S49-72 as an example, the well depth is 3250-3375m, and the horizons are the Shihezi Formation and the Shanxi Formation. A total of 7 layers are interpreted by ion chromatography, including 3 gas-bearing water layers, 2 gas-water layers, 1 poor gas layer, and 1 gas layer. The data such as calculated water saturation, irreducible water saturation, logging interpretation, and ion chromatography interpretation are shown in Table 2.

[0097] Table 2

[0098]

[0099] As can be seen from the above results, at a well depth of 3351-3353m, the logging interpretation is a poor gas layer; the calculated water saturations by ion chromatography are 45.4% and 58.6% respectively, exceeding 10% compared with the irreducible water saturation of 36.9%, and the ion chromatography interpretation is a gas-water layer. Fracturing and flowback were carried out at this well depth. After the flowback of the fracturing fluid ended, the flowback rate exceeded 60%. During the production stage, the daily gas production was 0.5×10⁴ m³, and the daily water production was 15.7 m³, which is a typical water production characteristic, Figure 3 which is consistent with the ion chromatography interpretation in the ion chromatography comprehensive diagram of Well S49-72 shown.

[0100] It should be noted that the terms "including" and "having" and any variations thereof in the description, claims, and above-mentioned drawings of the present invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0101] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other, and the key point of each embodiment is to illustrate the differences from other embodiments. Moreover, the system embodiments described above are only illustrative. The modules and units described as separate components may or may not be physically separated, that is, they may be located on one network unit or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative efforts.

[0102] The embodiments of the present invention have been introduced in detail above. In this text, specific implementation manners are used to elaborate on the present invention. The description of the above embodiments is only used to help understand the method and system of the present invention. They are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The content of this specification should not be construed as a limitation to the present invention. Therefore, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the water content in a gas layer based on ion chromatography analysis, characterized in that, The method includes: Establishing a quantitative characterization model for the water saturation of the gas layer based on ion chromatography analysis; Obtaining and recording drilling operation data and data related to the rock-breaking volume; Using the quantitative characterization model for the water saturation of the gas layer, the operation data, and the data related to the rock-breaking volume to determine the water saturation of the gas layer; Evaluating the water content of the gas layer according to the water saturation of the gas layer.

2. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 1, characterized in that, The operation data includes any one or more of the following: bit diameter, gas layer thickness.

3. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 2, characterized in that, The data related to the rock-breaking volume includes: porosity φ, formation water salinity TDS1, total salinity of the drilling fluid at the outlet TDS2, total salinity of the drilling fluid at the inlet TDS3, and volume of the drilling fluid outlet sample V2.

4. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 3, characterized in that, The establishing of the quantitative characterization model for the water saturation of the gas layer based on ion chromatography analysis includes: establishing a gas layer salt content calculation model M1; Based on the data related to the rock-breaking volume, determining the salt content of the drilling fluid M2 through ion chromatography analysis; and establishing a quantitative characterization model for the water saturation of the gas layer according to the gas layer salt content calculation model M1 and the salt content of the drilling fluid M2.

5. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 4, characterized in that, The establishing of the gas layer salt content calculation model M1 includes: Establishing a gas layer salt content calculation model M1 according to the rock-breaking volume V1 during drilling and the total salinity A of water in the rock-breaking volume: M1 = V1 × A; Wherein, A = φ × S w × TDS1 × 10 -4 , S w is the water saturation of the gas layer.

6. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 5, characterized in that, The rock-breaking volume V1 is expressed by the volume of a cylinder.

7. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 4, characterized in that, The determining of the salt content of the drilling fluid based on the data related to the rock-breaking volume through ion chromatography analysis includes: Calculating the salt content of the drilling fluid M2 according to the following formula: M2 = (TDS2 - TDS3) × V2.

8. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 7, characterized in that, According to the gas layer salt content calculation model M1 and the salt content of the drilling fluid M2, the established quantitative characterization model for the water saturation of the gas layer is: Among them, S w is the water saturation of the gas layer.

9. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to any one of claims 1 to 8, characterized in that, The evaluating of the water content of the gas layer according to the water saturation of the drilling fluid includes: Determining the gas layer type according to the water saturation of the drilling fluid.

10. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 9, characterized in that, The gas layer types include: gas-bearing water layer, gas-water co-existing layer, gas layer.

11. The method for evaluating the water content in a gas layer based on ion chromatography analysis according to claim 10, characterized in that, The method further includes: Generating development suggestions according to the gas layer type.

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