Shale reservoir rock debris surface free water removal method applied to nuclear magnetic resonance detection

Abstract

The invention relates to a shale debris surface free water removal method applied to nuclear magnetic resonance detection. Water molecules in a water film on the surface of shale debris can interfere with accurate measurement of nuclear magnetic resonance signals of fluid in the debris and influence judgment of fluid properties in pores and reservoir characteristics. The shale debris is cooperatively treated through multiple steps of centrifugal dewatering, hot air drying, vacuum treatment and the like, free water on the surface of the shale reservoir debris can be efficiently removed, and the debris treatment efficiency is improved. In the treatment process, a mild cleaning agent is adopted, and parameters such as temperature and pressure are strictly controlled, so that damage to the structure and the property of the rock debris is avoided, and the quality of the rock debris and the accuracy of subsequent analysis and detection are guaranteed. The equipment and the process adopted by the invention are relatively simple, and the cost is low. The whole method is simple in operation process and easy to master and implement, and convenient conditions are provided for popularization and application of the method.

Description

Technical fields:

[0001] This invention relates to the field of shale reservoir cuttings processing technology. Shale gas, as an important unconventional natural gas resource, occupies an increasingly important position in the global energy landscape. During the exploration and development of shale gas, drilling generates a large amount of cuttings, and the processing and analysis of these cuttings is a crucial step in shale gas development. Background technology:

[0002] In shale oil development and other processes, the treatment of shale reservoir cuttings is crucial. The surface of cuttings often contains free water, which not only increases the cost of transportation and storage but also interferes with subsequent nuclear magnetic resonance (NMR) analysis, affecting the accuracy of such tests. Currently, there is a lack of an efficient, reliable, and cost-effective method for removing free water from the surface of shale reservoir cuttings.

[0003] Cuttings nuclear magnetic resonance (NMR) logging can accurately determine the porosity of cuttings in shale reservoirs. Porosity is one of the key parameters for measuring reservoir storage capacity. By performing NMR measurements on cuttings, the distribution of different pore sizes can be obtained quickly and accurately, providing reliable data for assessing the storage space of shale oil reservoirs. Besides porosity, permeability is also an important physical property parameter affecting shale oil development. Cuttings NMR logging can indirectly assess reservoir permeability by analyzing the diffusion characteristics of fluids in the cuttings. Cuttings NMR logging can effectively distinguish between oil and water based on the characteristic differences of different fluids in the NMR signal. By measuring parameters such as the relaxation time of fluids in the cuttings, the properties and content of the fluids can be determined.

[0004] In nuclear magnetic resonance (NMR) detection, the relaxation time of hydrogen nuclei is a crucial measurement parameter used to analyze information such as the pore structure and fluid type of rock cuttings. Water molecules in the water film on the rock cutting surface generate additional NMR signals, interfering with the accurate measurement of fluid signals within the rock cuttings. The presence of a water film may increase the overall signal intensity, leading to inaccurate measurements of the relaxation time of the fluid within the rock cuttings and affecting the assessment of fluid properties and reservoir characteristics. Therefore, exploring a method for removing free water from the surface of shale rock cuttings for NMR detection is essential. Summary of the Invention:

[0005] The purpose of this invention is to provide a method for removing free water from the surface of rock cuttings in shale reservoirs using nuclear magnetic resonance (NMR) detection, comprising the following steps:

[0006] Step 1: Screening and Cleaning

[0007] Shale reservoir cuttings are initially screened to remove larger particles (greater than 0.5 cm) and foreign matter. A mild cleaning agent (nonionic surfactant, amphoteric surfactant, citric acid, malic acid, etc.) is used to initially clean the cuttings, removing surface dirt and some soluble substances. The cuttings are then rinsed with purified water to prepare for subsequent free water removal.

[0008] Step 2: Use a sponge to absorb water.

[0009] Place the pre-treated rock fragments onto a sponge. If the sponge has large pores or the rock fragments are small, absorbent paper can be placed on the sponge. Then press the rock fragments to allow the sponge to absorb the water. Depending on the moisture content of the rock fragments and the size of the watermarks on the absorbent paper, this process can be repeated until no obvious water stains are visible on the surface of the rock fragments.

[0010] Step 3: Centrifugation and dehydration

[0011] Centrifugal dehydration is performed at specific speeds and times. Centrifugal force separates most of the free water from the surface of the rock cuttings. The centrifuge speed and time are adjusted according to the characteristics and water content of the rock cuttings to achieve the best dehydration effect.

[0012] Step 4: Cold air drying

[0013] The centrifuged rock fragments are placed in a low-temperature air (below 10 degrees Celsius) drying device. The flow of low-temperature air accelerates the evaporation of free water on the surface of the rock fragments. The airflow rate and drying time are controlled to ensure effective removal of free water without damaging the structure and properties of the rock fragments. At the same time, excessively high temperatures are avoided to prevent changes in the content of organic matter and water in the rock fragments.

[0014] Step 5: Testing and Quality Control

[0015] The treated rock cuttings should have a dry surface, without obvious water droplets or films. This can be checked visually or with the aid of a magnifying glass. If the surface of the rock cuttings is dry and shows no signs of moisture, the free water content can be considered to have met the predetermined standard. In addition, changes in the color and texture of the rock cuttings can be observed. If the treatment process did not significantly affect the structure and properties of the rock cuttings, and the color and texture showed no significant change compared to before treatment, this can also be used as a reference for whether the free water content meets the standard.

[0016] If the test results do not meet the requirements, return to the corresponding steps for reprocessing until the free water content on the rock debris surface reaches the predetermined standard.

[0017] Step Six: Nuclear Magnetic Resonance Imaging

[0018] Nuclear magnetic resonance (NMR) tests were performed on the processed rock cuttings to observe whether the signal intensity and spectral line shape matched the expectations. If the signal intensity was stable, the spectral line shape was clear, and there was no interference from moisture, then the free water content could be considered to have met the requirements. Detailed implementation method:

[0019] A method for removing free water from the surface of rock cuttings in shale reservoirs using nuclear magnetic resonance imaging (NMR) according to the present invention includes the following steps:

[0020] Step 1: Screening and Cleaning

[0021] Preliminary screening of shale reservoir cuttings, such as Figure 1 As shown, larger rock fragments (greater than 0.5 cm in size) and foreign objects are removed. A mild cleaning agent (nonionic surfactant, amphoteric surfactant, citric acid, malic acid, etc.) is used for initial cleaning of the rock fragments to remove surface dirt and some soluble substances. Then, the fragments are rinsed with purified water to prepare for subsequent free water removal.

[0022] Step 2: Use a sponge to absorb water.

[0023] Place the pre-processed rock fragments on a sponge, such as Figure 2 As shown, if the sponge has a large pore size or the rock fragments are small, absorbent paper can be placed on the sponge, and then the sponge can be pressed to absorb the water. Depending on the water content on the surface of the rock fragments and the size of the watermark on the absorbent paper, the process can be repeated until no obvious water stains are visible on the surface of the rock fragments.

[0024] Step 3: Centrifugation and dehydration

[0025] Centrifugal dehydration is performed at specific speeds and times. Centrifugal force separates most of the free water from the surface of the rock cuttings. The centrifuge speed and time are adjusted according to the characteristics and water content of the rock cuttings to achieve the best dehydration effect.

[0026] Step 4: Cold air drying

[0027] The centrifuged rock fragments are placed in a low-temperature air (below 10 degrees Celsius) drying device. The flow of low-temperature air accelerates the evaporation of free water on the surface of the rock fragments. The airflow rate and drying time are controlled to ensure effective removal of free water without damaging the structure and properties of the rock fragments. At the same time, excessively high temperatures are avoided to prevent changes in the content of organic matter and water in the rock fragments.

[0028] Step 5: Testing and Quality Control

[0029] The treated rock cuttings should have a dry surface, without obvious water droplets or films. This can be checked visually or with the aid of a magnifying glass. If the surface is dry and shows no signs of moisture, the free water content is considered to have met the predetermined standard. Additionally, observe changes in the color and texture of the rock cuttings. If the treatment process did not significantly affect the structure and properties of the rock cuttings, and the color and texture remained largely unchanged compared to before treatment, then the free water content of the rock cuttings met the requirements.

[0030] If the test results do not meet the requirements, return to the corresponding steps for reprocessing until the free water content on the rock cutting surface meets the requirements.

[0031] Step Six: Nuclear Magnetic Resonance Imaging

[0032] The processed rock cuttings were subjected to nuclear magnetic resonance (NMR) testing to observe whether the signal intensity and spectral line shape matched expectations. If the signal intensity was stable, the spectral line shape was clear, and there was no interference from moisture, subsequent NMR analysis could be carried out. Attached image description:

[0033] Figure 1 Shale reservoir rock fragments with a size of 1-5 mm.

[0034] Figure 2 Shale fragments placed on a sponge (left) and on absorbent paper (right).

[0035] Figure 3 Flowchart for the removal of free water from the surface of rock cuttings in shale reservoirs.

Claims

1. A method for removing free water from the surface of rock cuttings in shale reservoirs using nuclear magnetic resonance (NMR) detection, characterized in that, The screening step mainly removes rock fragments smaller than 1 mm that cannot be detected by NMR and removes non-target layer rock fragments larger than 5 mm. Then, solvent cleaning is used to remove dirt and some soluble substances from the surface of the rock fragments, eliminating the influence of organic matter rich in oil-based mud or water on NMR detection.

2. A method for removing free water from the surface of rock cuttings in shale reservoirs using nuclear magnetic resonance imaging, characterized in that, The sponge absorbs water primarily to remove easily flowing water from the surface of rock cuttings and organic matter rich in mud, so as not to affect the accuracy of the nuclear magnetic resonance detection process.

3. A method for removing free water from the surface of rock cuttings in shale reservoirs using nuclear magnetic resonance (NMR) detection, characterized in that, Centrifugal dehydration mainly uses centrifugal force to further reduce the free water content on the surface of rock cuttings without damaging the rock cuttings themselves.

4. A method for removing free water from the surface of rock cuttings in shale reservoirs using nuclear magnetic resonance (NMR) detection, characterized in that, Cold air drying removes water stains from the surface of rock fragments by using low-temperature, dry airflow, while the low temperature maximizes the retention of organic matter and moisture inside the rock fragments.

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