Water Injection Technology Research Articles

Wettability and physical modification of coal under vacuum saturation invasion of SiO2 nanofluids

Coal seam water injection technology could improve the water content of coal seam, which is an effective technical measure to reduce dust generation in the mining process. Water-based silica nanofluids are a green wetting agent for coal seam water injection. To understand the wetting mode of nanofluids in coal, it is necessary to explore the physico-chemical properties of nanofluid-modified coals. First, a new idea of saturation and intrusion of nanofluid into coal was proposed by using vacuum pressurized saturation device. Then, the physical and chemical properties of the modified coal were studied by Fourier transform infrared spectrometer, low-temperature liquid nitrogen adsorption experiments, and uniaxial compression mechanics experiments. The results showed that the content of oxygen-containing functional groups in the modified coal increased, which was positively correlated with the concentration of nanofluids. The pore structure of the modified coal sample changed from complex to simple, and the nanoparticles blocked the micropores to make the coal surface smooth. The saturation invasion of SiO2 nanofluids changed the mechanical properties of coal samples, and the compressive resistance of coal was weakened, and the minimum strength of the coal invaded by 1.5 wt. % SiO2 nanofluid saturation was 13.68 MPa. The saturation intrusion of SiO2 nanofluids has a negative effect on the surface adsorption of coal samples and the blockage of microporous structures, and makes the coal seam easier to be wetted, which contributes to the application and development of nanofluids in the field of coal seam water injection.

Microstructural Evolution and Damage Mechanism of Water-Immersed Coal Based on Physicochemical Effects of Inorganic Minerals.

Coal seam water injection technology enables seam permeability enhancement and facilitates outburst risk reduction. This study investigated the microscale effects of water infiltration on coal and the evolution mechanisms of its mechanical properties. To this end, we systematically analyzed dynamic changes (such as mineral composition, pore structure, and mechanical performance) in coal soaked for various durations using X-ray diffraction, low-field nuclear magnetic resonance (NMR), and uniaxial compression testing. The results indicate: (1) the coal NMR T2 spectrum displays three characteristic peaks, corresponding to rapid water absorption, uniform transition, and stabilization stages of soaking traditionally divided according to peak area variation trends. (2) The coal strength decreases with progressive soaking, influenced by water content, pore volume, mineral composition, etc. Its compressive strength and elastic modulus drop by 22.4% and 19.5%, respectively, compared to the initial values. (3) The expansion of clay minerals during immersion reduces average pore size. In contrast, quartz particle displacement, pore water movement, and soluble mineral dissolution increase pore volume, reducing the overall structure strength. (4) The dominant factors driving the degradation of mechanical properties vary across immersion stages, including water content and specific mineral concentration. This work offers new insights into how hydraulic technology alters coal seams, providing theoretical support for optimizing water injection strategies in the seam.

Mesoscale modeling on the influence of surfactants on seepage law during water injection in coal

To investigate the mesoscopic influence of surfactants on seepage law during water injection in coal seam, this paper innovatively establishes a fluid transport lattice Boltzmann (LBM) model by incorporating the seepage resistance generated from the porous media and external forces, which embodies the impact of wettability degree resulted from cocamidopropyl betaine (CAB), sodium dodecyl sulfate (SDS), and coconutt diethanol amide (CDEA) reagents at a 0.1% concentration. The main conclusions derived from this investigation are as follows: Firstly, as the lattice number in the X direction increases, the average seepage velocities in coal samples treated by deionized water, 0.1% CAB, 0.1% SDS, and 0.1% CDEA reagents (Nos. 1, 2, 3, and 4) exhibit three distinct stages: rapid decline, slow decline, and steady decline; in comparison to raw coal sample, modified coal samples demonstrate decreases of 20.84%, 33.91%, and 61.70%, respectively. Secondly, the critical values of displacement pressure difference exist during the phenomenon that modified reagents spread out in the entire flow channel, which are 3.5, 3.5, and 5.2 MPa, respectively, for coal samples Nos. 2, 3, and 4; this signifies that surpassing these critical values help prevent issues such as blank belts within the wetting range and insufficient dust control. Finally, at a displacement pressure difference of 0.01 (lattice unit), the average velocity ratios for samples (Nos. 2, 3, and 4) are 0.78, 0.56, and 0.37 (lattice unit), respectively; notably, the water flow velocities in modified coal samples are lower compared to that in raw coal sample, indicating that the addition of surfactants impede the seepage process of water injection in coal seam. Moreover, when the displacement pressure difference reaches 0.03 (lattice unit), the velocity ratio of CDEA-modified coal sample exceeds 100%; this means that when the displacement pressure difference surpasses 15.6 MPa, the water injection effect of CDEA-modified coal sample begins to be improved. These research findings offer a theoretical basis for enhancing water injection technology in coal mines.

Pressure Analysis of Vertical-Wells with the Hydraulic Fracturing Assisted Water Injection in Low-Permeability Hydrogen and Carbon Reservoirs.

Enhancing the energy of hydrogen and carbon reservoirs is crucial for the extraction of these resources. Currently, the conventional water-flooding technology faces challenges in replenishing the energy of hydrogen and carbon reservoirs due to the low injection rates caused by their low-permeability properties. To address this, hydraulic fracturing-assisted water injection technology has been employed to enhance the energy of these reservoirs. However, there has been a lack of research on pressure analysis for vertical wells using this technology. Existing studies on pressure analysis are not applicable to this scenario due to the unique behavior of dynamic fracture propagation. In this article, we present a pressure analysis model for vertical wells with hydraulic fracturing-assisted water injection in low-permeability hydrogen and carbon reservoirs, considering dynamic fracture propagation. The model examines the effects of key parameters on the pressure and fluid flow fronts, and it is applied to field wells for validation. Our findings include the following: the typical pressure response curve for vertical wells with hydraulic fracturing-assisted water injection in low-permeability hydrogen and carbon reservoirs can be divided into six stages: dynamic fracture propagation region, linear flow region in hydrogen and carbon reservoirs, bilinear flow region, radial flow region, transition flow region, and boundary control flow region. The production rate affects the pressure and pressure derivatives in the later stages of the process. However, reservoir permeability influences all flow regions, causing the pressure and pressure derivative curves to shift left with increasing permeability. Increases in both the injection rate and production rate result in a rise in the position of fluid fronts. The impact of permeability on fluid fronts is more significant in the early stages than in later stages. This work is of great significance for the development of low-permeability hydrogen and carbon reservoirs, providing a deeper understanding of the pressure dynamics involved in hydraulic fracturing-assisted water injection.

Research and Field Application on Extreme Subdivision Water Injection Technology for Low Permeability Reservoirs

Abstract Low permeability Block A is about to enter the development phase of extremely high water cut. Due to the low overall recovery degree and residual oil scattered sporadically, the efficient development meets more difficulty and conventional residual oil analysis and adjustment methods cannot fulfil the current needs of precise development. To enhance the reservoir utilization degree, we conduct extremely concise zonal water injection experiment from three aspects: sand body description, policies establishment, and proper technique application. In terms of sand body description, four types of sand-body distribution patterns were summarized through fine characterization of vertical, planar, and spatial single sand bodies, clarifying the origin and potential distribution of residual oil. In terms of development policy, numerical simulation and reservoir engineering methods have been comprehensively applied to determine the subdivision combination of injection layers and reasonable water allocation boundaries, and subdivision principles have been established, considering single septation to thin and thick layer with combining enhancing -controlling. In terms of supporting technology, we have studied the small space subdivision process of small compartments, optimized the testing and adjustment methods, and finally achieved accurate separation, strict clamping, and accurate matching of water injection layers. Through the research and practice, it realized the finest septation of the water injection to extremely enhance the subdivision degree and the efficiency of the injection. It also have strengthened the utilization of thin and poor layers and effectively controlled the decline.

Research on Refined Water Injection Technology for Medium and High Water Cut Reservoirs in Nanpu 4 Block

Abstract For water injection development reservoir, the key is to control the di-rection and flow field of the injected water in the reservoir to adjust the tapping of the remaining oil between wells. This paper presents that, by applying the comprehensive discrimination technique of inefficient cir-culation flow field, a flow field evaluation model containing permeabil-ity, overwater multiplier and water saturation seepage characteristics parameters is established and the small layer flow field distribution is quantitatively evaluated by numerical simulation. Based on the geo-logical characteristics, development characteristics and grid inefficient circulation coefficients, the flow field is qualitatively classified into three types: streamline not established, streamline primary and sec-ondary, and streamline fixed and difficult to adjust. Based on the re-search of domestic and foreign literature and numerical simulation, the management system of different types of flow fields is studied to clari-fy the reasonable development technology policy of reservoir flow field adjustment and tapping the remaining oil between wells, so as to achieve the purpose of controlling the reservoir water content rise rate, reducing the water content rate and improving the recovery rate. The mine field experiments conducted in Nanpu 4 block showed that the recovery rate of the block increased by 4 percentage points, indicating that the block development achieved significant results. This is an im-portant guideline for reservoir development in low recovery, medium to high water-bearing reservoirs with water injection development.

Theoretical study on nonlinear seepage mechanism in fractal dendritic fracture network of low permeability coal with water injection

Coal seam water injection technology is adopted by many mines as an effective means of dust reduction in coal mines. There is a threshold pressure gradient phenomenon in the process of water injection in low permeability coal seam, which makes the flow of pressure water in the fracture structure of coal body present nonlinear seepage characteristics. To reveal the theoretical relationship between the structural parameters of coal and the nonlinear seepage characteristics, firstly, the Bingham fluid constitutive equation is used to describe the non-Newtonian behavior in low-permeability coal. Combined with the fractal tree-like bifurcation fracture network model, a mathematical analytical model of threshold pressure gradient is established. Secondly, the model was verified by high-pressure water invasion and radial seepage experiments, and the sensitivity of the model was analyzed. The results show that the error between the theoretical calculation value and the experimental measurement value is between 8.65 % and 42.4 %, which verifies the validity of the model. The above research results can provide a theoretical basis for improving the water injection effect of low permeability coal seam.

Effect of [C12mim][Cl]-NaCl compound solutions on pore structure and wetting characteristics of bituminous coal based on Pearson correlation coefficient

Water injection technology is a compelling technical measure to improve the water content of coal seams and reduce dust generation during mining. At present, the methods to enhance the wetting effect in the research progress are limited to increasing the dosage of a single wetting agent and using a variety of anionic and cationic wetting agents in large doses. More research is needed on the synergistic enhancement of the wetting effect by inorganic salts and ionic liquids. Aiming at this problem, this paper studies the influence of the combination of NaCl and surface active ionic liquid [C12mim][Cl] on the wetting effect and pore structure of bituminous coal. The influence of composite solution and ratio change on coal pore structure and wetting characteristics is studied based on Pearson correlation coefficient, combined with the experimental results of nitrogen adsorption at low temperature, scanning electron microscope and wetting characterization. The results show that bituminous coal exhibits different sizes of hysteresis rings after [C12mim][Cl] and NaCl treatments. With the change in composite ratio, the pore connectivity of coal samples is improved, and the surface roughness of modified bituminous coal is affected by the shift in composite ratio. With the enhancement of the wetting effect, the pore depth increases. On the other hand, adding 0.6 mol/L NaCl makes the composite solution reach a critical micelle concentration, which could synergistically enhance the surface activity and wetting effect of [C12mim][Cl] solution. There is a negative correlation between the volume of bituminous coal macropores and the contact angle, which indicates that the optimal solution ratio can be determined by analyzing the bituminous coal macropore volume change.

The formation process of the gaseous pollutant emissions in pure ammonia fueled engines with pre-chamber jet ignition

Ammonia, as a carbon-free fuel, can serve as an alternative fuel for future engines, which is consistent with the requirements of national carbon reduction policies. However, the higher concentrations of NOx, unburned ammonia and hydrogen emissions of ammonia-fueled engines need to be controlled seriously to meet the increasingly stringent emission regulations. In this study, a pre-chamber jet ignition single-cylinder engine with port pure ammonia injection was carried. The formation process of gaseous pollutants during engine operation was investigated using CFD simulations in the equivalence ratio range of 0.8–1.3. And, the study also discusses different methods for reducing gaseous pollutant emissions. The results reveal that under lean burn conditions, the ITE can exceed 49%, and unburned ammonia and hydrogen emissions are extremely low. However, the NO emission concentration is relatively high, reaching above 1500 × 10−6, and primarily dominated by thermal NO. N2O is primarily distributed near the flame front, The low temperature at the cylinder walls decelerates the pyrolysis of N2O, coupled with the influence of secondary combustion, both leading to higher N2O emission concentrations, with maximum value reaching 78.6 × 10−6. NO2 emissions are primarily generated in the burned regions. Under rich burn conditions, the ITE significantly decreases, with an ITE of only 34.6% at an equivalence ratio of 1.3. The unburned ammonia emissions rise with an increase in the equivalence ratio, and hydrogen emissions are mainly generated through the pyrolysis of residual ammonia in the burned region, so that the elevated unburned ammonia emissions could lead to an increase in hydrogen emissions. Fuel NO is dominant in NO emissions, and the reduction reaction of unburned ammonia results in extremely low emission concentrations, and also leading to the low levels of N2O and NO2 emissions. According to a comprehensive evaluation of pollutant emissions and engine thermal efficiency, stoichiometric condition is deemed optimal for engine operation, as it can achieve a balance between ITE and gaseous pollutant emissions. Moreover, the adoption of water injection technology can further reduce NOx emissions. Furthermore, the EGR technology and direct liquid ammonia injection will also achieve lower NOx emissions. However, it is insufficient to meet the national emission regulations that only controlling gaseous pollutant emissions during the combustion, and development of the special aftertreatment systems for ammonia fueled engines should not be neglected.

Chichimene field T2 sand: a successful application of cycles in a water injection project on heavy crude oil, enabled by a novel smart selective completion system adapted for water injection

This paper presents the application of injection in cycles, assisted by the first smart selective completion system with remote valve operation. The completion system was installed in the Chichimene Field unit T2 (Fm. San Fernando). The results were compared with conventional water injection, technology that utilizes a simple selective completion system, in the aspects of recovery factor, water consumption, operation style, and others. The target unit has been subjected to selective water injection since 2016, this process consisted of injection of a controlled amount of water within 3-4 zones in equilibrium with the extractive system on producers wells to find a better crude oil movement and a commercial recovery factor. Despite this, the surveillance evidence suggests that some zones consume too much water due its high permeability (heterogeneity) and this impacts on high water cut on producers due to the (adverse mobility ratio), but also suggested that there is a better way to improve even more the recovery factor. This enhancement was enabled with a smart selective completion system by promoting a scheduled temporal closure of zones while production continues, achieving pressure-production restoration effects on the closed zones, allowing an efficiency increase of the vertical and areal sweep. To determine if this could work, a smart completion system was installed in one well in August 2019. During more than one year, the operation and interpretation of the DAS measuring tool (Continuous sound recording) was understood, from which injected water per zone is daily known, with this, the optimization of the injection rate per zone allowed enhancement of the production pattern behaviour. In February 2021, the injection cycles started on the well by zone, and to the current date, more than 25 monthly cycles have been done, increasing the recovery factor, with a considerable reduction in water and energy consumption, maintaining a continuous measurement of zone injection, this level of information has never been reached in the industry. The case study establishes a new frontier in the field of selective injection and in cycles as well, allowing an evolution step in water injection technology. This pilot combined in one design: selective injection, intelligent remote operate completions, continuous layer injection measuring by DAS, extra heavy oil WF, management of high permeability variations and it is aligned with the latest regulations in decarbonization (water and energy saving). From a reservoir point of view, it has never been there, a surveillance in injectors with this level of quality to enhance performance, and on the surface, this technology has allowed an important reduction in the use of wirelines for well operations and improve some well cleaning interventions with coiled tubing.

The injection capacity evaluation of high-pressure water injection in low permeability reservoir: numerical and case study

Low permeability oil reservoir resources are rich and their efficient development is considered an important way to solve energy security issues. However, the development process of low permeability oil reservoirs is faced with the challenges of insufficient natural energy and rapid production decline. The high-pressure water injection technology is a method that relies on high-pressure and large-volume to inject fluid into the reservoir to replenish energy. It is considered as an important technical means to quickly replenish formation energy. This study focuses on the injection capacity for the high-pressure water injection technology of low permeability oil reservoir. Firstly, the fluid-structure interaction mathematical model for two-phase fluid flow was established. The solution of the mathematical model was then obtained by coupling the phase transport in porous media module and Darcy’s law module on the COMSOL numerical simulation platform. The numerical model established in this study was verified through the Buckley-Leverett model. The study on the injection capacity of high-pressure water injection technology was conducted using the geological background and reservoir physical properties of Binnan Oilfield (Shengli, China). The results show that the production pressure difference is the key factor in determining the injection capacity. When the production pressure difference increases from 5 MPa to 30 MPa, the cumulative injection volume increases by 8.1 times. In addition, sensitivity analysis shows that the injection capacity is significantly influenced by the properties of the reformation area. The effect of these parameters from high to low is as follows: stress sensitivity factor, permeability, rock compressibility, and porosity. Compared to the reformation area, the influence of the physical parameters of the matrix area on the injection capacity is negligible. Therefore, effective reservoir reformation is essential for enhancing the injection capacity. This research provides a theoretical basis for the design and optimization of the high-pressure water injection technology schemes for low permeability oil reservoir.

DC electric field assisted heat extraction evaluation via water circulation in abandoned production well patterns: Semi-analytical and numerical models

Geothermal energy, recognized for its clean and vast developmental potential, finds untapped promise in many oil fields developed through water injection. However, challenges such as the high costs associated with drilling and development, the expansion of water-clay expansion, and low rock permeability have constrained the broader exploitation of geothermal resources. Here, to address these challenges and harness low-permeability geothermal energy from abandoned wells, this work introduces a novel approach: DC-assisted circulation water injection technology. This study employs the Green function, Newman product, and boundary element methods to develop semi-analytical and numerical models, incorporating a DC electric field to simulate the optimization effect of this field on heat extraction. This work evaluates and optimize the lifetime and economic effects of abandoned wells using the Non Sorting Genetic Algorithm II. Results show that the semi-analytical model monitors the reservoir temperature parameter to optimize the timing for circulation water injection. Additionally, our numerical model demonstrates that, over a span of 5000 days, a network of wells could generate a revenue of $9.158 million. In summary, DC-assisted abandoned wells to develop geothermal reservoirs is not only feasible but also enhances reservoir permeability and porosity through an electrical conductivity effect, significantly improving heat energy recovery.

Design of Intelligent Control Systems for Layered Water Injections in Oilfields

With rapid socio-economic growth and increased energy demand, exploration and exploitation of oil and gas resources have become crucial. Long-term exploitation leads to problems such as pressure drop and production reduction in oil fields, and water injection technology has become a common method to improve these problems. The traditional direct water injection for oil extraction has problems such as high injection cost and low oil recovery efficiency. Therefore, an intelligent control system for different oilfield reservoirs is needed. This study focuses on the layered water injection intelligent system based on advanced sensor technology, digital signal processing and intelligent algorithms. The article reviews the advantages of layered water injection system and the current research status, designs an intelligent control structure including hardware circuits and modular software processes, and adopts adaptive particle swarm optimization algorithm as the core of intelligent control.

Research and Application of the Fourth Generation Stratified Water Injection Technology in Daqing Oilfield

Stratified water injection is the most important characteristic technology in Daqing oilfield development, providing technical support for efficient oilfield development. With the oilfield entering the ultra-high water cut stage, the remaining oil is highly dispersed, the oil-water relationship is complex, the qualified rate of water injection decreases rapidly, and the difficulty of stabilizing oil and controlling water is increasing. In order to solve the contradiction between the increasing workload of water injection well testing and the limited testing team, and mee t the needs of oilfield precision development, the cable-controlled layered water injection technology has been developed. In this technology, the pressure monitoring system, flow monitoring system and flow control system are placed in the preset cable intelligent water distributor. At the office end, the technicians send control instructions on the server software, and send them to the ground control box through the oilfield production wireless network. The cable carrier technology is used to transmit the instructions to the intelligent water distributor through the cable, so as to achieve real-time communication, obtain the downhole layering parameter information, and control the downhole layering injection volume. Ten intelligent injection technology demonstration areas have been built to verify the process adaptability under different development contradictions. The cable-controlled layered water injection technology improves the proportion of water absorption thickness, effectively controls the water cut rise rate and natural decline rate, and has obvious oil increase effect, promoting the digital transformation and intelligent development of the oilfield.

High-pressure capacity expansion and water injection mechanism and indicator curve model for fractured-vuggy carbonate reservoirs

Water injection for oil displacement is one of the most effective ways to develop fractured-vuggy carbonate reservoirs. With the increase in the number of rounds of water injection, the development effect gradually fails. The emergence of high-pressure capacity expansion and water injection technology allows increased production from old wells. Although high-pressure capacity expansion and water injection technology has been implemented in practice for nearly 10 years in fractured-vuggy reservoirs, its mechanism remains unclear, and the water injection curve is not apparent. In the past, evaluating its effect could only be done by measuring the injection-production volume. In this study, we analyze the mechanism of high-pressure capacity expansion and water injection. We propose a fluid exchange index for high-pressure capacity expansion and water injection and establish a discrete model suitable for high-pressure capacity expansion and water injection curves in fractured-vuggy reservoirs. We propose the following mechanisms: replenishing energy, increasing energy, replacing energy, and releasing energy. The above mechanisms can be identified by the high-pressure capacity expansion and water injection curve of the well HA6X in the Halahatang Oilfield in the Tarim Basin. By solving the basic model, the relative errors of Reservoirs I and II are found to be 1.9% and 1.5%, respectively, and the application of field examples demonstrates that our proposed high-pressure capacity expansion and water injection indicator curve is reasonable and reliable. This research can provide theoretical support for high-pressure capacity expansion and water injection technology in fracture-vuggy carbonate reservoirs.

Integrated technology for layered sand control and layered water injection

In order to solve the problem of water injection string failure caused by pipe creep and sand production in layered water injection wells, an integrated technology of layered sand control and layered water injection has been developed. A suspended large-radiuslayered mechanical sand control pipe column has been designed, providing sufficient design and usage space for the layered water injection pipe column. Developing a new type of anti-creep sealed packer can effectively improve the anti-creep performance of the water injection string and extend the validity period of the string. This technology integrates and optimizes layered water injection and sand control technology, large channel backwashing technology, integrated testing and allocation technology, and anti-creep technology of the pipe string. While effectively solving sand production in offshore water injection wells, it extends the service life of the water injection pipe string and reduces operating costs. Since 2018, this technology has been implemented in over 200 wells in Chengdao Oilfield, with a maximum of 6 layers for prevention and injection, a maximum well inclination of 48.8°, and a construction success rate of over 90%. It has achieved very good development results and economic benefits.

Application of separate layer water injection in high differential pressure wells

With the development of a heavy fine-RRB-layering system and dynamic adjustment, the number of large differential pressure wells increases gradually. The effect of high-pressure difference wells on water injection development is that it is difficult to separate water injection allocation, low pass rate of layers and short effective period of separate sealing, which affects the development effect of water flooding. For this reason, the research on stratified water injection technology with large pressure differences is carried out using step-by-step throttling. The throttling pressure difference borne by the water nozzle is reduced. The large throttling pressure difference produced by the water nozzle is realized. The qualified rate of the layer section is increased to improve the anti-creep performance of the expansion Packer and the sealing effect of large pressure difference injection wells and to extend the service life of the Packer. The field application results of 216 wells in the Shengli Oil Field show that the technique can effectively improve the pass rate of the layers and the sealing effect of the layers and prolong the life of the string.

Numerical Simulation Study of Pressure-Driven Water Injection and Optimization Development Schemes for Low-Permeability Reservoirs in the G Block of Daqing Oilfield

Pressure-driven water injection technology shows significant potential in addressing the key challenges of low-permeability oil reservoirs, improving water flooding development efficiency. Grounded in FDEM theory, this study establishes fluid matrix constitutive equations and employs FDEM to resolve rock stress–strain fields. A numerical simulation method for pressure-driven water injection in low-permeability reservoirs is developed to study the impact of different well pattern densities. The results indicate that the 90° horizontal well pattern using the five-spot method yields optimal outcomes, with approximately 32.32% higher cumulative liquid production than vertical well patterns. The 45° horizontal well pattern with the reversed nine-spot method also performs well, with about 30% higher cumulative liquid production than single-row vertical wells. Pressure-driven water injection improves matrix oil–water permeability and expands water flooding coverage. Based on the pressure gradient distribution driven by different well patterns, an evaluation method for the inter-well utilization capacity and its effectiveness was established. This method quantitatively assesses the reservoir depletion under various horizontal well encryption schemes. For research on timing of water injection in pressure-driven water flooding. Compared to pressure-driven water injection after 90 days, there is increased cumulative oil production after 40 days, emphasizing the importance of early pressure maintenance for higher cumulative oil production and enhanced recovery rates in low-permeability reservoir development. These findings provide crucial theoretical and practical support.

A New Methodology for Determination of Layered Injection Allocation in Highly Deviated Wells Drilled in Low-Permeability Reservoirs

During the water injection development process of highly deviated wells in low-permeability reservoirs, the water flooding distance between different layers of the same oil and water well is different due to the deviation of the well. In addition, the heterogeneity of low-permeability reservoirs is strong, and the water absorption capacity between layers is very different. This results in poor effectiveness of commonly used layered injection methods. Some highly deviated wells have premature water breakthroughs after layered water injection, which affects the development effect of the water flooding reservoirs. Therefore, based on the analysis and research of the existing layered injection allocation method and sand body connectivity evaluation method, considering the influence of sand body connectivity, the real displacement distance of highly deviated wells, reservoir physical properties, and other factors, a new methodology for determination of layered injection allocation in highly deviated wells drilled in low-permeability reservoirs is proposed. In this method, the vertical superposition and lateral contact relationship of a single sand body are determined using three methods: sand body configuration identification, seepage unit identification, and single sand body boundary identification. The connectivity coefficient, transition coefficient, and connectivity degree coefficient are introduced to quantitatively evaluate the connectivity of sand bodies and judge the connectivity relationship between single sand bodies. The correlation formula is obtained using the linear regression of the fracture length and ground fluid volume, and the real displacement distance of each layer in highly deviated wells is obtained. The calculation formula of the layered injection allocation is established by analyzing the important factors affecting the layered injection allocation, and a reasonable layered injection allocation is obtained. The calculation parameters of this method are fully considered, the required parameters are easy to obtain, and the practicability is strong. It can provide a method reference for the policy adjustment of layered water injection technology in similar water injection development reservoirs.

Study on the Fractal Characteristics and Seepage Properties of Channels Filled by Coal Particles.

Studying the seepage process in fracture channels (where coal particles are deposited) is of great significance for improving the performance of both on-site coal seam water injection and dust reduction technology. Through a self-developed simulation experiment of water-borne coal particle migration and accumulation and computer graphics, we investigated the influencing factors of particle accumulation in water injection and their influence law on seepage, discussed the interaction relationship between the fractal structure of coal and the characteristics of accumulated coal particles, and established a new fractal model of fracture permeability based on different particle accumulation states. The results show that the seepage velocity and the particle size jointly affect the migration and accumulation process of water-borne coal particles. When the coal particle size is constant and the seepage velocity increases, then the output of the coal powder increases, the deposition decreases, and the structure fractal dimension D3 of fractures decreases. At the same seepage velocity, with the increase of the coal particle size, the output of coal powder decreases, the deposition increases, and the structure fractal dimension D3 of fractures increases. In addition, the amount of coal powder produced in the intermittent water injection process is smaller than that produced in the continuous water injection process, more easily leading to accumulation. The variation law of the theoretical permeability with porosity remains consistent for different particle accumulation states: with the increase of porosity, the structure fractal dimension D3 of fractures decreases, while the theoretical permeability increases. The above research results can provide a theoretical basis for reducing the seepage damage of coal under the particle blocking effect.