Fossil Hydrogen Energy Research Articles

New insight into imbibition micromechanisms and scaling model in fossil hydrogen energy development of tight reservoirs based on NMR

Spontaneous imbibition is an important mechanism for developing fossil hydrogen energy. However, the research of imbibition micromechanisms and scaling methods in tight reservoirs with complex lithofacies remains limited. This study employed Nuclear magnetic resonance (NMR) monitoring to investigate imbibition at multiscale pores in tight sandy conglomerate samples. Then, a modified shut-in time-scale model was developed analyzing the imbibition modes and control factors. The results showed that the imbibition concludes three stages: suction, diffusion, and stable. The diffusion stage is crucial for promoting recovery. Two modes of imbibition in four lithofacies were distinguished: stable type (recovery>40 %) and sensitive type (recovery<20 %). Samples with medium permeability (0.2mD-0.6mD), bimodal pore distribution, and less illite/smectite mixed-layer (relative content<50 %) had high recovery. Nanopores provided foremost oil supply, while macropores facilitated fluid interchange. “Relay imbibition” from micropores to macropores was an important recovery mechanism. Hydrogen signals during clay expansion and microcracks propagation were identifiable by NMR-T2 after accounting for ferromagnets and temperature. The imbibition diffusion radius derived from T2 accumulation was found to modify the normalized time-scale model for complex lithofacies tight reservoirs. Consequently, the reasonable shut-in time for stable and sensitive reservoirs was concluded to be 32 and 11 days, respectively.

A novel polymer encapsulated silica nanoparticles for water control in development of fossil hydrogen energy—tight carbonate oil reservoir by acid fracturing

This paper introduces and evaluates performance of a novel polymer encapsulated silica nanoparticles (CM-NPs) as RPM on reducing water-cut in tight carbonate oil formations with multistage hydraulic fractures. CM-NPs as RPM were prepared by graft-polymerization and quaternization and then identified by FT-IR method. Changes in the core surface properties and oil/water relative permeability were identified by SEM, XPS, wettability measurements and core flooding experiments. Certain changes occur, as confirmed by SEM and XPS, in the element compositions and microstructure of the core surface after introducing CM-NPs on the reservoir rock surface. Such changes irreversibly alter its wettability from the hydrophobicity to hydrophilicity. During the displacement experiments, there exists a disproportionate permeability reduction on relative permeability of the oil-water systems. Because of microstructure change of core surface, water relative permeability is reduced up to 60% and water flow restricted by hydrophilic polymer chains on the surface of CM-NPs while oil relative permeability decreases by less than 15% at different stages of water saturation. In addition, the rheological measurements and water drive tests shows the CM-NP solution has good acid resistance and strong adsorption on the core surface, keeping a long-term period of water control after acid fracturing in tight carbonate oil reservoir.

Enhancing filter cake removal by engineering parameter optimization for clean development of fossil hydrogen energy: A numerical simulation

Long-term zonal isolation is crucial for the development of fossil hydrogen energy, while efficient filter cake removal is the basis for successful zonal isolation. However, enhanced filter cake removal usually relies on adding chemicals into preflush fluid, which are potential pollutants to the environment. In this study, engineering parameter optimization is used to realize enhanced filter cake removal. Firstly, filter cake removal was identified as multiple-phase fluid flow, and a new three-fluid numerical model was established accordingly. The effects of five engineering parameters on the removal efficiency were simulated and the results showed that borehole enlargement and casing eccentricity reduced removal efficiency. The critical borehole deviation angle and casing rotation speed for optimal removal efficiency were 45° and 40 rpm, respectively, while the removal efficiency monotonously increased with flushing velocity. After all engineering parameters were optimized, the maximum removal efficiency was as high as 89.34%, which was comparable to that achieved by using potentially polluting chemicals. The borehole enlargement rate was identified as the most sensitive parameter, followed by casing eccentricity, flushing velocity, borehole deviation angle, and casing rotation speed subsequently. Two empirical models to predict removal efficiency were developed for convenient field application. Briefly, the complex removal behaviors of the filter cake are better understood for reducing the risks of failed zonal isolation and avoiding chemical overuse, which potentially contributes to the cleaner and more environment-friendly production of fossil hydrogen energy.

A generalized analytical model for hydrocarbon production using multi-fractured horizontal well with non-uniform permeability distributions

The multi-fractured horizontal well (MFHW) has significantly facilitated the exploitation of unconventional hydrogen-carbon compound reservoirs, which is an abundant source of fossil hydrogen energy. The composite linear flow models were frequently adopted to analytically evaluate the hydrocarbon production using MFHW. Most of the existing composite linear flow models assume uniform permeability in the primary fractures and the Stimulated Reservoir Volume (SRV) region. However, due to the non-uniform proppant distribution in the primary fractures and the heterogeneity in the density of the secondary fractures in SRV region, the permeability field in both regions are non-uniform. For the first time, a generalized analytical model incorporating continuous permeability heterogeneity in both the primary fractures and SRV region is proposed for the hydrocarbon production of MFHW. Any arbitrary permeability distribution functions can be treated as inputs to the proposed model. The mathematical model is solved using the perturbation technique and the Laplace transform method.The good match with the numerical solution verifies the accuracy of the proposed analytical model. Subsequently, the proposed solution is assigned with different modes of permeability heterogeneity to investigate their impacts on well production performances, i.e., cumulative hydrocarbon production and transient bottom-hole pressure (BHP). The results reveal that the incorporation of permeability heterogeneity will enhance the production rate and lower the BHP drawdown compared to the homogeneous case with the same average permeability. Besides, a field case is presented to demonstrate the applicability of the proposed model.

Fractal characterization of pore structure and its influence on salt ion diffusion behavior in marine shale reservoirs

Hydraulic fracturing becomes a significant way to develop fossil hydrogen energy from marine shale. Some marine shale formations have a higher salt ion concentration in flowback fluid, about which the mechanism is still unclear. In this study, both the fractal characterization of pore structure and its influence on salt ion diffusion was researched. The fractal dimension D1 can reflect the roughness of pore surface, and the fractal dimension D2 can reflect the complexity of pore structure. The fractal dimension D1 of Sichuan Niutitang Formation is only 2.0069 and the ones of other shale samples are between 2.5291 and 2.6341, which means that the pore surface of Sichuan Niutitang Formation is far smoother than the ones of other samples. The fractal dimension D2 ranges from 2.7396 to 2.9546, which indicates that all samples have complex pore structure. The salt ion diffusion rate is mainly controlled by specific surface area, median pore-throat radius and clay content. A higher specific surface area provides more surface for the interaction between liquid and matrix, and lots of salt ion was released into imbibed liquid. A larger median pore-throat radius benefits to salt ion diffusing out of sample, thus a higher salt ion diffusion rate appears. The liquid can cause the clay-swelling which has the potential to reduce the salt ion diffusion channel, thus the higher the clay content, the lower the salt ion diffusion rate. Our research is conducive to understanding the fractal characterization of marine shale and its impact on high salt ion concentration in flowback fluid.

Impacts of low harm fracturing fluid on fossil hydrogen energy production in tight reservoirs

The polymer fracturing fluid has been gradually used in the fossil hydrogen energy field. However, its impacts on the fields are still unclear. In this study, a series of experiments were conducted to solve the problem. First, a new method called the pressure transmission test (PTT) was used to evaluate the permeability damage induced by polymer fracturing fluid. Then several rock properties were tested to reveal rock potential damage induced by the aqueous fracturing fluid, after that the interactions between polymer fracturing fluid and rock were discussed in detail. Results showed that the average permeability pollution is 10.6. Permeability and X-ray diffraction (XRD) tests stated that the core is easier to be blocked by particles in the formation or fracturing fluid residue. Blocking and scanning electron microscope (SEM) tests showed that the nanoscale polymer would stick on the rock surface, and reduce the pore size. Our work provides a new method to evaluate the impact of polymer fracturing fluid on tight reservoirs. Moreover, the mechanism of permeability damage caused by the polymer fracturing fluid was also revealed.

Enhanced fossil hydrogen energy recovery through liquid nanofluid huff-n-puff in low permeability reservoirs

Surfactant huff-n-puff can enhance fossil hydrogen energy recovery from low permeability reservoirs. However, due to the high cost and adsorption of surfactant, its commercial application is limited. Liquid nanofluid (LNF) has been widely used in hydraulic fracturing since it can significantly reduce the adsorption. In this study, a series of experiments were conducted to investigate the potential of LNF huff-n-puff. First, the spontaneous and dynamic imbibition with NMR was conducted to study the imbibition oil recovery for the LNF. The results showed that the spontaneous imbibition recovery of LNF is 1.43 folder than brine. Besides, the LNF enters the small pores first in spontaneous imbibition. In the process of dynamic imbibition, the LNF enters the larger pore with smaller resistance first, then enters the small pore around the flow path. After dynamic imbibition, the imbibition recovery in small pores increased 54%. Moreover, pressure transmission tests (PTT) were conducted to evaluate the increasing rate of reservoir pressure. This work provides a new view of how surfactant or LNF functions in the process of huff-n-puff.

Impacts of pore structure and wettability on distribution of residual fossil hydrogen energy after imbibition

Due to the heterogeneity of the pore structure, there is still much residual fossil hydrogen energy in the pore space. In this study, the distribution of residual fossil hydrogen energy after imbibition with liquid nanofluid (LNF) has been studied through the. Firstly, relevant properties of the LNF were tested, including particle size, wettability alteration, and interfacial tension (IFT). Then, one micromodel under both oil-wet and water-wet conditions was used to elucidate the difference of residual oil after imbibition. Moreover, the difference of imbibition processes with oil-wet and water-wet models was further studied. Finally, the influence of dimensions and coordination numbers of pores was investigated. Besides, the impact of fluid type on imbibition efficiency was also compared through microfluidic experiments. Results show that the residual oil saturation is significantly higher in the oil-wet micromodel than in the water-wet micromodel, even the wettability alteration additive was used. There are four kinds of locations for residual oil after imbibition in water-wet micromodel, while only three kinds of locations for residual oil in oil-wet micromodel. The imbibition rate and residual oil saturation in small pores are higher than the larger ones. Due to the unbalanced force at pore throats, a micromodel with a high coordination number has lower residual oil saturation. Besides, the lower residual oil saturation is obtained by adding the LNF. This paper provides a micro-visual method to understand the imbibition process under different wettability and pore structures in fossil hydrogen reservoirs.

Experimental investigations of fracturing fluid flowback and retention under forced imbibition in fossil hydrogen energy development of tight oil based on nuclear magnetic resonance

Experimental works have proved that imbibition under forced pressure (FP, the difference between hydraulic fluid pressure and original pore pressure) has a positive effect on fossil hydrogen energy development in tight oil reservoir. However, the knowledge of the influence of imbibition under forced pressure (forced imbibition, FI) on fracturing fluid flowback and water retention is still limited. In this paper, experiments were designed and conducted to reveal the mechanism of fracturing fluid flowback and water retention under imbibition effect in tight sandstones. As a comparison, unconsolidated sandstones were also investigated in this study. Core samples were divided into two categories: the imbibition ones (treated by imbibition) and the filtration ones (treated by displacement), in accordance with the real oil-water distribution after well shut-in. An imbibition core and a filtration core were stitched together to conduct a flowback experiment. During the experiment, fluid distribution in different pore sizes was monitored continuously by using a low-field nuclear magnetic resonance device. Results show that the flowback recovery in tight sandstones is much lower than that in unconsolidated sandstones due to the difference of pore structure. Meanwhile, forced imbibition leads to higher oil recovery than spontaneous imbibition (SI) in tight sandstones since forced pressure enhances water imbibition. The water imbibed into small-macro and macro pores contributes the major flowback recovery, but the imbibed water in micro pores is rather difficult to displace and finally retains in these pores during the flowback process. Overall, forced imbibition not only enhances oil recovery but also increases water retention, explaining the mechanism of well productivity increase by using the shut-in method in the field. This study can help to clarify the influence of forced imbibition on fracturing fluid flowback and enhancement of fossil hydrogen development, and further provide guidance for flowback designs.

A new type of double dispersion system for water control in fossil hydrogen energy development

Water cut is generally rising with the increase of water injection during water flooding development of fossil hydrogen energy reservoir. Conventional chemical profile control agents fail to work for a long time because they are easily affected by the temperature and salinity of fossil hydrogen energy reservoir to form crossflow channel. In this paper, a new dual-disperse profile control agent and flooding system (DDS) is proposed, which uses polymers and microspheres to plug polymer crossflow and improve oil recovery in fossil hydrogen energy development. The viscosity, suspension property, thermal stability and microsphere size expansion of the DDS are tested, and the oil displacement performance is evaluated. The results show that the viscosity of polymer solution is not affected by the addition of microspheres, and the DDS system has good suspension and thermal stability. Due to the adsorption of microspheres in polymers, the particle size of microspheres tends to increase with time. But the expansion slows down gradually, which is beneficial to deep migration. In terms of plugging efficiency, the optimum concentration of DDS is 1500 mg/L polymer and 500 mg/L microsphere, and the optimum injection volume is 0.5Pv. Compared with single polymer flooding system, the new dual dispersion system has better washing resistance and enhanced oil recovery in fossil hydrogen energy development.

The effect of completion strategy on fracture propagation from multiple cluster perforations in fossil hydrogen energy development

The hydraulic fracturing is extensively used to stimulate the production of fossil hydrogen energy. Perforation parameters have a great influence on the performance of hydraulically fractured horizontal wells in fossil hydrogen energy development. In this work, a practical model to study the effect of a completion scheme on simultaneous fracture propagation is proposed, in which the coupling fluid flow and stress interaction is considered, and a fracture propagation uniform index model is used to optimize the completion strategy. Moreover, this model is well validated by Wu's model and Zhang's model. The numerical study results indicate that a uniform completion scheme causes a non-uniform fracture development; an optimal completion method is proposed by reducing the cluster number, non-uniform spacing, and practical limited entry technique in a fracturing stage. Furthermore, the combined use of unequal cluster spacing and a limited entry strategy can significantly reduce the suppression effects between multiple clusters, improve the fluid flow into each cluster, and enhance the uniform propagation to achieve the maximum production. Our present work illustrates a better understanding of the effect of the completion strategy on the multiple fracture propagation, and paves a path for a more optimal completion design for fossil hydrogen energy development.

An innovative technology of directional propagation of hydraulic fracture guided by radial holes in fossil hydrogen energy development

Conventional hydraulic fracturing fails to develop low permeability reservoirs of fossil hydrogen energy that are not located in the direction of maximum principal in-situ stress. A new technology of fracture propagation guided by radial holes is proposed, which can realize directional propagation of hydraulic fracture along radial holes in fossil hydrogen energy development. In order to verify this new technology, a model of radial holes combined with hydraulic fracturing is established by the ABAQUS extended finite element method. Simulation results show that radial holes play a guiding role in fractures propagation. The influence extent of seven factors on the directional propagation of hydraulic fracture is listed as follows (from strong to weak): azimuth of radial holes > horizontal in-situ stress difference of fossil hydrogen reservoir > injection rate of fracturing fluid > Young's modulus of rock > permeability of fossil hydrogen reservoir > Poisson ratio of rock > viscosity of fracturing fluid. True tri-axial experiment is carried out to verify the accuracy of numerical simulation, and the result is consistent with numerical model, which indicates that numerical simulation is reliable.