查看更多>>摘要：Acidic fuid fow in geologic formations leads to mineral dissolution and, under certain circumstances, to localized dissolution forming a dendritic pattern, known as wormhole. Such patterns of conduits and caves are often observed in karstic aquifer and deliberately engineered in oil and gas well stimulation with acid injection. Two different kinds of instability are thought to cause wormholes. One is heterogeneous property in rocks. The other is a process itself such as reaction infltration or viscous fngering. To assess each one properly, we need to separate one from the other. While most numerical studies rely on randomly seeded material heterogeneities to induce wormholes, Daccord and Lenormand (1987a) demonstrated that even water injection into a homogeneous plaster can form wormholes. Here, we focus on the process instability driven by reaction-infltration in homogeneous materials. We apply a phase-feld approach, which diffuses a sharp interface in a continuous manner and show that it is capable of simulating wormhole without random seeds by accounting for the energy expenditure in the dissolution topology. We verifed the model against the sharp interface counterpart in one-dimensional simulations. We then performed the two-dimensional simulations to qualitatively validate wormhole formation and growth patterns against acid injection experiments on carbonate rocks under radial fow conditions. Our simulation results indicate that the injected acid is rapidly consumed near the acid entry point at low injection rates while the live acid becomes available at the tip of the dissolved cavity under high rates and thus wormhole starts to grow resulting in much faster acid breakthrough.
查看更多>>摘要：Wellbore scaling affects the high-efficient geothermal reinjection. It is important to predict the scaling risk accurately in the reinjection wellbore and take effective anti-scaling measures. In this study, using the geothermal water in Xining Basin, China, a series of scaling experiments were carried out to explore the scaling amount of geothermal water, the scaling adhesion ratio on the pipe wall, and the influences of related factors. An improved prediction model of scale layer thickness in reinjection wellbore was established based on the scaling deposition kinetics, and the scaling and blockage risk in the reinjection wellbore at different conditions were assessed. The results show that there is a large-scale adhesion ratio on the pipe wall at a static condition. But in a real reinjection wellbore, the water scaling tendency will decrease significantly because of the small temperature rise in the wellbore. Only a very small amount of scale particles can attach to the pipe wall, while most of them will invade the formation and damage the injectivity. Long injection time, large injection rate, and high injection temperature can eliminate the scaling risk in the wellbore totally, which is the most economical anti-scaling measure.
查看更多>>摘要：The oil and gas well drilling operations are primarily dependent on the shale inhibition features of the drilling mud. Our current study describes the consequence of poly-acrylic acid-acrylamide modified nanosilica (PAM-SiO2NPs) on the swelling inhibition of clay and rheological properties of the drilling mud. The unique characteristics of the PAM were combined with nano-silica to get the PAM-SiO2NPs nanocomposite. Large surface area, effective functionalization of SiC^NPs make PAM-SiC^NPs a very appropriate and efficient additive for the water-based mud. The drilling mud was kept under hot-rolling for 16 h at 212 °F and 500 psi, later on, apparent viscosity, plastic viscosity, yield point, and gel strength of the water-based drilling mud were studied. To assess the shale inhibition features of PAM-SiC^NPs the dispersion, shale inhibition durability, and linear swelling tests were conducted. The results demonstrate that PAM-SiC^NPs modified water-based mud (PAM-SiO2NPs-WBM) shows an improvement in the rheological properties. Moreover, the shale cutting treated with PAM-SiO2NPs-WBM displayed the highest % recovery (86.6%) as compared to KCl (49.2%) or the commercial inhibitor modified mud (74.7%) in the dispersion test. The shale inhibition stability of shale treated in PAM-SiO2NPs-WBM demonstrates higher stability for up to 2 days. Additionally, PAM-SiO2NPs prominently control the swelling rate to 33% as compared to 87% in water, 41% in the unmodified drilling mud, and 37.5% in the commercial shale inhibitor. The PAM-SiO2NPs adsorption on the surface of the shale and its inhibition mechanism was explored by different characterization techniques such as FT-IR analysis, TGA, FE-SEM, and EDX. The proposed inhibition mechanism of the PAM-SiO2NPs demonstrates that the PAM-SiO2NPs carry functional groups that can disrupt the hydrogen bonding and plug the nanopores on the shale surface that cause a prominent decrease in the clay swelling. Consequently, the clay surface is being protected against the reactive action of water.
查看更多>>摘要：In this study, the effects of tool geometry such as rake angle, and cutting parameters such as depth of cut on the cutting forces were studied and correlated with the built-up edge during the material removal process of a rock-like workpiece. Cutting or scratch tests were performed on low and high strength simulated rock-like materials using a tungsten carbide tipped orthogonal drag tool with three different rake angles (0°, 10° and 20°) in a custom-made machining set-up incorporating a high-speed video camera. Force data were measured by a tri-axial dynamometer and a compatible data acquisition system, and specific cutting energy was calculated to assess the material removal performance. Experiments showed that a cutting tool with a 20° rake angle produced an efficient cut. The high-speed video at the cutting edge were analysed to comprehend the formation and growth of the built-up edge. Novel insight was gained by characterising the shape and was observed that the constantly evolving shape was unique to each rake angle used, this creates an apparent rake angle. By varying the rake angle and cutting parameter, the measured cutting force and thrust force showed that the material strength, cutting tool geometry and depth of cut played important roles in removing materials. Higher cutting efficiency was indicated by lower specific cutting energy at higher depth of cut for all cutting conditions. The formation of the crushed zone in relation to the cutting force revealed that the cutting force increased with the size of the crushed zone having two types of chip formation modes;; shearing and fracturing. Numerical simulations were performed using a commercially available tool called ELFEN, a hybrid finite-discrete element software package. The simulations correlated well with experimental investigation. The simulations also showed the formation of crushed zone and crack growth as observed experimentally through the use of high-speed video and also shed light on the state of stress state at the cutting edge.
查看更多>>摘要：Destabilized asphaltenes cause serious flow assurance problems such as asphaltenes precipitation. This study investigates the impact of clays and salinity on the stability of asphaltenes for five different crude oil samples. First, both n-pentane and n-heptane insoluble fractions of five crude oils were examined under microscope after the interaction with water, brine, and porous media. The porous media was prepared with clay, sand, or sand-clay mixture. A monovalent (NaCl) and a divalent (CaCl2) salts at 0.2% and 4% concentrations were used to prepare the brine solutions. Several systematic microscopic analyses were conducted on the asphaltenes-water and the asphaltenes-brine blends. We have observed that both n-pentane and n-heptane asphaltenes clusters are getting dispersed in water-phase in smaller pieces. This dispersion of asphaltenes clusters form lacework-like structures in the water-phase. The void spaces within these dispersed asphaltenes clusters trap water droplets. This interaction is due to the polar nature of both asphaltenes and water. Further in our systematic analysis, the general trend showed that the polar-polar attraction between water and asphaltenes clusters was disturbed in the presence of dissolved sodium and chlorine ions especially for some oil samples which already contain sodium in its asphaltenes fractions. This phenomenon is observed with the bridge-like formations in the asphaltenes-brine solutions. This indicates that asphaltenes have charged surfaces and the repulsion forces between the surface of the asphaltenes cluster and the dissolved ions in the brine solutions make the asphaltenes cluster align to form a line in the brine solution. The presence of clay in the porous medium reduced the water-asphaltenes or the brine-asphaltenes interaction and resulted in big chunks of asphaltenes-clay mixtures. Our study showed that asphaltenes interact with brine, water, and reservoir fines. Understanding these interactions may help us to mitigate many flow assurance issues such as asphaltenes precipitation and water-in-oil emulsion formation.
查看更多>>摘要：Mud pulse telemetry (MPT) is one of the essential means to ensure a high transmission rate of downhole data. Continuous-wave mud pulse has a high transmission rate, strong stability, and outstanding adaptability, the most widely used downhole data transmission mode. One factor that restricts the high transmission rate of downhole data is the quality of the pressure wave generation signal. However, there is a lack of complete mathematical modeling research methods. Based on CFD theory, a numerical model of the integration of pulse generator and upstream and downstream pipelines was established for the first time, as well as the corresponding grid division process, which was to simulate the pressure wave generation and propagation process under drilling conditions, and the sensitivity analysis of parameters was carried out. The results show that the pressure drop curve derived from the thin-wall throttling theory is not the actual pressure wave, so the optimization results have a particular theoretical error. In fact, with the periodic change of the flow area, the upstream and downstream synchronously generate compression waves and expansion waves, which propagate and gradually decay. The amplitude of pressure wave increases with the increase of displacement and density but decreases sharply with the increase of gap height. Meanwhile, the amplitude does not change with the frequency and viscosity, but it aggravates the propagation attenuation of the pressure wave. Moreover, it is observed that the pressure wave is not a perfect sine wave in the case of sinusoidal rotor rotation, which needs further study. The research results of this paper provide a technical means for the optimization of downhole pressure wave generation, transmission, and noise reduction and help improve the transmission rate of downhole data.
查看更多>>摘要：Based on the rock scratch test and the finite element model, the 2D discrete element rock cutting model is established in this paper. The model adopts spring-mass-damping system to load the cutter, which is different from the previous single cutter rock breaking model. In this way, the model can effectively reproduce the vibration and stick-slip phenomena in actual rock cutting and enable the simulation of rock breaking by an individual cutter under a horizontal impact load. Then, the effects of the vertical force on the cutter, the driving velocity, and the system stiffness on rock breaking and the stick-slip vibration of the cutter are studied. The results show that the stick-slip vibration is easy to occur under the conditions of larger weight on bit, lower driving speed and smaller system stiffness. Although an increase in the driving velocity of the system can significantly restrain stick-slip vibration, when cutting speed increases from 0.5 m s~(-1) to 2.5 m s~(-1) , the specific energy consumption of rock breaking increases by 68.83% and the cutting depth decreases by 41.14%. In contrast, when the horizontal impact load is used to suppress the stick-slip vibration, it has less effect on the specific energy consumption of rock breaking and the cutting depth. This study provides a theoretical basis for suppressing stick-slip vibration and efficient rock breaking in well drilling.
Mustafa Al IbrahimLeyla IsmailovaVictoria Dochkina
10页
查看更多>>摘要：Estimation of drill cuttings particle sizes provides near real-time information that can be utilized in drilling operations. The analysis and interpretations of these rock samples is largely manual. Results are qualitative and can be inconsistent. We propose a practical automated method for estimating drill cuttings particle sizes using digital images. The proposed method is robust and combines several well-known and time-tested techniques like;; K-means clustering, numerically stable ellipse fitting, and standard morphological operations. Images are first preprocessed and clustered based on color values. The resultant grain mask is enhanced using binary morphological operations. Measurements are then extracted from the mask based on the major and minor axis fitted to the particles. The developed method is tested on drill cuttings digital images from four wells with varying lithologies and particle sizes. Sensitivity analysis on imperfect images shows the robustness of the methodology. The automated results validated against manual measurements show a difference of less than ten percent. Performance of the algorithm is in the order of seconds, which allows for its use in near real-time applications.
查看更多>>摘要：Market-induced production shut-downs and restarts offer us an opportunity to gather step-rate and shut-in data for pressure transient analysis (PTA) and rate transient analysis (RTA). This study presents a unified transient analysis (UTA) to combine PTA and RTA in a single framework. In this new approach continuous production data, step-rate data, shut-in data and re-start data can be visualized and analyzed in a single superposition plot, which can be used to estimate both Af√k and infer formation pore pressure in a holistic manner by utilizing all available data. Most importantly, it shows that traditional log-log and square root of time plots can lead to false interpretation of the termination of linear-flow or power-law behavior. Field cases are presented to demonstrate the superiority of the newly introduced superposition plot, along with discussion on the calibration of long-term bottom-hole pressure with short-term measurements.
查看更多>>摘要：Tectonism caused strong deformation of the Wufeng-Longmaxi Formation in the periphery of the Sichuan Basin, which affected the pore-fracture of the organic-rich shale and migration of shale gas. Samples of structurally deformed shale from the anticline and detachment structure and imdeformed shale were collected in the Northeast Chongqing area, China. The investigations of shale structural deformation and its pore-fracture system were performed using optical microscopy, field emission scanning electron microscopy (FE-SEM), low-pressure gas adsorption (LP-GA), and small-angle X-ray scattering (SAXS). The research shows that deformed samples with curved beddings and friction mirrors on the macro level, as well as the microscopically curved organic matter (OM) bands and OM folds, indicate the significant structural transformation and predominantly ductile deformation. The micro-fractures in deformed samples are more developed with different combinations in the two geological structures, showing brittle deformation. Compared with undeformed samples, the number of OM pores in deformed samples is reduced significantly, while the interparticle (interP) pores, intraparticle (intraP) pores, and micro-channels are more developed. The connected pore size distribution (PSD) of all samples is mainly from 0.3 nm to 10 nm. The pore volume (PV) of micropore in the deformed samples is between 0.100 and 0.500 cm3/l00 g, and the specific surface area (SSA) is in the range of 2.175-13.554 m2/g. Undeformed samples have a larger PV and SSA than the deformed samples. TOC and the structural deformation control the structure of connected pore, and their PV and SSA are positively correlated with TOC content. Fractal dimension reveals that the surface of connected and closed pore (pore size 3.81-95.34 nm) becomes more complex, and the distribution of small pore (pore size 1.25-3.81 nm) becomes more uniform under the structural deformation of the shale. As the degree of shale deformation increases, the mesopore and macropore volume of connected pores decrease significantly, while the strongly structural deformation of samples results in a substantial increase in micropore volume and SSA. Besides, the PV of both closed and connected pores tends to decrease and the average pore size increases linearly. Furthermore, the shale deformation result in a weakening of the methane adsorption capacity. Shale gas can migrate through the fracture network to the central zone of the detachment structure or the core of the anticline, which has a significant effect on shale gas enrichment and preservation.
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