查看更多>>摘要：The gas flow in the organic matter with multiple flow regimes is critical to the shale gas production from shale gas reservoirs, but simultaneously simulating the full flow regimes of shale gas in the nanopores of the fractal shale organic matter is still unavailable. This paper presents a modified lattice Boltzmann model with effective relaxation time to simulate the shale gas micro-flow behaviors in fractal organic matter for permeability prediction. Firstly, some fractal shale organic matters are reconstructed by the quartet structure generation set (QSGS) algorithm, and the structural parameters such as fractal dimension, lacunarity and average pore diameter are calculated to characterize the complexity of the fractal shale organic matter. Secondly, effective viscosity and Knudsen layer are introduced into the effective relaxation time to formulate a modified lattice Boltzmann model. Thirdly, this modified lattice Boltzmann model is verified by comparing with the theoretical permeability models for the gas flow in the body centered cubic (BCC) arrays. Finally, a series of gas flow simulations in reconstructed fractal shale organic matter are conducted to explore the effects of structure parameters on permeability. Numerical simulations show that the modified lattice Boltzmann model can simulate the full gas flow regimes and predict the permeability of the fractal shale organic matter. The logarithm of permeability is negatively linearly correlated with fractal dimension and positively linearly correlated with lacunarity of the shale organic matter. This permeability exponentially increases with the increase of average pore diameter and a power law is observed between the fractal dimension and average pore diameter of these fractal shale organic matters. The anisotropic structures have great impacts on the directional permeability of shale organic matter. The permeability kx in the horizontal direction increases first and then decreases with the increase of anisotropic ratio (AR) and reaches the peak when AR is about 20. The permeability ky in the vertical direction monotonically decreases with the increase of AR.
查看更多>>摘要：During the operation of the oil-gas multiphase pump, due to the variable gas content of the incoming flow, the medium pressure at the high-pressure end fluctuates widely, which is easy to cause the stress change at both ends of the mechanical seal compensation ring and "instability" phenomenon. In this paper, a three-dimensional spiral groove seal film model is established. Considering the cavitation effect of liquid film gap, the variation law of end face cavitation and sealing performance of liquid film seal is explored according to the effect of pressure pulsation in the pump on the inner diameter side (Static mechanical seal, PLAN74 flushing scheme in API 682) and outer diameter side (Rotary mechanical seal, PLAN53A flushing scheme in API 682). The results show that the local pressure drop in the sealing liquid film is the main cause result to cavitation of liquid film. The inner diameter side pressure fluctuation has a great impact on the end face cavitation, and the wave peak is about 100 times that of the outer diameter side pressure. The inner diameter side pressure fluctuation should be avoided in engineering application. There is hysteresis between gas volume fraction (GVF) and boundary pressure fluctuation. The synchronization between sealing performance parameters and outlet pressure fluctuation is good, but there is phase difference with inlet pressure fluctuation. The inner diameter side pressure fluctuation has a great change on the sealing performance. The peak is about 5-20 times that of the outer diameter side pressure, which is easy to cause vibration of the mechanical seal. The amplitude and period of pressure fluctuation have a great impact on the GVF and sealing performance. The larger the fluctuation period is, the less obvious the hysteresis of GVF is, and the closer to the variation law of pressure fluctuation. During the actual operation of the oil-gas multiphase pump, the mechanical seal connected with the medium in the pump is rotary, and the flushing scheme ought to be PLAN53A to ensure the safe and stable operation of the oil-gas multiphase pump.
Aoun, Ala EddineSoto, RicardoRabiei, MinouRasouli, Vamegh...
19页
查看更多>>摘要：Accurate estimation of in-situ stresses is of great importance in the oil and gas industry from the exploration to the field development and production phases. The collected logs and mini-frac data in the last 15 years in the Hassi Messaoud Field (HMD), Algeria, shows that the reported state of stresses in this field is not consistent. This called for further studies to estimate more accurately the state of stresses, which more specifically will be used for the design of hydraulic fracturing at a later stage. This paper presents the results of the Mechanical Earth Model (MEM) constructed for the HMD field in Algeria. The results of the MEM, which is continuous logs of formations' elastic and strength properties, as well as the state of the in-situ stresses will be the direct input to the hydraulic fracture (HF) design. Hydraulic fracturing is the prime technique used in the field in order to enhance recovery from this tight sandstone reservoir. MEM is built beyond the conventional correlation with both a Generalized Linear Model (GLM), which serves as a simplified "ground truth" and three Artificial Neural Networks (ANN) layers: the first one is training mechanical properties from lab data, the second one trains shear and compressional sonic waves from acquired log data and the last one uses mini-frac data to calculate and train stress regimes from a poro-elastic model. The model is calibrated with the observed breakouts and fracturing data and a close agreement is observed. The work presented in this paper elaborates a detailed roadmap to accurately approximate and synthesize missing data using ANN's and extend it across the rest of the field to build, a 3D MEM. It is hoped that the results of this study can improve the HF operations in the field, which is currently reported to be not efficient.
查看更多>>摘要：Shut-in after hydraulic fracturing can make full use of fracturing fluid imbibition and improve well productivity. However, how to determine a scientific shut-in time is an important problem for reservoir engineers. Therefore, an efficient model was proposed in this paper to fill this gap and then applied in the shale oil reservoirs. An analytical model of pressure distribution and stimulation reservoir volume was first developed, which includes the process of fracturing fluid injection and well shut in. A good agreement was obtained between the calculated pressure data and field data. Afterward, the imbibition experiments of 15 core samples from shale oil reservoir were carried out and the imbibition equilibrium time was observed. Finally, we calculated the shut-in time by summation of the time of fracturing fluid volume stabilization (stimulation volume stabilization) and imbibition equilibrium time. Results show that pressure diffuses during fracturing fluid injection and the pressure balance during well shut-in both impact the time of fracturing fluid volume stabilization (stimulation volume stabilization). Furthermore, a higher permeability can increase fluid flow capacity and accelerate the time of fracturing fluid volume stabilization. A scientific shut-in time should include pressure balance time and fracturing fluid imbibition equilibrium time. This work can provide a strong basis for optimization the shut-in time and useful insights into fracturing operation in shale oil reservoirs.
查看更多>>摘要：Shale with extraordinarily high organic matter content (EHOMC) formed in the margin of the Sichuan carbonate platform during the late Guadalupian in the eastern Paleo-Tethys. So far, not much consideration has been given to the enrichment of EHOMC. Here, integrated lithological and geochemical analyses of the top Maokou For-mation black shales in the northwest Sichuan basin were undertaken to investigate the EHOMC. The black shales were divisible into three units (i.e., Units 1 to 3 in ascending order); EHOMC occurred in Unit 2. Unit 1 was deposited during the early stage of the transgression under the small-scale upwelling in an anoxic environment with lower paleo-productivity than Unit 2, considering the moderate Cd/Mo ratios and the concentration of Mo, U, V, P, Cu, and Zn. Unit 2 exhibited high Cd/Mo ratios and high concentrations of elements (Mo, U, V, P, Cu, and Zn), suggesting that the shales with EHOMC were deposited through an intense upwelling in an euxinic-sulfidic environment with high paleo-productivity. Unit 3 demonstrated moderate paleo-productivity and anoxic-suboxic conditions, while the nutrient elements were derived through increased terrestrial detrital input. Unit 2 exhibited the highest total organic matter content (TOC) (17.72-32.58 wt%); it is inferred that the enrichment of EHOMC was mainly caused by a euxinic-sulfidic environment, while high paleo-productivity was another key factor. Besides, the euxinic-sulfidic environment and high paleo-productivity in Unit 2 occurred approximately during the intense upwelling, the occurrence of the high sea-level, and the biological extinction during the end of Guadeloupe. These factors together promoted the enrichment of EHOMC in Unit 2.
查看更多>>摘要：Economic production from shale oil reservoirs relies on the longevity of conductive fractures. Choke or draw-down management is believed to better preserve the fracture conductivity during the early life of the wells, which thus potentially leads to higher ultimate oil recovery. However, there is no strong consensus among the previous literature as to whether choke management can offer incremental oil recovery in the long term. Even if it can, the mechanism is not well understood, and the economic benefit can be challenged, because the choke management slows down the early oil production, which is worth the most in terms of Net Present Value (NPV). In this study, a series of coupled flow-geomechanical numerical simulations is performed to examine the effect of choke management on the ultimate oil recovery and NPV. We built multiple reservoir realization models, each of which is validated based on the same field production data from Middle Bakken shale-oil reservoirs to perform probabilistic production forecasts. The different reservoir realization models are built to assess the uncertainty in the Stimulated Reservoir Volume parameters, including natural fracture spacing, water saturation in the matrix and fracture, and formation compressibility. The different reservoir parameters lead to each model having different primary recovery driving mechanisms of oil recovery, including imbibition and compaction drive. This study quantitatively demonstrates that the choke management seems to increase both the ultimate oil recovery and NPV if the oil recovery is strongly driven by imbibition. A mechanistic discussion for this claim is presented.
查看更多>>摘要：In recent years, machine learning has been adopted in the Oil and Gas industry as a promising technology for solutions to the most demanding problems like downhole parameters estimations and incidents detection. A big amount of available data makes this technology an attractive option for solving a wide variety of drilling problems, as well as a reliable candidate for performing big-data analysis and interpretation. Nevertheless, this approach may cause, in some cases, that petroleum engineering concepts are disregarded in favor of more data-intensive approaches. This study aims to evaluate the impact of drilling data measurement correction on data-driven model performance. In our study, besides using the standard data processing technologies, like gap filling, outlier removal, noise reduction etc., the physics-based drilling models are also implemented for data quality improvement and data correction in consideration of the measurement physics, rarely mentioned in most of publications. In our case study, recurrent neural networks (RNN) that are able to capture temporal natures of a signal are employed for the rate of penetration (ROP) estimation with an adjustable predictive window. The results show that the RNN model produces the best results when using the drilling data recovered through analytical methods. Moreover, the comprehensive data-driven model evaluation and engineering interpretation are conducted to facilitate better understanding of the data-driven models and their applications.
查看更多>>摘要：This case study highlights that shale wells drilled with tight well spacing in the same landing zone using the same fracture treatment plan, commonly show large variance in well productivity. Searching for the root cause(s) of this variance in performance, we conclude that the factory model - which assumes wells can be engineered in reproducible and identical ways - is not yet feasible in practice. For each well, largely similar fracture treatment schedules result in different fracture half lengths. Also, a significant proportion of perforations may fail to create any hydraulic fractures at all. This new reality means that underperforming wells in otherwise promising acreage are more likely an indication of varying fracture treatment response, rather than a result of poor source rock. Research focusing on the reduction of fracture treatment variance therefore deserves priority and may help steady the performance of future wells.
查看更多>>摘要：The prediction of pipe sticking accidents due to wellbore uncleanness is significant for safe drilling, while existing qualitative prediction methods result in inaccuracy and lateness. To cover the shortages, a novel quantitative pipe sticking prediction method is established to achieve pipe sticking prediction early in drilling preparatory stage. First, the additional axial forces and torques on the drill string exerted by accumulated cuttings are calculated in tripping out, tripping in, back reaming and reaming processes based on granular mechanics. Second, the torque and drag model is modified considering additional axial forces and torques to calculate the hook load and the top drive torque. Finally, the pipe sticking prediction is conducted according to the critical hook load and the critical top drive torque in a specific drilling process. A case study including comparison with the classical model and sensitivity analysis is conducted. Under the given condition, pipe sticking risk is predicted with the new mothed by anticipating hook loads (5524.67 and -667.71 kN) and top drive torques (60.87 and 66.36 kN m) exceeding the critical values. The hook load and the top drive torque change exponentially with the travelling distance. In tripping out and back reaming processes from 4350 to 4250 m, the hook load and the top drive torque respectively increase for 1894.36 kN and 53.99 kN m. In tripping in and reaming processes from 3450 to 3550 m, the hook load decreases for 29925.66 kN and the top drive torque increases for 157.3 kN m. According to the sensitivity analysis, low frictional coefficients, initial cutting volume fractions, torque and drag frictional factors and high junk slot ratios are required to reduce the risk of pipe sticking. This study provides a timely and quantitative prediction method for pipe sticking accidents due to wellbore uncleanness in long horizontal drilling.
NSTL
Elsevier