查看更多>>摘要：Water-control for horizontal wells is a worldwide problem, while it is even harder for limestone reservoir because of the developed fractures and caves. The formation water can be connected to the wellbore by fractures or caves directly or indirectly. Make the wells easily water flooded. Segmented water-control is the consensus of the current mainstream mechanical water-control technologies for horizontal wells, the segments confine the water break-through influence scope to the segment where the water break-through formed. In order to achieve that, all the potential water break-through fractures and caves connected to wellbore should be concentratedly divided into less segments, but that depends on the distribution of fractures and caves. Otherwise, the number and the sealing location of the packers are also relying on the engineering technology and the well status. Fracture/cave axial channeling inside the formation is another problem. The fractures and caves interwoven inside the formation. The formation water can easily flow around the packers by fractures/caves and cause the sealing failure of packers and invalid segment. Meanwhile the conventional mechanical water-control methods have no ability to limit the flow conductivity of fractures and caves. In the segments with fractures/caves developed, the producing degree of the matrix will be low. As a result, the application effect of conventional water-control methods in limestone reservoir horizontal wells is limited. To conquer the fracture/cave channeling and achieve the water-control effect at the meantime, the article proposed a novel mechanical water-control method which combined particle-filling with inflow control device screens. The particle-filling is not an absolute sealing, but a limitation of flow rate in the pack area. Calculations show that the flow conductivity of a 5 mm fracture will decreased to 0.1% of the original after particle-filling. The particles filled into the annulus between the screens and the borehole wall can limit the axial annulus flow enormously, replaces the traditional packer sealing. The particles filled into the fractures will reduce the flow conductivity sharply, and no need to concern about the channeling inside the fractures and caves interwoven. Inflow-control devices are utilized to control radius flow rate and balance the production profile near well. The novel water-control method obtained the outstanding application results especially in the limestone reservoir, with the function of deep production profile control combined with wellbore water control, has the advantage of both chemical water shut-off and mechanical water-control methods. Successful application in reef limestone reservoir demonstrates the excellent feasibility of this novel water control method. The oil rate increased 3.9 times after application to well A4A in Liuhua oil field South China Sea. For well A3, the initial water-cut is only one third of the average value compared with wells drilled in recent years at the same layer. It is found that the production effect of oil wells is positively correlated with overfilling amount. For higher overfilling amount, filling process optimization is carried out, and micro-fracturing is formed by increasing filling rate to the target reservoir. The max filling rate of oil well reached 292% by the improvement of filling technology.
查看更多>>摘要：The numerical simulation of matrix acidization in fractured porous media is continuous work in the reservoir simulation community. However, existing works mainly depend on two kinds of models to describe fractured porous media: the discrete fracture-matrix (DFM) model and the continuum fracture (CF) model. In addition, most of the works use Darcy's equation to describe the flows. The DFM model can accurately describe the fracture and the flow in the fracture at the cost of the complexity of the simulation framework. On the other hand, the CF model treats the fracture and the matrix uniformly, which reduces the complexity of the simulation framework, but the accuracy of the results is not as good as that of the DFM model. In summary, the challenge of this area is that the accuracy of the results cannot be guaranteed by a sufficiently simple model. The DarcyBrinkman-Forchheimer (DBF) framework was originally developed to handle an issue in matrix acidization simulation, i.e., the flows in the high-porosity zones cannot be well described by Darcy's law. Considering the similarity of the fracture and the high-porosity zones, it is anticipated that the proposed DBF framework can also describe the flows in the fracture well., i.e., the accuracy of the results guaranteed by the DFM model can also be guaranteed by the DBF framework. Compared with the DFM model, the DBF framework is much simpler. Moreover, the DBF framework can be naturally integrated with the CF model. Thus, this work leverages the CF model and the DBF framework to simulate matrix acidization in fractured porous media, by which accurate results can be achieved with a simple simulation framework. The simulation results in this work are compared with those of Khoei's work, by which the reasonability of this work is demonstrated. After that, the thermal DBF framework, which is an expansion of the DBF framework, is leveraged to investigate matrix acidization in fractured porous media under different thermal conditions, and many helpful conclusions that benefit realistic operations are drawn. For example, the fracture orientation can have different effects on matrix acidization under different temperature conditions.
查看更多>>摘要：Elbows are widely used in piping systems to change the direction of flow. However, it is also extremely sus-ceptible to erosive damage, which may lead to the leakage of petroleum and gas pipelines. Therefore, revealing the erosion process and accurately predicting erosion rate are of great importance to pipeline safety. In this study, the unsteady slurry erosion process in the 90 degrees elbow is investigated numerically using LES Eulerian-Lagrangian methodology. The Large eddy simulation (LES) is coupled with Lagrangian particle tracking to simulate slurry flow and erosion process in elbows. The erosion prediction model is validated using experimental data before investigating the unsteady erosion process in elbows with different radius. The results show that the unsteady secondary flow can be precisely captured using LES and thus the prediction accuracy of the fluid flow velocities and turbulent intensities are improved by this model comparing to RANS. The particles movement coupled with the unsteady secondary flow and boundary separation in elbows with different radius can be successfully revealed using this methodology. The LES Eulerian-Langragian erosion model presented is helpful to understand the flow and slurry erosion in elbows and improve the accuracy of the CFD-based prediction of slurry erosion rate.
查看更多>>摘要：Fracture is the primary channel of gas seepage in coal seams and controls the drainage efficiency of coal bed methane (CBM). However, the seepage characteristics and dynamic evolution law in the fractures of gas-bearing coal under external loads are yet to be clearly revealed. In this study, an industrial computer tomography (CT) scanner equipped with a triaxial loading system was used to conduct gas-seepage and CT scanning experiments under triaxial compression conditions. The results showed that the fracture volume and permeability decreased first and then increased during the complete stress-strain process of gas-bearing coal, displaying an approximate U-shaped variation trend involving a decrease stage, an increase stage, and a jump-increase stage. The lattice Boltzmann method (LBM) was applied to make the seepage processes of gas-bearing coal reappear, and a modified nonlinear permeability model was developed to represent non-Darcy seepage inside fractured coal. The LBM simulation results mirrored the dynamic evolution of the gas seepage field and gas permeability controlled by fracture propagation. The proposed modified nonlinear permeability model effectively reflected the nonlinear variation behaviour of gas permeability and was superior to the traditional Darcy's model in describing nonlinear seepage of gas-bearing coal.
查看更多>>摘要：Shale oil is a promising alternative unconventional energy to conventional fossil fuels. Its exploration and production are critical to improve the present energy consumption pattern and mitigate dependence on foreign energy. Particularly, the key factors determining shale oil occurrence are the most important issues for its production. In this review, we briefly summarize the dominant space of shale reservoirs for accommodating shale oil. We also provide a comprehensive overview of occurrence state of shale oil and analyze in detail the factors such as pore size, organic matter, inorganic minerals of oil-bearing shale and reservoir burial depth. Finally, we discuss the existing challenges and perspectives on how to explore and address occurrence of shale oil in practical shale reservoirs to promote the future shale oil production. An accurate description of shale oil occurrence through viable research methodology, advanced instrument characterization and theoretical simulation is crucial for estimating shale oil reserves, optimizing and enhancing shale oil production.
查看更多>>摘要：Hydraulic fracturing has become the dominant development technology for unconventional reservoirs. The accurate prediction of rock breakdown pressure is key to fracturing design in deep formations where the wellbore shape is prone to deform into an ellipse. However, few of the presented theoretical models for breakdown pressure focus on the wellbore deformation, which may lead to inaccurate results. Therefore, a theoretical model for analyzing fracture initiation from a perforated elliptical wellbore is proposed by using the conformal mapping method. Additionally, the analytical solution for the breakdown pressure and the initiation angle at the fracture tip is obtained by using the derived stress intensity factor at the perforation tip based on the fracture mechanics and the maximum tangential stress (MTS) criterion. The model is verified by comparing the previous experimental and theoretical breakdown pressure data for perforated circular wellbores. The effects of the wellbore deformation, perforation orientation, perforation depth, and fracture toughness on fracture initiation are analyzed. It is shown through theoretical analysis that a breakdown pressure predicted without considering the wellbore deformation will be overestimated, and it is unwise to optimize the perforation orientation based on the fracture toughness of rocks. To reduce the breakdown pressure and avoid excessive fracture curvature near the wellbore, the recommended optimal perforation depth is about 1.5-2 times the size of the wellbore and it is better to control the perforation orientation that is adopted within 20 degrees. The proposed model is a new attempt to calculate the rock breakdown pressure of a perforated elliptical wellbore, which can provide some guidance for the perforation optimization in a deep formation.
查看更多>>摘要：One of the challenging issues during underbalanced drilling (UBD) is the prediction of frictional loss in the presence of three-phases of drilling fluid, cuttings, and air. In the current work, three innovative machine learning-based algorithms based-on Gradient tree boosting (GTB), Adaptive neuro-fuzzy inference system (ANFIS), and Extreme learning machine (ELM) have been suggested to calculate the frictional loss in gas-based drilling fluids containing cuttings in inclined annuli. A number of 216 real frictional pressure loss data in terms of hole inclination, pipe rotation, rate of penetration, and flow rates of each phase have been collected to train and validate the frictional pressure loss models. The visual and statistical comparisons of the frictional pressure loss models and actual values reveal that models have a fascinating ability in prediction of the frictional pressure loss for inclined wells. Besides, the GTB model has the best performance with R-2 = 1, RMSE = 0.0031, MRE = 0.415, STD = 0.0023, and MSE approximate to 0 in comparison with actual frictional pressure loss values. Furthermore, an exciting sensitivity analysis has been used to identify the effectiveness of each operational parameter on frictional pressure loss for inclined annuli. Due to these facts, the current work can be applied as an assistant in the development of drilling simulators in complicated field conditions.
查看更多>>摘要：In order to study the salinity of fracturing fluid flowback from shale gas wells and its damage to reservoirs, shale gas wells in PS (Peng Shui) and CN (Chang Ning) areas of Sichuan Basin (China) were taken as research objects in the current work. Immersion experiments of shale particles and single mineral particles were carried out using distilled water. The conductivity of distilled water during immersion was monitored using a conductivity meter, and the ionic composition and the content of immersed fluid were analyzed using ion chromatograph and atomic absorption spectrophotometer. Meanwhile, the flowback fracturing fluids from shale gas wells in PS and CN areas of Longmaxi reservoir in Sichuan Basin, China were collected, and their salinity and composition were analyzed. The results of shale particle immersion experiments showed that the mass concentration of salt in shale was 1 mg salt/g of shale. Furthermore, the salinity of flowback fracturing fluid was found to be about 30,000 mg/L. Compositional analyses of shale particle immersion fluid and field flowback fluid show that the contents of Na+ and Cl in shale reservoir are the highest. The analysis of field flowback fracturing fluid in shale gas wells shows that the salinity of flowback fracturing fluid is much higher than that of fracturing fluid. High salinity flowback fracturing fluid would produce salt crystals in the later stage of flowback and production stage, blocking fractures and pores, and reducing gas seepage capacity.
Hamdi, Sinan S.Alzanam, AliMohyaldinn, Mysara E.Muhsan, Ali S....
10页
查看更多>>摘要：Scale inhibition squeeze treatment is a common practice to prevent scale deposition within the downhole utilities, valve applications, and tubular components of the oil and gas producing wells. The conventional squeeze treatment has a short lifetime due to the reservoir rocks' limited adsorption of scale inhibitors and the quick desorption rate. As a result, this process has to be repeated multiple times per year, leading to massive increases in operational costs. Carbon-based nanomaterials are known for their high specific surface area, making them an attractive coating agent to enhance the capability of rocks' surfaces to adsorb chemicals such as scale inhibitors. In this paper, carbon-based nanomaterials of graphene nanoplatelet (GNPs) and three different types of carbon nanotubes (CNTs) are proposed as novel nanocoating to extend the lifetime of the conventional scale inhibitor squeeze treatment. A natural polymer of Gum Arab (GA) was used to graft the nanomaterials surfaces to ensure a homogeneous and stabilized coating solution. The adsorption of diethylenetriamine penta (methylene phosphonic acid) (DTPMP) scale inhibitor into GNPs and CNTs was investigated using a UV-Vis spectrophotometer. Various characterization techniques such as FTIR, Raman spectroscopy, and XPS were performed to evaluate the interaction between DTPMP and the proposed nanocoating (GNPs/CNTs). Based on UV-Vis results, GNPs was found to be the optimal coating agent with an adsorption capacity of 135 mg/g at ambient temperature and 114 mg/g at 96 degrees C. Its coating gets saturated with DTPMP within 1 h of interaction. Increasing the initial scale inhibitor concentration was found to increase the adsorption capacity of GNPs. Based on the core flooding conducted on Berea sandstone, the injection of nanocoating into the core sample reduces the permeability by only 12%. Finally, the injected nanomaterial was safely transported through the core, and the primary retention mechanism was adsorption rather than physical filtration/plugging.
Roshan, HamidLv, AdelinaAghighi, Mohammad AliSarmadivaleh, Mohammad...
9页
查看更多>>摘要：Detachment of clay particles from clay-rich interburdens is the main source of solid production in coal seam gas wells (CSG), costing the Australian operators millions of dollars every year. Several techniques have been proposed to reduce the solid production and consequent pump failure in already constructed open hole/slotted liner wells. Amongst all remedial techniques for these existing problematic wells, chemical stabilization seems to be the most practical method. The high cost of chemical additives, their environmental issues, potential low effectiveness and technical difficulties for their placement downhole have, however, hindered their wide application. In particular, the long-term effect of current chemical additives on interburden stability and their influence on coal seam matrix gas diffusion need further investigation. In this study, the application of colloidal silica nanoparticle solution (silica SOL) as a long-term chemical stabilization method for clay-rich interburden in CSG wells was investigated. A series of comprehensive experiments were performed to investigate the effect of the silica SOL on stability of pure compacted dry smectite clays and clay-rich sandstone samples in stationary and turbulent conditions (resembling the wellbore condition during gas production) using a uniquely designed experimental setup. Additionally the effect of silica SOL on coal and its gas adsorption was analyzed. The results of this study demonstrated that the silica SOL is a suitable candidate for long-term chemical stabilization of clay minerals as a cost-efficient and environmentally friendly additive. Its non-reactivity with coal and its inert response on gas sorption is another significant benefit of the proposed chemical solution.
NSTL
Elsevier