查看更多>>摘要： In fractured-caved carbonate oil reservoirs with well-developed dissolved caves, most of the caves are generally connected by large fractures to form separate and independent fractured-caved systems. The oil well basically intersects some fractures, and fractures connect one or two large-scale dissolved caves in series or parallel model to form an independent fractured-caved unit. Moreover, due to the large size of the dissolved cave in the fractured-caved unit, it no longer follows Darcy's law, but shows features belongs to pipe flow, free flow or a seepage-pipe flow. In this case, the conventional equivalent multiple porous media seepage mathematical model is inaccurate to characterize this kind of fractured-caved reservoir units. This study simplifies the structure of the large bead-shaped fractured-caved reservoir and shows how the well-cave and cave-cave units are connected through fractures. Results show that the connected fracture flow exsits in the periphery of the large cave dissolved caves in the area far from wells. Thus either a linear series or a parallel mathematical model is applied to simulate the connection of the two dissolved caves. The fluid flow in fractures is still considered as seepage flow, while in large dissolved caves it is considered as free flow. Therefore, the dual-cave dual-fracture series mathematical model and dual-cave single-fracture parallel mathematical model considering seepage-free flow coupling are established. Laplace transform is then used to mathematically solve the model, and Stehfest numerical inversion is conducted to draw the typical rate transient analysis curves. Finally, sensitivity analysis is applied to discuss the relationship between controling factors of the flow and actual reservoirs. Based on the rate transient analysis type curves, geometric parameters such as radius of cave, permeability and length of the large-scale fracture and dynamic reserves can be obtained. Finally, a field case in a bead-string fractured-caved reservoir unit of Tarim basin is implemented to verify the effectiveness of the proposed models and methods. The parameters obtained by type curve match support exploitation of fractured-caved reservoirs.
查看更多>>摘要： In fractured reservoirs, block-to-block interactions (re-infiltration and capillary continuity) significantly affect gravity drainage performance. Re-infiltration controls the drainage rate. This process may significantly delay oil production. Despite the numerous attempts to study the re-infiltration process, there is still much controversy about the factors that affect this phenomenon. This work focused on designing two sets of 2D models aimed at improving the simulation and visualization of multiphase flow in fractured porous media while providing a more realistic understanding of the pore-scale phenomena and flow communication between matrix-fracture and matrix-matrix. The simulation was performed in COMSOL Multiphysics in the single-porosity model. Moreover, the impact of different parameters such as rock type, physical properties of the fluids, tilt angle, matrix block height and area, fracture opening, and matrix blocks porosity-permeability on gravity drainage performance, especially block-to-block interactions, has been examined. Besides investigating the effect of each parameter, combined effects of those parameters have likewise been investigated. To rank the most critical observed parameters on the re-infiltration process, the grey relational analysis was applied. The results of this analysis showed the physical properties of the fluids have the most influence on re-infiltration. In addition, it was demonstrated that tilt angle reduces the degree of re-infiltration in deviated blocks. Also, a combination of oil-wet rocks and high irreducible water saturation results in a decrease in oil recovery, a delay in production, and a decrease in the degree of re-infiltration. Additionally, fractures with small openings and taller blocks promote greater re-infiltration; however, their impact on ultimate recovery is not significant. The findings of this study can help for a better understanding of the relative influence of different reservoir parameters on gravity drainage performance and block-to-block interactions.
查看更多>>摘要： The Spatio-temporal sequence residual modeling neural network (STSRM-net) is built to address the geophysical problem of obtaining P-impedance of the subsurface from the zero-offset seismic data and initial model of P-impedance. The initial model is used as the initial value of STSRM-net, and the modification value of the initial model and the residual between the modified initial model and true P-impedance are learned during the training. The Spatio-temporal characteristics of the data could be fully dug by STSRM-net. Limited by the inadequacy of labeled data, the semi-supervised learning inversion framework is constructed to train the STSRM-net. The performance of the STSRM-net and some deep learning inversion methods are compared on the synthetic dataset. The test results indicate that STSRM-net has higher inversion accuracy, stronger continuity, and better anti-noise performance. In addition, the robustness experiments indicate that the STSRM-net has excellent fault tolerance to the initial model. Finally, the STSRM-net is applied to the field data and compared with the sparse pulse inversion method, which also proves high inversion resolution, inversion accuracy and robustness to the choice of training wells of the proposed method.
Dea Indriani AstutiIsty Adhitya PurwasenaNeil Priharto
8页
查看更多>>摘要： Biostimulation is a method of microbial enhanced oil recovery (MEOR) by injecting nutrients into an oil well to stimulate the growth of indigenous bacteria and their activities dealing with the increasing of oil recovery. This study aimed to obtain an optimum nutrient formulation at laboratory scale to be applied for MEOR field biostimulation pilot project. Field monitoring of chemical and bacterial composition in oil well was also carried out up to twelve weeks after biostimulation. The ojl composition was analyzed by GC-MS and column chromatography. Bacterial community analysis was performed using 16S rRNA gene as the biomarker, which was sequenced by Illumina Miseq Sequencing. Based on Response Surface Methodology (RSM), the optimum nutrient concentrations that increase bacterial growth and decrease oil viscosity were molasses 5% (w/v), NPK 0.5% (w/ v), and DAP 0.5% (w/v). The relative abundance of the bacteria and the community composition constantly changed during the monitoring process. Injection of molasses stimulated the growth of the hydrocarbonoclastic bacteria until the end of monitoring period.
查看更多>>摘要： Spontaneous imbibition is an important recovery method of low permeability and tight reservoirs. However, the mechanism and influencing factors of imbibition on the addition of low-salinity brine are seldom studied. In this study, the effects of ion type and concentration on the interfacial properties and the oil recovery of imbibition with low-salinity water were investigated by measuring the oil-water interfacial tension, contact angle and recovery of imbibition. The effects of temperature, pressure and other factors on the imbibition recovery under low-salinity conditions were analyzed. The results showed that the oil-water interfacial tension gradually increased with decreasing salinity of solutions at low salinity conditions, among which Ca~(2+) had the greatest influence on the oil-water interfacial tension. With decreasing salinity, the contact angle decreased. The contact angle showed the largest variation (22.14°) during the dilution process of formation water. The solutions of different ion types showed a different production rate and oil recovery by imbibition, among which the NaCl solution with a concentration of 5000 mg/L had the highest oil recovery. Moreover, the oil recovery of imbibition increased with increasing temperature. Compared with low pressure, the production rate in the early stage under high pressure conditions was obviously improved. With increasing pH value, the oil recovery also increased.
查看更多>>摘要： Electrical and acoustic image logs are the best evaluating subsurface fracture and In-situ Stress wellbore data among direct and indirect methods. In this study, which had done by using the 24 Asmari reservoir well data in the Aghajari giant oilfield firstly were determined and categorized subsurface natural fracture, fault and In-situ Stress from common conventional well log, electrical and acoustic image logs, dipole sonic logs and 3D seismic data. Then, the relationship between determined features are evaluated in terms of genesis, events and different structural setting as the interaction between fault and In-situ Stress on the kinematic and subsurface natural fracture of Aghajari oilfield in southwest of Iran. The maximum and minimum horizontal in-situ stress direction is derived from image and dipole data had a good correlation except regions due to the fault effect. the integration of data evinced that the perturbation of regional stresses inherited from seismic faults and the effect of both regional stress and fault effect in the construction of a transforming fold as detachment type in SW nose to forming fault propagation and bending fold towards central and SE nose, respectively, which it could be useful for fracture modeling to enhance oil production, especially in heterogeneous carbonate fractured reservoirs.
Mohammad NajjarpourHossein JalalifarSaeid Norouzi-Apourvari
18页
查看更多>>摘要： Rate of penetration (ROP) management is a matter of importance in drilling operations and it has been considered in different studies. Different machine learning methods such as simple and optimized artificial neural networks (ANNs), support vector machines (SVMs), fuzzy logic (FL) or adaptive neuro-fuzzy inference system (ANFIS), ensemble methods of machine learning and meta-heuristic algorithms have been used for this purpose so far. In this article, some of the studies by using these methods as the main approach for ROP management are reviewed to achieve a better understanding of this concept, its economic benefits and also its research capacities. Results indicate that ANNs are the most popular machine learning method in ROP management, while simple ANNs excel the modified types in this regard. Still, modified ANNs outperform simple ones in terms of prediction accuracy, but as ANNs fall short in superior prediction performance, other machine learning approaches of ROP management such as linear regression (LR), random forest (RF) and gradient boosting method (GBM) have compensated this shortcoming and proved their efficiency and applicability.
查看更多>>摘要： We study the effect of borehole ovalization and large-scale irregularities during primary cementing of a horizontal section of well. We use a two-dimensional gap-averaged model that can compute the displacement within varying annular geometries: both eccentric and elliptic. We study displacement of a drilling mud by a spacer within both, elliptical-uniform cross-sections and those which vary irregularly in the axial direction, based on field caliper measurements. The combination of eccentricity and ellipticity adjusts the azimuthal positioning of the wide and narrow gaps producing a variety of characteristic behaviours, e.g. the front may advance in the form of 2 peaks at off-centre positions. The irregularities can induce additional azimuthal flow when compared to uniformly circular wellbores. In cases when the displaced mud has a significant yield stress, the displacement can leave patches of residual mud at the top of eccentric horizontal wellbores: not usually found without ellipticity.
查看更多>>摘要： The fractured rock mass is a discontinuous, heterogeneous, anisotropic medium in nature, including single multiple or a network of joints with regular or irregular patterns located between the intact rocks. Anisotropy, as an inherent feature of rock mass, is a factor that causes the mechanical properties of rock to be various in different directions, so it is very important and necessary to be considered in the design of rock engineering structures. This study aims to investigate the effect of rock anisotropy on induced stresses around an opening like a borehole located in the fractured rock mass. For this purpose, the combination of discrete fracture network (DFN) method to construct a geometric model of rock mass, with distinct element method (DEM) to the numerical analysis of stress, was used. All coupled DEM-DFN models were developed based on the field data of the rock and joint system of the Sellafield site in the UK. The discrete fracture network models with different degrees of anisotropy, including a circular opening with two different cross-section areas placed at the center of model, were used for stress analysis. In each type of model, by applying different boundary conditions, the magnitude of induced stresses at selected points around opening is calculated, and then the obtained results are compared with the Kirsch method as a popular closed-form solution. The numerical results of this study showed that the presence of irregular joints with different orientations in the model caused anisotropy in the magnitude of induced stresses obtained around the opening. This is an important issue that the Kirsch method is not able to consider in the calculations.
J. Duran ArmasLante Carbognani OrtegaCarlos E. Scott
13页
查看更多>>摘要： The current research work contributes one further step in developing the heavy oil in-situ upgrading technique, The experimental work was carried out using a dolomite corepack as a porous medium at temperature and pressure already investigated in In Situ Upgrading Technology (ISUT). Crude oil was saturated in the corepack to simulate the oil in place in the reservoir; then, hot vacuum residue (VR) plus nanocatalyst, and in the presence of hydrogen (H2) was continuously injected into the porous medium. The nanocatalyst was composed of ultra-dispersed Ni-Mo and deposited in three incremental steps in the corepack. Depositing catalyst in the corepack aimed to create a reactor in which upgrading reactions can occur. After each incremental nanocatalyst deposition step, the hot VR and H2 continuously flowed at a selected temperature, pressure and residence time through the corepack. The products of every VR plus H2 step were analyzed with techniques such as microcarbon (MCR), simulated distillation (SimDist). The products from the stage with the highest catalyst concentration were determined to have lower VR contents, much lower viscosities, lower sulfur content, and stability; this latter indicating the necessity of carefully controlling processing severity levels. Chemical tracers were added to the crude oil (Phenanthrene) and the VR (1-methylnaphthalene and n-octadecane) at a 1.0 wt% level; their distributions were studied throughout the process via chromatography and mass spectrometry analyses. Cracking, plus olefin and aromatic hydrogenation reactions were evidenced to occur during the ISUT process.
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