查看更多>>摘要：Determining the potential of reservoirs and production zones is very important to reach maximum product performance and decrease hydrocarbon recovery costs. The calculation of the Water Saturation (S-W) significantly affects oil-in-place estimations. The Saturation-Height Function (SHF) is operated to predict the saturation in the reservoir for a given height above the free water level. Typical approaches for predicting water saturation as a function of rock properties and height above contact include two types, those based on capillary pressure curve averaging and log-based techniques. The goal of this study is to define an appropriate SHF and S-W using the usual functions to delineate production zones using rock typing with an example from the Dorood oilfield in the Persian Gulf. In this study first, the reservoir has been divided into different rock types and water saturation is estimated by different methods in each rock type. The Reservoir Quality Index (RQI) along with Water Saturation profile for representative rock types were used for determining reservoir zones. Accordingly, a formulation was developed to model the behavior of Capillary Pressure (P-C) as a characteristic of S-W and to determine the Free Water Level (FWL) based on laboratory data. To achieve this goal, the appropriate saturation-height functions and their coefficients were chosen for representative reservoir rock types. The Pc curves are classified based on Discrete Rock Types (DRT) and a proper saturation-height function was assigned for individual rock types. Finally, some of the most common equations for calculating SHF were fitted to the representative Pc curve of each rock type and coefficients of the equation for any rock type were determined by using the MATLAB software in the studied carbonate reservoir. After investigating the results of fitting different SHF, water saturation was calculated using a modified lambda function and compared with the log-derived water saturation. The SHF applied, could be used to estimate saturations of unreachable zones of the field.
查看更多>>摘要：To characterize matrix pores and microfractures which are widely developed in unconventional reservoirs and also to analyze flow law in multiscale flow region, some related research has been carried out in this study. Based on the statistical characteristics of microscale and nanoscale scanning images of cores, digital cores of micro fractures are reconstructed by an improved Voronoi method and the digital cores of matrix pores are reconstructed by the quartet structure generation set (QSGS). By means of regional superposition algorithm, the digital cores of microfractures are firstly magnified in each divided region and then integrated with the corresponding digital cores of matrix pores. After the superposition is completed in whole regions, numerical model after superposition is reduced to the original size of the digital core of microfractures. Finally, the multiscale digital core is reconstructed. Based on reconstructed multiscale digital core, flow simulation considering the permeability of matrix is carried out by the gray lattice Boltzmann method (GLBM). The results show that by constraining the generation areas of random points, the improved Voronoi method can better reflect the geometric characteristics of specific microfractures and the average relative errors of the two-point function and variation function are 13.36% and 2.52% respectively compared with the original microfractures. The multiscale digital core reconstructed by the regional superposition algorithm integrates the anisotropy of matrix pores while retaining the original characteristics of microfractures. With the increase of permeability of matrix, pressure drop range in the flow simulation region expands, and the average velocity at the outlet of microfractures increases. Compared with the case not considering the permeability of the matrix, the maximum increase of average velocity at the outlet of microfractures can reach 48.37% when the permeability of the matrix is set as 0.75 mD. When the flow direction in the microfractures is transverse, compared with the multiscale digital core with transverse connectivity in the matrix, the multiscale digital core with longitudinal connectivity in the matrix has higher flow velocity at the outlet of microfractures, and the average increase of velocity is up to 1.73%.
查看更多>>摘要：Estimating undeveloped reserves in unconventional reservoirs has important practical and legal implications. Unconventional reservoirs lend themselves to the use of statistical workflows which often first determine a distribution of well EURs and then treat the EURs at the undeveloped locations as regionalized variables. This approach was formalized by the Society of Evaluation Engineers in Monograph 3 published in 2010 which presents a workflow to assess proved undeveloped reserves in unconventional assets based on the statistical bootstrap approach. However, the recommended workflow makes the strong assumption of spatial independence amongst well pairs which significantly limits the application of the workflow as this assumption is often violated in practice. Further, applying this workflow to reservoirs that violate the independence assumption can result in the underestimation of uncertainty and thus overconfident estimates. To overcome this limitation, we introduce a geostatistical workflow that honors the spatial context of the data by bootstrap sampling with the effective number of independent data, n-effective, rather than the total number of data, thus generating uncertainty estimates that honor the spatial context of the data and extend the applicability of the workflow to fields with spatially correlated data.
查看更多>>摘要：Hydrocarbon-water interface plays an important role in many cases and industries. However, the effect of polar oil molecules on hydrocarbon-water interfacial properties is still unclear. In this work, 9 molecular scale heptanewater interface models containing different polar oil molecules were established by molecular dynamic simulation to study the effect of polar oil molecules on hydrocarbon-water interface properties. Interfacial tension (IFT), molecular configuration, molecular orientation and interaction energy between oil and water were calculated to quantitatively characterize the heptane-water interfacial properties containing different oil components. The IFT results show that IFT decreases as the molecular polarity increases. The molecular configuration results indicate that the stronger polar oil molecules tend to adsorb to the interface while the weaker polar oil molecules tend to stay in the oil bulk space. The molecular orientation shows that the polar oil molecules possess more orderly regularity at the interface while nonpolar oil molecules can only randomly adsorb at the interface. Specifically speaking, chain polar oil molecules tend to be perpendicular to the interface while the ring structure polar oil molecules tend to be parallel to the interface. The ring oil molecules containing branched functional groups should also tend to be perpendicular to the interface under the influence of the branches. The heptanewater interaction energy results indicate that the interaction energy increases as the molecular polarity increases. Furthermore, the electrostatic energy predominates over van der Waals energy when the oil contains polar oil molecules while van der Waals energy predominates over electrostatic energy when the oil contains nonpolar oil molecules. The conclusions in this work should provide some fundamental understanding of interfacial information and some industries involving hydrocarbon-water interface.
查看更多>>摘要：In the middle and late stages of water flooding development in oil fields, oil wells will have the characteristics of low production fluid and high water cut content, making traditional production profile combination instruments unable to meet field needs. In order to accurately obtain the flow rate of each phase of the oil-water two-phase flow under the condition of low velocity, this paper proposes a new production profile logging method that combines an ultrasonic Doppler logging tool and a combined annulus logging tool. The measurement characteristics are verified by simulation experiments. Through frequency spectrum transformation of the original ultrasonic logging data, the power spectrum curve of the oil-water two-phase flow is obtained, the oil frequency, oil amplitude and other parameters are obtained by Gaussian fitting, and the distance analysis of the obtained experimental data is performed to obtain the correlation between the variables. Finally, the PLS-SVR algorithm is used to predict the oil and water flow. The mean absolute percentage error of oil flow is 7.96%, and the mean absolute percentage error of water flow is 9.4%. The prediction results show that the proposed low-velocity oil water two-phase split-phase flow prediction model can meet actual needs, and has higher accuracy than support vector regression (SVR) and back propagation (BP) neural network prediction models, which can provide a new theoretical support for logging interpretation of production profiles.
查看更多>>摘要：There are complex strike-slip fault systems in the Ordovician carbonate strata in the T-sh area of Tarim Basin. They are the primary storage space and flow channel of hydrocarbon resources. Scientific evaluation of internal space and conductivity of different parts along the main faults is the decisive factor for efficient development of the T-sh reservoir. Based on the 3-D seismic and the coherent body data, the fault structure models in the reservoir of the S1 and S5M fault zones are established. The original regional geomechanical parameters are determined according to the core testing results and logging data. The local stress field near the fault is studied based on the numerical simulation method. The sliding trend coefficient, expansion coefficient, and comprehensive conductivity coefficient of faults in the reservoir of S1 and S5M fault zones are quantitatively evaluated. The results show that the Ordovician strata in S1 and S5 fault zones are in a strike-slip faulting stress regime. The vertical stress (S-V) gradient is 0.0243 MPa/m, the maximum horizontal stress (S-H) gradient is 0.0246 MPa/m, the minimum horizontal stress (S-h) gradient is 0.0177 MPa/m, and the orientation of S-h is 166.27 degrees-197.25 degrees. Based on the simulation results, it is found that there is an apparent correlation between the sliding trend coefficient of the faults and mud loss. The expansion coefficient is positively correlated with venting and production. The research results have practical significance for geological sweet spots prediction and drilling construction in the T-sh oilfield.
查看更多>>摘要：Modeling and simulation of oil and gas facilities has been done by several authors in closed-source commercial applications, with low flexibility for model adaptation. A few authors used free modeling environments, which results in a differential-algebraic equations (DAE) system and lets the model be adaptable for plantwide simulation. Still, it has limitations in obtaining the model's initial conditions and to perform dynamic simulations when the compositional approach is used. The Modified Black-Oil (MBO) approach, which models the thermodynamic equilibria in a simpler way, has been used by several authors for reservoir modeling but not for topside facilities. This work proposes the use of the MBO approach for topside dynamic modeling. This was done in EMSO (c), obtaining a large index-1 DAE system and successful obtention of consistent initial conditions. Disturbances on specific variables were applied and shows the potential use of the MBO approach for new dynamic studies.
查看更多>>摘要：We investigate the injection of a viscoplastic fluid, through an injector, into a channel filled with a lower density Newtonian fluid. The two-dimensional model problem is informed by plug & abandon practices in Western Canada and is analogous to the early stages of the balanced plug method in placing off-bottom plugs (Trudel et al., 2019). We present a systematic study of the effect of the injector size and position on the flow dynamics and fluid accumulation. When the injector and the channel are centralized, an unstable displacement flow develops below the injector. The instability leads to the formation of a mixing layer below the injector that diverts the injected fluid toward the space between the injector and the channel (the gap). The unsteady development of the mixing layer leads to the episodic mixing of the injected fluid that enters the gap. The frequency and magnitude of these contaminated regions change nonmonotonically with the injector width but decrease with the length of the mixing layer. When the injector is not centralized with the channel, the injected fluid flows toward the wide side of the gap. This leads to the formation of a series of vortices below the injector and a relatively short mixing layer. While the fluid that enters the wide side of the gap remains primarily unmixed with the Newtonian fluid, significant periodic mixing is persistent on the narrow side. On the narrow side of the gap, the average degree of mixing of the fluid entering the gap increases significantly with eccentricity while the velocity of the advancing front of the injected fluid decreases. Our results suggest there may be an optimal range of diameter ratios that minimize the mixing of cement slurry and wellbore fluids. In the absence of a mechanical or non-mechanical barrier, the injected fluid may flow toward the gap and accumulate at the target position irrespective of the relative position of the injector within the wellbore. The quality of the accumulated slurry, however, may vary notably with the size and position of the injector.
查看更多>>摘要：Fracture stress is the key parameter relating the laboratory evaluations of bulk gels to their plugging efficiency. By the in-situ gelling method, the complete deformation curves of polyacrylamide (PAM) gels are successfully obtained. We observe the strain hardening behavior from all the interested gels, which exhibits an exponential relation between the apparent modulus and the strain. Based on the exponential equation, the fracture stress is factorized into three rheological parameters, i.e., the plateau modulus, degree of stiffening, and fracture strain. In this article, we focus on the concentration dependence on these mechanical properties of PAM gels. It is observed that the plateau modulus of unentangled gels is dominated by the crosslinking density, and the entangled gels exhibit a scaling law with exponent of 2.2-2.3 between the plateau modulus and polymer concentration. In general, the degree of stiffening would be advanced by increasing the crosslinker concentration or decreasing the polymer concentration, while the fracture strain is reduced with both of them. In addition, these variations would be significantly exacerbated if the polymer concentration exceeds the entanglement concentration. As a result, the contribution of gellant concentration to the fracture stress of gels is weakened due to entanglement. Around the entanglement concentration, the fracture stress-polymer concentration curves of the organic gels are continuous but the increasing rates are decreased, while the inorganic gels experience a sudden reduction of fracture stress. Finally, we briefly discuss the fingering-rupture process of the bulk gels, and find the rupture pressure gradient is in linear relation with the fracture stress.
查看更多>>摘要：The computational cost of simulation on fine-scale reservoir models can be prohibitively expensive. While upscaling typically helps in reducing cost, it also results in a reduction in accuracy. Two-scale approaches such as dual mesh methods (DMM) have been developed over time in an attempt to reduce simulation cost while maintaining near fine-scale levels of accuracy and resolution. While these two-scale methods can be very effective in improving accuracy, they can be quite expensive as well. This paper presents two multimesh methods, namely, the Triple Mesh Method (TMM) and the Extended Triple Mesh Method (ETMM). Both methods involve introducing a third grid at an intermediate scale between the coarse and fine scales. These involve two levels of upscaling of the grid properties and two levels of downscaling the solutions to the flow equation. TMM involves two successive local downscaling steps of the flow solution from the coarsest to the finest mesh. ETMM on the other hand involves two successive extended local downscaling steps of the flow solution from the coarsest to the finest mesh. Each downscaling step in ETMM involves the application of 'Directional Oversampling' first introduced in the extended dual mesh method EDMM. These two methods along with DMM and EDMM methods were tested on different waterflooding problems and results compared with the coarse-scale and fine-scale solutions. The results show both ETMM and TMM to be effective in error reduction and also more cost effective than their respective dual mesh alternatives.
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