查看更多>>摘要：Determination of representative saturation functions for permeable reservoir sandstones requires consideration ofmm-cm scale laminations and crossbedding common in these heterogeneous porous media. Modelling selected laminated sandstones from CO2CRCs Otway International Test Centre in Victoria, Australia as bimodal composites of different rock types, we analyse drainage relative permeability parallel and perpendicular to the laminae for a range of driving gradients. The results from these numeric drainage experiments are curve fit across a continuous range of flow rates between the capillary and viscous limits. Our analysis shows that laminae-related small, but spatially correlated grainsize and permeability variations give rise to flow-rate dependent drainage behaviour at the bed scale. The flow direction-and rate-dependent behaviour is captured by a new set of anisotropic extended saturation functions that are implemented and presented in a form that is suitable for compositional simulation in the system CO2-H2O-NaCl. For the first time, these new constitutive relationships permit an investigation of feedbacks between the reservoir-scale flow regime and bed-scale phase mobility. To illustrate the application of these functions in reservoir simulation, meter-scale plume spreading simulations are presented for a suite often homogenised fluvial-to-estuarine sandstones from the Otway facility.
查看更多>>摘要：As real production data of a well have an irregular pattern, accurate prediction of oil rate demands a powerful model to capture the nonlinear behavior of data. In addition to the traditional methods such as Decline Curve Analysis (DCA), Machine Learning methods can be considered as one of the effective predictive tools of engineers. This paper employs a comparative approach to find an appropriate network to forecast the oil production rate of an Iranian Oil field. The performance of several networks such as Rough Neural Network (Rough NN), Long-Short-Term Memory (LSTM), Artificial Neural Network (ANN) with only dense layer, and ID Convolutional Neural Network (CONV~(-1)D) were monitored by investigating various statistical parameters such as error value, the cross plot of real data and predicted data and error distribution. A combination of five inputs static and dynamic parameters was considered as input to the model. All networks were trained for 80% of all data (10025 points) and the rest were divided equally for testing and validation. The highest performance was observed in the results of Rough-NN with a coefficient of determination of 0.82 for predicting test data. The results showed an accuracy slightly less than Rough-NN for the case of CONV~(-1)D (R2 = 0.79). However, the worst performance referred to ANN and LSTM where their R-squared was about 0.54. Finally, the precision of the superior network (Rough-NN) was compared with DCA for several wells. It was revealed that DCA cannot predict the oil production rate accurately specifically when the well comes into production after a long shut-in. In contrast, Rough-NN is capable of predicting the oil production rate accurately regardless of the production history of the well.
Juliana A.G. LopesWalter E. MedeirosVincenzo La Bruna
18页
查看更多>>摘要：We present a multiscale approach to develop a deterministic Discrete Fracture Network (DFN) model including fracture enlargement due to karstic dissolution in low-porosity carbonate rocks. The result is a DFKN (Discrete Fracture and Karst Network) model from which it is possible to quantify, in a practical manner, the impact of fracture enlargement due to karstic dissolution on the fracture network transmissivity. We provide a case study using two large outcrops in the Jandaira Formation, an intensely karstified carbonate platform of Turonian-Campanian age in the Potiguar Basin, Brazil. The study is based on scanlines collected both in field and from Unmanned Aerial Vehicle (UAV) imagery, allowing to cover three orders of magnitude in length and aperture of fractures. We found that if karstic dissolution is low, aperture-length data plotted on bi-logarithmic graphs can be fitted by straight lines, thus following the aperture-length power law typical of mechanical apertures. However, advanced stages ofkarstification modifies the aperture-length relationship due to the fact that dissolution causes similar fracture enlargement regardless of fracture length. As a result, the aperture-length curve gradually degenerates to a constant value as the degree of dissolution increases. This behavior is the key to quantitatively taking into account fracture enlargement, by simply adapting an aperture-length curve according to the known stage of karstic dissolution of the modeled carbonate rocks. We show that fracture enlargement can increase the transmissivity of a karstified fracture network by up to five orders of magnitude without changing its connectivity. Our approach can be useful to better understand the behavior of fluid flow in carbonate reservoirs with fracture networks affected by karstic dissolution.
查看更多>>摘要：The suitability of using Deep Eutectic Solvents for chemical Enhanced Oil Recovery operations is analyzed from the nanoscopic viewpoint using classical molecular dynamics simulations. Four different eutectics were considered based on Choline Chloride, as hydrogen bond acceptor, plus urea, glycerol, ethylene glycol or levulinic acid, as hydrogen bond donors. Two main effects were studied to study their suitability;; i) eutectic solutions-oil interfacial tension and ii) wettability of oil droplets on calcite surfaces in presence of eutectic solutions to study the possible evolution from oil wet to water wet behavior. Different eutectic concentrations in water halide solutions, as a model of brine in reservoirs, are studied. The main physical properties such as interfacial tension or contact angle are analyzed as well as the behavior of the oil in presence of the eutectic solutions in terms of intermolecular forces, energy of interactions, molecular arrangements and adsorption at the corresponding interfaces. The reported results allow to infer the nanoscopic effects on the basis of the use of eutectics for enhanced oil recovery operations, thus providing the information which may contribute to the development of environmentally friendly operations using these low-cost green solvents.
查看更多>>摘要：The viscous fingering morphologies at a particular stage of emulsion displacements are observed to follow similar development patterns as that of the partially-miscible viscous fingering behavior (existent between the commonly studied fully miscible and immiscible systems). Chemically-induced viscous fingering before and after the finger droplet development resembling the partially-miscible fluid behavior is investigated using fractal dimensions and various-classic and modified-dimensionless scaling groups. We demonstrate, through the quantitative analysis using the empirical data collected from our previous experimental study, that the finger droplet formation morphologies observed in partially-miscible injection are indicative of an emulsion hydrodynamic instability behavior. The dominant parameters responsible for such droplet formation and their relationship to fractal dimension and hydrodynamic stability are mapped in a phase diagram with the original experimental images.
查看更多>>摘要：The water-alternating-gas (WAG) operating scheme and reservoir permeability heterogeneity are the main crucial parameters, which highlyaffect WAG displacement process. The novelty of this article lies in the development of an analytical model for WAG incremental oil recovery as function of WAG ratio, viscous gravity ratio and mobility ratio for the stratified heterogeneous reservoir. We have investigated the effect WAG ratio on WAG incremental oil recovery with variation horizontal permeability heterogeneity, vertical permeability anisotropy and dip angle of the reservoir. The critical operating parameters investigations were carried to optimize WAG displacement process in both homogeneous and heterogeneous reservoirs. Finally, we have estimated all the benefits of the most suitable techno-economical WAG operating scheme as tapered WAG (TWAG) over uniform WAG (UWAG). The developed analytical model showsreasonably similar results as numerical simulation. The results of the analytical and numerical analysisshow that the incremental oil recovery accelerated bya decrease WAG ratio. However, this effect is more noticeable at high viscous gravity (VGR). The increase in reservoir dip angle subsequently increases vertical and displacement sweep efficiencies compared to the horizontal reservoir for different WAG ratio. While increasing WAG ratio decreases vertical sweep and increases displacement sweep of inclined reservoir compared to the horizontal reservoir. The increase of oil recoverywas observed by higher Kv/Kh with a lower WAG ratio. However, this effect is less evident at lower Kv/Kh-The WAG ratio with a higher proportion of water is beneficial for the heterogeneous reservoir. The infill implemented before WAG start shows faster oil recovery compared to WAG start first then infill implemented in the heterogeneous reservoir. The TWAG incremental recovery over water flood was 18% in homogeneous and 8% in heterogeneous reservoirs, while EUR was approximately similar to UWAG. The TWAG shows more efficient techno-economic benefits over UWAG due to better economics, faster oil recovery rate, more efficient use of injected gas and reduces response time in both homogeneous and heterogeneous reservoirs.
查看更多>>摘要：Low-salinity water flooding (LSWF) is an EOR method applicable to both sandstone and carbonate reservoirs. In recent years, LSWF has become an attractive technique but still some uncertainties concerning the governing mechanisms exist in studies. Mechanisms such as wettability alteration, osmosis, and fluid flow diversion by fines migration are proposed to explain the incremental oil recovery by LSWF in sandstones. Flow diversion is still being debated as to whether this mechanism works and, if it does, to what extent. This mechanism occurs due to clay swelling and fines migration, which results in pores blockage, diversion of the fluid flow to unswept areas, and enhanced oil displacement. Hence, the presence of clays is claimed to be a necessity for the success of LSWF in sandstone reservoirs. Here we proposed a new approach to study effects of different mechanisms of LSWF alone and in combination of each other using micromodels to track fluid flow diversion and the reason behind it and its subsequent benefits in case of oil recovery, visually. In this paper micromodel tests in different wetting and clay presence conditions were designed and conducted to investigate the standalone fluid flow diversion mechanism and the combination of it with wettability alteration and osmosis effects during LSWF. Tests conducted in water wet and oil wet states showed that the presence of clays is not the main criterion for activating the LSWF effect and the initial wettability is more critical. Our studies showed that the fluid flow diversion share in oil recovery is only 30% of the total incremental oil displaced by LSWF, while about 70% of the oil is produced by wettability alteration and osmosis mechanisms. It is reasonable to say that, although flow diversion is an active mechanism, it is not the dominant one and on the other hand wettability alteration is.
查看更多>>摘要：Brazilian presalt carbonate reservoirs are highly heterogeneous. This feature is mostly justified by the nature of the original depositional system and subsequently diagenetic processes. Consequently, reserve estimates and production forecasting are under large uncertainties. In this geologic context, it is of great relevance to develop techniques that helps to obtain a detailed description on the spatial distribution of these different rocks. In doing so, it contributes to the understanding of presalt carbonate sedimentary deposits, providing inputs for more predictive reservoir models. Traditionally, these carbonates are grouped into three classes, from which only one exhibits reservoir properties. Using a dataset from Buzios Field, this work proposes a characterization of presalt carbonate reservoir rocks by grouping them in terms of their mineral composition. Taking advantage of rock physics concepts, we aim to potentialize the use of elastic parameters for multiple rock type discrimination. We explored several attempts for rock classification by using a Bayesian approach. Among all the tested propositions, a two-step workflow for five lithotypes classification, emerges as the most appropriate for the Buzios Field. In this scheme, three lithotypes represent good-quality reservoirs and the other two are low-porosity and Mg-clay-rich carbonates. The average root-mean-square error of the most likely a posteriori rock proportions is around 8.4%, only approximately 1% higher than the conventional three lithotypes configuration. To support that, we compared different methodologies for Bayesian classification at well-log scale through acoustic impedance and compressional to shear velocity ratio. Potential applicability of the proposed methodology at field scale is reinforced by similar results achieved using well-logs filtered to the seismic bandwidth.
查看更多>>摘要：The tight sandstone reservoirs of the Xujiahe Formation of the Western Sichuan Basin Depression typically exhibit characteristics such as low porosity, low permeability, and strong heterogeneity, resulting in weak seismic response differences between gas and water. In present study, we developed an unsupervised learning gas reservoir prediction method using a self-organizing neural network (SOM) to identify and predict tight-sand gas reservoirs in areas with few or no wells. First, we extracted seismic attributes data and obtained multi-component seismic composite attributes. Then, the multi-component composite attributes were fed into the SOM network for training, obtaining the gas reservoir prediction results. Simultaneously, the designed SOM prediction scheme was also applied to PP-wave and PS-wave seismic data respectively for gas reservoir identification and prediction. The prediction results of the multi-component composite attributes exhibited good correspondence with available gas drilling information, indicating their unique merits in resolving issues pertaining to the deep tight gas sandstone reservoir identification. Finally, based on geological data and drilling information, we evaluated the effectiveness of the prediction results of proposed methods, and predicted favorable exploration areas. Effective implementation contributes substantially to tight-sand gas reservoir identification and prediction in less or even no well area.
查看更多>>摘要：The Lower-Middle Ordovician reservoir bitumen (RB) results from various geological events (deep burial of strata, volcanic activity and thermocliemical sulfate reduction) in the Shunnan area, Tarim Basin. The understanding of its characteristics and origins sheds light on the accumulation process of hydrocarbon reservoirs. A combination of polarizing microscopy, fluorescence microscopy, and laser Raman microspectroscopy was used to study the characteristics and origins of the RB. In the wells (SN4 and SN7) with obvious hydrothermal activity, the occurrence of RB in each formation includes stylolites accompanied with silicification in the microcrystalline limestone of the Yijianfang (O_(2yj)) Formation, stylolites and dissolution pores in the granular limestone of the Yingshan ((O_(2yj)) Formation, and stylolites and intercrystalline pores of saddle dolomite in the limy dolomite of the Penglaiba (O1p) Formation. In the wells (SN5, SN501, SN5~(-2), and SN6) without hydrothermal activity, the occurrence of RB in each formation includes stylolites in (O_(2yj) and Oi_2y Formations and stylolites and dolomite intercrystalline pores in O1p. Moreover, the RB contents of the wells with hydrothermal activity are about two times as large as those of the wells without hydrothermal activity in each formation. From (O_(2yj) to O_(1 2y) and then to O1p, the effect of hydrothermal activity and dolomitization on reservoir transformation is gradually enhanced, and the RB content is gradually increased. In addition, the average maturity of the RB (Ro%caic) in wells SN4 and SN7 is 2.2196~(-2).36%, whereas that in wells SN5, SN501, SN5~(-2), and SN6 is 1.90%~(-2).11%. The cracking of deeply buried crude oil is the key factor controlling the widespread distribution of RB. The hydrothermal activity in Early Permian produced abnormally high maturity of the RB in wells SN4 and SN7. Thermocliemical sulfate reduction (TSR) promoted the cracking of crude oil, which had a positive impact on the formation of RB.
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