Journal of Petroleum Science and Engineering最新文献

In-situ mining of lignite requires dehydration, pyrolysis, gasification, and other stages. The injected fluid, dehydrated water, and pyrolysis products are transported in the developing pores and fractures. The internal structure and properties of lignite change significantly under the joint action of temperature and fluid pressure. In this study, X-ray computed tomography (X-CT) was used to scan lignite samples in the temperature range of 25°C–450 °C. Grayscale images and three-dimensional reconstruction images of the internal structure were obtained to investigate the evolution of the internal pore structure during lignite pyrolysis. It is found that the porosity of lignite increased as the temperature rose from 25 °C to 250 °C. The porosity was 6.54% at 250 °C. At 350 °C, the porosity decreased to 2.45% due to channel blockage and softening of the coal. At 450 °C, the pyrolysis of the lignite organic matter resulted in numerous large and interconnected honeycomb pore clusters. At this temperature, the porosity was 16.02%. X-CT and nuclear magnetic resonance enabled detailed and quantitative characterization of the internal structure of lignite. The research results provide theoretical and technical information on the evolution of migration channels in lignite for the potential improvement of in-situ pyrolysis and gasification efficiency of in-situ lignite mining.

Seismic inversion is a significant technique for estimating petroleum reservoir parameters. The low frequency component of the initial model represents the geological background information, which plays an important role in the seismic inversion. It is challenging to precisely depict the actual geological model in seismic inversion because of the inherent velocity-depth ambiguity. Therefore, the initial model which is closer to genuine geological backdrop is essential. We propose a workflow which estimates a fusion initial model based on data fusion algorithms. It is well known that seismic facies analysis can provide more low-frequency information about the geological background. For example, the boundaries of sedimentary bodies can be represented by seismic facies classification data. We utilize a combination of the seismic facies classification data and well curves interpolation initial models to accurately invert the special geological body with the support of a feature-level fusion algorithm. Then, a practical pre-stack seismic inversion method is implemented, and a field data example further demonstrates its applicability and steadiness in seismic inversion.

The growing advancement in drilling technology had necessitated the development of self-destructive mud cake, which is composed of encapsulated thermochemical fluids (TCF) to facilitate dissolution of filter cake. However, segregation of weighting component, commonly the Barite particles, can lead to various operational problems that should be avoided. In this investigation, the segregation potential of Barite particles (“Barite Sag”) in drilling fluids has been investigated. The experimental data from rheological studies have been employed to guide CFD modeling and simulation of multiphase flow of a dense suspension mimicking the conventional oil-based mud (OBM), water-based mud (WBM), and those comprises thermochemical additives viz. OBM_TCF and WBM_TCF. The results revealed that the drillings fluids conform to the shear thinning pseudoplastic behavior within the conditions operated in this study. Notably, the apparent viscosity of the WBM was observed to decrease with increasing temperature between 25 and 50 °C but increased afterwards. Evaluation of gravitational settling characteristics revealed that the conventional OBM might have lower sagging potential, at lower temperature, compared with the conventional WBM, due to higher settling velocity of Barite particles in the later. In comparison, at higher temperature, which corresponds to the conditions of the newly formulated muds (i.e., the OBM_TCF and WBM_TCF), it was found that the WBM_TCF exhibit lower potential for Barite sag due to lower settling velocity of the particles compared with that of OBM_TCF. The reason essentially has to do with higher viscosity of the WBM_TCF. The CFD studies have considered both the hydrodynamic forces and shear induced migration of the particles. Analyses of various simulation results including particle flux, particle mass fraction, mixture viscosity, and the pressure drop, consistently revealed that the WBM_TCF might have lower Barite segregation potentials compared with other types of drilling fluids considered in this study.

Movable fluid content and permeability are important reference factors for reservoir quality evaluation and recovery enhancement. In this study, based on multiple experimental results, 10 typical samples from a tight sandstone gas reservoir in the coal measure strata of the Shanxi Formation along the southeastern margin of the Ordos Basin were divided into three lithofacies to discuss the factors influencing movable fluid content and permeability. The results show that the fluid has a strong seepage capacity and a high degree of mobility in relatively large pore throats. The relatively large pores in the study area are secondary dissolved pores of various origins. High quartz and feldspar contents are conducive to the formation of secondary pores, while the presence of carbonate minerals and clay minerals play an inhibitory role. The pore throat size range of 0.05–0.1 μm is the critical interval for the conversion of bound fluid to movable fluid. The movable fluid saturation and movable fluid porosity are affected by submicron- and micron-scale pore throats of >0.1 μm, while the permeability is controlled by micron-scale pore throats sizes of >1 μm. The volumetric proportion of the relatively large pore throats is influenced by the mineralogical composition of the rock, the size of the pore throats, and the degree of sorting, which further control the amount of moveable fluid and its percolation capacity. The highest movable fluid content and permeability appear in the massive gravel-bearing coarse to medium sandstone lithofacies (Lm) with a high proportion of submicron- and micron-scale pore throats, whereas the lowest occurs in parallel bedding or ripple laminations，medium to fine sandstone lithofacies (Lpr) with a high proportion of nano-scale pore throats. The lithofacies with cross bedding and medium sandstone (Lc) is also dominated by nano-scale pore throats, which shows the characteristics of low movable fluid content and medium permeability due to the retention of some micron-scale pore throats. This study describes the mobility of fluids with different pore throat sizes in detail and determines the pore throat size range corresponding to the transition from bound fluid to movable fluid, which can provide a reference for the evaluation of movable fluid seepage in other regions.

Current flow models for fault-karst reservoirs are mostly described as a single fault formation, which cannot be applied in recent-developed multibranched fault-karst reservoirs. This paper established a novel analytical model to investigate pressure response behavior of a horizontal well in multibranched fault-karst reservoirs. The model is able to describe the influence of the physical properties and spatial structure of fracture-cave system on pressure transient response. The flow model considers different flow behaviors in each region, which includes Darcy flow (gravity included) in fault-fracture, large-scale storage flow in karst-cave, and Poiseuille-law-based horizontal laminar flow in the horizontal wellbore, respectively. These assumptions enable the model to match complex situations in multibranched fault-karst reservoirs. Then, the model was retrograded to compare with a single fault-karst reservoir model to verify its accuracy. Further, the solutions were graphed on log-log plots, and we discussed the effect of fluids mobility, formation storability, and structure characteristics (e.g., length, angle, depth, distance) of fracture-cave branches on transient pressure responses. Results show that (a) the number of fracture-cave branches in a reservoir can be directly observed by counting the number of V-shaped appearances on the pressure derivative curve. (b) The exact shut-in time when V-shape appears is affected by volume and distance between two neighboring fracture-cave branches. (c)The characteristics of the V-shape are affected by fluid mobility, formation storability, and length of fracture region. (d) The slope of the pressure derivative curve in the boundary-dominated flow regime can be used to evaluate the gravity effect. (e) The pressure response behavior exhibits a near-well effect when a horizontal well commingled production in the multibranched fault-karst reservoir. Finally, we applied our model and resulting observations to analyze pressure build-up data tested from SHB Oilfield, which demonstrated a workflow to identify the number of fault-karst branches and also to estimate reservoir properties.

When a gas hydrate reservoir is depressurized for gas production, the production tendency and dissociation behavior may differ depending on conditions such as the bottom hole pressure and depressurization rate. Gas hydrate dissociation is a complex process that involves the transfer of materials and heat, and on-site analysis based on laboratory-scale results is critical. In the present study, a field-scale numerical analysis was performed to reflect the conditions of the Ulleung Basin in the East Sea of Korea. The dissociation behavior, which varies depending on the conditions in the gas hydrate-bearing sediment, was analyzed under various conditions of bottom hole pressure and depressurization rate. This study also identified the effects of depressurization conditions on gas hydrate saturation. As the bottom hole pressure decreased and the depressurization rate increased, the production rate and cumulative production of gas and water increased, and the radius of the pressure propagation effect at the beginning of production increased. In sediments with a gas hydrate saturation of ≥70%, the pressure propagation was unstable and the dissociation rate was low. These results can serve as preliminary data for the field production of gas hydrates in the Ulleung Basin.

Microbial enhanced oil recovery (MEOR) is a well-known oil recovery method that is greatly influenced by the growth and metabolism of the microorganisms. Given the complexities and uncertainties associated with identifying the growth mechanism of microorganism, developing an approach to estimate bacterial concentration versus different factors viz. Salinity, temperature and time is still deemed a challenge. Hence, in this study, seven different machine learning methods namely Artificial Neural Network, Support Vector Machine, Decision Tree, K-nearest Neighbors, Ensemble Learning, Random Forest and Adaptive Boosting are utilized to predict bacterial cell concentration. A databank including 110 data points of bacterial cell concentration entailing the incubation time, salinity, temperature and yeast extract has been collected and used for preparation of these models. Graphical and statistical comparisons are used to analyze the performance and accuracy of each integrated model. The retrieved results revealed that the trained ensemble learning model is the most accurate method in estimating the bacterial growth with correlation coefficient and mean squared error of 0.9163 and 0.0542 on the tested dataset, respectively. Moreover, the KNN model with correlation coefficient and mean squared error of 0.6111 and 0.1192, respectively, is the worst model among the seven estimators. This model has great accuracy in training phase while it is not accurate in validation and testing phase. Due to this fact, it can be concluded that KNN model suffers from overfitting problem. In addition, the impacts of incubation time, yeast extract, temperature and salinity on bacterial cell concentration are also ascertained using sensitivity analysis. It is discerned that the temperature and yeast extract are the most and least effective factors on growth of microorganism, respectively.

Geomechanical effects monitoring on reservoir rock and fluid properties response during the oil production curve are essential to improve oil recovery in a petroleum field. Incorporating geomechanics to flow models become the mathematical formulation regarding well-test and reservoir engineering more realistic because geomechanical parameters, e.g., in situ and overburden stress, as well as Biot’s coefficient, play a fundamental role in pressure response. Hence, permeability stress-sensitive oil reservoirs are the scope of various research in the petroleum industry for minimizing formation damage during drilling, completion, and stimulation operations. In this context, mechanical formation damage control plays a key role in preventing early-permeability loss that may result in reservoir compaction and oil field disinvestments. This work develops a new analytical solution for the nonlinear hydraulic diffusivity equation (NHDE) with instantaneous point-source/sink effects in permeability effective stress-sensitive oil reservoirs. The proposed model considers Biot’s effective stress change in the permeability response, and a new deviation factor is derived from comparing the nonlinear effect concerning the constant permeability classical solution and a decoupled case available in the literature. The calibration methodology is performed using a numerical simulator named IMEX®, widely used in formation evaluation works, and the results presented high convergence. The findings of this study allowed us to notice the role of overburden stress, oil flow rate, deviation factor, and Biot’s coefficient in permeability change during production in the diagnostic plots. Thereby, the modeling developed in this paper becomes a useful and attractive tool for predicting and monitoring permeability loss, oil flow rate specification, and reservoir history matching.

Different numerical methods have been applied to simulate the proppant transport in petroleum engineering, which can be roughly categorized as the Eulerian-Eulerian and Eulerian-Lagrangian models. Recently, a hybrid Eulerian-Lagrangian (E-L) approach, the multiphase particle-in-cell (MP-PIC) method, has been successfully applied to model large-scale proppant transport problems by introducing the concept of parcels (clusters of particle). In the MP-PIC method, particle-particle interaction force is expressed as the gradient of particle stress. The calculation of this gradient strongly depends on the interpolation between particle properties and Eulerian grids, which could lead to problems such as non-physical particle suspension, particle agglomeration and non-conserved interparticle interactions. In this study, a new method, the volumetric-smoothed particle hydrodynamics (V-SPH) method, is proposed to improve the calculation accuracy of the particle-particle interaction forces in the original MP-PIC method. In the V-SPH method, the calculation of the particle stress gradient no longer depends on the background Eulerian grids and the conservation of the interparticle stress is also guaranteed. In this paper, detailed introduction of the V-SPH based Eulerian-Lagrangian framework is provided. The reliability of the proposed V-SPH method is validated against both the numerical and experimental results in literature. By comparing with the original MP-PIC method, we observe that the non-physical particle agglomeration, as well as non-physical particle suspension problems can be well solved with the proposed new model. In addition, the impact of some key parameters in the V-SPH method on simulation results are also investigated. The choice of the PPP (number of particles per parcel) and the treatment of boundary particle deficiency are found to play important roles in model accuracy and efficiency. The V-SPH method proposed in this work can provide more accurate results than the original MP-PIC method, especially in the regions of dense proppant concentration, with comparable computing efficiency. With proper treatment of boundary deficiencies, it is promising to be used in more complex field-scale proppant transport problems.

In view of the continuous occurrence of coal and gas outbursts (hereafter as ‘outbursts’), and the dynamic behavior and quantitative mechanism of water injection in coal seams preventing outbursts are not still unclear. In the study, the characterization of mechanical action and expansion energy release of gas initial desorption (GID) in coals with different moisture contents is revealed to clarify the influence of moisture on gas dynamic effect in coals. The results show that during the GID of gas-containing coals, the increased moisture content will decrease the pressure and momentum of gas from coals significantly. And the gas pressure reduction rate shows an increasing trend, with the decreasing reduction rate of gas momentum. Therefore, the ability of gas damaging coals with high moisture contents is weakened by reducing the degree of pressure-induced mechanical action on the coal surface and the impact intensity on the cracks in coals. Meanwhile, the gas-released cumulative expansion energy from the coals is significantly reduced, with the decreasing increase rate of the gas energy. Therefrom, the moisture in the coal masses synthetically weakens the dual effects of pressure attribute and expansion effect of gas decreasing the damage ability of gas to coals, which can prevent the further development of outburst preparation process. It is concluded that the correlation between moisture content and the initial expansion energy of released gas is linearly and negatively correlated. For moisture content with the every 1% increase in coal masses of Xuehu Coal Mine, the energy decreases by about 11% on average. Accordingly, the quantitative water injection in coal mining face is carried out to eliminate the local abnormal zone containing gas.