Journal of Petroleum Science and Engineering最新文献

Natural gas hydrate-bearing sediment permeability, which influences the flow behavior of fluids, is a key physical parameter used to determine the exploitation efficiency of hydrate. However, no comprehensive overview of existing research related to its measurement and application development has been conducted to date. In this review, the related advances in sediment permeability are systematically summarized in terms of experiments, models, numerical simulations, and its influence on hydrate exploitation. The sediment permeability measurement and their influencing factors have been comprehensively analyzed. In particular, the effects of hydrate phase transition on sediment permeability are discussed in detail. In addition, the normalized models of sediment permeability and numerical simulations of sediment structure are investigated. However, no universal normalized models of sediment permeability and numerical simulation of hydrate phase transition are available. The mechanism by which sediment permeability magnitude and anisotropy influence the hydrate exploitation efficiency has also been discussed. Finally, future efforts should focus on dynamic evolution, high-precision measurement, multifactor coupling effect, generalization of models, and optimization of numerical simulations, which are beneficial to improve guidance for the commercial exploitation of hydrate.

In this work, the flooding processes of low salinity waterflooding and low salinity polymer flooding (LSWF and LSP) in sandstone reservoirs were mechanistically modelled at nano-and macro-scales. Triple-layer surface complexation models were utilised to simulate interactions at the oil-brine and sandstone-brine interfaces. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was applied to describe the stability of interfacial films in crude oil-brine-sandstone rock systems. The novel application of the maximum energy barrier (MEB), calculated from the interaction potential of the DLVO theory, as an upscaling and interpolant parameter to adjust relative permeability curves as a function of reservoir properties is proposed in this work. Numerical simulations using the commercial simulator CMG-STARS were used in tandem with the surface complexation models and film analysis to evaluate the performance of LSWF and LSP in sandstone reservoirs.

Results of the numerical simulations showed that the LSP gave significantly higher oil recovery compared to standard polymer flooding because of its utilisation of wettability alteration due to LSWF and the improved mobility control due to LSP. A comparison between studied injection processes i.e. low and high salinity waterflooding, and low and high salinity polymer flooding, revealed that oil recovery as a result of wettability alteration is significantly higher than that of mobility control. Further analysis indicated that temperature affects the wettability alteration favourably, and the polymer slug viscosity unfavourably. However, the temperature effect on the wettability was found to be more pronounced. The workflow presented in this study provides valuable guidelines in screening the appropriate sandstone reservoirs for LSWF and LSP applications using the numerical simulation techniques through the upscaling from nano-to-macro-to-field scale.

Horizontal multi-well pads are frequently used in unconventional reservoirs. Along with infill wells and hydraulic fracturing, interference between multiple multi-fractured horizontal wells (MFHWs) has become a major concern. The current rate transient analysis (RTA) makes the assumption that the unconventional formation contains a single MFHW. This study introduces a novel multi-MFHW solution and associated analysis methodology for analyzing the performance of targeted well rates in a multi-MFHW system.

The constant bottom-hole pressure (BHP) condition and the Laplace transform can be used to obtain multi-MFHW solutions for transient flow. We investigated interference between various fractures and MFHWs using the superposition of various constant BHP solutions. The variable BHP of the targeted well is calculated using a variable dimensionless BHP function in the Laplace domain without performing any convolution or deconvolution. The proposed method is rigorously validated using a commercial numerical simulator for cases involving offset MFHWs and multi-MFHW with variable BHP. With this multi-MFHW analysis, we can analyze a target well in the pad using the total material balance of the multi-MFHW system. Offset well interference frequently occurs following the onset of infinite-acting radial flow (IARF) in the target well's hydraulic fracture. It results in an increase in the pressure derivative curves for elliptical flow and IARF, as well as the rate-normalized pressure (RNP) derivative. Inverse semi-log derivatives exhibit the inverse trend. The proposed deviation pressure integral and RNP can be used to diagnose the flow region caused by the offset well's flow rate in a unique manner, displaying the horizontal line, V-shaped dip, and unit slope, respectively, during IARF, cross flow, and boundary-dominated flow (BDF). Sensitivity analysis of well spacing demonstrates that as well spacing increases, the “transition flow” between wells transitions from elliptical to formation linear flow and can exhibit transitional flow characteristics in more common cases.

There are a lot of exploration examples of far-source reservoirs, but the description of the connotation and accumulation mechanism is very rare. The Dongsha Uplift is one of the major oil-producing areas in the eastern Pearl River Mouth Basin in the northern South China Sea. The uplift lacks generally hydrocarbon source rock and is far from the generative kitchen, making it a typical far-source oil and gas reservoir. The accumulation mechanism of crude oil in the reservoirs are still unknown. By systematically comparing biomarkers, nitrogenous compounds and isotopic characteristics of the crude oil and source rocks with those in the neighboring depressions, and combining with fracture, sand body, unconformity migration conduits and barrier conditions, this paper simulates oil and gas migration paths and formation time with Pathway and IES software, and analyzes oil and gas accumulation process from a dynamic perspective. We found that the deep lacustrine hydrocarbon source rocks of the Wenchang Formation in the H26 Sag of the Huizhou Depression reached peak oil production at the end of the Hanjiang Formation deposition. Influenced by the strong tectonic activities at the final deposition of the Hanjiang and Yuehai formations, two episodes of hydrocarbon charging occurred at the top of the Dongsha Uplift. The accumulation of hydrocarbons far from the source rocks in the Dongsha uplift is mainly controlled by the efficient carrier system at hydrocarbon generation period. The oil is mainly accumulated in L4-1 and L11-1 oil fields through the long-distance stepped migration mode. The spatial and temporal relationship between hydrocarbon generation of source rock and episode of fault activity are mainly responsible for accumulation in the far-source reservoirs of the Dongsha Uplift.

Breakthroughs in shale gas exploration in the Upper Ordovician-Lower Silurian strata of the Upper Yangtze Platform have attracted interest in its sedimentary-tectonic evolution, but the tectonic background of the northern margin of the Upper Yangtze Platform remains unclear. In this paper, the Wufeng-Longmaxi formations on the northern margin of the Upper Yangtze Platform were investigated. Based on geochemical and mineralogical analyses of the tuffs/K-bentonites of the Wufeng Formation and the barite in the Longmaxi Formation, as well as previous research results, it was concluded that the northern margin of the Upper Yangtze Platform was in an extensional tectonic background during the Late Ordovician-Early Silurian. Detailed analysis revealed that, (1) the U–Pb zircon age of the tuff in the Bajiaokou section in South Qinling is 443.91 ± 0.92 Ma. The Zr/TiO₂–Nb/Y diagram of the tuffs/K-bentonites indicates that their protoliths were alkaline-subalkaline basalt and andesite series rock. Based on the Th–Hf/3-Ta, Th–Tb*3-Ta*2, and TiO₂–Nb/3-Th diagrams, there are undiscovered intraplate tension calc-alkaline basalts in the northern Yangtze Platform or the southern Qinling region, which provided volcanic clastic materials to the Ziyang, Lan'gao, Chengkou, Yichang and other regions. (2) Scanning electron microscopy revealed that the barite crystals in the Longmaxi Formation exhibit dissolution features and have a large particle size. Energy spectrum analysis of these barite crystals revealed that they have C, O, S, and Ba contents of 8.48 wt%, 22.98 wt%, 13.09 wt% and 55.44 wt%, so they are speculated to have been formed via cold methane seep genesis in a weak extensional tectonic setting. The ⁸⁷Sr/⁸⁶Sr ratios of the barite revealed that different types of barite were simultaneously formed in this area under the influences of hydrothermal and cold methane seeps. (3) The analysis of the heavy minerals in the Lower Silurian strata in the Bajiaokou section revealed that the provenance in the South Qinling area changed significantly during the late Early Silurian. Based on the above analyses, the northern margin of the Upper Yangtze Platform was in an extensional tectonic setting during the Late Ordovician-Early Silurian. The distribution of the total organic carbon content indicated that the extensional tectonic background provided good conditions for the enrichment and preservation of organic matter. The results of this study provide an understanding of the regional sedimentary-tectonic pattern and evolution of the Yangtze Platform during this period, as well as a reference for future shale gas exploration in this region.

Dynamic appraisal in carbonates with excess permeability is critical to successful reservoir modeling and depletion planning. Accurate recognition and characterization of a dual-porosity system may translate to improved project performance. We present a catalog of diagnostic signatures that elevate pressure transient analysis beyond the traditional V shape, to aid in identifying non-matrix features’ presence, extent, and contribution to reservoir performance. We reviewed 152 well tests from the Brazil Pre-Salt, integrated with multi-scale static and dynamic data (conventional core, borehole image logs, seismic, and drilling losses). A recurring set of eight signatures with characteristic slopes and shapes stood out, which we reconciled with geologic concepts and tested with numerical modeling. These signatures reveal key insights into excess-permeability architecture and non-matrix types, from touching vugs to caves, from natural fractures to fault damage zones. They will assist subsurface teams to optimally frame well test objectives and maximize value of information during early appraisal and field development. They will help enhance reservoir performance prediction, by enabling a comprehensive use of well test data in geologic and reservoir simulation models.

Water-based working fluids are widely applied in the development of tight gas formations. However, these fluids’ flowback rate is generally low than 50%, resulting in a large amount of water retention to dramatically decline the gas delivery. Typical tight sandstone core samples are selected in this study to perform the gas-driven water displacement experiment to investigate the underlying mechanisms for the low water flowback behaviors in tight gas reservoirs. Results show that the average water flowback rate for 15 tight sandstone samples by gas-driven water displacement is obtained to be only 31.31%, which in turn causes an average gas permeability damage rate of 58.94%. Analysis suggests that multiscale pore structures, ultra-low connate water saturation phenomenon, filling of hydrophilic clay minerals, and insufficient pressure drop contribute to the congenitally unfavorable geological factors of low water flowback capacity. On the other hand, irreversible formation damages like water phase trapping, salting out issues, and residual water film effect caused by water retention are the main elements that restrict water removal during a gas-flow drying process. The findings of this study provide useful insights into the control mechanisms of low water flowback behaviors and the formation damages induced by water invasion in tight sandstone gas reservoirs.

To achieve high-speed and undisturbed core drilling, the standing wave vibration of the drill string in a sonic drill is excited by a high-frequency inertial vibrator; the resulting high alternating stress cycle in the drill string can easily cause fatigue damage. In order to minimize the fatigue failure of drill-string at the stage of its design, it is necessary to assess the fatigue damage caused by alternating stress to guide engineering practice. In this paper, based on one-dimensional wave theory, we analyse the standing wave vibration in a drill-string excited by a sonic vibrator, and theoretically prove that the dynamic resonant stress of a drill-string is the key factor influencing the fatigue damage. By using the Palmgren–Miner fatigue damage rule, we establish a theoretical formula for the cumulative fatigue damage of a variable-length standing wave vibration drill string and reveal the fatigue damage mechanism of the variable-length resonant drill string. Furthermore, the effects of sonic drill systems and process parameters on the damage are quantified. It was found that by an appropriate choice of a drill-pipe length, the fatigue damage can be reduced whilst the axial stress concentration factor (aSCF) $k_{\sigma }$ on threaded connections can significantly increase it. At the fundamental frequency of the resonant sonic drilling, the maximum fatigue damage point, $x_f$, is located approximately $l_a/2$ above the drill bit, not exceeding the theoretical sonic standing wave starting length, $l_a$, and unrelated to the hole depth. This study promotes the theoretical understanding and exploration of variable-length standing wave oscillators.

Interwell Stratigraphic Correlations Detection (ISCD) guides reservoir modeling and oil development. Many existing AI (artificial intelligence) methods have been proposed for ISCD. However, it is difficult to generate labels for large-scale geological data, which leads to the problem of small samples. In this paper, we propose a few-shot learning-based approach to detect stratigraphic correlations for overcoming this challenge. Specifically, we design a Knowledge Enhanced Few-shot Transformer ISCD model (KEFT-ISCD) to enhance reservoir sample features. We design a dynamically balanced marginal softmax ($dbm\text{-}softmax$) to further optimize the model loss for identifying edge features, which improves the stratigraphic matching effects. In addition, we design a bi-window co-sliding approach to address the cross-matching problem in practical stratigraphic matching. To the best of our knowledge, this is the first work to use few-shot learning for the ISCD. We evaluate the proposed method with different well sections in a pair of adjacent wells from a real-world well logging dataset. Experimental results indicate that the proposed KEFT-ISCD performs well and achieves a detection accuracy of 91.12%. We also conduct experiments on different wells and blocks. The results further demonstrate the generalizability of the proposed approach.

With the advantages of high separation efficiency and less footprint, the inline gas-liquid cyclone separator has gained wide attention in the fields of petroleum, chemical industry, nuclear energy and aerospace. However, single-stage gas-liquid cyclone separator usually cannot accommodate a large range of inlet gas volume fractions. For gas-liquid cyclone separator operating in series with the same structure, it is difficult to operate the second stage efficiently. Therefore, a new two-stage inline gas-liquid cyclone separator is designed in this study considering the bubble size and the variation of inlet gas volume fraction. It integrates the advantages of horizontal and vertical inline gas-liquid cyclone separator, so as to meet the separation requirement for both gas and liquid. The tangential velocity, gas volume fraction and pressure distribution inside the separator are studied by numerical simulation using Computational Fluid Dynamics. The experimental results show that the optimal standardized flow split is about 1.0. When the inlet gas volume fraction varies from 10% to 90%, the degassing efficiency gradually increased with a maximum value of 8.88%. Meanwhile, the dehydration efficiency gradually decreases, with a maximum value of 4.24%. In addition, the maximum pressure drop of the two-stage inline gas-liquid cyclone separator is only 140 kPa during the process of experimental test. This research can provide efficient solution to the working condition with wide range of inlet gas volume fraction and to meet the requirement of high compactness as well.