Journal of Petroleum Science and Engineering最新文献

The advancement of downhole sensor technology in the past twenty years has led to the discovery of the phenomenon of high frequency torsional oscillations (HFTOs), which has received increasing attention in the well construction industry in recent years. HFTOs are attributed to self-excited torsional resonance, often encountered while drilling harder rock formations, and are observed to be localized in the lower bottom-hole assembly (BHA) or lower part of the drillstring only. Downhole tangential acceleration and its frequency spectrum are usually used to identify the occurrence of HFTOs, which are believed to be responsible for downhole tool failures such as electronic component failure, cracks on drill collars in the BHA, and loose connections. Various insights into the HFTO mechanism have been gained in the literature through field experiments and observations, data analysis, numerical simulation, and laboratory tests.

In this paper, a comprehensive review is presented on recent advancements in understanding HFTOs, with discussion of their typical propagation patterns, dynamic models describing their behavior, laboratory tests investigating their characteristics, field data indicating their presence, and their harmful consequences during drilling operations. On this basis, we discuss several remaining issues to better understand, detect, and attenuate/eliminate HFTOs.

Although the state of occurrence and characteristics of shale oil form the basis for studying the mobility of shale oil, studies on the state of occurrence and characteristics of shale oil, as well as factors affecting its mobility, are presently lacking. Molecular dynamics simulation is a very effective method for studying the state of occurrence of shale oil and the factors affecting its mobility. We used molecular dynamics (MD) simulation to study the adsorption behavior and distribution of shale oil within a nanoscale slit medium. Results show that fluid density is not uniform throughout the slit and that its oscillation from the solid wall surface to the central plane is attenuated, indicating distinct adsorbed layers and bulk-phase fluid. We studied the effects of slit aperture, temperature, pressure, oil composition, and slit medium on the volumes and densities of the adsorbed layers. We found that (a) there were multiple adsorbed layers of liquid hydrocarbons, (b) the number of adsorbed layers depended largely on the slit medium, slit size, and oil composition, (c) the adsorption propensity of heavier hydrocarbons were more pronounced, and (d) the adsorption capacity of the slit medium differed for different types of hydrocarbon molecules.

Pressure pulse telemetry as a novel and effective method of communication has received more and more attention in the field of separate layer water injection for the intelligent oilfield, and identification of the effective pulses and their positions is one of the key technologies. For the logging while drilling process, the fixed threshold method is widely used to identify the pressure pulse. However, in the process of water injection, the amplitude of pressure pulse changes with the change of flowrate controlled by process, which will lead to low recognition rate of traditional fixed threshold pressure pulse. Therefore, a pressure pulse recognition method based on flow-adaptive double threshold with fixed time window is proposed. The packet length of instructions and responses is designed to be short and fixed in order to reduce communication time and failure cost, and the fixed time window method is adopted to improve the decoding efficiency of for a frame of data. The pressure pulse recognition method based on flow-adaptive double threshold is used to identify the effective pulses and their positions to adapt to the change of pressure pulse amplitude induced by different flowrates. The first threshold which is set to fixed and lower than the pulse peak with minimum possible flowrate, is used to filter the most of noise and catch the effective pulses with little noise pulses. The second threshold which is adaptive to changes of the flowrates, is determined by average of three maximum peaks of caught pulses from the first threshold, and is used to identify the effective pulses and their positions. In the experimental well with 2000 m deep, the test results show that the error rate of pulse recognition reduce to 0.003% and communication success rate significantly increase from 50% to more than 96.5%. It means that the proposed double threshold method can be adaptive to identify effective pressure pulse under different flowrates, and then can significantly reduce the error rate of pulse recognition and improve two-way communication performance between the wellhead controller and downhole distributors.

Parameters optimization during fracturing to form fracture networks is important to improve the permeability of reservoirs. In this paper, fracture growth in natural coal-rock blocks under different stresses with different fracturing medium and injection rates was studied, and the injection pressure evolution and acoustic emission dynamic response were further analyzed. The results indicate that the stress state, fracturing medium and injection flow rate significantly affected the fracture propagation behavior. When the stress difference was greater than or equal to 7 MPa ($\Delta \sigma \ge 7\text{MPa}$), the fracture could penetrate the coal-rock interface. In the same stress state (${\sigma }_v=12MPa,{\sigma }_H=8MPa,{\sigma }_v=5MPa$), the fracture geometry and injection pressure evolution significantly differed when using different fracturing media (SC–CO₂ and H₂O). When supercritical CO₂ (SC–CO₂) was used as the fracturing medium, secondary fractures were created with small residual fracture widths. When H₂O fracturing was adopted, single and straight fractures were obtained with a large residual fracture width, penetrating the coal-rock interface straightly. There existed significant differences in the critical stress difference, injection pressure evolution and the acoustic emission dynamic response between natural and artificial coal-rock block fracture during interface penetration. The results could provide important references for fracturing parameter optimization in the efficient exploitation of coalbed methane.

The Permian Taiyuan Formation contains alternate shale and coal lithologies which are vital for the exploration of shale gas reservoirs. However, previous studies have neglected the influence of paleosedimentary environment on the formation and distribution of marine-continental shale. A better understanding of the evolution characteristics of the paleosedimentary environment of the marine-continental strata is particularly critical to the accurate prediction of high-quality shale reservoirs. In this study, the geochemical and mineralogical characteristics of Taiyuan Formation, marine-continental strata in the Southern North China Basin, were carried out using lithology identification, element analysis, and X-ray diffraction analysis. These interpretations were helpful to develop a sedimentary depositional model by principles of sedimentology and sequence stratigraphy. The evolution of the paleosedimentary environment and the control of the paleosedimentary environment on the organic matter abundance, mineral composition, lithofacies, and gas enrichment of shale were analyzed. The results show that the vertical variation of the paleosedimentary environment had obvious stages during the Taiyuan Stage of the Early Permian. Based on sequence identification and division, a multi-stage superimposed marine-continental sedimentary model of transgressive and regressive assemblages was established. From tidal flat facies to lagoon facies and then to restricted platform facies, the contents of felsic and clay minerals decreased, while the contents of TOC and carbonate minerals increased sequentially. The lithofacies types of limited platform shale and tidal flat shale were different and relatively single, while the lagoon contained the shale lithofacies types of the above two sedimentary microfacies due to its sedimentary microfacies development location. The lagoon facies shale of highstand system tract had high-quality paleo-productivity, and was distributed in a stretch on the plane and superimposed in multiple stages vertically of the basin, which could be selected as a favorable facies belt of marine-continental facies shale gas.

Based on recovered core observations and thin section identifications combined with scanning electron microscopy images and statistics for physical properties, XRD analysis, and data for trace elements and carbon and oxygen isotopes, the genesis of under-compacted sandstone in the Lower Ganchaigou Formation of the Paleogene in the Lenghu VII structure in the northern Qaidam Basin has been confirmed through a detailed comparison with normal intervals for petrology, sedimentary environments and diagenetic characteristics. The results showed that under-compacted sandstone, developing in underwater distributary channels, was characterized by abnormal high porosity and large amount of intergranular pores. The genesis of intergranular pores is the intrusion of organic acid fluids, dissolution of calcite cements and restoration of primary pores. Conclusions could be drawn from the comprehensive comparison with normal interval. First, honeycomb-like chlorite grain coatings were much abundant (33%–58% in total clays) in the under-compacted sandstone comparing to it in normal interval and sandstone in adjacent area (<30%), indicating an intrusion of Mg-rich fluid leading to transformation from I/S to chlorite. Second, the carbonate cements content of the under-compacted sandstone (5.7%–17.3%) and the normal range (4.1%–20.3%) were both dominated by micrite calcite, and large amounts of early calcite residues resulting from dissolution were only found in the under-compacted sandstone. The δ¹⁸O value (17.36‰ ∼ −10.54‰) and the δ¹³C values (−5.12 to −3.51‰) indicated inorganic carbon dominated in carbonate cements; however, the small negative bias for δ13C in the under-compacted sandstone indicated that more organic carbon was contained than is typical. Third, the minor changes in the V/Zr, Ni/Zr, Co/Zr, Sr/Zr and Mo/Zr values suggested similar and stable paleoenvironments in both intervals. The weaker correlations among U/Zr, Ni/Zr and V/Zr indicated that U/Zr was affected by both the environment and fluid intrusion in the under-compacted sandstone. However, U/Zr was much larger (3.6–23.9) in the under-compacted sandstone than it is in normal sandstones (0.83–3.69), which indicated the invasion of acidic fluids originating from source rock.

Crucial components of the exploration and exploitation of deep-sea oil and gas resources include the identification of pre-disaster emergency resource storage locations and the appropriate scheduling of emergency resources. Frequently, integer linear programming or integer nonlinear programming is used to investigate them. Both techniques may result in optimization, but it is difficult to determine the global optimal solution. Consequently, this study presents a two-stage optimization model of emergency resource storage location-scheduling that not only surpasses the limitations of independent research but also applies an intelligent optimization algorithm to discover the global optimal solution. In the first phase of the model, the objective of optimization is to decrease the emergency response time. Uncertainty and unpredictability are incorporated as marine environmental components in the goal function. Using the analytic hierarchy method, the effect of resource storage and location is evaluated, and the genetic algorithm (GA) and immune algorithm (IA) are used to determine the goal model's optimal solution. The objective of the second stage is to optimize resource scheduling satisfaction, and the resource storage locations determined in the first stage are assigned using a fuzzy trigonometric function formula and mathematical programming algorithm. The two-stage optimization methodology is shown using the deep-sea fire explosion incidence as an example. The results suggest that the transit time of resources from the resource storage site selection points to the operation points calculated by GA is 50% less than that obtained by IA, and the 4 time of IA is at least 5 times that of GA. The overall resource scheduling time is lowered by 41.1% compared to conventional shore-based terminals, the economic cost of an accident is minimized, and the life safety of on-site operators is improved. Throughout 1000 different seasons, the objective ideal value and average value of GA and IA are compared. GA has a slower convergence rate than IA, but its convergence quality is much higher. The quantity of emergency supplies given by each resource storage site may meet the resource need of the operational point. We believe that the model proposed in this study can guarantee the accuracy of prediction results in situations of small sample sizes, and its validity and applicability have been validated.

Hydraulic fracturing using water-based fracturing fluids is widely used in coalbed methane (CBM) reservoir development. However, the stimulation efficiency of conventional hydraulic fracturing in CBM reservoir is low. Liquid nitrogen (LN2) cryogenic fracturing is one possible method to improve the stimulation efficiency. To test the feasibility of the LN2 cryogenic fracturing, laboratory fracturing tests were conducted to investigate the performances of different LN2 cryogenic fracturing methods in this paper. The breakdown pressure and fracture morphology of water fracturing, LN2 direct fracturing, LN2 freeze fracturing, LN2 freeze-thaw fracturing and LN2 compound fracturing were compared. And the mechanisms of different cryogenic fracturing techniques are revealed. The results demonstrate that thermal damage caused by LN2 freezing is the main reason for the complicated fracture pattern in cryogenic fracturing. LN2 freeze-thaw fracturing has the lowest breakdown pressure and can create the most complex fractures among these cryogenic fracturing methods due to the huge thermal damage. LN2 freeze fracturing has the highest breakdown pressure. Because the thermal damage cracks and natural fractures in frozen rock are in freezing shrinkage, which activation are difficult. LN2 compound fracturing is the most potential technologies, which can produce more complex fracture networks than water fracturing and LN2 fracturing.

Pore-scale forces have significant effects on the macroscopic behavior of multi-phase flow through porous media. We develop a robust and accurate accelerated process-based method for the computation of relative permeability from direct simulations of pore-scale two-phase flow on micro-computed tomography images. In the pressure drop calculation, we take advantage of an existing analysis that establishes a relationship between pore-scale forces and Darcy-scale pressure drops using an energy-conservation approach. We establish a thermodynamically consistent approximation of Darcy-scale viscous pressure drops as the rate of energy dissipation per unit flow rate of each flowing phase for the first time within the context of a free-energy lattice Boltzmann method (LBM). In addition, we propose and test a new computationally efficient partial-mirror periodic boundary condition for a fully coupled visco-capillary pore-scale flow simulator based on a free-energy LBM. The new boundary condition is imposed only in the main flow direction and significantly reduces the computational cost of the process-based relative-permeability computation protocol at a small compromise on accuracy.

We first compute primary-drainage and subsequent imbibition relative permeability curves for a reservoir sandstone rock sample. We use this real-reservoir dataset to validate the pressure drop computation method and the partial-mirror periodic boundary condition. We then simulate the entire drainage and imbibition cycle using an extensively studied Berea sandstone dataset. We quantitatively demonstrate that pore-scale direct numerical simulation-based relative permeability curves computed with our novel process-based method agree well with experimental steady-state relative permeability measurements. We also quantitatively demonstrate that the new partial-mirror periodic boundary condition accelerates the relative permeability computations 4 to 13 times.

By the expansion of production from source-related unconventional petroleum resources, accurate approximation of Total Organic Carbon (TOC) through well logs has become progressively important. Accordingly, recent studies have mainly focused on increasing the precision of TOC estimation by using different types of AI techniques and/or optimizing algorithms. Along with utilizing these approaches, this study emphasized on removing an unaddressed source of error inherited from lithological heterogeneity with the same goal. Like organic matter quantity, lithological variations within a source interval also induce well log responses, which may interfere with the training process of Artificial Intelligence (AI) techniques. In the present research, the effect of lithological variations on the performance of TOC estimators was evaluated by employing Adaptive Neuro Fuzzy Inference System (ANFIS) and Multilayer Perceptron network (MLP). Firstly, ANFIS and MLP models were constructed and trained using a database containing different lithologies (original models). Then, a new methodology was developed based on modeling the relationship between log data and TOC values for each type of lithology (litho-based method). The result showed that the litho-based method estimates more reliable and accurate TOC values, proving the adverse effect of lithological variations on the original models. Furthermore, the litho-based ANFIS models provide the most promising results. Since metaheuristic algorithms are usually employed to optimize AI techniques, Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) were also implemented into the original models (hybrid models). Accuracy of TOC values estimated by the hybrid models is slightly higher than those derived from the original models. However, these hybrid approaches are not as efficient as the litho-based method. Applicability of the proposed approach was guaranteed by performing it over Pabdeh source rocks in a well of SW Iran. Based on its high efficiency, the newly developed litho-based method can be used as a powerful tool to reliably evaluate unconventional hydrocarbon resources, as well as the potential of the conventional petroleum sources. Moreover, it can be utilized, instead of/along with traditional optimization approaches, to approximate other geochemical factors as well as petrophysical parameters from log data.