Petroleum Science最新文献

In-situ conversion presents a promising technique for exploiting continental oil shale formations, characterized by highly fractured organic-rich rock. A 3D in-situ conversion model, which incorporates a discrete fracture network, is developed using a self-developed thermal-flow-chemical (TFC) simulator. Analysis of the model elucidates the in-situ conversion process in three stages and defines the transformation of fluids into three distinct outcomes according to their end stages. The findings indicate that kerogen decomposition increases fluid pressure, activating fractures and subsequently enhancing permeability. A comprehensive analysis of activated fracture permeability and heating power reveals four distinct production modes, highlighting that increasing heating power correlates with higher cumulative fluid production. Activated fractures, with heightened permeability, facilitate the mobility of heavy oil toward production wells but hinder its cracking, thereby limiting light hydrocarbon production. Additionally, energy efficiency research demonstrates the feasibility of the in-situ conversion in terms of energy utilization, especially when considering the surplus energy from high-fluctuation energy sources such as wind and solar power to provide heating.

Finite-difference (FD) method is the most extensively employed numerical modeling technique. Nevertheless, when using the FD method to simulate the seismic wave propagation, the large spatial or temporal sampling interval can lead to dispersion errors and numerical instability. In the FD scheme, the key factor in determining both dispersion errors and stability is the selection of the FD weights. Thus, How to obtain appropriate FD weights to guarantee a stable numerical modeling process with minimum dispersion error is critical. The FD weights computation strategies can be classified into three types based on different computational ideologies, window function strategy, optimization strategy, and Taylor expansion strategy. In this paper, we provide a comprehensive overview of these three strategies by presenting their fundamental theories. We conduct a set of comparative analyses of their strengths and weaknesses through various analysis tests and numerical modelings. According to these comparisons, we provide two potential research directions of this field: Firstly, the development of a computational strategy for FD weights that enhances stability; Secondly, obtaining FD weights that exhibit a wide bandwidth while minimizing dispersion errors.

Currently, deep drilling operates under extreme conditions of high temperature and high pressure, demanding more from subterranean power motors. The all-metal positive displacement motor, known for its robust performance, is a critical choice for such drilling. The dimensions of the PDM are crucial for its performance output. To enhance this, optimization of the motor's profile using a genetic algorithm has been undertaken. The design process begins with the computation of the initial stator and rotor curves based on the equations for a screw cycloid. These curves are then refined using the least squares method for a precise fit. Following this, the PDM's mathematical model is optimized, and motor friction is assessed. The genetic algorithm process involves encoding variations and managing crossovers to optimize objective functions, including the isometric radius coefficient, eccentricity distance parameter, overflow area, and maximum slip speed. This optimization yields the ideal profile parameters that enhance the motor's output. Comparative analyses of the initial and optimized output characteristics were conducted, focusing on the effects of the isometric radius coefficient and overflow area on the motor's performance. Results indicate that the optimized motor's overflow area increased by 6.9%, while its rotational speed reduced by 6.58%. The torque, as tested by Infocus, saw substantial improvements of 38.8%. This optimization provides a theoretical foundation for improving the output characteristics of all-metal PDMs and supports the ongoing development and research of PDM technology.

The loss of hydrocarbon production caused by the dynamic behavior of the inner boundary and propped fractures under long-term production conditions has been widely reported in recent studies. However, the quantitative relationships for the variations of the inner boundary and propped fractures have not been determined and incorporated in the semi-analytical models for the pressure and rate transient analysis. This work focuses on describing the variations of the inner boundary and propped fractures and capturing the typical characteristics from the pressure transient curves.

A generalized semi-analytical model was developed to characterize the dynamic behavior of the inner boundary and propped fractures under long-term production conditions. The pressure-dependent length shrinkage coefficients, which quantify the length changes of the inner zone and propped fractures, are modified and incorporated into this multi-zone semi-analytical model. With simultaneous numerical iterations and numerical inversions in Laplace and real-time space, the transient solutions to pressure and rate behavior are determined in just a few seconds. The dynamic behavior of the inner boundary and propped fractures on transient pressure curves is divided into five periods: fracture bilinear flow (FR1), dynamic PFs flow (FR2), inner-area linear flow (FR3), dynamic inner boundary flow (FR4), and outer-area dominated linear flow (FR5). The early hump during FR2 period and a positive upward shift during FR4 period are captured on the log-log pressure transient curves, reflecting the dynamic behavior of the inner boundary and propped fractures during the long-term production period.

The transient pressure behavior will exhibit greater positive upward trend and the flow rate will be lower with the shrinkage of the inner boundary. The pressure derivative curve will be upward earlier as the inner boundary shrinks more rapidly. The lower permeability caused by the closure of un-propped fractures in the inner zone results in greater upward in pressure derivative curves. If the permeability loss for the dynamic behavior of the inner boundary caused by the closure of un-propped fractures is neglected, the flow rate will be overestimated in the later production period.

Understanding the acoustic characteristics of hydrates in various sediments is crucial for hydrate resource detection and safe and efficient exploitation, as hydrate occurrence patterns vary greatly in different sediments. In this work, sediments with different bentonite contents, water saturations, and types were prepared to investigate the characteristics of P-wave velocity (reflecting the magnitude of hydrate saturation in the sediment) and amplitude (reflecting the degree of hydrate-sediment cementation) during hydrate formation and depressurization. During hydrate formation, the P-wave velocity and amplitude have similar trends. As clay content increases, the P-wave velocity increase rates quickened. On the other hand, the increased rate of P-wave velocity slows down with the increase of water saturation in the clay-bearing sediments. Comparing various types of sediment shows that the water absorption and swelling of bentonite reduce the pore space, speeding up the cementation of the hydrate with the sediment and increasing P-wave velocity at a faster rate. Correspondence between P-wave velocity and hydrate saturation is strongly related to sediment type, clay content, and water saturation. The rapidly decreasing amplitude in the early stage of hydrate depressurization indicates that hydrate in clay-bearing sediments is weakly cemented to the sediments, which is prone to stratigraphic instability. The findings of this study offer guidance for hydrate resource assessments in clay-bearing sediments as well as geologic risk estimations during hydrate mining.

Erosion wear is a common failure mode in the oil and gas industry. In the hydraulic fracturing, the fracturing pipes are not only in high-pressure working environment, but also suffer from the impact of the high-speed solid particles in the fracturing fluid. Beneath such complex conditions, the vulnerable components of the pipe system are prone to perforation or even burst accidents, which has become one of the most serious risks at the fracturing site. Unfortunately, it is not yet fully understood the erosion mechanism of pipe steel for hydraulic fracturing. Therefore, this article provides a detailed analysis of the erosion behavior of fracturing pipes under complex working conditions based on experiments and numerical simulations. Firstly, we conducted erosion experiments on AISI 4135 steel for fracturing pipes to investigate the erosion characteristics of the material. The effects of impact angle, flow velocity and applied stress on erosion wear were comprehensively considered. Then a particle impact dynamic model of erosion wear was developed based on the experimental parameters, and the evolution process of particle erosion under different impact angles, impact velocities and applied stress was analyzed. By combining the erosion characteristics, the micro-structure of the eroded area, and the micro-mechanics of erosion damage, the erosion mechanism of pipe steel under fracturing conditions was studied in detail for the first time. Under high-pressure operating conditions, it was demonstrated through experiments and numerical simulations that the size of the micro-defects in the eroded area increased as the applied stress increased, resulting in more severe erosion wear of fracturing pipes.

In the application of polymer gels to profile control and water shutoff, the gelation time will directly determine whether the gel can “go further” in the formation, but the most of the methods for delaying gel gelation time are complicated or have low responsiveness. There is an urgent need for an effective method for delaying gel gelation time with intelligent response. Inspired by the slow-release effect of drug capsules, this paper uses the self-assembly effect of gas-phase hydrophobic SiO₂ in aqueous solution as a capsule to prepare an intelligent responsive self-assembled micro-nanocapsules. The capsule slowly releases the cross-linking agent under the stimulation of external conditions such as temperature and pH value, thus delaying gel gelation time. When the pH value is 2 and the concentration of gas-phase hydrophobic SiO₂ particles is 10%, the gelation time of the capsule gel system at 30, 60, 90, and 120 °C is 12.5, 13.2, 15.2, and 21.1 times longer than that of the gel system without containing capsule, respectively. Compared with other methods, the yield stress of the gel without containing capsules was 78 Pa, and the yield stress after the addition of capsules was 322 Pa. The intelligent responsive self-assembled micro-nanocapsules prepared by gas-phase hydrophobic silica nanoparticles can not only delay the gel gelation time, but also increase the gel strength. The slow release of cross-linking agent from capsule provides an effective method for prolongating the gelation time of polymer gels.

Low-permeability reservoirs are generally characterized by low porosity and low permeability. Obtaining high production using the traditional method is technologically challenging because it yields a low reservoir recovery factor. In recent years, hydraulic fracturing technology is widely applied for efficiently exploiting and developing low-permeability reservoirs using a low-viscosity fluid as a fracturing fluid. However, the transportation of the proppant is inefficient in the low-viscosity fluid, and the proppant has a low piling-up height in fracture channels. These key challenges restrict the fluid (natural gas or oil) flow in fracture channels and their functional flow areas, reducing the profits of hydrocarbon exploitation. This study aimed to explore and develop a novel dandelion-bionic proppant by modifying the surface of the proppant and the fiber. Its structure was similar to that of dandelion seeds, and it had high transport and stacking efficiency in low-viscosity liquids compared with the traditional proppant.

Moreover, the transportation efficiency of this newly developed proppant was investigated experimentally using six different types of fracture models (tortuous fracture model, rough fracture model, narrow fracture model, complex fracture model, large-scale single fracture model, and small-scale single fracture model). Experimental results indicated that, compared with the traditional proppant, the transportation efficiency and the packing area of the dandelion-based bionic proppant significantly improved in tap water or low-viscosity fluid. Compared with the traditional proppant, the dandelion-based bionic proppant had 0.1–4 times longer transportation length, 0.3–5 times higher piling-up height, and 2–10 times larger placement area. The newly developed proppant also had some other extraordinary features. The tortuosity of the fracture did not influence the transportation of the novel proppant. This proppant could easily enter the branch fracture and narrow fracture with a high packing area in rough surface fractures. Based on the aforementioned characteristics, this novel proppant technique could improve the proppant transportation efficiency in the low-viscosity fracturing fluid and increase the ability of the proppant to enter the secondary fracture. This study might provide a new solution for effectively exploiting low-permeability hydrocarbon reservoirs.

The umbilical cable is a vital component of subsea production systems that provide power, chemical agents, control signals et al., and its requirement for reliability is exceedingly high. However, as the umbilical cable is a composite structure comprising multiple functional units, the reliability analysis of such cables involves numerous parameters that can impact calculation efficiency. In this paper, the reliability analysis of a new kind of umbilical cable with carbon fiber rod under tension is analyzed. The global dynamic analytical model is first established to determine the maximum tension load, then the local analytical model of umbilical cable including each unit are constructed by finite element method (FEM). Based on the mechanical analytical model, the reliability of umbilical cable under tension load is studied using response surface method (RSM) and Monte Carlo method. During the calculation process, a new tangent plane sampling method to calculate the response surface function (RSF) is proposed in this paper, which could make sampling points faster come close to the RSF curve, and it is proved that the calculation efficiency increases about 33% comparing with traditional method.