考虑爆燃气体滤失和多裂缝的复合射孔裂缝扩展动态模拟

裂缝几何尺寸参数的准确预测是复合射孔优化设计和增产增注效果评价的前提条件,在复合射孔实施过程中,爆燃气体滤失和多裂缝会对裂缝扩展形态产生影响。在分析中外爆燃气体驱动裂缝扩展数学模型的基础上,结合流体力学、弹性力学和线弹性断裂力学理论,建立了全面考虑爆燃气体滤失和多裂缝的复合射孔裂缝扩展数学模型,通过假设与多个变量相关的裂缝内爆燃气体压力分布函数,利用迭代法实现了模型的数值耦合求解,获得了裂缝几何尺寸随时间的动态变化规律。实例计算结果表明:地层渗透率和裂缝条数对复合射孔裂缝扩展形态影响很大,缝长随地层渗透率和裂缝条数的增加而减小;不考虑爆燃气体滤失和多裂缝导致计算得到的缝长偏大,且相对误差随地层渗透率和裂缝条数的增大而增大。

地层参数对爆燃气体压裂裂缝扩展形态影响分析

在对油井储层实施爆燃气体压裂过程中,地层参数会对裂缝扩展形态产生影响。建立爆燃气体在裂缝内的流动方程,通过设定与时间相关的气体压力分布函数,实现了爆燃气体沿裂缝压力梯度的求解。应用线弹性断裂力学、弹性力学理论模拟在爆燃气体驱动下裂缝的张开与闭合,得到了裂缝尖端应力强度因子、裂缝扩展速度及裂缝几何形态与气体载荷及地层特性之间的关系方程。模型分析结果表明:在离散时间域内,在特定气体压力作用下,裂缝起裂后,首先迅速以稳定速度传播,后期速度逐渐衰减,且在裂缝扩展过程中显示出相应的动态效果;与裂缝断裂韧性相比,地应力对裂缝形态影响更为明显,是裂缝扩展的主要阻力,地应力越大,裂缝起裂越晚,且裂缝传播速度越小;高弹性模量的岩层有利于裂缝的延伸,可以获得更长的裂缝长度,有利于压裂效果的改善。

射孔水平井爆燃气体压裂裂缝起裂研究

爆燃气体压裂技术可实现水平井的经济高效开采,压裂过程中水平井方位、射孔相位与裂缝起裂密切相关,影响施工成败和压裂效果。应用叠加原理将作用于油水井壁裂缝的复杂载荷分解为单个简单载荷,根据弹性力学、线弹性断裂力学理论,基于两孔相交应力集中的力学模型推导了射孔完井方式水平井井壁处的应力场,得到了爆燃气体压裂井壁岩层动态起裂条件,通过设定与时间相关的井筒推进剂燃烧气体压力脉冲函数,可以实现水平井方位角与射孔相位角及裂缝起裂压力、起裂角及起裂时间关系的迭代求解。算例分析表明,与裸眼井相比,射孔完井裂缝的起裂压力和起裂角受水平井方位角和射孔相位角双重制约,射孔可有效降低爆燃气体压裂水平井起裂压力,不同的水平井方位角对应于不同的最优射孔相位角使起裂压力最低。

复合射孔器爆燃气体压力计算模型

为获得适合工程应用的爆燃气体压力计算方法,并分析装药燃烧形式以及爆燃气体压力变化过程,对复合射孔器爆燃气体压力计算模型进行了研究。基于装药燃烧满足几何燃烧定律,燃气体特性参数均匀分布,注水区和岩石区在爆燃气体作用下分别发生弹性压缩和塑性压缩等假设,考虑装药燃烧、射孔扩展过程、注水区运动和压缩过程等因素对爆燃气体压力的影响,推导出了计算模型微分方程组。算例分析表明:该模型能正确反映爆燃气体压力的基本特性,并具有操作性强、能够反映压力变化过程等特点。

多级脉冲气体加载压裂技术

多级脉冲气体松弛岩层地应力、压裂地层的过程中，裂缝内爆燃气体压力分布影响裂缝起裂扩展。应用叠加原理将作用于油水井壁裂缝的复杂载荷分解为单个简单载荷，通过设定与时间相关的气体压力分布函数，根据弹性力学、线弹性．断裂力学理论推导油水井射孔后高地应力约束条件下裂缝尖端应力强度因子，得到了爆燃气体压裂井壁岩层起裂扩展条件，该条件可以反映裂缝内随时间变化的气体压力梯度对裂缝形态的影响。算例分析和现场对比试验结果表明，多级脉冲气体加载压裂与单级高能气体压裂相比，起裂压力升高，止裂压力降低，对地层作用时间显著延长，得到的岩层裂缝长度是后者的。2～3倍，与水力压裂联作可显著降低地层破裂压力，进一步提高和改善地层渗透性。

Explosion limits for combustible gases

Combustible gases in coal mines are composed of methane, hydrogen, some multi-carbon alkane gases and other gases. Based on a numerical calculation, the explosion limits of combustible gases were studied, showing that these limits are related to the concentrations of different components in the mixture. With an increase of C4H10 and C6H14, the Lower ExplosionLimit （LEL） and Upper Explosion-Limit （UEL） of a combustible gas mixture will decrease clearly. For every 0.1% increase in C4H10 and C6H14, the LEL decreases by about 0.19% and the UEL by about 0.3%. The results also prove that, by increasing the amount of H2, the UEL of a combustible gas mixture will increase considerably. If the level of HE increases by 0.1%, the UEL will increase by about 0.3%. However, H2 has only a small effect on the LEL of the combustible gas mixture. Our study provides a theoretical foundation for judging the explosion risk of an explosive gas mixture in mines.

Numerical simulation for explosion wave propagation of combustible mixture gas

A two-dimensional multi-material code was indigenously developed to investigate the effects of duct boundary conditions and ignition positions on the propagation law of explosion wave for hydrogen and methane-based combustible mixture gas. In the code,Young's technique was employed to track the interface between the explosion products and air,and combustible function model was adopted to simulate ignition process. The code was employed to study explosion flow field inside and outside the duct and to obtain peak pressures in different boundary conditions and ignition positions. Numerical results suggest that during the propagation in a duct,for point initiation,the curvature of spherical wave front gradually decreases and evolves into plane wave. Due to the multiple reflections on the duct wall,multi-peak values appear on pressure-time curve,and peak pressure strongly relies on the duct boundary conditions and ignition position. When explosive wave reaches the exit of the duct,explosion products expand outward and forms shock wave in air. Multiple rarefaction waves also occur and propagate upstream along the duct to decrease the pressure in the duct. The results are in agreement with one-dimensional isentropic gas flow theory of the explosion products,and indicate that the ignition model and multi-material interface treatment method are feasible.

Dynamic response of fixed-roof oil-storage tank structure under blast loading

In order to investigate the damage and deformation mechanism of large scale steel fixed-roof oil-storage tanks under the combustible gas explosion, a series of explosion experiments of scaled models are conducted. The l： 25 scaled numerical models of oil-storage tanks with a capacity of 5 000 m3 are also set up by ANSYS/LS-DYNA software, and their damage processes under the blast impact are numerically simulated. Both the experimental results and the numerical simulations show that the blast loading curve displays a pressure jump instantaneously at the moment of contact with the experimental models, and the overpressure peaks at the stagnation area of the outer surface on the blast side. The yield range first appears at the stagnation area and then propagates to the neighboring parts, and the irregular plastic hinge circle obviously appears around the deformation area, which results in the concaved buckling of the tank inner surface. During the whole process, the inner liquid not only impacts on the structures, but also absorbs and consumes part of the blast energy.

Gas concentration monitoring system for small and medium-sized coal mines based on gas-sensing detection and single-chip control

This paper is aimed at the actual conditions of disaster caused by gas in small and medium-sized coal mines. A new gas concentration monitoring system for coal mines is developed on the basis of gas-sensing detection and single-chip control. The monitoring system uses the tin oxide as the main material of N-type semiconductor gas sensors, be- cause it has good sensitive characteristics for the flammable and explosive gas （ such as methane, carbon monoxide）. The QM-N5-semiconductor gas sensor is adopted to detect the output values of the resistance under the different gas con- centrations. The system, designedly, takes the AT89C51 digital chip as the core of the circuit processing hardware structure to analyze and judge the input values of the resistance, and then achieve the control and alarm for going beyond the limit of gas concentration. The gas concentration monitoring system has man）, advantages including simple in struc- ture, fast response time, stable performance and low cost. Thus, it can be widely used to monitor gas concentration and provide early wamings in small and medium-sized coal mines.

Flammability and Explosion Property of Gases in the One-Step Process of Propane Oxidation to Acrylic Acid

Abstract： In order to study the flammability and explosion property of gases during the propane oxidation to acrylic acid process, the explosion limits and the safety oxygen content of gases at the recycle gas compressor outlet, the reactor inlet, and the reactor outlet were theoretically calculated and experimentally tested. Finally, the inert limit was also determined. It showed that gases at the recycle gas compressor outlet and the reactor outlet were nonflammable based on three indicators： the explosion limits, the safety oxygen content and the inert limit. The C3H6 and O2 contents were higher at the reactor inlet, which made the mixed gases easily ignitable. However, the large amount of inert gases suppressed the possibility of explo- sion effectively. As a consequence, no explosion phenomenon would happen in all three locations. But gases at the reactor inlet are most dangerous, where more supervision on the concentration of gases and more strict control on the temperature and pressure should be implemented. Besides this, open flame, hot surfaces and other sources of ignition are prohibited in working spaces. The experimental results can be applied to similar process for oxidation of propane.

TRANSITION FROM A DEFLAGRATION TO A DETONATION IN GAS DYNAMIC COMBUSTION

The transition from a deflagration to a detonation (DDT) in gas dynamics is investigated through the process of a deflagration with a imite width flame overtaken by a shock. The problem is formulated as a free boundary value problem in an angular domain with a strong detonation and a reflected shock as boundaries. The main difficulty lies in the fact that the strength of reflected shock is zero at the vertex where the shock speed degenerates to be the same as the characteristic speed. The conclusion is that a strong detonation and a retonation (a reflected shock) form locally. Also the entropy satisfaction of this solution is presented.