煤层气直井水力波及压裂可行性论证

发布时间：2019-05-10 10:38

【摘要】：煤层气作为一种优质、清洁的非常规天然气资源,倍受国内外学者广泛关注。国内煤层气资源量丰富,煤层气高效开发利用在环境保护、能源保障和经济发展等方面具有重要意义。我国煤层气储层低压、低孔、低渗等特点决定了煤层气井钻完井后普遍需要增产才能产气,但现有增产技术对煤层气产量提高效果较差,不能实现煤层气高效经济开采。分析发现,煤层气以吸附气为主的赋存方式、以降压解吸为主的生产特点及煤层气储层低孔、低渗的地质特征决定了提高煤层气产量的关键在于增大裂缝网络与煤岩基质的接触面积,而煤岩中发育的面、端割理系统为裂缝网络的形成提供了必要条件。基于此,本文在前人研究基础之上,综合运用岩石力学、弹性力学、断裂力学、流体力学、水力压裂力学、高等数学和计算机编程等多学科知识,以增大煤层气藏增产改造体积波及范围为目标进行研究,取得了以下主要成果及认识： (1)深入分析了煤层气储层工程地质特征和现有增产措施工艺原理、技术特点及存在的不足,提出了利用缝间应力干扰作用增大煤层气藏增产改造体积波及范围的煤层气直井水力波及压裂工艺技术,建立了两口正对的煤层气直井水力波及压裂物理模型。 (2)推导了适用于分析水力波及压裂多裂缝产生的应力扰动问题的位移不连续数值计算方法及其求解步骤,利用MATLAB编程,对比分析了单一压裂主缝和水力波及压裂主缝缝间应力干扰作用的差异,划分出了近场复杂缝网和远场复杂缝网,分析了水力波及压裂缝间应力干扰作用对复杂缝网形成的影响；研究了压裂裂缝半缝长、缝内净压力、煤岩泊松比和井间距对水力波及压裂应力干扰作用的影响规律。 (3)分析了诱导煤层气储层中面、端割理系统破坏形成分支裂缝的最大缝内净压力与地应力差的关系以及分支裂缝延伸至单井压裂时的应力各向同性点以后的延伸方向,证明了煤层气直井水力波及压裂有利于复杂缝网的形成。 (4)利用二维离散元分析软件UDEC编程,对比分析了单口煤层气直井压裂和两口正对的煤层气直井水力波及压裂裂缝网络扩展形态,论证了煤层气直井水力波及压裂增大煤层气藏增产改造体积波及范围的可行性；研究了初始水平主应力差、煤岩泊松比、井间距、压裂主缝半缝长和压裂液黏度对水力波及压裂缝网扩展形态的影响规律。通过本文的研究,论证了煤层气直井水力波及压裂相比于单独压裂能进一步增大煤层气藏增产改造体积波及范围,敏感性参数分析对水力波及压裂施工设计和井层优选具有指导意义,近场复杂缝网和远场复杂缝网分区为下步经济优化提供了方向。
[Abstract]:As a kind of high quality and clean unconventional natural gas resources, coalbed methane (CBM) has been widely concerned by scholars at home and abroad. The resources of coal bed methane are abundant in our country. The efficient exploitation and utilization of coal bed methane is of great significance in environmental protection, energy security and economic development. The characteristics of low pressure, low porosity and low permeability of coalbed methane reservoir in China determine that it is generally necessary to increase gas production after drilling, but the existing production increasing technology has poor effect on increasing coalbed methane production and can not realize high efficiency and economic exploitation of coalbed methane. It is found that the coalbed methane occurs mainly by adsorptive gas, and the production characteristics of low porosity of coalbed methane reservoir are mainly characterized by depressurization and desorption. The geological characteristics of low permeability determine that the key to improve the production of coalbed methane lies in increasing the contact area between fracture network and coal and rock matrix, and the surface and end cutting system developed in coal and rock provide the necessary conditions for the formation of fracture network. Based on this, on the basis of previous studies, this paper makes comprehensive use of rock mechanics, elasticity, fracture mechanics, fluid mechanics, hydraulic fracturing mechanics, advanced mathematics and computer programming. The main achievements and understandings are as follows: (1) the engineering geological characteristics of coalbed methane reservoir and the principle of existing measures for increasing production are analyzed in depth, and the main achievements and understandings are as follows: (1) the engineering geological characteristics of coalbed methane reservoir and the principle of existing measures to increase production are deeply analyzed. The technical characteristics and existing shortcomings are put forward, and the hydraulic and fracturing technology of coalbed methane vertical well is put forward to increase the volume and range of production increase and transformation of coalbed methane gas reservoir by using the effect of interfracture stress interference. The physical models of hydraulic and fracturing of two straight wells of coalbed methane are established. (2) the numerical calculation method of displacement discontinuity and its solving steps are derived, which are suitable for analyzing the stress disturbance caused by hydraulic and fracturing multiple cracks. The method is programmed by MATLAB. The difference of stress interference between single fracturing main seam and hydraulic fracture main seam is compared and analyzed, and the near field complex seam net and far field complex joint net are divided. The influence of stress interference between hydraulic and pressure cracks on the formation of complex seam network is analyzed. The effects of half fracture length, net pressure in fracture, Poisson's ratio of coal to rock and well spacing on hydraulic and fracturing stress are studied. (3) the relationship between the maximum fracture net pressure and the ground stress difference caused by the failure of the end cutting system in the induced coalbed methane reservoir is analyzed, and the extension direction of the stress isotropism point when the branch fracture extends to the single well fracturing is analyzed. It is proved that hydraulic and fracturing in straight wells of coalbed methane is beneficial to the formation of complex fracture network. (4) using two-dimensional discrete element analysis software UDEC programming, the hydraulic and fracture network expansion patterns of single coalbed methane straight well and two positive coalbed methane straight wells are compared and analyzed. It is proved that it is feasible for straight well hydraulic and fracturing of coalbed methane to increase the volume and range of stimulation and reconstruction of coalbed gas. The effects of initial horizontal principal stress difference, Poisson's ratio of coal to rock, well spacing, half fracture length of main fracture and viscosity of fracturing fluid on the propagation pattern of hydraulic and fracturing fracture pattern are studied. Through the study of this paper, it is proved that hydraulic and fracturing in straight wells of coalbed methane can further increase the volume spread range of production increase and transformation of coalbed methane reservoirs compared with single fracturing. The analysis of sensitivity parameters is of guiding significance for hydraulic and fracturing construction design and well layer optimization. The division of near-field complex fracture network and far-field complex joint network provides a direction for the next step of economic optimization.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE357

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