煤层地震波各向异性响应及裂隙预测

There are many kinds of fractures in coal seams. Coal seams with fracture are anisotropic. In oil exploring and earthquake fields, many researches have studied seismic anisotropy technique and have achieved fruitful results. But there are not systemic studies in seismic anisotropy exploring in coal beds with different anisotropy..At present, four kinds of anisotropic media, including VTI, HTI, OA and TTI, can be explored by seismic technique. Because the applicant has been doing a VTI coal research by youth fund, this project mainly discusses seismic anisotropy technique in HTI, OA and TTI coal seams. It produces seismic records by numerical simulation of elastic wavefield and physical modeling with fracture-bearing coal seam to develop new seismic data acquisition methods in different anisotropic coal seams and get seismic records with high resolution and high signal-noise ratio..Seismic anisotropic response in coal beds includes anisotropic parameters, velocity anisotropy, AVO anisotropy and attenuation anisotropy. It does an analyzing research on anisotropic response in coal seams with different kinds of anisotropy by comparing the precision among the existing analyzing methods and getting some revised equations in seismic anisotropic response. It develops a set of anisotropic response parameters technique. It discusses the sensitivity of anisotropic response parameters independently, and then concludes the most sensitive parameters to different anisotropy or the combination of sensitive parameters, which is the basis of parameters inversion and fracture prediction. .Considering coal seam's unique features-comparatively thin to seismic wavelet, reflected P-wave from top and bottom interfaces of coal seams coupling together and difficult to recognize valid information from seismic records, it optimizes calculating method of anisotropic response parameters and fracture parameters inverting technique. In parameters inverting, different methods are applied in coal seams with different anisotropy. Through analyzing the relationship of anisotropic response and fracture in coal seams, it gets parameters related to anisotropy and fracture parameters by inverting. According to relevant parameters, fractures in coal seams can be determined whether it is water-saturated or dry and it realizes fracture reservoir prediction. Fracture parameters analyzing and recognition technique are also adapted to coal seams with different anisotropy. All the techniques are demonstrated the feasibility in the experiment areas. It gives different processing flows to seismic data acquired from HTI,OA,TTI coal seams respectively..All researches are based on the study results in forward and inversion in VTI media during Doctor and funded project by education department of Shanxi provincial government, especially youth fund by national natural science foundation of China, transforming a developed seismic anisotropic technique in earthquake and oil seismic exploration field into coal seismic survey. It makes fullest use of seismic exploration in coal seams and it is of great importance for coal bed methane development and safe production in coal mining.

煤层中广泛发育裂隙，含裂隙的煤层是一种各向异性介质。各向异性地震技术，由于其具有较高裂隙描述潜能，在石油勘探和天然地震领域已经取得一定成效，而在煤矿地震勘探中至今还未进行全面应用与开发。目前，四类各向异性（VTI，HTI，OA，TTI）问题可以用地震勘探技术解决，由于申请人在青年基金中已经全面研究过VTI型煤层各向异性技术，本课题以HTI，OA，TTI型煤层为研究对象，围绕各向异性结构的特点，通过数值模拟、物理模型，研究各向异性煤层中地震资料采集方法；推导适于不同各向异性煤层的各向异性响应分析公式，优化各向异性参数与裂隙预测算法，实现不同各向异性煤层中各向异性与裂隙信息的分析与识别技术；通过试验场地采集实际资料，验证方法的可行性，建立不同各向异性煤层的有效工作流程和方法。项目研究结果将进一步挖掘地震勘探技术在煤矿探测上的潜力，对我国煤层气的开发及煤矿裂隙型灾害预测具有重要的理论和实际价值。

传统的煤田地震勘探通常将煤层作为各向同性介质来处理，而实际煤层由于裂隙的发育而表现出各向异性。项目主要针对HTI，OA，TTI型等多种各向异性煤层，通过模拟地震波群、相速度及地震波场变化，研究地震波在复杂介质中的传播规律；引入裂隙表征参数，实现不同介质的各向异性介质参数反演；研究各向异性参数与裂隙指示因子的关联，实现裂隙预测。项目取得的主要成果包括：.1. 结合各向异性介质弹性参数和裂隙理论，推导含有不同充填物的裂隙介质中各向异性参数表达式，通过改进的交错网格差分法和各向异性Christoffel方程波场分解法，得到地震波合成记录和分解后的P波和SV波记录，进行裂隙介质地震波各向异性响应分析。.2. 基于各向异性介质PP波反射系数近似公式，分析各向异性参数对PP波反射系数的影响，不同各向异性介质地震波AVO响应特征，引入遗传算法、模拟退火法，粒子群算法等多种非线性反演算法，实现各向异性介质地震波参数反演。.3. 利用Thomsen各向异性参数表征公式，Hudson裂隙等效理论以及Bakulin裂隙流体指示因子等裂隙介质相关理论，建立与各向异性相关的目标函数，通过叠前AVO反演，从裂隙密度、裂隙对称轴倾角和裂隙充填物状态等方面实现裂隙有效预测。.研究实现了各向异性介质地震波正、反演和裂隙预测技术，对于煤矿裂隙型灾害预测具有一定的理论和应用价值。