硬脆性页岩地层井周裂缝形成与形态调控基础研究

Hard-brittle shale formation is the occurrence of economically recoverable shale oil and gas resource, and also the geologic body of wellbore instability and downhole accident and complexity occurred frequently as well. Low-cost regular long section horizontal wellbore and stimulation reservoir volume are the key and major difficulty. In such kind of formation, "fracture formation mechanism" is the foundation of drilling wellbore instability mechanism and stabilization techniques establishment, and also the important base of stimulation reservoir volume of shale gas formation, thereby needed to be studied eagerly. This project is based on the rock mechanics experimental research, to combine digital image processing and numerical computation technology; study the multiple action to rock failure pattern due to water effect, stress, etc in anisotropic meso-scale; develop numerical computation model suitable for anisotropic formation horizontal well; calculate and study the effect to around horizontal wellbore formation rock failure zones and fracture generation and patterns due to shale structure, strength, in-situ stresses and horizontal wellbore trajectory under drilling unloading and bore hole fluid column pressure; and sum up the master control element and regulate and control method of around horizontal wellbore fracture pattern. The result will surely promote the technologies of wellbore stability and stimulation reservoir volume in shale formation, and the relative theory should also be instructive to regular wellbore stabilization and fracturing problems.

硬脆性页岩既是当前可经济开采页岩油气资源的赋存体，也是钻井过程中井壁不稳定、井下复杂多发的地质体。低成本打成长井段规则井眼的水平井及体积改造是页岩气开发的核心关键技术及重大技术难点。"裂缝形成机制"是该类地层钻井井壁失稳机理及稳定技术建立的基础，是页岩气藏有效体积改造的重要基础，亟待研究。本项目以岩石力学实验研究为基础，将数字图像处理技术和数值计算技术相结合，在非均质细观尺度下，开展应力、水作用等多因素协同作用对岩石破坏模式的影响；构建非均质地层水平井数值计算模型，计算研究钻井卸载及高井筒液柱压力作用下，页岩结构、强度、地应力、水平井眼轨迹及井筒液柱压力等对水平井井周地层岩石破坏区域、裂缝形成及形态的影响，研究总结该类地层水平井井周裂缝形成与形态主控因素及调控方法。成果必将促进该类地层钻井井壁稳定技术及页岩气储层体积改造技术的发展，相关理论对常规井壁稳定及压裂问题也具有指导意义。

硬脆性页岩既是当前可经济开采页岩油气资源的赋存体，也是钻井过程中井下复杂情况多发的地质体。“裂缝形成机制”是该类地层钻井井壁失稳机理及稳定技术建立的基础，同时也是页岩气藏有效体积改造的重要基础，亟待研究。本项目通过岩石力学实验与数值模拟相结合，认识了硬脆性页岩的力学强度特征与破坏模式，系统研究了结构面、孔隙压力、卸载作用、地应力、温度等因素对其变形破坏特征的影响，探讨了页岩的变形破坏机理；综合三轴压缩、结构面直剪等试验，实现了对非均质页岩力学强度的表征；通过系统分析结构面对页岩力学强度的影响，优选了弱面-摩尔库仑理论为硬脆性页岩强度准则；在非均质地层水平井数值计算模型构建的基础上，数值模拟研究了钻井卸载作用及高井筒液柱压力作用下，页岩结构、力学强度、地应力、水平井眼轨迹、井筒液柱压力以及射孔参数、压裂分段等对水平井井周地层岩石破坏区域、裂缝形成及形态的影响，研究表明地质特征参数与工程参数均为硬脆性页岩地层井周裂缝形态的控制因素，其中井周地应力、页岩结构等地质特征参数为基础，影响更为直接显著。进而研究提出了井周压裂缝形态调控的思路、方法：基于地应力、岩石力学参数、结构面发育产状，考虑钻井卸载作用及钻井诱导缝影响，从井壁稳定性、压裂缝形态及压裂难易程度考虑，首先优选钻井方位；进而从利于横向缝、缝网形成角度出发，从水压加压速率、分段压裂、射孔相位、射孔密度、孔眼直径等工艺参数着手优化，实现对井周裂缝形态的有效调控。研究成果对硬脆性页岩地层钻井井壁稳定技术及页岩储层体积改造技术具有借鉴、指导意义。