深层页岩气开发关键技术难点与攻关方向

为了实现深层页岩气的规模效益开发,通过对比四川盆地川南地区上奥陶统五峰组—下志留统龙马溪组龙一1亚段深层与中浅层页岩储层地质工程特征的差异,梳理了其高效开发面临的难题:较之于中浅层,我国深层页岩气储层的工程特征参数总体上呈现"五高"特点(泊松比和弹性模量高、地层温度高、水平应力差值高、破裂压力高、闭合压力高)。虽然深层页岩气在近期取得了战略突破,但其开发关键技术还欠成熟,表现在以下方面:①抗高温的旋转导向工具未实现国内商业化生产,地质导向技术对储层的预测精度低,"一趟钻"技术尚未形成,满足地层防塌与防漏需求的钻井液性能还不成熟;②深层页岩气井压裂后难以形成复杂缝网,同时裂缝起裂和延伸困难,而且加注支撑剂的难度也大,导致不易获得具有高导流能力的裂缝;③深层页岩储层孔隙中CH4相态仍不清楚,导致深层页岩气多尺度流动规律及开发技术对策不明确。为此,需要针对钻井工程、压裂工程、开发技术对策等方面开展技术攻关:①构建多源信息融合三维地质导向技术,实施"高转速、大排量、长循环"井眼强净化工艺技术,加强对油基钻井液高效微纳米封堵材料、专用堵漏材料的研发,实现水平井钻得更好更长更快;②建立深层页岩应力应变本构关系和Ⅰ、Ⅱ与Ⅲ型断裂韧性模型、考虑层理弱面力学性质的流—固—热多场耦合人工裂缝扩展模型,以及考虑页岩蠕变的支撑剂嵌入力学模型与评价方法,保障储层压得更碎更充分;③深入研究页岩储层中气体微观流动能力和产出机理,优化水平井关键参数,制订合理的返排制度和生产制度,进而优化立体开发模式,以实现深层页岩气的规模高效开发。

Key technological challenges and research directions of deep shale gas development

In order to realize scale beneficial development of deep shale gas, this paper analyzed the challenges in the efficient development of deep shale gas by comparing geological and engineering characteristics between the deep shale reservoirs of Upper Ordovician Wufeng Formation-Long₁¹ Submember of Lower Silurian Longmaxi Formation and the medium-shallow shale reservoirs in the southern Sichuan Basin. It is shown that compared with the medium-shallow shale reservoirs, the engineering characteristic parameters of deep shale reservoirs in China are characterized by "five highs", i.e., high Poisson's ratio and elastic modulus, high reservoir temperature, high horizontal stress difference, high fracturing pressure and high closure pressure. Recently, strategic breakthroughs have been achieved in deep shale gas, but its key development technologies are still limited in the following aspects. First, commercial production of high-temperature rotary steering tool has not been realized at home, reservoir prediction accuracy by geosteering technology is low, "one-trip" technology has not been formed, and drilling fluid to satisfy the need of anti-collapse and anti-leak is not mature. Second, after the fracturing of deep shale gas wells, complex fracture networks can be hardly formed, and fracture initiation and propagation is difficult. What's more, proppant injection is of high difficulty. Therefore, it is difficult to obtain fractures of high flow conductivity. Third, the phase state of CH₄ in the pores of deep shale reservoirs are still unknown, so multi-scale flow laws of deep shale gas and its development technologies and countermeasures cannot be determined. For these reasons, it is necessary to carry out technological researches in terms of drilling engineering, fracturing engineering and development technology and countermeasure. First, develop the 3D geosteering technology based on multi-source information fusion, apply the enhanced hole cleaning technology of "high rotation speed, large displacement and long circulation", and strengthen the research and development of efficient micrometer and nanometer plugging materials and special lost circulation materials used for oil-based drilling fluid, so as to drill horizontal wells better, longer and faster. Second, establish the stress-strain constitutive relationship of deep shale, the toughness model of type Ⅰ, Ⅱ and Ⅲ fracture, the fluid-solid-heat multi-field coupling based hydraulic fracture propagation model considering the mechanical property of weak plane, and the mechanical model and evaluation method of proppant embedment considering the shale creep, so as to ensure sufficient reservoir fracturing. Third, research the microscopic flow capacity and production mechanism of gas in shale reservoirs, optimize the key parameters of horizontal wells, formulate a reasonable flowback system and production system and then optimize the tridimensional development mode, so as to achieve the scale efficient development of deep shale gas.