构造应力场与低渗透油田开发
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摘要
古构造应力场是控制天然裂缝发育程度与分布的极重要因素，现代应力场则影响天然裂缝的保存状况。现代应力场对低渗透油田开发的影响体现在：①一般与最大主压应力方向近平行的裂缝开度最大、连通性最好，与其近垂直的裂缝开度最小、连通性最差；②随着油田开发的进展，在围压不变的条件下，与最大主压应力方向近平行裂缝的流体压力下降和开度降低的速率最大（有可能成为无效裂缝），而与最大主压应力方向近垂直的裂缝开度和流体压力下降都相对缓慢（到一定开发阶段有可能成为对渗流起主导作用的裂缝）；③低渗透储集层可分为纯裂缝型、双介质型和孔隙型，它们的裂缝储渗作用不同，因此现代应力场对３类储集层剩余油分布的控制作用不同；④孔隙型储集层人工压裂缝延伸方向与最小主压应力方向垂直，纯裂缝型储集层人工压裂缝延伸方向与最小主压应力方向和先存天然裂缝方向均有关。在研究受古构造应力场控制的天然裂缝分布的基础上，结合现代应力场分布的研究，可以有效地指导制定低渗透油田开发方案、注水管理、水平井设计，并可预防油、水井套管变形。图１
Paleo tectonic stress field is the main factor controlling the development and the distribution of the natural fracture systems, while modern tectonic stress field affects the retention of thesefracture systems. The effects of modern tectonic stress field will be: ①The opening of fractures is maximum in the direction parallel to the major stress and their interconnection is best, while the opening will be minimum and the interconnection will be least in the direction nearly perpendicular to the maximum stress; ②The declining in the fluid pressure and the opening of the fractures will be faster (may become closed fracture systems finally) in the direction parallel to the maximum stress under constant confining pressure as development proceeds, while both the opening and fluid pressures in fracture systems in the direction nearly perpendicular to the major stress decrease at a much slower rate (may become major permeable fracture system at a certain development phase); ③Low permeable reservoirs can be classified into 3 types of double porosity, porosity, or purely fractured, their fracture systems play a different role in each type of reservoir; thus modern tectonic stress field plays a different role controlling the distribution of remaining oil in each type of reservoirs stated above; ④In a porosity type reservoir the direction of fracture extension by artificially hydrofracturing depends upon both the minimum formation pressure and the directions of natural fracture systems previously existed. On the basis of studying the distribution of natural fracture systems controlled by paleo tectonic stress field, a study of the distribution of modern tectonic stress field can give a guide to make a development program, management of water injection, design of horizontal wells in the development of a low permeability reservoir effectively and can prevent the casing distortion of production and/or injection wells.
Paleo tectonic stress field is the main factor controlling the development and the distribution of the natural fracture systems, while modern tectonic stress field affects the retention of thesefracture systems. The effects of modern tectonic stress field will be: ①The opening of fractures is maximum in the direction parallel to the major stress and their interconnection is best, while the opening will be minimum and the interconnection will be least in the direction nearly perpendicular to the maximum stress; ②The declining in the fluid pressure and the opening of the fractures will be faster (may become closed fracture systems finally) in the direction parallel to the maximum stress under constant confining pressure as development proceeds, while both the opening and fluid pressures in fracture systems in the direction nearly perpendicular to the major stress decrease at a much slower rate (may become major permeable fracture system at a certain development phase); ③Low permeable reservoirs can be classified into 3 types of double porosity, porosity, or purely fractured, their fracture systems play a different role in each type of reservoir; thus modern tectonic stress field plays a different role controlling the distribution of remaining oil in each type of reservoirs stated above; ④In a porosity type reservoir the direction of fracture extension by artificially hydrofracturing depends upon both the minimum formation pressure and the directions of natural fracture systems previously existed. On the basis of studying the distribution of natural fracture systems controlled by paleo tectonic stress field, a study of the distribution of modern tectonic stress field can give a guide to make a development program, management of water injection, design of horizontal wells in the development of a low permeability reservoir effectively and can prevent the casing distortion of production and/or injection wells.
引文
1万天丰：古构造应力场；地质出版社（北京），1988。2万天丰：中国东部中新生代板内变形、构造应力场及其应用；地质出版社（北京），1993。3安欧：构造应力场；地震出版社（北京），1992。4王仲茂：地壳应力在低渗透砂岩油田开发中的应用；石油勘探与开发，1992，19（4）91～96。5王平：有天然裂缝的砂岩油藏开发；石油学报，1993，14（4）69～74。
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