摘要
中国渤海湾盆地广泛分布裂缝性致密变质岩油气藏。与常规储层相比，致密变质岩储层具有黏土矿物丰富、溶蚀孔隙及微裂缝发育、非均质性强等特点，钻井液漏失容易诱发储层损害，堵塞孔喉，降低储层渗流能力，阻碍油气井稳产。文中以渤中某区块太古界变质岩岩样为例，开展了钻井液动态损害实验和滤饼承压实验，明确了钻井液的动态损害程度和滤饼承压能力；基于扫描电镜，分析了敏感性矿物的类型和钻井液固相颗粒的赋存特征。实验结果表明：岩样气测渗透率越大，钻井液滤失量越大，返排突破压力越小，最大返排恢复率越大，最大返排恢复率对应的压差越小；钻井液对于200 μm及以下宽度的裂缝能够完全封堵，对于200 μm以上宽度的裂缝则不能够进行有效封堵，随着裂缝宽度的增加，滤饼的承压能力降低，并且钻井液侵入裂缝内的固相含量增大。研究区黏土矿物以丝片状和丝缕状伊利石、伊/蒙混层及钠长石为主，钻井液滤液的长期浸泡导致黏土矿物水化膨胀，堵塞粒内溶蚀孔隙，封堵储层孔喉。
Abstract
Fractured tight metamorphic rock reservoirs are widely distributed in Bohai Bay Basin of China. Compared with conventional reservoirs, tight metamorphic rock reservoirs are characterized by rich clay minerals, developed dissolution pores and micro?鄄fractures, and strong heterogeneity. Drilling fluid loss can easily induce reservoir damage, block pore throats, reduce reservoir seepage capacity, and hinder the stable production of oil and gas wells. Taking the Archean metamorphic rock samples in a block of Bozhong as an example, the drilling fluid dynamic damage and the filter cake pressure?鄄bearing evaluation experiments were carried out, and the drilling fluid dynamic damage degree and the filter cake pressure?鄄bearing capacity were clarified. The types of sensitive minerals and the occurrence characteristics of solid particles in drilling fluid were analyzed based on scanning electron microscope. The experimental results show that the larger the rock sample gas logging permeabilty, the more the drilling fluid loss, the smaller the flowback breakthrough pressure, the larger the maximum flowback recovery rate, and the smaller the pressure difference corresponding to the maximum flowback recovery rate. The drilling fluid can completely seal the cracks of 200 μm and below, but cannot effectively seal the cracks above 200 μm. As the fracture width increases, the pressure?鄄bearing capacity of the filter cake decreases, and the solid phase content that the drilling fluid invades into the fractures increases. The clay minerals are mainly filamentous flake and filamentous thread illite, illite/smectite mixed?鄄layer and albite. The long?鄄term immersion of the drilling fluid filtrate will cause the clay minerals hydration swelling, which blocks the intragranular dissolved pores and the reservoir pore throats.
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