裂缝性碳酸盐岩储层的钻井液侵入预测模型

裂缝/孔隙性碳酸盐岩储层钻进时的主要损害机理是钻井液中固相和滤液对储层裂缝的侵入。针对平均缝宽不超过100 μm的低渗透裂缝性油气藏，建立了钻井液在单一裂缝中的侵入预测模型，模型中裂缝开度随有效应力连续变化。利用该模型对塔里木油田某区块现有钻井液体系的碳酸盐岩储层裂缝侵入程度进行了预测，并与该钻井液体系性能室内评价结果进行了对比分析。预测和评价结果表明，在钻井过程中，泥饼的形成速率和形成质量是保护裂缝性碳酸盐岩储层技术的关键。通过调整钻井液快速弱凝胶的结构和优化体系粒径级配，可将钻井液对储层裂缝的侵入量控制到最低。

The prediction model for the drilling fluid invasion in fractured carbonate reservoirs

The major damage caused by drilling in fractured or porous carbonate reservoirs is an invasion of particles and filtrate of drilling fluid into reservoir fractures.Carbonate reservoirs in the Tarim Basin are basically characterized by abundant natural fractures and vugs.In terms of low-permeability fractured reservoirs with an average slot width less than 100 μm,a prediction model for the invasion of drilling fluid into single fracture was established,and in the model the aperture of fractures continuously varies with actual stress.Using this model,the invasion extent of drilling fluids used currently for carbonate reservoirs in a block of the Tarim Basin was predicted,and a correlation between the predicted result and the outcome derived from the lab assessment of properties of these drilling fluids was made.The prediction and assessment results demonstrated that the sealing rate and quality of mud cakes were the key of techniques that intended to protect fractured carbonate reservoirs,and it was possible to minimize the invasion into reservoir fractures by intensifying fast weak-gel structures and optimizing the systematical size grading of drilling fluids.