泥页岩微裂缝模拟新方法及封堵评价实验

A New Method of Simulating Micro Fractures in Shale and Plugging Evaluation Experiment

目前泥页岩微裂缝模拟方法较多,但都存在一定局限性,且不能真实模拟高温高压下泥岩与钻井液接触后水化分散过程。针对该难题,在对平滑钢块模拟法、砂床封堵实验法、劈裂岩样人造裂缝模拟法和透明钢化玻璃模拟法进行分析的基础上,采用干法钻取取样岩心以获得标准岩心柱,对岩心柱进行造缝,并在岩心缝面垫上不同厚度的锡纸,模拟宽度为10~100μm的微裂缝;将岩心柱放入夹持器中,与动态失水仪相连,可形成一套泥岩微裂缝封堵能力评价装置。介绍了封堵评价实验装置的组装和实验操作步骤,及其功能和优点,给出了微裂缝缝宽的推导公式,并通过精确测量数据换算出了等效裂缝宽度。室内实验表明,该微裂缝模拟方法有精度高、重复性好等优点。研究结果表明,该方法及评价装置不仅能模拟泥页岩与外来液相接触后的水化分散、膨胀等过程,还能真实模拟井底高温高压条件下钻井液对微裂缝的封堵情况,为深入研究微裂缝的封堵机理、封堵材料优选及钻井液配方优选提供可靠的实验方法和数据支撑。

There are many methods available presently for the simulation of micro fractures in Shale. All these methods have limitations, and are unable to trulysimulate the hydration and dispersion processes of shales in contact with water at HTHP conditions. To solve this problem, several simulation methods, such as the smooth steel block simulation method, sand bed plugging experiment method, simulation with artificial fracture （on split rocks） method and transparent tampered glass simulation method etc. were analyzed, and based on the analysis, a new method has been developed. In thenew method, a standard core plug is obtained by dry drilling samples,and artificial fractures are then made in it.The surface of the artificial fractures is covered with tinfoil of different thickness to simulate micro fractures of 10-100 μm in width. The core plug is put into a core holder that is connected with dynamic filter press, and a device for evaluating the capacity of plugging micro fractures in shale is formed. The assembly of the device, the experimental procedure, the function and the advantages of the device are introduced in this paper. An equation for the calculation of the width of micro facture is presented, and the equivalent widths of micro fractures are calculated through conversion of accurately measured data. Laboratory experiment has shown that this simulation method has high precision and good repeatability. This method can be used not only to simulate the hydration, dispersion and swelling of shale in contact with liquids, but also to simulate the plugging of micro fractures by drilling fluid on bottom hole at high temperature and high pressure. The simulation can be used to extensively study the plugging mechanism of micro fractures to provide reliable experiment method and datasupport for the selection of plugging agent and optimization of drilling fluid formulation.