Evaluation on the compression strength of lost circulation materials considering in-situ stress and fracture width/particle size ratio

Lost circulation is one of the complex engineering problems in the process of drilling and completion, and that in fractured reservoir intervals can result in serious reservoir damage and reduce integrated well construction benefit. Plugging the leakage channels by using lost circulation materials is the main method to control the leakage of working fluids in fractured reservoirs, and its key lies in the formation of the fracture plugging zones with stable structure and high pressure bearing capacity. The compression strength of the rigid lost circulation materials with the function of bridging plays a leading role in the structural stability and pressure bearing capacity of fracture plugging zones. At present, however, there is no operable experimental test method to measure the compression strength of rigid lost circulation materials. In this paper, a method for evaluating the compression strength of rigid lost circulation materials was established by taking the crushing rate as an evaluation index, and the experimental pressure was set according to the difference between minimum formation principal stress and pore pressure, so as to meet the evaluation demand of rigid lost circulation materials in deep and ultradeep wells. In addition, considering the bridging fracture width/particle size ratio relationship inside the rigid particle fracture, the compression strength of rigid lost circulation materials was experimentally tested under the room temperature by means of the lost circulation material compression strength tester. The experimental results show that based on the crushing rate, the commonly used rigid lost circulation materials are ranked as calcite＞quartz sand＞walnut shell＞organic polymer material＞ceramsite, and the same type of rigid lost circulation materials is ranked as coarser size material＞finer size material and single-layer laying＞double-layer laying＞three-layer laying. It is indicated that the compression crushing of rigid lost circulation materials under high fracture closure pressure is an important factor leading to the repeated plugging failure in deep fractured reservoirs. Therefore, to control the lost circulation in deep fractured reservoirs, it is necessary to carry out rigid lost circulation material compression strength test in the in-situ condition and the engineering operation environment and select the suitable rigid lost circulation materials.