Plugging Technology for HTHP Wells in the Yingqiong Basin of the South China Sea

The Yingqiong Basin in western South China Sea is characterized by complex geological conditions, high bottomhole temperatures and pressures, and lost circulation which occurs frequently during drilling into the target layer. In order to solve the problem of frequent lost circulation in target layer, the main causes of lost circulation were analyzed, the idea of combining the high temperature resistant rigid plugging materials with high temperature resistant elastic plugging materials was followed, and a plugging slurry was prepared by adding DXD (a high temperature resistant rigid plugging material) and TXD (a high temperature resistant elastic graphite plugging material) into drilling fluid. The performance evaluation showed that the density of plugging slurry could reach 2.40 kg/L and the temperature resistance could reach 200 °C. The DXD could form bridges in the induced fractures, while the TXD could enter the residual pores of induced fractures under pressure difference, preventing the induced fractures from further opening and expanding, blocking the induced fractures and improving the pressure-bearing capacity of formation. This plugging slurry had been applied in several high temperature and high pressure (HTHP) wells in the Yingqiong Basin with the success rate of plugging increasing from 30% to 80%, indicating that the plugging slurry could block the induced fractures in the target layer of the Yingqiong Basin, improve the pressure-bearing capacity of formation and the success rate of plugging, and solve the problem of frequent lost circulation in the target layer.