Application of Two-Stage Strengthened Bridging Technique in Well Nanpu27-Ping201

Wells drilled in the Dongsan member of the 2-27 block, the 2nd Structure in Jidong Oilfield penetrate several sections of igneous rocks with fractures, vugs and low pressure-bearing capacity. In the same interval of the wells, there are dark gray colored shales with high collapse pressure and very narrow safe drilling window. In deviated well drilling, the coexistence of wellbore collapse and mud losses is frequently encountered, resulting in many downhole accidents. In the drilling operation of the well Nanpu27-Ping201, mud losses were encountered several times. One of the severe mud losses, lost circulation, took place when drilled to 4,574 m. Bridging method was tried twice without success in controlling the lost circulation. Based on the analysis of the downhole situations, it was decided to use the two-stage strengthened bridging method to cure the mud loss. In the first stage, the lost circulation control slurry was formulated mainly with fine and medium particles and 3% solidifying agent. Laboratory test results showed that when the solidifying agent was added, the lost circulation control slurry still has good pumpability, the particles pack much denser, and the internal friction of the slurry was increased by 6 times. In the second stage, a high temperature, high-temperature resin particles in triangular-cone shape were used to control the mud loss. The resin particles are easy to go into the channels through which the mud was lost, and are easy to be retained in the channels. If it is necessary, the resin particles are also easy to flow back. The lost circulation control slurry was pushed and squeezed into the channels and the mud loss was controlled in the first try. In subsequent drilling operation, no mud losses occurred again.