Study on an Acid Soluble LCM Used for Multi-Target Well in Tahe Oilfield

The underdeveloped carbonate reservoirs in the Tahe Oilfield have fractures and vugs that are small scaled and production through a single well generally cannot realize its expected economy. Use multi-target well to penetrate multiple fractured reservoirs or reservoirs with vugs through one well, the production potential of a single well can be economically increased. The problem with the multi-target well drilling is mud losses in the complex fracture structures, which restrict the realization of fast and high efficiency drilling. By analyzing the characteristics of the mud losses taking place in fractured reservoirs and the difficulties encountered during drilling, an acid-soluble gel particle lost circulation material (LCM) was developed to solve the mud losses in reservoir drilling. Percent acid solubility of this LCM is 86%. After swelling, the volume of the LCM can be 3-5 times of its original volume, and the swollen LCM has good toughness and deformability. The acid soluble gel particle LCM, through orthogonal test, was mixed with an acid soluble flexible fiber and a flaky material to form a compound acid soluble LCM based on the mechanisms of mud loss control with gel particles. The compound LCM can be used at temperatures up to 150 ℃ and has percent acid solubility of 85%. It can used to stop mud losses through fractures of 0.1-3.0 mm in width and pores of 4-10 mesh. The pressure bearing capacity of the LCM layer is 9 MPa on the front side and 5 MPa on the opposite. Field application has shown that this compound acid soluble LCM can be used to solve mud losses into the complex fractures developed in carbonate rock reservoirs and should have broad application prospects.