A High Temperature Block Removal Fluid for Offshore Application

The sandstone reservoir penetrated by the well X-1 in an offshore oilfield has the characteristics of high temperature, abnormally high pressure and low permeability. Dissolution pores are developed in the reservoir rocks. Intergranular fractures in the reservoir rocks are full of various kinds of clays which are easy to cause water sensitivity and flow velocity sensitivity. To solve these problems, a blocking removal fluid was developed for use in the high temperature low permeability sensitive reservoirs. Laboratory experimental results showed that at 170℃, the average corrosion rate of the steel strip in the blocking removal fluid is 62.880 g/cm²·h, meeting the first-grade standard of the industry. The blocking removal fluid has lower surface tension, the surface tensions of the fresh acid and residue acid are all less than 24.0 mN/m. The blocking removal fluid has good ferric ion stability, it can stabilize 263 mg/mL of ferric ions in a system. The blocking removal fluid has good clay swelling inhibition capacity, the final rate of swelling of a sample can be controlled below 32.19%, this is helpful to effectively inhibit water sensitivity impairment to the reservoir. After injecting the blocking removal fluid into a core, the permeability of the core was apparently increasing. The blocking removal fluid is ideal for removing blocks existed in high temperature low permeability reservoirs because the dissolution rates of the blocking removal fluid to clay minerals and the matrix of the rock are high, the blocking removal fluid do not cause pore throats to be blocked by the produced sands, and the permeability of the core can be increased by 3.5 times. Field application showed that the blocking removal fluid removed almost all the blockage near the wellbore. Comparison of the daily gas production rates before and after acidification of the reservoir showed that the acidizing job has done very well in removing the blockage in the reservoir formation.