Research On Clay-free And Plugging Drilling Fluid

Lost circulation is one of the hardest problems to deal with in the process of drilling engineering. The cost of lost circulation is the main source of drilling costs. At present, our country is in the late stage of oilfield development, the most of the Wells we have developed are ultra-deep wells, horizontal wells and other complex wells which put forward higher requirements. There are a variety of plugging materials, but they often perform poorly in the controlling fluid loss because of the poor deformability and water-swelling capacity. The current conventional drilling fluid is usually with clay as a basis for adjusting of properties of fluid. The existence of the clay causes much sabmicron particles, which lead to reduce drilling rate and damage the oil gas reservoir.Through a large amount of laboratory research, the paper synthetised a new blocking agent which has suitable swelling ability heat resistance and the capacity of resistance to temperature is above 150℃. Experimental data shows that at room temperature, the new blocking agent can be stretched for five times, aging stretching ratio is 5.4 times at 150℃, swelling ratio is more than 6.8 times in water and saline water. The new blocking agent has a role of thickening, blocking and compatibility with drilling fluid treatment agent is good.On the basis of developing a new type of plugging agent, optimizing the viscosifiers, fluid loss agent, lubricant, inhibitors to form a strong clay-free plugging drilling fluid formula. The strong clay-free plugging drilling fluid can work in temperature up to150℃.It provided a solution for polymer degradation when plugging agent was used in high temperature.This drilling fluid has strong sealing ability, with the maximum bearing pressure reaching 7.0MPa. HTHP fluid loss less is 9.2 mL, sand bed invasion depth at room temperature is about 3cm. The system has higher mud cake removal rate in acid and oxidizing solution and good reservoir protection.