Studies On Water Shutoff For Horizontal Well In The Western Zone Of South China Sea Oil Field

As for the limitations of water shutoff in offshore oilfield, problems, such as low success ratio and large formation damage and so on, exist in water shutoff for horizontal well in the western zone of South China Sea oil field. The key aspects about water shutoff for horizontal in the western zone of South China Sea oil field were studied in this paper, including water breakthrough mechanism, water shutoff agent, matching treatment fluid and water shutoff technology etc. Water breakthrough mechanism of horizontal well in the western zone of South China Sea was studied by means of numerical simulation, which indicates the water breakthrough manner is bottom water cresting, including partial water invasion and mass water invasion. Gel-type, silicate precipitation-type and clay dispersing-type water shutoff agents were chosen for further study according to the formation conditions of the western zone of South China Sea oil field. YG102 gel, YG103 gel, YG107 gel and environmental PEI gel were studied at medium temperature, which is about gel application properties including quiescent corrosion rate, different lithologic character, resistance to shearing, shut off capacity and resistance to erosion etc, and about the effects of temperature and salinity. This research gains a serial of gel formulation with adjustable gelation time, strength and satisfactory stability. Silicate precipitation-type and clay dispersing-type water shutoff agent were studied about the effects of total salinity, temperature and concentration of calcium ion and magnesium ion on the silicate precipitation at high temperature, obtaining related formulation with competent shutoff capacity and satisfactory stability etc. Preflush and temporary blocking gel agents were studied at the western zone of South China Sea condition, obtaining preflush formulations fit for different oil sample and serial temporary blocking gel formulations. Visualization experiments demonstrate that water shutoff agents can go into high transmissibility path with high water saturation preferentially, controlling the raise of bottom water efficiently to improve the oil recovery. To increase the water shutoff cycle times can enhance the operation effects. Sandpack simulation experiments demonstrate that commingled water shutoff to toe water breakthrough can hurt the formation dramatically, and the preprocessing with preflush and temporary blocking gel agent can improve the selectivity of commingled water shutoff.