New technologies on reservoir protection in complex reservoir exploration

The new technologies presented in this paper include formation sensitivity prediction technology in the exploratory well, drilling fluid technology for complex reservoir protection, and drilling fluid density adjustment technology according to the up-return velocity of oil and gas. The sensitivity prediction tech nology can present the detailed predicting reports on velocity sensitivity, salt sensitivity, water sensitivity, acid sensitivity, and alkali sensitivity, etc. , based on the database files, and provide the backups for making out the specific measures for each well. For the loose sand rock reservoir, use the so called one-step drilling fluid, PAM-MMH drilling fluid and MEG-MMH drilling fluid; use polyol drilling fluid, calcium-alcohol complexing water based drilling fluid and MEG drilling fluid for the water sensitive reservoir; and for fractured and porous formation, use clay free drilling fluid and high temperature tolerant clay free and low solids drilling fluid. These drilling fluid systems effectively solve such problems as wellbore stability, lubricity, toxicity and formation damages in complex reservoir exploration. During drilling of the explora- tory well, adjust the drilling fluid density according to the up-return velocity of oil and gas timely, thus maximize the oil and gas discovery and minimize formation damage. When drilling the main reservoirs in Shengli Oilfield, by adjusting the up-return velocity, the oil and gas was kept in a sub-active state, and this minimized drilling fluid damage and effectively protected the reservoirs.