Drilling technology for carbonate reservoir with dual density drilling fluid of drilling tool and annulus

Due to the strong heterogeneity of carbonate reservoirs, multiple sets of pressure systems may exist in the same formation, leading to incidents such as coexistence of severe circulation loss and overflow. Conventional drilling techniques fail to effectively balance the issues of safe drilling and drilling costs. To address this, a dual-density unconventional drilling technology based on bit nozzle and annular space was proposed. Different densities of drilling fluids were used in the annular space and the bit nozzle on drilling tool, eliminating the need for circulation during drilling. Simultaneously, the changes in formation pressure were monitored in real time by measuring the annular fluid level and casing pressure, and the optimal drilling fluid density was promptly selected, enabling rapid drilling in complex formations. This technology was successfully applied in over 10 wells in different blocks of the Tarim Oilfield, achieving a successful penetration depth of 1 881.62 meters using low-density drilling fluid, which not only increased the penetration depth but also reduced drilling fluid costs. The application results show that this technology can penetrate formations with severe circulation loss and frequent high casing pressure without causing plugging or requiring additional equipment. This technology significantly improves production efficiency while achieving cost savings, which meets well trajectory monitoring requirements and can be directionally drilled when necessary to ensure the trajectory conforms to design specifications. This technology can maximize reservoir exposure, achieve geological objectives, release production capacity, and further meet the requirements of efficient development, demonstrating promising application prospects.