Efficiency Improvement in Deep Drilling of Archean Buried-Hill Reservoirs: A Case Study from Bozhong 19-6 Gas Field

Abstract Bozhong 19-6 gas field is the first 100 billion cubic meter condensate gas field in Bohai Bay, which is also a benchmark for deep oil and gas resource development there. The main target is Archean buried-hill, and fractures are well developed, the challenges in drilling include "deep depth (TVD 5500 meters), high temperature (204°C), poor drillability (The compressive strength reaches 276MPa), and high lost circulation risk". To overcome these challenges, drilling speed improvement method of each well section and formation protection measures have been proposed. Firstly, bit, bottom hole assembly and drilling parameters are evaluated and optimized to improve rate of penetration. Secondly, high-temperature resistant lubricants are developed to reduce drag and torque with long open hole section. To alleviate lost circulation risk and reduce formation damage, precise managed pressure drilling technology is employed during the drilling of high risk well sections and reservoir sections. Moreover, new high temperature resistant solid-free drilling and completion fluid system are developed to reduce formation damage. The bit suitable for different strata are designed and the rate of penetration has been increased combined with new bottom hole assembly. The footage of a single drill bit in the Archean buried-hill formation is greater than 200m, and the average rate of penetration is greater than 5.5m/h. The new lubricant can function well in the temperature of 220 °C. In field operations, surface torque has been reduced by 20% upon lubricant discharge from the drill bit. With the help of precise managed pressure drilling technology, the equivalent circulation density during drilling and tripping are controlled, and the mud density has been reduced by 0.1sg. These technologies have made economic development of Archean buried-hill reservoir come true. In this drilling campaign, the deepest well with MD 6088 meters has been successfully drilled.