Difficulties and countermeasures for ROP improvement of horizontal drilling in the conglomerate oil reservoir of the Mahu sag: A case study of the Jinlong-2 well district

The drilling interval of the Upper Wuerhe Formation of the Mahu conglomerate oil reservoir has high heterogeneity and is prone to collapse. Moreover, the drilling interval of the Jimuhe Formation suffers from low drillability and frequent lost circulation caused by well-developed microfractures. The rate of penetration (ROP) is low, the casing program is complex, and the cycle of drilling and well completion is rather long. Given the above technical difficulties, with the Jinlong-2 well district in the Mahu sag as an example, the plans to optimize the drilling fluid performance and casing program and introduce impregnated PDC hybrid bits were proposed after comprehensive analysis of the geology, lithology, formation pressure system, drilling complexities, and drilling cost. The field application shows that, in the Upper Wuerhe Formation mudstone in the Jinlong-2 well district, the average reaming ratio of wells is reduced from 45.2% to 13.8%, and the drilling/completion period per well is shortened by 50.5%; in the Jiamuhe Formation, the average lost circulation count of wells in horizontal section is decreased by 73.7%, the average volume of lost circulation is reduced by 94.3%, and the ROP is improved by 55.4%. This research provides theoretical support for safe and efficient drilling/completion of horizontal wells in the Mahu conglomerate oil reservoir, and it is highly valuable for building the production capacity of 5 million tons in the Mahu area.