Drilling Fluid Technology for Drilling Deep Broken Formations in the Exploratory Well Huashen-1x

Well Huashen-1x, designed to drill to 5713.16 m, is the deepest exploratory extended-reach well deployed by CNPC in Fushan oilfield, Hainan. This well was drilled to ascertain the reservoir engineering data of the member Liu-3 located on the top of a fault nose structure. This well is located in the Fushan depression in the Beibuwan Basin, and the formation at the deep part of the well is the so-called Liushagang formation of the Paleogene System, which is complex. Faulting, broken belt of 1300 m in length, hard and brittle mudstone, developed micro fractures and beddings, strong water sensitivity of the formation rocks which are very instable and easy to slough, and high well temperature of up to 180℃, are all challenges to drilling fluid operations. The maximum displacement of the well designed was 3208 m. Extended-reach well places higher requirements on the rheology, inhibitive capacity and lubricity of the drilling fluid. During drilling, lack of understanding of the lithology of the formations resulted in severe sloughing in the highly deviated fourth interval and three times of sidetracking in this interval. In the third sidetracking, a drilling fluid formulated with organic salts and inorganic salts was used. This compounded salt drilling fluid, with its strong inhibitive capacity, good plugging capacity and high temperature resistance, resolved the borehole instability problems encountered in the broken belt between the Liu-2 member and Liu-3 member of the Liushagang formation, ensuring safe drilling and other operations in the fourth interval.