Research and application of small-diameter drilling technology for kilometer-scale weakly cemented sand-bursting strata

Abstract:

Aiming at the long-term technical bottleneck of difficult construction of small-diameter core drilling for solid mineral resources in kilometer-scale loose strata in China， this study takes the YZK01 borehole in a mining area of Qinghai Province as the engineering example. Through industry-university-research collaborative study， a complete set of small-diameter wireline coring drilling construction technology system is established. The borehole reaches a final depth of 1120 m， and the entire hole section consists of weakly cemented mud-sand strata with continuous water and sand bursting phenomena. An innovative precise pressure-controlled drilling fluid technology of "drilling fluid recharge + stepwise weighting" is proposed. Through differentiated layered design and dynamic regulation， the control accuracy of drilling fluid density is improved to 0.02 g/cm³， and the drilling fluid colloidal stability rate is increased from 65% to more than 98%. A self-developed negative pressure sand cleaning drilling tool assembly is adopted， which forms instantaneous negative pressure through a one-way valve during fishing operations to effectively remove fine-grained rock powder （less than 0.75 mm） at the bottom hole， with the cleaning efficiency more than three times higher than that of the traditional dry grabbing deslagging method. Meanwhile， a refined drilling parameter system characterized by "low speed， low pressure and small footage" is established， in which the weight on bit， rotational speed and run footage are controlled at approximately 50%， 60% and 30% of the conventional values， respectively. Field application results show that the average daily drilling footage is increased from the initial 3.2 m to 24.25 m， increased by about 658%. All key indicators including borehole verticality and core recovery rate meet the specification requirements. The novelty search report verifies that the research results fill the domestic technical gap of small-diameter drilling in kilometer-scale weakly cemented sand-bursting strata， and possess important engineering application value for deep mineral exploration in complex overburden areas of western China.