| With rapid growth of national economy and demand for natural resources in China, mineral exploration is going toward more deep-hole operations and complicated ground formations at a fast pace. Compared to advanced exploration drilling technologies in the world, China is still behind many other countries in terms of drilling equipment and drilling methodology. In the field of deep-hole complex-ground wire-line core drilling, lots of new drilling technologies have not been well promoted and used in exploration drilling operations in China. Deep-hole complex-ground drilling is among the current hot and challenging topics in the industry of mineral exploration. The key technical challenges involve equipment deployment, accident prevention and treatment, drilling fluid control, drilling parameter design and site management, etc.In this paper, we are going to do a summary of national and international technologies related to deep-hole complex-formation exploration drilling in areas of drilling equipment, drill rods and drill tools and drilling techniques. We will make a thorough study on the geological condition and down-hole characteristics of a deep-hole complex-formation drilling project in Yunan province, South China. We will then define the main challenges for the drilling tasks and raise key topics of the study. The study of this paper will focus on how to fulfill the tasks in drill-hole design, drilling equipment selection, drilling process set-up, drilling fluid utilization, drilling accident control, etc. with on-site examinations on the key operational techniques at the drilling project. With all the studies, this paper will lead to the following achievements:1. Drill-hole design and drilling equipment selectionBased on the specific characteristics of the ground formation of the mine site and general principles of wire-line core drilling, this paper will introduce the guidelines for drill-hole design, drilling process selection and drilling fluid application, risk control and accident handling, as well as guidelines about how to use accessorial equipment for drilling and pumping. 2. Drilling process and techniquesBased on the complexity of the up-layer overburden and caving formations, this paper will analyze the general techniques of overburden drilling and then configure practical drilling process for the specific ground formation. It will also define the productive ways on how to select the drill bits, drill rods, drill tools and drilling parameters.3. Drilling fluid system designIn view of the great ground stress existing at the mine site, this paper will stipulate the ways to predict the shear and collapse stress of the ground by testing the leaking rate and fluid density in the drill-hole. It is defined that the balance condition of the drill-hole is Pw+PH<Pp+Popm or Pw+PH+Pops≤Pp, while the proper range of the fluid density is1.08～1.15g/cm3. This paper will give recommendations on two types of fluid system to deal with the complexity of the ground formation. The first is0.15～0.20Quick-Gel+0.04～0.07%EZ-MUD Gold+0.07～0.11%Liquid-Pol+0.07～0.20%Quick-Trol Gold or0.20～0.28%AUS-Trol+PAC-R or PAC-L+<0.2%CR650+Bit Lube or Torq Free; The second is1.43～2.15%of Quick-Gel+0.7%PAC-R+0.7～1.43%+<0.2%CR650+Bit Lube or Torq Free. Meanwhile, this paper will analyze the proper methods to process, maintain, and use drilling fluid at the worksite and the requirements on quality control.4. Down-hole risk control and accident handlingDown-hole risk control and accident handling is key drilling technologies. This paper will explore in both theory and practice the application of ground stress prediction, stuck-point calculation, and drilling fluid control techniques to reduce and resolve drilling accidents effectively with output of innovative experiments in the field of exploration wire-line core drilling.5. Research on application of key drilling technologiesThis paper examines the use of press-break leaking test method to predict ground stress and leaking pressure, which provides a good foundation of fluid design and technique selection of the Yunnan drilling project. This paper also offers guidelines on the utilization of drilling fluid products in terms of fluid processing, fluid solid control, and fluid quality maintenance. This paper shows the feasibility of resolving drill-hole accidents in the way of stuck point prediction and stuck point handling.The methods explored by this paper were tested at a drilling project in Yunnan province in South China, where all the drill holes were completed down to the designed depths (650-1500m).The result of the tests approves that those methodologies can be general guidelines for deep-hole complex-formation drilling operations. |
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