حفاری جهت دار در محیط های ناپایدار و متزلزل

ABSTRACT Directional drilling in unstable environments

Directional drilling has been developed and evolved as a safe and reliable means to position boreholes in coal seams and the surrounding strata to allow gas drainage, exploration ahead of development and water management [1–7]. But any drilling requires a stable environment to provide stable boreholes while drilling and for those boreholes to remain open through their functional life.

Coal seams have been subjected to numerous and various forces which create areas of fractured coal and unstable strata. Drilling into or through areas of unstable ground has always been a major problem for drillers. Even with precautions, caving can occur and bog the drill string in the borehole. This can result in the loss of drilling performance and equipment, project delays while attempts are made to retrieve the string, and steel left in the coal seam to be later intersected by mining.

The cost of equipment at risk is increasing as drilling technology improves and more expensive equipment is being used in-hole. Before any drilling is undertaken, it is logical to assess and define the potential drilling environment. Drilling projects can then be planned to manage the environment and to successfully complete the project while avoiding the adverse effects of intersecting unstable drilling conditions.

Unfortunately, even with the best planning and prior knowledge, drilling equipment does get bogged with potential loss at high expense. With increased exposure to adverse drilling conditions and bogging events, over-coring to recover bogged equipment has become an established practice.