METHOD FOR OPENING FORMATION CHARACTERIZED BY DISASTROUS LOST CIRCULATION BY DRILLING THEREOF Russian patent published in 2005 - IPC

FIELD: oil and gas well drilling, particularly for exposing formation characterized by disastrous drilling mud losses.

SUBSTANCE: method involves determining loss interval and such characteristics as loss intensity, presence of drilling tool falling in and penetration speed change on the base of drilling material and geophysical investigations carried out in neighboring wells; determining formation pressure and opening thereof by performing drilling process with the use of sludge treated with filling agent. Before sludge preparation formation pressure of the formation is determined from mathematical relation. Opening of loss interval characterized by partial losses is begun with the use of sludge having funnel viscosity of 35-40 s and density providing drilling mud head pressure excess over formation pressure for 0.3-0.4 MPa and including fibrous filler in amount of 8-10% of drilling mud volume. Bottomhole assembly has weighted well tube of 75-100 m length and 165-178 mm diameter and including drilling bit without nozzle. Well bottom flushing is performed with the use of above drilling mud at throughput of not more than 14-15 l/s. In the case of drilling mud loss threaded filler content in the drilling mud is increased up to 25-35 %. Well bottom flushing during well deepening is performed with pumping capacity of 3-4 l/s up to circulation restoring. After full loss interval penetration loss area is consolidated by cement grout injection.

EFFECT: possibility of loss area isolation during opening thereof and, as a result, decreased cost of formation opening.

3 cl, 1 ex