METHOD OF PRODUCING GAS-BEARING FORMATION DRILLING-IN Russian patent published in 2003 - IPC

FIELD: drilling of gas wells with regulation of hydrostatic pressure in wellbore; applicable in drilling-in large-thickness overpressed formation. SUBSTANCE: method includes calculation of drilling mud minimal density in initial stage of drilling-in; determination of hydraulic losses in well annular space; building up of wellhead initial pressure to rated value; determination of gas-saturation permissible limits of drilling mud; drilling of the first interval and next interval of producing formation for controlled time with continuous monitoring of pressure in pipes and flow rate of drilling mud at well outlet. In the course of drilling of the first interval, when pressure in pipes remains invariable or reduces with simultaneous increase of drilling mud flow rate at well outlet, actual gas saturation of drilling mud is determined and compared with permissible limits, and if they equal each other, drilling of the first interval is continued by increasing wellhead pressure to maximum permissible value; and drilling is ended. When actual gas content in drilling mud exceeds the permissible limits, drilling is discontinued, formation fluid is washed out, maximum density of drilling mud is corrected, wellhead pressure is built up to maximum permissible value and drilling of formation is ended. When actual gas content in drilling mud does not attain limit value, drilling of the first and subsequent intervals is continued with initial wellhead pressure and with monitoring the pipe pressure. At the first interval, permissible limit pressure drop in pipes is determined, and, if actual pipe pressure drop is equal to permissible limits, drilling of next intervals is continued with increase of wellhead pressure to maximum permissible value, and drilling of formation is ended. In case of absence of gas inflow, i.e. at constant pressure in pipes and flow rate of drilling mud at well outlet, rated pressure differential is built up for tapped interval. Drilling is continued until increase of drilling mud flow rate at well outlet, and drilling program provided for drilling of the first interval and for the subsequent intervals is repeated with corresponding change of drilling parameters of the first interval with those of tapped interval. Drilling program is based on mathematical computations of actual data on drilling. EFFECT: improved quality and higher safety of formation drilling-in. 3 dwg, 1 ex