煤层气欠平衡钻井环空注气工艺优化

充气欠平衡钻井技术是目前煤层气钻井中减少煤储集层伤害、保护煤储集层最常用的措施之一.针对煤层气羽状水平井充气欠平衡钻井技术特征,优选了水平及竖直井筒内多相流动压降计算模型,确立了井底欠压值的求解方法,给出了求解的计算流程.根据沁水盆地煤层气田某羽状水平井实际资料,通过对不同注气压力、不同注气量以及不同钻井液排量条件下井底欠压值的计算和分析得出:当环空注气压力一定时,井底欠压值随钻井液排量的增大而单调递增,且环空注气量越大,井底欠压值越小;在最佳环空注气压力条件下,当钻井液排量一定时,井底欠压值随着环空注气量的增大而单调递减,当环空注气量一定时,井底欠压值随着钻井液排量的增大而增大.利用该计算模型和计算方法,结合现场欠平衡钻井工程要求.可以优化出最佳的环空注气工艺参数.

Optimization of annular gas injection technology in coalbed methane aerated under-balanced drilling

Aerated under-balanced technology is one of the commonly used technologies in coalbed methane (CBM) drilling for protecting the coal seams from pollution. Based on the characteristics of the aerated under-balanced drilling (UBD) for CBM pinnate horizontal wells, the mathematical models for calculating multiphase flow pressure drops both in horizontal wells and in vertical wells are optimized, and the solution to bottom hole under-pressure value and its calculating flow diagram are also proposed. With the established models and the data from a CBM field of Qinshui Basin, the bottom hole under-pressure values were calculated under different gas injection pressures, different gas injection rates, and different mud flow rates. The analysis shows that when the gas injection pressure is constant, the bottom hole under-pressure value increases with the increase of mud flow rate, and the bigger the annular gas injection rate, the smaller the bottom hole under-pressure value; under the optimum gas injection pressure, the bottom hole under-pressure value decreases as the annular gas injection rate increases when the mud flow rate is constant, and the bottom hole under-pressure value increases with mud flow rate when the gas injection rate is constant. By using the calculating models and methods, the optimal parameters of annular gas injection could be acquired according to field requirements of under-balanced drilling.