渭北煤层气老井改造优化设计与实践

渭北煤层气田传统定向井和直井面临压裂改造效果差、单井产量低等生产难题，根据井网部署和煤层地质特点，提出了适合渭北煤层气老井改造的水平井布井方案。针对渭北煤层气田上部地层漏失、下部煤层埋深和厚度变化大、煤层易垮塌等水平井钻井难点，利用Petrel软件进行地质建模，准确标定煤层层位，通过Landmark钻井工程设计软件计算并精确建立了入靶井斜-靶前距-井眼狗腿度计算图表，实现不同地层倾角、厚度下的井眼轨迹优化设计；配套优选可循环微泡沫钻井液，解决上部地层漏失和煤层垮塌严重问题。现场应用表明，水平段位于煤层以上3 m范围，水平井全井段钻井液漏失量低，钻进速度快；同时通过集成应用分段压裂改造技术，水平井在主力11#煤层横向上可一次改造6口低效生产井，压裂缝网之间和井间干扰明显，有助于增大泄流面积，提高水平井单井产量。

Optimal design of old well stimulation in the Weibei CBM Field and its application

In the Weibei CBM Field, traditional directional wells and vertical wells are faced with several production difficulties, e.g. poor fracturing stimulation effect and low single-well production. In order to deal with these difficulties, this paper proposed a horizontal well deployment scheme suitable for the old well stimulation of Weibei CBM Field based on well pattern arrangement and geological characteristics of coal beds. In view of the drilling difficulties of horizontal well in the Weibei CBM Field (e.g. circulation loss in the upper formation, great variation of coalbed burial depth and thickness in the lower part, and caving coal bed), the geological modeling was carried out using the software Petrel, so as to calibrate the horizons of coal beds accurately. The chart for calculating target-entering deviation-frontal distance from target point-hole dogleg was prepared accurately using the drilling engineering design software Landmark, so as to optimize the design of wellbore trajectory at different formation dips and thicknesses. The matched circulating micro-foam drilling fluid was selected to deal with the circulation loss in the upper formation and the serious coalbed collapse. Field application indicates that when the horizontal section is set 3 m above the coal bed, the circulation loss in the whole horizontal well is low and the rate of penetration is high. And combined with the staged fracturing stimulation technology, horizontal well can stimulate six low-efficiency production wells laterally in the principal coal bed (11# coal bed) in one time, leading to obvious interference between hydraulic fracture networks and between wells, which is conducive to increase the drainage area and improve the single-well production of horizontal wells.