微泡沫钻井粗泡沫堵漏工艺在TBK气田的应用

TBK气田海拔1125m,表层主要是无压裂缝性碳酸盐岩地层,井眼直径914.4mm。钻井过程中的主要困难是严重漏失和大井眼清洁。用膨润土钻井液、正电胶钻井液和清水钻进时,有进无出,而盲钻常常砂卡钻具。微泡沫钻井液既可降低井筒液柱压力,又可在近井壁形成一个类似于"液体套管"的滞留层,因而在钻井过程中具有非常好的防漏作用。粗泡沫堵漏工艺,是在钻穿漏层后,将适量微泡沫钻井液配成密度略高、可循环、但不太稳定的泡沫钻井液,缩短泡沫稳定时间,故意让泡沫液进入裂缝。在低流速或静止状态下,微泡沫就会变成"蜂窝"状的结构强度很大的泡沫凝胶,对漏失通道产生"气锁"和凝胶封堵,防止固井水泥浆漏失。现场应用表明,微泡沫钻井液密度低,黏切高,可循环,成本低,不需增加任何设备,具有非常好的防漏作用和岩屑携带能力;粗泡沫堵漏工艺操作简单,施工方便,堵漏效果好,注水泥固井一次成功。

Application of Micro-Foam Drilling Fluid and Coarse-Foam Plugging Fluid in TBK Gasfield

TBK Gasfield is located at an elevation of 1125 m, with its surface formation mainly consisted of fractured carbonate, and the hole size is ?914.4 mm. The main troubles encountered during drilling were severe lost circulation and poor cleaning in large hole, and when clay drilling fluid, MMH fluid and clean water were used no fluid returned up to the surface, while pipe sticking often took place when drilling was continued. Micro-foam drilling fluid drops borehole hydraulic pressure and at the same time forms a resorting layer similar to a fluid casing in the near wellbore area, thus it exhibits very good lost circulation prevention during drilling. Coarse foam plugging technology involves mixing certain amount of micro-foam drilling fluid into recyclable foam drilling fluid of higher density and minor stability, aiming at shortening the foam stabilization time and letting foam fluid entering into the fractures. In the condition of low flow velocity or static, the micro-foam then turn into cell like foam gel of high structure strength, and forms gas block and gel sealing to the lost circulation communications, and this in turn prevents cementing slurry from losing. Field applications showed that the micro-foam drilling fluid has such advantages as lower density, higher visco-shearing, recyclable, low cost, minimum equipment requirements, and good cuttings transportation; while coarse foam plugging technology is easy to operate and conduct, and it produces good plugging results and cementing quality.