土库曼斯坦阿姆河右岸B区高风险气藏安全钻井技术

在土库曼斯坦阿姆河右岸B区钻井史上,由于存在高压浅层次生气层、高压盐水层、高压高产气藏以及巨厚盐膏层的复杂地层,因而井喷、卡钻、高压盐水结晶导致井筒报废等事故频发,钻井成功率仅为64%,钻井安全风险极高,部分气田已禁止钻井施工。为此,针对性地开展了如下安全钻井技术试验与应用:(1)针对浅层次生高压气层,采用小尺寸领眼试钻,很大程度上减少了井筒容积,使进入井筒油气的量大大降低,减少了加重钻井液,加快了压井作业时间,提高了钻遇复杂层的安全性,同时在浅层气井区外围采用了钻大斜度井定向井强采方案;(2)针对高压巨厚盐膏层,优选了与盐膏层相配伍的欠饱和—饱和盐水钻井液体系,优选了盐岩蠕变模型,建立了盐膏层井眼缩径方程,形成了钻井液密度图版,确定了盐膏层安全钻井液密度,有效地提高了盐膏层段钻井液的抗污染性和抗蠕变性,保证了井筒安全。相关配套技术已推广应用近百口井,钻井成功率达100%,井喷发生率为零,解放了"钻井禁区",较好地解决了该区域高风险天然气井安全钻井难题。

Drilling safety technologies for high-risk gas reservoirs in Block B on Right Bank of the Amu Darya River,Turkmenistan

In the Block B on the Amu Darya River Right Bank, Turkmenistan, the formations are complex with high-pressure shallow secondary gas zones, high-pressure brine zones, high-pressure high-yield gas reservoirs and huge thick salt-gypsum layers. In its drilling history, therefore, blowout, pipe sticking and high-pressure brine crystallization often result in well abandonment, so the success ratio of well drilling is only 64%. Obviously, its drilling risk is so high that drilling of some gas fields have been prohibited. In view of this, a series of safe drilling technologies were tested and applied in this block. As for high-pressure shallow secondary gas zones, small-size pilot hole trial drilling was adopted to reduce borehole volume to a large extent, so that the oil and gas flowing into the borehole was reduced significantly and heavy weight drilling fluid was reduced. Well killing operation lasted a shorter time and the safety of drilling complex formations was improved. Moreover, the enhanced recovery program of drilling high inclination directional wells was applied in the periphery of shallow gas well blocks. As for high-pressure huge-thick salt-gypsum layers, the drilling fluid of undersaturated-saturated brine compatible with salt-gypsum layers was optimized. Salt rock creep model was optimized, and borehole shrinkage equation of salt-gypsum layers was established. Drilling fluid density chart was prepared and the density of drilling fluid for safe drilling in salt-gypsum layers was confirmed. The pollution resistance and creep resistance performance of drilling fluid in salt-gypsum layers were improved efficiently, and borehole safety was guaranteed. These technologies have been applied in almost 100 wells with a drilling success ratio of 100% and a blowout accident rate of zero. As a result, the "prohibited drilling zones" could be drilled, and the challenges against drilling safety of high-risk gas wells in this block is better met.