沥青层钻井液柱压力关键影响因素及控制技术

 沥青层安全钻井问题困扰Y 油田的开发，微小的钻井液柱压力波动即可引起沥青流动侵入井内而发生复杂事故或弃井。分析表明，污染后钻井液性能恶化快、沥青易黏附固相颗粒、高温可流动性好、钻井液与沥青的置换型漏失等造成钻井液柱压力难以控制，进而造成沥青侵入速度与程度得不到有效控制。室内和现场试验表明，保持钻井液膨润土含量1%、随钻堵漏材料含量8%左右有利于钻进时钻井液柱压力控制；稠化封堵技术可减慢停止循环时的沥青侵入速度；控压钻井（MPD）技术可有效调控井筒液柱压力，以较低钻井液密度钻穿沥青层，降低沥青与钻井液置换量、侵入速度与程度到可控水平。

Key Influencing Factors and Control Technology of Drilling Fluid Pressure in the Bitumen Zone

The exploration of Y oilfield seriously suffered from safety problems in the bitumen zone. Slight fluctuation of low drilling fluid pressure may trigger the mobilization and invasion of near-wellbore bitumen, which may lead to complex accidents or well abandonment. Analysis indicated that it is hard to control the drilling fluid pressure because properties of bitumen-contaminated drilling fluid quickly got worse. Bitumen has good liquidity at high temperature and adhered solid particles easily. Even worse, displacement loss of drilling fluid and bitumen accelerated invasion of bitumen. Thus, the degree and speed of bitumen invasion got out of hand. Test results in lab and field showed that, in order to control drilling fluid pressure, the contents of bentonite and plugging materials at about 1% and 8% respectively in drilling fluid are crucial while drilling. Meanwhile, invasion speed of bitumen can be reduced by thickening and plugging technology during circulation stop. The managed pressure drilling (MPD) technology can be used to effectively control wellbore drilling fluid pressure and drill through bitumen formation with lower drilling fluid density. Then the displacement amount of bitumen and drilling fluid, invasion degree and speed were reduced to a "controlable" level.