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欠平衡钻井(UBD)作为一种降低储层伤害的方法在油田中得到广泛应用。在钻达目的层时,当井筒压力小于地层孔隙压力,即井筒压力与地层孔隙压力之间存在一个压差,这样就能降低对储层的伤害。通常认为井底压差越大,储层受到的伤害越小,因此井的产量也越高。但较大的井底压差可能引起钻井操作过程中的其他问题,例如井筒崩塌引起的井筒损坏、过多的地层流体流入井筒而需要地面处理。在考虑地质条件的情况下,找到和使用一个优化合理的压差,通过合理的井筒压力平衡井眼周围地层的损害是目前迫切需要的。
Underbalanced drilling (UBD) is widely used in the field as a method of reducing reservoir damage. When drilling the target layer, when the wellbore pressure is less than the formation pore pressure, there is a pressure difference between the wellbore pressure and formation pore pressure, which can reduce the damage to the reservoir. It is generally accepted that the greater the pressure at the bottom of the well, the less damage the reservoir is exposed to and the higher the production of the well. However, larger bottom hole pressure differences may cause other problems during drilling operation, such as wellbore damage caused by wellbore collapse and excessive formation fluid flowing into the wellbore and requiring ground handling. In considering the geological conditions, it is urgently needed to find and use an optimal and reasonable pressure drop to balance the damage around the wellbore with reasonable wellbore pressure.