单相地层流体取样筒的研制与应用

Development and Application of Downhole Mono-phase Sampling Tank

在电缆地层测试取样作业时,当取样筒回到地面后,温度的降低会导致取样筒中的地层流体样品油气分离。采用塑性失效准则和爆破失效准则对单相地层流体取样筒MPST的承压能力进行计算,研制一种单相地层流体取样筒。采用预充氮气压力补偿技术,消除因温度降低引起的样品压力减小,使回到地面的地层流体样品压力保持与井底所处地层压力相同甚至更高,从而获得高质量的单相地层流体样品。试验井测试和海上作业的成功应用证明了单相地层流体取样筒的有效性和可靠性。

As the sample returns to the surface, the lowering temperature results m a pressure drop within the sealed tank, which in most cases causes the sample to pass through the bubble point line to a gas and liquid mixture. A Mono-phase Sampling Tank （MPST） is developed to solve this problem. We calculate the loading capacity of MPST with plastic failure criterion and burst failure criterion. The MPST consists of two floating pistons with a pre-determined charge of nitrogen between the pistons. Expansion of the pressurized nitrogen gas compensates for the pressure drop in the sample due to temperature loss as the sample is retrieved from the well and transported to the lab. The pressure compensating feature provides sample recovery at pressures equal to or greater than reservoir pressure. So the high-quality reservoir fluid can be recovered. Functions and reliability of MPST are proved by the experiments and offshore downhole logging applications.