A Study On Dynamic Kill Of Relief Well

The relief well is one of effective measures to address blowout accidents.However,the study on relief well killing is not sufficient and there are few killing models which consider multiphase flow.For the direct intersection,there are insufficient researches concerning gas-liquid two-phase flow below the injection point.And few models are present for the case of fracturing intersection.In addition,the lack of relief well killing software has seriously restricted the application of national relief well technology.In this paper,the experimental study of gas-liquid two-phase flow below the injection point(namely,zero liquid superficial velocity flow,ZLSV flow)is carried out in a 12-m long,100-mm ID vertical pipe,and the flow pattern transition criteria are established.The mechanism of flow pattern transition of ZLSV flow is revealed,which lays a foundation for studying the gas-liquid two-phase flow law below the injection point.Considering multiphase flow and the falling of the killing fluid at the injection point,the model and algorithm for the relief well killing are established.Additionally,the model for the case of fracturing intersection is proposed based on the pseudo-3D fracture model and the software module of the relief well killing is developed.It is found that the predicted results by published flow pattern transition model are larger than experimental values of ZLSV flow.The new model for bubble-to-slug flow transition is based on the theory of central bubble coalescence.Considering the disturbance of the strong wake effect on the liquid slug,a slug-to-churn flow transition model is established.The predicted values of new models are in good agreement with experimental results.For the case of direct intersection,in the early stage of killing,the killing fluid does not fall at the injection point due to the large gas velocity.As the bottom hole pressure increases and gas production rate decreases,the killing fluid begins to fall when the gas velocity at the intersection point becomes less than the critical velocity,and ZLSV flow forms in the open hole,which can significantly increase the pressure drop in the open hole.The higher killing rate and the heavier killing fluid will help increase the bottom hole pressure and shorten the killing time.The influence of killing fluid density on wellbore pressure is more obvious when the killing rate is lower.For the case of fracturing intersection,for the sand-filling fracture,the pump pressure is mainly consumed in the fracture while for the non-sand-filling fracture,the pump pressure is mostly consumed in the wellbore.The increase of fracture size can obviously reduce the pressure loss for sand-filling fractures while this effect is insignificant on that of nonsand-filling fractures.However,the required pump pressure for the case of non-sand-filling fracture is always lower than that of the sand-filling fracture.Therefore,when the blowout well is successfully intersected,it is better to use the non-sand-filling fracture to perform the killing operation.