Kick Detection And Well Control Technology During Deepwater Drilling

As greatly increasing oil&gas demands due to rapid national economic growth,the E&P of deepwater oil and gas reservoirs is one of the important measures to ensure the national energy security,the E&P of deepwater oil and gas reservoirs has suffered many technology challenges related to seawater depth and offshore environment,especially the deepwater well-control risk.Once the blow-out occurs during deepwater drilling,there will be irretrievable casualties and prolonged damage to the offshore environment.In order to provide adequate kick warning time,it's pressing priority to develop the early kick detection devices for deepwater drilling.The presence of shallow gas and shallow flow in the formation near the mud line also bring potential risks for surface drilling in deepwater.It is necessary to understand the occurrence and growth of kick with a suitable pressure transmission model among the formation-wellbore-equipment on the surface by using riser.Once the kick occurs,feasible method can be proposed to control kick in the safety range of well control equipment.Such early kick detection device and kick control technology have great theoretical and practical significances on deepwater drilling safetyBased on extensive research in early kick detection methods during deep water drilling at home and abroad in recent years,ultrasonic attenuation in fluid with high solid content was studied,frequency of ultrasonic sensors was optimized.In order to improve measurement accuracy,according to the ultrasonic Doppler effects and annulus geometry,arrangement of ultrasonic sensors was optimized.The transmitting and receiving circuit,the DSP(digital signal processing)circuit were designed.A non-invaded apparatus for the early kick detection to measure the annular velocity was developed,lab-testing was carried out to obtain the data of different annular velocity with various drilling fluid densities,flow rates and gas injection rate.Measurement results show annulus velocity of fluid with less than 10%gas content can be accurately measured with relative error of less than 10%.Based on deep research on DKD theory,combining the basic theory of multiphase flow and the characteristics of variable flow rate and variable density,this paper presented calculation model to determine fluid density,pressure friction loss and pressure within annulus at different time.The outlet density of the mixing bunker is calculated at different time during DKD.The variation of bottom hole pressure and annulus pressure with time under different flow rate combination were investigated and drilling parameters on DKD were optimized as well.The simulations of wellbore pressure in three Gulf of Mexico deepwater wells DKD demonstrate the validity of DKD model.Actually,the friction pressure loss with annulus during the dynamic kill drilling is too small to affect the distribution of wellbore pressure,the key aspect of DKD lies in the adjustment of flow rate ratio of weighted drilling fluid and seawater.Considering the heat exchange among drilling fluid,casing/formation and riser/sea water,the calculation model of transient temperature during deep-water drilling was proposed,transient circulation temperature distribution within annulus by using the water-based and oil-based drilling fluid were simulated,which provides the basic parameters to calculate annular pressure.Based on multiphase theory,a mathematic model was proposed to simulate the wellbore pressure transmission among the formation,wellbore,riser and rig pressure control equipment.Using drilling data of the South China Sea oil field,effects of gas invading volume on velocity of hybrid fluids,ratio of liquid,annulus pressure were analyzed,bottom hole pressure,gas invading volume,annulus pressure distribution with time were simulated.The results show that the annulus flow rate will increase dramatically below 300m of the drilling platform in a kick,which causes risks for the safety of deepwater drilling.Considering effects of annulus temperature,payzone inflow,pressure at choke manifold,well-killing models of the deep-water driller's and engineer's methods were proposed,standpipe pressure and pressure at choke valve with time during the well-killing operations were simulated.The pressure friction loss in the choke line cannot be ignored during the deepwater well control practice.Since the maximum choke pressure of Engineer's method is less than that of the Driller's method,the Engineer's method should be the first priority in the deepwater well killing process if the preparation ability of the killing mud is not strictly limited.These killing models were applied to simulate the well killing processes of two deepwater wells in South China Sea and West Africa Sea,the simulation results show the relevant theory can meet the needs of deepwater well control.Through the research above,this paper presents comprehensive theories and technology on early kick detection and deepwater well control.The non-invading early kick detection method,DKD theoretical models with variable density and flow rate and theoretical models to simulate standpipe pressure and pressure at chock valve during deepwater well-killing practice were innovative in this area.The results of this paper provide fundamental theory and technical supports for early kick detection and well control practice during deepwater drilling.