Research On Prediction And Control Of Annular Pressure Buildup In Deep Water Oil And Gas Wells

Offshore oil and gas resources are one of the most important parts of the global oil resources.As the deepwater drilling and exploitation of oil and gas resources is harsher than the onshore conditions,the technology is more complicated.And the phenomenon that the high temperature fluid flowing from the bottom of the well to the wellhead,leading to the annular pressure buildup because of transferring the heat through the several layers of medium is one of the major problems in the production of deepwater oil and gas wells.Condsidering the problem of Annular Pressure Build-up encountered in the development of oil and gas fields in deep water,foreign countries formed a more mature approach to governance.However,the domestic research started late,which has not yet formed a completely independent comprehensive management measures.Therefore,in order to break the monopoly of foreign technology quickly,it is very important to study the prediction and control technology of Annular Pressure Build-up in deepwater oil and gas wells to meet the urgent need for comprehensive Annular Pressure Build-up control measures and technology.Combined with the calculation and evaluation method of wellbore temperature and pressure,the transient and semi-state model heat transfer model of wellbore temperature prediction in deepwater oil and gas wells is established.By studying both the domestic and aborad wellbore structure and production status of deep-water wells,it is recommended to use the transient heat transfer model to solve the annular temperature.The transient heat transfer model is used to solve the annular temperature,which is time dependent through the whole working process and both radial and axial heat transfer are taken into account.According to the temperature distribution of natural gas,it can be seen that the results of the transient heat transfer model are closer to the measured results,the maximum error is about 3%,and the maximum error of the semi-state heat transfer model is more than 7.5%.Considering the influence of axial heat transfer,the results of transient heat transfer model do not show the discontinuous curves in the calculation results of semi-state heat transfer model,which is more consistent with the actual temperature distribution of deep-water oil and gas wells.The trapped annular pressure prediction model of coupled annular volume and temperature is established,and the prediction model of connected annulus is deduced.The influencing factors of the annulus pressure are studied from three aspects:production measures,annular fluid properties and uncontrollable factors.The trapped annulus pressure increases with the increase of production time.Especially in the early stage of the production,the trapped annular pressure rises rapidly and exceeds the Maximum Allowable Working Operation Pressure.And the annulus pressure increases with the increase of the production rate.When the production rate is low,which is less than 1 million cubic meters per day,the output control can effectively reduce the annulus pressure.However,economic benefits must be considered,the production rate needs to maintain a high level.Therefore,annulus pressure control measures need to take to control the annulus pressure.The annular pressure increases with higher the expansion coefficient of the annular fluid,the smaller the compression coefficient,and the higher the thermal conductivity.The higher the geothermal gradient,the greater influence will be fot the annulus pressure bulid-up.The annulus pressure increases with the increase of the annulus length,while the other annular pressure changes have little effect.Based on the prediction model of annular pressure build-up,the working threshold of annular pressure relief tool is determined by the design analysis of casing strength and the Maximum Allowable Working Operation Pressure calculation method.In the case of a well in the LS gas filed of the South China Sea,and the process of the annular pressure control under different working conditions is simulated.At the beginning of the production test,the pressure on the annulus increases rapidly and the annulus exceeds the Maximum Allowable Working Operation Pressure in a few hours.The temperature return to the ground temperature gradient after the well shutting in,and the annular pressure eliminates.The annulus pressure quickly increased beyond the Maximum Allowable Working Operation Pressure after the well is re-opened to produce.Using the annular pressure relief tool combined with the annular pressure relif valve,which connectes the wellhead and the A annulus.And the annular pressure is relieved trough expelling the expansion liquid.In the production test,shutting down and recovering the well,well production process,the annulus pressure is always maintained within the Maximum Allowable Working Operation Pressure.