The Thermal And Hydraulic Analysis Of Banbei's Unheated Oil Gathering

The increased water cut in the well stream provides the possibility for the gathering pipelines to be operated without heating.However,corresponding to the complex multiphase flow of oil-gas-water in the gathering pipeline and the gel deposit of crude oil on pipe wall,the traditional calculation method of temperature profile and pressure profile of pipeline was challenged.In order to realize the boundary operating conditions for the unheated gathering pipeline,the adaptable hydraulic calculation method needs to be obtained by taking into account the effect of gel deposit and decreased viscosity of oil-water 1mixtures of high water cut.In this paper,the gathering pipelines in Banbei block of Dagang oilfield was objected for the study of boundary operating conditions.By analyzing both the thermal and hydraulic conditions,a comprehensive method was obtained to assess the feasibility of unheated operation.Firstly,the basic properties and rheological properties of the Banbei crude and the oil-water mixtures of higher water cut were measured,including the crude's density,pour point,wax characteristics and viscosity-temperature characteristics.The oil-water mixture of higher water cut was regarded as a dispersion system of W/O emulsion in free water.Five calculation methods were analyzed and compared.Using the regressed parameters,the recommended Yu Chenyang model provided the lowest average deviation of 13%to the measured viscosities.This method is featured of taking into account the contribution of stable emulsified water on the viscosity of the mixture.Based on the flow characteristics and field data of the high water cut oil gathering pipeline in the Banbei block,9 pressure drop calculation models were assessed.The recommended Mojiawo-Rao calculation model was proper for Banbei gathering pipeline,which provided the lowest average relative deviation of 18%.The calculation method also take into account the elevation loss and decreased flowing area caused of gel deposit.For the thermodynamic calculation,the effect of Joule-Thomson effect was considered.For the case data of 17 groups,the calculated temperatures were close to that calculated by PipePhase and OLGA.The averaged deviation was separately 0.99 ~oC and 0.94 ~oC.Based on the recommended thermal and hydraulic calculation methods,a calculation software was compiled.By using the criteria of wellhead pressure lower than 1.5MPa and the node temperature not lower than the starting temperature of gel deposit,the maximum oil-gathering radius of each node in Banbei gathering pipeline was calculated.The actual length of the pipeline was compared with the maximum radius to determine the feasibility of the unheated operation.According to the production data of the Banbei block in 2016,the actual lengths of pipelines were lower the respected maximum oil gathering radius of each node,the unheated gathering pipeline can be safely operated.