Supercritical　water　injection　is　a　promising　technology　for　heavy　oil　thermal　recovery.　Predicting　and　regulating　the　thermophysical　parameters　of　supercritical　water　at　bottomhole　are　the　prerequisite　for　achieving　high　recovery　efficiency.　In　this　paper,　a　novel　numerical　model　was　proposed　to　simulate　wellbore　flow　and　heat　transfer　of　supercritical　water　injection.　A　modified　correlation　of　frictional　coefficient　was　developed　to　calculate　water　flow　resistance　near　its　critical　point,　where　its　properties　change　abruptly.　The　unsteady　heat　loss　to　the　formation　was　calculated　directly　by　solving　two-dimensional　unsteady　heat　conduction　equations.　They　were　respectively　coupled　in　momentum　and　energy　balance　equations　using　an　iterative　scheme.　This　model　was　proved　to　be　accurate　by　two　oilfield　cases　in　which　the　relative　errors　of　wellbore　fluid　pressure　and　temperature　are　less　than　1%.　Then　parameters　sensitivity　analysis　of　the　injection　pressure,　temperature,　mass　flux　and　the　apparent　heat　conductivity　of　insulating　tube　was　conducted.　The　results　indicated　that　the　temperature　variation　of　wellbore　fluid　depended　on　both　enthalpy　drop　(or　heat　loss)　and　Joule-Thomson　effect.　An　abnormal　phenomenon　that　the　fluid　temperature　increased　with　wellbore　depth　near　the　critical　and　pseudo-critical　points　was　found　because　of　the　sudden　increase　in　high　heat　capacity　and　Joule-Thomson　coefficient　of　water.　Raising　the　bottomhole　fluid　temperature　was　the　key　to　enhanced　oil　recovery　by　supercritical　water　injection.　Low　apparent　heat　conductivity　of　insulating　tube　contributed　richly　to　raise　bottomhole　fluid　temperature　by　enlarging　thermal　resistance　and　reducing　wellbore　heat　loss.　There　existed　an　optimal　mass　flux　for　maximizing　bottomhole　temperature,　because　when　the　mass　flux　increased,　the　shortened　resident　time　within　wellbore　and　the　decreased　fluid　pressure　favored　temperature　increase　and　decrease　respectively.　Selecting　an　injection　pressure　near　the　critical　or　pseudo-critical　point　and　raising　the　injection　temperature　would　increase　the　bottomhole　temperature　and　reduce　relative　fluid　heat　loss.　©　2022　Elsevier　Masson　SAS