Development of downhole temperature and pressure simulation program 'WhiteCoal T'for drilling/completing methane hydrate zones

摘要

A downhole temperature and pressure simulation program for drilling, especially for safe methane hydrate drilling, has been developed under a joint R & D project led by Japan National Oil Corporation. The simulation program integrates a dataase management, a numerical computation core, and a graphical user interface(GUI)in a Windows-based application. It aims to support the control of emthane hydrate drilling by simulating wellbore temperature and pressure simultaneously. Three key models are employed in the computation core, 1) a one-dimensional flow dynamics model, 2) a two-dimensional heterogeneous heat conduciton model, and 3) a wellbore-formaction interface model. New features in the developmetn include, 1) computtion of circulating temperature profiles of not only the wellbore but also radially in the formation, 2)the ability to show the in-situ P-T conditions and hydrate equilibrium curve simultaneously, 3) use of mulatiple heat transfer corelation and rheology model opticons,4)ability to simulate heat transfer in a marine riser including buoyancy modules, 5) capability to simulate enviromental effects, such as current, sea temperature, etc., and 6) friendly GUI. The validation and fverificaiton(V & V)have been performed using field data. The comparision showed a good areement based on the return and downhole circulating temperature and st adpipe pressure. After the work of V & V, the simulation program has been successfully applied in the planning of, and during the drilling of the Japan MITI methane hydrate exploratory well"NANKAI TROUGH".