Research On Pressure Distribution And Productivity Law For Horizontal Cycle Steam Stimulation Wellbore

Cycle steam stimulation by horizontal well is an important method for early developmentof heavy oil reservoir. Following questions need to be studied seriously: downward flowmechanism of steam in vertical wellbore, variation of porosity and permeability after steaminjecting into formation, coupled thermo-hydro analysis for steam flow in horizontal wellboreand reservoir. All the questions have important theoretical guidance to improve thedevelopment effectiveness of cycle steam stimulation.Downward flow pattern transition criterion and corresponding pressure drop modelswere studied based on gas-liquid two-phase theory. Steam dryness and temperaturedistribution along vertical wellbore were deduced on the principle of energy conservation.Solution procedures for above models were given in the paper. Under the consideration ofvariable mass flow and interaction of fluid physical parameters, temperature and pressuredistribution of steam and produced fluid in horizontal wellbore were derived by combingmass conversation, energy conversation and momentum conversation. Variation of porosityand permeability caused by temperature change was studied based on the definition of volumestrain. According to energy conversation principle, model for dynamic temperaturedistribution of reservoir was deduced. Difference equation of the model was derived by firstlyseparating differential equation into radial and axial and then integrating. Seepage law ofoil-water two-phase and pressure distribution in reservoir were studied on the basis ofpotential superposition principle. Under the consideration of coupled thermo-hydro betweenhorizontal wellbore and reservoir, variation of porosity and permeability caused bytemperature, Models for dynamic temperature field, pressure field, steam absorption profile,production profile and saturation distribution in reservoir were established. The solution procedures for coupling model were shown in the paper. Calculation program was written.Results obtained by program were analyzed and compared with measured data.Comparison shows that calculation results derived by the models in paper are closer tothe measured data than traditional Beggs-Brill method when pressure drop of downward flowis calculated. The maximum error of models in the paper is lesser than5%. For theproductivity calculation in horizontal segment, results calculated by the models in paper havehigher coincidence degree with measured than CMG. Models in the paper need relatively fewbasic data and are easier to use.