The Research On Numerical Well Testing Of Carbonate Reservoirs

Carbonate reservoirs plays an important role in the distribution of oil and gas filed in the world. Based on the numerical reservoir simulation technology, the numerical well test interpretation technology provides a more accurate method in well testing of carbonate reservoirs.Based on the detailed research of articles about well testing of carbonate reservoirs and the method of numerical well testing analysis, PEBI grid is chosen in the spatial dispersion of reservoir region. Mathematical model of well test interpretation for single-phase and two-phase of pore-based carbonate reservoirs, mathematical model of well test interpretation for single-phase of pore-fracture based carbonate reservoirs are established on consideration of wellbore storage coefficient, skin factor and boundary property. Finite volume method is used to discrete the well testing model, and then, the log-log curves of bottom hole pressure and pressure derivative are plotted. The effect of complicated boundaries and interfering wells are also considered in this article.Results of the sensitivity analysis suggest that: in pore-based carbonate reservoirs, the wellbore storage coefficient and skin factor affect the early stage of well testing curve. Permeability affects the height of straight line on the well testing curve. The bigger permeability, the lower the straight line it is. The changes of water saturation, oil-water relative permeability curve and oil-water viscosity ratio have led to the total mobility changed. If the total mobility improves then the curve goes down. In pore-fracture based carbonate reservoirs, storativity ratio and inter-porosity flow coefficient are the two basic characters of pore-fracture based carbonate reservoirs, the fewer fluid in matrix, the shorter time of inter-flow stage it is, if there are few fluids in matrix the well testing curve will turn into homogeneous reservoir character. The better connectivity between matrix and fracture, the earlier inter-flow stage it is. Moreover, complicated boundaries and interfering wells also affect the shape of type curves. With the same area, the shape factor and distance between well and boundary of different shape of reservoir and different location, is different. The smaller shape factor, the earlier shows the property of boundary. If there exist interfering wells, testing well should enhance the difference of pressure to maintain constant oil rate, so that, the type curve will go up. The more interfering wells the greater the upward amplitude.In addition, based on the models mentioned above, well test interpretation software for carbonate reservoirs is developed, in which auto-matching technique using genetic algorithm is incorporated. The software can generate PEBI grid of complicated boundary shape. The real well test data is analyzed by the software and satisfactory result is achieved.