Trajectory Optimization Of Horizontal Wells In Cave - Type Carbonate Reservoirs

Nowadays people at home and aboard mainly optimize the horizontal section length and vertical position of the horizontal wells to optimize horizontal well trajectory on the basis of fine geological modeling, from the perspective of reservoir engineering.As the carbonate rocks are cracks developed, they are strong heterogeneity, and the oil-gas-water distribute in the pores is complex, which make formation hard to explore. To obtain the maximum yield, reservoir engineers and production engineers mainly design the horizontal well trajectory orthogonal to the crack, because the more the cracks the larger the drainage area. However, the downhole drilling engineers avoid drilling the hole and caves to reduce accidents. Therefore, to achieve drilling and completion operations high-quality, fast and low-cost and the maximum increase level of well productivity, the needs of integrated drilling, reservoir and production engineering have to be taken into consideration at the same time to.The essay used a certain kind of vuggy carbonate reservoirs. Using basic physical parameters and strength parameters from laboratory experiments and pore pressure acquired from log data, the author using the numerical simulation to study horizontal well path optimization. The simulation was based on a FEM software, and took the well stability and post-fracture stimulation factor into consideration. And obtained the following results:(1) The vuggy carbonates of the studied region are strong heterogeneity. And under the natural high confining pressure, the rocks have high strength generally.(2) Compared with Equivalent Depth Method and Eaton Method, the Effective Stress Method is the fittest one to predict the layer pore pressure of carbonate formations. The error between predict value and real pore pressure of Effective Stress Method is within10%, which is engineering acceptable.(3) Optimal orientation of horizontal wells is primarily controlled by crustal stress. If the crustal stress is a potential strike-slip one, the optimal orientation is0°～40°to the horizontal maximum principal stress. If the crustal stress is a potential down-fault or potential abnormal-fault, the most steady orientation is opposite to the aspect that easiest to create artificial cracks. Hence, it’s necessary to combine the influence of cracks and caves with in-situ needs when determining the optimal orientation of horizontal wells.(4) The spacing between cracks, density and attitude of cracks, cave size, well azimuth and the interval between horizontal wells and caves are elements that effect the well stability and the formation of artificial cracks. So it’s important to deal with relations of cracks, wells and caves.(5) According to in-situ drilling and fracturing data, using software to simulate the optimal well track is effective to prevent underground accidents. And the software can also simulate fracturing. By these means, preferable deliverability will be acquired.