Sepehr Arbabi

Effects of Pressure Drop in Horizontal Wells and Optimum Well Length

As the length of a horizontal well is increased, its contact with the reservoir increases. But at the same time, the resistance to flow in the well also increases, which has a direct negative effect on the productivity of the well. The overall performance of a horizontal well depends on the balance of these two opposing factors. No reliable tools are currently available that account for both these factors in the evaluation of horizontal well performance. A semi-analytical well-model is developed which can quantify the effects of both single phase oil and two-phase oil/gas flow pressure loss in the well on the overall well performance. The model is quite flexible and can incorporate any friction factor correlation. A methodology is developed to show the effects of various reservoir, fluid and well parameters on well productivity. We demonstrate that ignoring frictional effects could lead to unrealistically higher production estimates and low breakthrough times for water or gas. As a result of pressure drop in the well, breakthroughs occur first at the heel of the well. A methodology is also developed to calculate the optimum horizontal well length.

Practical Procedure To Predict Cresting Behavior of Horizontal Wells

Water and gas cresting in horizontal wells are important phenomena in reservoirs that have an aquifer and/or a gas-cap. In practical situations, many reservoirs are produced under supercritical rates and a breakthrough of the displacing phase becomes inevitable. At the beginning of a reservoir simulation study, it is desirable to make an estimate of the breakthrough time and the post-breakthrough behavior. Grid sensitivity runs are also required to obtain the appropriate grid block sizes. An accurate representation of cresting behavior requires a very fine grid, which is not always practical. In this work a procedure was developed to obtain accurate breakthrough times using just coarse grid simulations. The flow equations were written in dimensionless form and important parameters affecting multiphase flow were identified. Simple correlations for a quick estimate of breakthrough time, maximum oil rate and post-breakthrough behavior were derived based on an appropriate set of dimensionless variables and an extensive number of simulation runs. The effects of gridblock size and grid pattern were investigated in detail. Effects of rate, mobility ratio, well drainage area, well height, and end-points and shapes of relative permeability curves were also included. A procedure to derive pseudofunctions either using numerical correlations or coarse grid simulations is also presented. These pseudofunctions can be used to improve the performance of coarse grid simulations. An optimum grid pattern to start a reservoir simulation study is proposed. Application to a real field example shows that the correlations and procedures derived are reliable and accurate, and can be used for quick estimates before starting a reservoir simulation study.