Efficiency Survey of a Drainage Wellbore and Well Placement in Gas Fields

The paper describes the assessment process of methods for the construction and operation of gas wells with a large water-gas ratio. One of the ways to tackle the issue of poor performance of high WGR wells is to drill a drainage wellbore with an ESP to lift accumulating water. In addition, various configurations of well placement through gas-bearing and water-bearing reservoirs have been considered. To evaluate the efficiency of a drainage wellbore with an ESP installed for lifting water that comes from the main, productive, wellbore, industry-recognized non-stationary dynamic multiphase flow simulator was used, as well as a more refined tool, such as the physical simulator based on the finite volume method (computational fluid dynamics, CFD). A non-stationary dynamic simulator was also used to assess the impact of well placement through gas- and water-bearings reservoirs. Well data, fluid data, physical parameters were entered into the models and, by varying the input parameters, dependencies and results were obtained, allowing to draw a conclusion about the efficiency of each method, as well as about the software capabilities and limitations. The applicability and technical efficiency of an additional drainage borehole with an ESP tto ensure stable operation / high productivity of the well strongly depend on the value of the water-gas ratio, the higher it is, the lower the efficiency of the method. In addition, efficiency also decreases with increasing gas rate. To assess the correctness of the calculation made with dynamic multiphase flow simulator, which is the industry standard, a verification calculation was also carried out on a physical simulator using the finite volume method, which shows the same trends, but with different absolute values. It also made it possible to assess the influence of the geometry factor on the distribution of flows, which could not be done by the non-stationary multiphase flow simulator. Apart from this, it was concluded that the location of a water-bearing reservoir in the last lower part of the wellbore is preferable, since then the impact on production is less than when it is located above the gas-bearing interval. Changing the well layout to a U-shaped one affects the dynamics of its operation insignificantly. The study helps to answer the question about the efficiency of using a borehole with an ESP and about the degree of influence of drilling through gas- and water-bearing reservoirs using the example of a real field, as well as it presents the method of conducting such an assessment for other fields.