Study On Horizontal Well Production Capacity Of Underground Openhole

Step-horizontal wells (referred stepped wells) could enhance well productivity and improve ultimate recovery when developing thin interbedded reservoir, fractured reservoir, heavy oil reservoir or bottom-water reservoir etc. Compared with ordinary horizontal wells, stepped wells is more economiclly efficient, and shall be the mainstream of oil and gas exploration. Based on achievements of former studies, a new detailed coupling model was established. The main progress and achievements are as follow:1) The new coupling model was established considering elements like anisotropy, filtering interference, pipe flow pressure drop and damage zone caused by drilling and/or completion. Compaired with traditional models, the new model has made advancement, for example:taking the effects by damage zone and completions into consideration, and having the ability to simulate stepped wells’ productivity in lays of any number and considering the influence due to the difference between the crude oil properties in different lay, the ability to simulate stepped wells’productivity not only in the thin interbedded reservoir but also in the reservoir with fault, and the capability to analyze the impact of changes in fault dip. All these advancements make the new coupling model more accurate and reflect the real situation better.2) A full set of iterative loop coupling model for solving the steady-state solution was made, and a "Step-horizontal Well Production Calculation Program" was programed. Through computer-aided calculation, flow rate distribution and flow pressure distribution were generated. The results indicate that filtering interference has significant effect on filtering flow, and the wellbore flow friction will reduce production capacity by reducing production pressure.3) Based on these results mentioned above, further single factor analysis was made to find out the productivity’s variation, and gets the influence of reservoir thickness, permeability, pressure coefficient, viscosity, wellbore length, completion method. A parameter group (ψi) which represents the variation of productivity generally impacted by reservoir parameters, wellbore parameters and completion method, and ψi presents a linear function effect. In addition, a larger fault dip may lead to a lower productivity. These conclusions have the actual guiding sense to the drilling and completion technology of stepped wells.4)27economic evaluation schemes considering reservoir buried depth, parameter group of reservoir properties(ψRi), production segment wellbore length were made, comparing stepped wells and common horizontal wells following these schemes, the results show that the deeper the reservoir is buried, more obvious the advantage of the stepped wells, and the common horizontal wells are not suitable for the reservoir buried more than4000m, and stepped wells are more suitable for the reservoir with poor properties than common horizontal wells, and common horizontal wells should not be considered when the ψRi is lower than70. Furthuremore, stepped wells are more suitable than common horizontal wells when the production segment wellbore length is not too long, and common horizontal wells should be considered when the production segment wellbore length is more than1000m. In short, stepped wells have higher economic benefit in most cases.