A coupled model is developed to simulate the pressure and flow rate distribution in both reservoir and horizontal wellbore simultaneously. Most conventional analytical and numerical solutions neglected the interaction of the fluid flow between reservoir and wellbore, which usually lead to erroneous predictions of performance behavior. In this paper, the multisegment horizontal wellbore model is coupled with a fully implicit reservoir model to study the effect of finite conductivity on flow in horizontal wellbore and the corresponding effect on the non-uniform influx distribution from the reservoir.
In this work, a three-dimensional black-oil reservoir simulator is developed using a hybrid technique (local grid refinement) around the horizontal wellbore. The multi-segment wellbore model is built by gridding the wellbore into segments that interact with the influx from reservoir sandface through the local reservoir hybrid grid (radial region). The wellbore model, which is coupled with the 3-D reservoir model, can deal with different types of pressure losses and the flow properties are updated with real-time local flowing conditions. Therefore, the coupled model reveals the fluid flow in the reservoir near the wellbore and also the realistic characteristics in the horizontal wellbore.
The principle of this coupled model is based on the pressure continuity and mass balance at the sandface. Flow in the reservoir is described as a parabolic type partial differential equation, while flow in the horizontal wellbore is a hyperbolic type partial differential equation. All the variables for both reservoir and wellbore domains are obtained by solving the integrated Jacobian matrix simultaneously, so the simulation results can reflect the characteristics and interactions of the fluid flow between the reservoir and wellbore. The corresponding pressure and flow rate around the wellbore also interact with the actual flow velocity in the wellbore.
The coupled model has several prospective applications, including horizontal well length optimization, completion design, water/gas breakthrough prediction and well performance prediction. A case study investigating the finite conductivity of horizontal wellbore is presented in this paper.
Horizontal wells are routinely used in many new oil and gas fields as well as in further development of mature fields because of their advantages over conventional wells. Many researchers have studied various aspects of horizontal well production and developed some models to simulate the production behavior for horizontal wells. Although some researchers [1,2,3] studied the pressure drop along a wellbore due to friction, most former developed simulators neglected the interaction of the fluid flow between the reservoir and wellbore, which usually led to erroneous predictions of performance behavior, especially for those with high-permeability and high production field cases.
In this work, a coupled model of the reservoir fluid flow and horizontal wellbore hydraulics is developed to reveal the realistic flow behavior in the reservoir near the wellbore and also the flow characteristics in the horizontal wellbore. To take advantage of the radial nature of flow around wellbore, the model adopts a hybrid grid system (local grid refinement) with Cartesian grid for the reservoir region and cylindrical grid for the wellbore region.
