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We developed a deliverability model to predict the performance of multilateral wells. We first constructed a horizontal lateral model, which couples a reservoir inflow model with a wellbore flow model to calculate the production rate from each lateral. Pressure drop along the lateral was considered in the model. Then we implemented the lateral model into a well system with more than one lateral commingled to a main wellbore. The production from each lateral, the overall production rate, and the pressure in the well system are predicted by the multilateral deliverability model. For reservoir inflow, we have developed a new model using an imaging well method to calculate a single-phase inflow performance relationship (IPR) for a segmented horizontal lateral. The results from the new model are compared with existing analytical models. For flow in the laterals, we adopted single phase and two phase wellbore flow models. The single-phase lateral flow model incorporates frictional and accelerational pressure drop, and also the pressure drop caused by inflow turbulence. The two-phase lateral flow model uses the Beggs-Brill correlation or Ouyang's homogeneous model which accounts for the effects of wall inflow, acceleration and flow patterns. The pressure drop in the tubing from the upper most lateral to the surface was calculated using a two-phase flow correlation. We present example calculations for a well with three laterals draining separate reservoirs. The examples illustrate the effect of interference between laterals on lateral and overall well performance. Introduction Multilateral wells offer the potential for substantial improvement in well economics1–5. In multilateral well completions, two or more horizontal wellbores are drilled from a single parent wellbore, enabling drainage of multiple reservoir targets. This technology allows the same magnitude of reservoir exposure with a lesser number of wells on the surface/platform. The benefits from multilateral well technology include increased production per platform slot, exploitation of reservoirs with vertical permeability barriers, and production from natural fracture systems. Modeling of multilaterals may be complex for particular configurations, because of the interplay between reservoir performance and pressure drop behavior in the wellbore. Also there is a dearth of information on methods to compute productivity, to devise procedures to evaluate the completion efficiency, and to forecast performance of the completion. Several methods have been presented to determine productivity indices or skin values for multilateral well systems6–11. In this paper we present a new approach to determine the deliverability of a multilateral well. Development of Horizontal Lateral Model The horizontal lateral model describes the reservoir inflow performance, and the flow inside the horizontal wellbore. The inflow model and the wellbore flow model are coupled. Reservoir Inflow Model. There have been several attempts to describe horizontal well productivity. A widely used approximation for the well drainage is a parallelepiped model with no-flow or constant-pressure boundaries at the top or bottom and either no-flow or infinite-acting boundaries at the sides. Most of the analytical work done in the past on horizontal well productivity either assumed that the well is infinitely conductive or the flow is uniform along the entire well length12–27. Two existing models were adopted in the deliverability model, and have been addressed before28. In this paper, a new segmented horizontal well model is developed and used to calculate reservoir inflow performance in the multilateral deliverability model. Two Existing Models for Horizontal Laterals. Joshi proposed a steady state model using potential-fluid-flow theory in 198817. This model is commonly used for first approximations and comparisons with vertical wells. The solution of the model is simple, but it usually underestimates the productivity. Reservoir Inflow Model. There have been several attempts to describe horizontal well productivity. A widely used approximation for the well drainage is a parallelepiped model with no-flow or constant-pressure boundaries at the top or bottom and either no-flow or infinite-acting boundaries at the sides. Most of the analytical work done in the past on horizontal well productivity either assumed that the well is infinitely conductive or the flow is uniform along the entire well length12–27. Two existing models were adopted in the deliverability model, and have been addressed before28. In this paper, a new segmented horizontal well model is developed and used to calculate reservoir inflow performance in the multilateral deliverability model. Two Existing Models for Horizontal Laterals. Joshi proposed a steady state model using potential-fluid-flow theory in 198817. This model is commonly used for first approximations and comparisons with vertical wells. The solution of the model is simple, but it usually underestimates the productivity. Two Existing Models for Horizontal Laterals. Joshi proposed a steady state model using potential-fluid-flow theory in 198817. This model is commonly used for first approximations and comparisons with vertical wells. The solution of the model is simple, but it usually underestimates the productivity.

Ion implanted CoSi 2 as a gate doping source has been studied as a compatible process to the Silicide-As Diffusion-Source (SADS) process which has been widely considered for shallow source/drain junction formation. The effects of the polysilicon gate microstructure on diffusion behavior and the thermal stability of CoSi 2 has been investigated. It has been found that CoSi 2 formed on reoxidized polysilicon gates has poor thermal stability but requires short time to achieve degenerate doping near the polysilicon/gate oxide interface. On the other hand, CoSi 2 formed on as-deposited amorphous silicon has excellent thermal stability but requires longer time to achieve degenerate doping near the polysilicon/gate oxide interface. The trade-off between the required thermal budget to achieve degenerate doping and thermal stability of the CoSi2/polysilicon gate structure will be discussed. In optimizing the process, our results indicated that reoxidized amorphous Si gates have both good thermal stability as well requiring short time to achieve degenerate doping. The thermal degradation of CoSi 2 was found to have little effect on the gate oxide breakdown voltage.

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