A Novel Autonomous Inflow Control Device: Design, Stracture Optimization, and Fluid Sensitivity Analysis
Authors: Wang Xiaoqiu , Wang Zhiming , Zeng Quanshu 
Published: March 2015

Abstract
In long horizontal wells, early water or gas may breakthrough into the wellbore due to the imbalanced production profile caused by the heel-toe effect, reservoir anisotropic, reservoir heterogeneity or fracture-existing. Once coning occurs, oil production may severely decrease due to the limited flow contribution from the non-coning regions. Inflow control devices (ICD) are installed to maintain the flow across production zones uniformly by creating an additional pressure differential which cancels out the imbalanced production profile. This will lower startup production, however, unwanted fluids from breaking through are significant delayed, and total oil production is maximized. Unfortunately, once water/gas does break through, they will take over the well, significantly reducing oil production.
In this paper, a novel autonomous inflow control device (AICD) design is proposed based on the combination of the Y-shaped fluid director and the disk-shaped restrictor. The proportion of flow through different paths of the fluid director will be adjusted automatically according to its fluid property and the stracture parameters, thus enter the restrictor differently and result in different flow resistances. The stracture parameters are then optimized, which enables the well to continue producing oil for a longer time while limiting water. And on the basic of optimized results, the influences of fluid with varying properties (flow rate, water content, and oil viscosity) are further discussed. The results show that the novel design has good performances during every phase of a well's life: high plugging resistance at startup, high erosion-resistant during peak production, continuous inflow control and low viscosity sensitivity during declining, and significantly flow resistance increase at eventual water onset.

1. Introduction
In long horizontal wells, early water or gas may breakthrough into the wellbore due to the imbalanced production profile caused by the heel-toe effect[1–2], reservoir anisotropic[3], reservoir heterogeneity[4] or fracture-existing[5]. Once coning occurs, water/gas fast track will be generated, and then oil production may severely decrease due to the limited flow contribution from the non-coning regions. To eliminate these issues, inflow control devices (ICD) are downhole tools which are placed in every screen joint to balance the production inflow profile across the entire lateral length and to compensate for permeability variations.
Currently, various ICDs have been developed in the industry. These ICDs can be divided into passive inflow control devices (PICD) and autonomous inflow control devices (AICD) according to whether their flow resistance ratings (FRR) are constant. The PICDs are usually installed to maintain the flow across production zones uniformly by generating an additional pressure drop. They use restriction mechanism (the nozzle-based type[6], and the orifice type[7]), friction mechanism (the labyrinth type[8], and the helical channel type[9]) or cooperating both the mechanisms (the hybrid type[10–11], and the tube type[12]) to generate the similar pressure drop. Their FRRs are fixed, and unfortunately, once water/gas does breakthrough, the low viscosity water/gas will take over the well, thus rendering the PICD useless and significantly decreasing the oil production.