Improved Multiphase Flow Performance Using AICV and its Potential Impact on Reservoir Recovery

Abstract

The global energy demand is growing, and oil and gas supply and consumption will evolve in the coming years. It is important to maintain the current oil production to meet the global energy demand. A major challenge in oil production is low oil recovery. Inefficient oil recovery can be due to the early gas and/or water breakthrough in the production wells. It is therefore essential to develop technologies that can overcome the challenges related to gas and/or water breakthrough and consequently contribute to sustain the oil production and increase the oil recovery.

Different types of inflow control devices (ICDs), passive and autonomous, reduce the negative effects of early gas and/or water breakthrough. Passive ICD was first developed in the 1990s and is today a proven method to improve the oil production and recovery. Additionally, autonomous inflow control devices (AICDs) have become a standard solution for many horizontal wells at the Norwegian Continental Shelf due to the promising results from many field installations. The autonomous inflow control valve (AICV) was developed in 2012 as a result of a continuous effort to develop technologies that contribute to improve the oil recovery. AICVs can choke back gas and water more than other existing technologies.

This PhD thesis addresses the key issues related to improved oil recovery using different types of flow control devices. The thesis focuses on testing and simulation of AICV under different reservoir conditions and for different applications. When gas and water breakthrough occurs, the water cut (WC) and the gas volume fraction (GVF) vary over time in the breakthrough zones. The multiphase flow behavior of the AICV in these breakthrough zones is important for the total recovery along the well. The main goal is to improve the multiphase flow performance of the AICV for use in thin-oil-rim reservoirs, and reservoirs using enhanced oil recovery (EOR) methods. The potential impact of the improved AICV performance on increased oil recovery is investigated by utilizing different types of commercial simulators.

The AICV design and multiphase behavior of AICV are improved. Several AICV prototypes were tested under realistic reservoir conditions to find the optimum design. The piston dimension and shape, the combination and dimensions of pilot flow elements, the housing dimension, and the inlet dimension and design are changed to obtain a better multiphase flow behavior.

Experimental work and simulation study were combined to achieve the main objective. The experiments were conducted in different setups and consist of mainly one-phase and multiphase flow tests for ICD and AICV using water, gas, and oil as the reservoir fluid. Simulations were performed with selected reservoir simulation tools. Reservoirs using steam assisted gravity drainage (SAGD) and CO2 for EOR in addition to thin-oil-rim reservoirs face a number of challenges that AICV can potentially mitigate. The relevant conditions for SAGD/CO2-EOR and thin-oil-rim reservoirs were used in the experiments and simulations.

The results from the experiments show that AICV restricts the gas and water flow rates significantly compared with an orifice-type ICD, in particular at higher GVF. This behavior makes the AICV technology unique compared with other inflow control technologies. The gas flow rates over the AICV and ICD at a 3-bar differential pressure are about 0.1 m3/h and 3.8 m3/h respectively, indicating that the gas reduction by using AICV is significant. The water flow rates for AICV and ICD at 3 bar are 0.07 m3/h and 0.44 m3/h, respectively. The simulations show that the gas/steam reduction can be up to 64% and the increase in oil production can reach up to 15%. Reduction in steam production will improve the overall SAGD operation performance. In addition, AICV in comparison with ICD, reduces the water and CO2 volume flow rates by approximately 58% and 82%, respectively. The results obtained from the corresponding simulations for a case study with CO2-EOR show that the production of water- CO2 is reduced by 20%. Choking back CO2 by using AICV may give a better distribution of CO2 in a larger area of the reservoir. This leads to a broader contact between CO2 and the residual oil in the reservoir, resulting in increased EOR. For the case study with light oil in a thin-oil-rim reservoir, at a 15-bar pressure drop, the gas and water flow rates through the passive ICD are approximately 7.35 and 2.4 times more than the flow rates through the AICV. The results indicate that the gas and water reduction by using AICV is significant. The simulations show that the oil production can be increased by approximately 48%. In addition, the wells completed with AICVs, keep the gas to oil ratio (GOR) at a relatively low level and this allows the wells to produce for a longer period at a high liquid rate without needing to choke back because of high GOR. It can be concluded that deployment of AICVs in the most challenging light oil reservoirs with high GOR can be beneficial in terms of increased production and recovery.

Mathematical models were developed for density and kinematic viscosity within the Bayesian statistical inference framework. The predictive accuracy of the models were validated against measurements, and it was within 90%. The models are based on the experimental data obtained during this work and can be used further to develop a model for AICV behavior. In addition, a model to describe the behavior of AICV was derived based on dimensional analysis. The model can be used in the experimental design and will significantly reduce the required number of experiments.

All the experiments and simulations demonstrate that the improved multiphase flow performance using AICV has a significant potential for increased oil production and recovery.