Abstract

Gas lift, a broadly applied method for producing oil, consists of gas injection into production wells to reduce the liquid density in the wells and increase the liquid inflow. Gas lift technology requires large gas volumes to he injected. If the reservoir pressure is depleted, the effectiveness of gas lift is dramatically reduced. To increase effectiveness and to extend gas lift applications to producing oil from depleted reservoirs, a foamed gas lift method producing oil from depleted reservoirs, a foamed gas lift method has been investigated in laboratory and oilfield experiments. The method consists of foaming agent injection into a gas-liquid flow.

A laboratory set-up based on scaling parameters was used to study the productivity of the gas lift well exploiting the drainage area of the well. The laboratory experiments were performed over a wide range of the sealing parameter, describing the reservoir pressure depletion, with and without foaming agent. The results show that foamed gas lift would be efficient, especially if the gas lift well cannot produce without the addition of foaming agent. Analysis of the gas-liquid flow structure inside a vertical tube displayed the conditions of effective application of the foaming agent to improve gas lift technology. Oilfield experiments analyzed with probability theory corroborated that foamed gas lift is a very effective technological method if the reservoir is depleted

Introduction

The gas lift oil production method has seen years of international use to carry liquids from underground deposits. A basic idea of gas lift technology is to decrease the flow specific density inside the wells. The method consists of natural gas or air injection into wells to create a gas-liquid mixture. That decreases the pressure gradient from the point of gas injection to the surface. The lower pressure gradient creates the lower bottom hole pressure and, pressure gradient creates the lower bottom hole pressure and, higher pressure gradient across the reservoir. The latter increases the liquid inflow. However, as permanent reservoir pressure declines, greater gas volumes are required in order to maintain liquid inflow.

Several regimes, bubble, slug, and annular, are observed in vertical gas-liquid flow. Each regime is determined by local pressure and the gas flow rate. The bubble regime formed under pressure and the gas flow rate. The bubble regime formed under very low gas flow rates is characterized by gas bubbles of small sizes. As gas flows upward, the pressure decreases and the gas flow rate increases. This pressure change causes an increase of a bubble size. The following bubble coalescence creates slugs of size close to the tubing diameter, forming the slug regime. A subsequent gas flow rate increase or pressure decrease is responsible for slug instability and transformation of the slug flow into the annular regime.

Many experimental and theoretical investigations of the gas-liquid structure and gas lift characteristics have been done to determine parameters of the gas lift wells and to estimate an optimal gas parameters of the gas lift wells and to estimate an optimal gas injection rate to maintain well productivity. 1-8 However, the gas lift well productivity decreases due to reservoir pressure depletion. To maintain productivity the injected gas flow rate must be increased. If the reservoir pressure is very low, the gas lift becomes ineffective even under high injection gas flow rates.

The current paper investigates the application of a foaming agent to improve gas lift if the reservoir pressure is very low. The idea of foam gas lift is explained by the following. Suppose the initial liquid column in a well of the depth l equals ho and a foaming agent is injected into the liquid to create a solution of concentration C. Assume a gas injected at flow rate Qg creates inside the well a foam of quality (G(Qg, C). If Gxh0 >1, a part of the liquid, equaled Aho (Gxho-1 will Come out the well, and the bottom-hole pressure will decrease by Alpig value. This product depends on the gas flow rate, Qg, and the concentration, C,. The effect of the foaming agent on die gas lift can be increased by varying Qg and C. The paper reports results of the experimental and oilfield investigations of the foamed gas lift to increase the well productivity. productivity. P. 75

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