Production of Waxy Low Temperature Wells with Hot Gas Lift

Abstract

Abstract An Oil reserve is discovered in a remote shallow water area offshore Africa, where the water depth is approximately 200 ft. The predicted production rate is approximately 500 BPD per well. The obtained oil samples indicate that the produced fluid has a high pour point (91°F) and a high wax appearance temperature (105°F). A dry tree completion is the planned option for this field. The wellhead flowing temperature (WHFT) is predicted to be below the wax appearance temperature (WAT) during normal flow without heating. Under certain specific field conditions, such as the development being considered, hot gas can be used as a means to maintain WHFT above the oil WAT and also be used as an artificial lift method to produce the low pressure / low temperature wells (LPLT). Economically, since the reserve is located remotely from gas market, the produced gas is "free." This paper describes the engineering evaluation of a hot gas lift design concept for a particular LPLT field. The hot gas lift method will avoid wax deposition, gelling and blockage problems in the wellbore. The wellbore thermal-hydraulic behavior is studied to optimize gas lift injection rates and temperature. Introduction Gas lift is a simple, reliable artificial lift method that is frequently used in offshore oil field developments1. It is one of the industry's first choices to develop low pressure fields, provided there is an adequate supply of injection gas. The gas after being injected into the casing-tubing annulus at the wellhead, enters the production tubing via a gas lift valve (GLV) situated in the gas lift mandrel (GLM). The gas injection entry point is designed such that the geothermal temperature is higher than the solid deposition temperature, in this case, WAT. One of the shortcomings of the conventional gas lift technique is that the injection gas would cool the production stream. Low temperature wells are particularly affected since the production temperature can be close to WAT. Typically, hot gas is not used to transfer heat energy because its heat capacity is low. However, with wellbore casing insulation, hot gas could heat production streams to maintain higher temperatures at the wellhead, possibly making certain marginal fields to produce. A schematic of a hot gas lift system is shown in Figure 1.