Flow Assurance Begins with Downhole Insulation
Authors: Lively Glenn 
Published: October 2008

Thin-Film (TF) insulation combined with an insulating packer fluid is an effective and proven method for insulating downhole production tubing and casing in order to preserve reservoir heat and to enhance startup conditions. Modeling indicates that this system can increase FWHT by as much as 25°F-30°F as flow rates decline. Combining these technologies enables heat losses at couplings, valves, gauges and other components without insulation to be controlled. An aqueous based packer fluid inhibits the formation of convection currents that commonly occur in standard brine completion fluids, resulting in an overall heat transfer coefficient that is more than 10 times lower than standard completion fluids. These technologies are cost effective, readily available and provide numerous advantages over traditional completion systems.

Until the last few years the only option for downhole insulation has been vacuum insulated tubing (VIT); however many applications cannot support the economics of VIT nor do they require the low thermal conductivity that VIT provides.

Any one of these technologies can be used alone or in combination with another depending on the application. In some applications all three may be required to accomplish the objective.

Introduction

Downhole insulation allows the project engineer to begin the flow assurance solution at the perforations rather than at the wellhead. Insulating production tubing and casing will improve heat retention in the production stream thus providing higher wellhead temperatures and faster, more efficient warmup after shut down. One effective method to reduce heat loss is Thin-Film (TF) insulation on the production tubing/casing or in combination with an insulating packer fluid.

Flow assurance is an issue for mature fields as well as for deepwater developments. In many cases, as the flow rates decline flow assurance issues develop in the form of wax and paraffin deposition in oil wells and hydrates in gas wells. Even in relatively shallow offshore developments in less than 1000' water depth, the seafloor temperature can be as low as 50°F. The cold water combined with a low flowing wellhead temperature (FWHT) is a tough combination to overcome, especially when field economics do not support extensive capital investment. Some wells have paraffin cloud points and hydrate formation at temperatures approaching the FWHT. In artificial lift wells where high pressure gas is injected through a gas lift valve, the venturi cooling effect on the production is significant thus impacting FWHT. In satellite wells where the produced fluid must flow to a host platform several miles away, the cold water often causes flow assurance problems in the flowline. In onshore fields where the winter temperatures fall below freezing the same problems encountered in offshore wells can exist. In all of these instances higher FWHT would help to counter the effects of the cold environment. TF insulation is a cost effective and versatile tool that is available to the project engineer for increasing FWHT. In many of these applications the high cost and long lead time for delivery of VIT eliminates that as an option.