This invention relates to an apparatus and method for heating a fluid, which has poor flowability or troublesome rheology due to the buildup of paraffin or asphaltenes on the walls of the tubing or in the well bore. More particularly, the present invention relates to an apparatus and method of improving flowability of subterranean formation fluid by using an inline heating method.
One of the problems associated with oil production is the deposition of paraffin or asphaltene on the walls of production tubing or the well bore. The oil is pumped to the surface or forced to the surface from a relatively hot area through a cool zone where the temperature of the formation is less that the solidification temperature of paraffin or asphaltene. Once paraffin or asphaltene separate from the crude oil fluid flow, they tend to adhere to the production line walls causing a restriction in the tubing. Over time, these high molecular weight hydrocarbons build up on the walls of the production tubing and significantly affect the production flow. As the crude oil is pumped to the surface, the gas from the reservoir also rises to the surface. Reservoir gas tends to decrease the reservoir pressure and increase the time the crude oil is flowing through the production tubing. As a consequence, the reduced flow of oil loses speed and pressure as it travels from downhole to the surface. The decreased temperature increases the viscosity of the oil and further reduces the flow rate.
This phenomenon is well known in the field and various methods have been employed to solve the problem. One such method is the so-called “Hot Oil Treatment.” According to the hot oil treatment method, steam is pumped under significant pressure into the area between the casing and the tubing. The pressure applied during this process forces paraffin residue into the production formation. This method is ineffective as interaction of steam pressure in the producing zone frequently results in clogged perforations and ultimately the decline or loss of production. The pressure steam method is also time consuming, and requires down time to complete, is expensive and presents significant risks to the operator.
Another method that is conventionally used in the oil industry to treat paraffin deposits requires stopping the production, retrieval of the tubing, cleaning by scraping or steam-cleaning the inner wall of the well string to remove the paraffin and asphaltene deposits and then replacing the tubing back into the well. This method is also time consuming and costly and does not prevent future paraffin deposits in the pipes. The method is merely a maintenance procedure that works for a short period of time. Additionally, the risk of loss of production while the well is shut-in, coupled with the maintenance expense, makes many wells unprofitable to produce if such method is used.
Still another commonly employed method is a chemical treatment using solvents that are introduced in the well bore in an effort to dissolve or liquify the heavy alkanes, including paraffin and asphaltenes, and improve the flow of crude oil. Long-term injection of chemicals is expensive.
All these methods and systems have minimal success in addressing the problem as it occurs. The conventional tools are single units with limited heating capabilities that cannot be extended or scaled up to cover a greater zone of treatment. Furthermore, the electrical heating devices used in conventional downhole heaters tend to allow hydrocarbon leakage at electrical connections or at wire feed-through areas, which can cause failure of the insulation around the conductors and fire or explosion in the volatile environment downhole.
One of the more serious problems is the failure of the conventional tools to detect and monitor downhole temperatures at the vicinity of the heater and thereby regulate the temperature in the critical areas to provide long-term economical thermal treatment in the well.
An embodiment of the present invention eliminates the need to install, heat the formation and then remove the heater assembly of existing heater technology. Instead, an inline downhole open-annulus heater is deployed for long-term service that can be controlled and regulated from the surface as it heats the oil before it is passed through the production tubing and moved to the surface. As other well production hardware is removed from the well for service or replacement, the embodiment of the present invention may be removed and checked for continued serviceability in the well. This open annulus heater system can also be employed to generate steam for enhanced oil recovery by deploying the heater with a pass-through packer which, upon installation creates a limited longitudinal zone for steam soaking or injection.
Water pumped into the annulus triggers a valve on the packer to open dumping water on the heater, which is rapidly vaporized into steam increasing the pressure and thereby closing a check valve to hold the steam and other fluids in the confined zone desired. As the steam is absorbed or reaches thermal equilibrium with the formation, the existing pressure from the water above the packer opens the valve again and the process repeats over and over as long as desired in cyclic fashion, thereby stimulating production from the desired zone or permitting the lower viscosity oil to be easily moved to the surface by the down hole pump system, which may either be a rod pump system or an electrical submersible pump system.