The geologic conditions that form heavy oil reservoirs and the chemistry of the oil itself present a host of well construction and completion challenges. In the last decade, however, research into heavy oil recovery has brought many advancements in cementing products and services, directional drilling, multilateral well construction, sand control and thermal completion technology. Improved artificial lift methods, such as high-volume Hotline™ electric submersible pump systems have also been developed for the high temperature production of heavy oil.

Well construction

Although every reservoir is unique, heavy oil developments typically include large numbers of relatively shallow and tightly spaced wells. Many of the new wells are horizontal or highly deviated, and some include multilateral completions that resemble rib bones or the tines of a pitchfork.

Well placement is important, both at the surface and downhole. To minimize the environmental footprint, several wells are often drilled from a single pad. That also improves the efficiency and economics of constructing the wells.

Drilling rates through unconsolidated oil sands can reach 1,000 feet per hour, so even complicated wells can be built in a few days. Top drive rigs, with their greater speed and efficiency, are now commonly used for drilling heavy oil wells.

With unconsolidated oil sands, it is often the heavy oil that holds the sand together, but friction from the rotating drill creates enough heat to lower the oil’s viscosity in the immediate area of the bit. Without the glue of heavy oil holding the sand grains together, the borehole becomes less stable. Drillers deal with the problem by selecting the right bit for high penetration rates, and the correct drilling fluid to simultaneously guarantee circulation and cool the bit.

At the surface, drillers have to make sure they have enough pumping capacity to keep fluids circulating, especially in long, complicated wells. Using the proper drilling mud can also keep the gooey, sticky and viscous oil from coating the borehole and tubing string, and from reaching the rig floor where it can create safety and environmental problems.

Completions

Most drilling engineers agree that when it comes to heavy oil, the drilling side of their business has outpaced the completions side. The reason is that heavy oil wells tend to be more complex than those in conventional reservoirs. With the industry’s ability to develop new technology, however, advanced guidance tools such as Periscope™ offer drillers the opportunity to reliably steer the drill bit through winding channels of oil sand, building wells that would have been impossible just five years ago.     

Although they are expensive to drill, multilateral wells are cutting the overall development costs in some fields by reducing the amount of infrastructure at the surface and the number of wells needed to develop the field. The downside is that well designs are much more challenging. In fields with a high number of shallow wells through multiple stacked reservoirs, the wells are so complex that drillers have to use collision avoidance tools and software to keep new boreholes from intersecting nearby wells.

Complexity and economics also limit completion options. Operators in Venezuela, for example, have built wells with horizontal sections running up to 5,000 feet (1,500 meters). Slotted liners, mesh or screens are installed to keep sand out, but multiple boreholes from the main trunk into adjacent sands are left open. Such decisions about sand control are often critical in the design of heavy oil wells.

Enhanced recovery

When the economics of a new field allow it, operators typically plan for enhanced recovery using heat, solvents, water, and CO2 or hybrid combinations to move the heavy oil, even if they initially use cold production. The most common technique is some form of thermal recovery, using steam to heat the formation, but wells designed only for cold production cannot handle steam. Thermal wells are more expensive than those designed only for cold production, but thermal wells often produce at much higher rates. 

One of the fastest growing areas of heavy oil technology is the development of high-volume electric submersible pumps (ESPs) that can survive the extreme temperature cycles generated by thermal recovery. There are now ESPs on the market with demonstrated run times of 900 days at operating temperatures up to 218 degrees C (425 degrees F). 

Industry trends

Intelligent wells, with enough hardware to control the flow of fluids from selected zones, are not common in heavy oil developments. The main reasons are the expense of the hardware and high temperatures downhole.

Industry is working on technology that allows operators to shut off sections of their wells to redirect production or adjust the steam injection rate. With it, they can fine-tune the performance of their wells and improve the profitability of new heavy oil developments, two important steps in meeting the world’s growing energy needs.