Baker Oil Tools
The problem of water production from oil and gas wells is as old as the industry itself. As fields mature, they tend to produce increasing amounts of water. Throughout the world today, the average well produces 3 bbl of water for every 1 bbl of oil. For US wells, the ratio is even higher: 7 bbl of water for every 1 bbl of oil.
All indications are that volumes and ratios of produced water will continue to increase over time. For example, water production within the lead operating units of one major oil and gas company has increased steadily from roughly 2.2 MMb/d in 1990 to nearly 6.3 MMb/d in 2001.
Excessive production of water is one of the main reasons for abandoning oil and gas wells and leaving large volumes of hydrocarbons untapped. The economic repercussions of produced water are significant, with the industry currently spending $40 billion per year in capital and operating expenses to mitigate and handle water-associated problems. One major operator alone estimates that it spends $1 billion annually on water management.
The ability to effectively shut off unwanted water production without jeopardizing hydrocarbon flow can have a significant, positive economic impact on E&P operations. In some geological environments, a water producing zone can be shut off while allowing the remaining exposed reservoir section to produce. Traditional water shut-off methods include squeezing cement across the offending zones, plugging the zone with the aid of mechanical isolation devices, pulling the completion and performing a complete workover, and using purpose-designed chemical water blocking agents. These methods, however, have limited effectiveness in certain situations and can be time consuming to implement due to the number of deployment runs needed.
More recently, operators have used standard production casing/tubing to reenter water-producing zones and "blank off" the zone of perforations where they believed excessive water production to be entering. These methods take less deployment time and offer a more definitive shut-off result due to the use of mechanical isolation devices below and above the desired blank-off zone. However, because casing/tubing that can drift through the existing hole is used as the blanking medium, production throughout and workover options are limited by the reduced inner diameter (ID).
With the advent of expandable tubular technology in the late 1990s, short-length clad liners were developed to repair existing casing and tubing and to shut off water and gas in cased-hole environments. With expandable tubulars, the blank-off liner is placed downhole at the desired water shut-off zone. The liner is then expanded against the wellbore wall, creating a sealed blank-off for fluid flow. Unlike conventional straddle strings of tubing, the short cladding does not restrict access to hydrocarbon production from the lower zone of the well.
In open-hole environments, water that flows with sand transport through the annular space between the wellbore and a sand control screen can erode the screen's exterior.
The deployment of expandable tubulars in an open-hole environment for flow restriction poses additional problems not present in cased-hole blank-off. These problems revolve around the ability to create an effective flow barrier against open-hole formations as well as the flow conduit that is deployed in the open-hole section such as screens.
In open-hole environments, water that flows with sand transport through the annular space between the wellbore and a sand control screen can erode the screen's exterior. In some situations, the annular flow becomes cut off from a specific area of the screen and is forced into the ID of the screen through a concentrated point. This condition, known as "hot spotting," can erode the screen to a point where all sand control ability is lost. Even if hot spotting does not occur, the flow of water around the screen may build sufficiently to cause water coning.
The evolution of expandable sand control screens paved the way for operators to benefit from expandable pipe's superior mechanical strength and reliability in open-hole applications. The screens are placed into the production reservoir similarly to a standard sand control screen. After placement, the screens are expanded outward. This outward expansion decreases the distance between the exterior of the screen and the production zone while increasing the ID of the screen. Fluid flow friction forces are reduced, along with the tendency for annular flow of fluids around the exterior of the screen.
Current expanded screen systems use a continuous screen with no definitive contact sealing areas along the length of the screen. As a result, the possibility of hot spotting remains, as does the potential for water coning.
Placing expandable open-hole packers at precise locations along the length of expandable sand screens can greatly reduce or even eliminate the annular space between the wellbore and the screen and, thus, improve water control in the open hole.
Expandable open-hole packers use expandable solids technology to place a rubber element against an open hole wall to prevent annular flow around screen and liner assemblies while maintaining a maximum wellbore ID. When expanded with the screens, the packer's rubber sealing element comes into contact with the formation reservoir, forming a mechanical barrier to deter fluid flow. Mounting the rubber element on a solid base pipe provides a solid sealing surface. This solid surface makes it possible to use cladding, straddling or other methods in the future to shut off water flow from selected zones.
The packers are connected in between the expanded screen sections. This connection allows for flexible placement at desired locations in the reservoir. It also enables placement to be customized for each application, depending on reservoir characteristics and zonal issues.
In a recent open-hole production well in Indonesia, three expandable open-hole packers were placed at uniform distances along a 500-ft horizontal section of expandable screens. Initial production rates were as predicted, with no sand production. Further, with the open hole packers already in place the mechanism for future water shut-off is present – an option that would not have been available with stand-alone expandable screens or slotted pipe.