Advanced Toe Valve Technologies

In my first article, Toe Valve Considerations, I highlighted the need for toe valves and what to consider when making your product decision. The majority of the valves run are designed to open after the application of a specific pressure. In its most basic form the construction of the valve has a piston that sees well pressure from one side and atmospheric pressure on the other. Either this piston is held in place with a shear media that keeps it from opening until a specific pressure is reached within the well, or is kept balanced until a specific pressure is reached, rupturing a disk that then exposes one side of the piston to well pressures. These have proven to be reliable options for creating a pump down path or for stimulating the first zone in the well. 

Most oil and gas regulatory bodies require the operator to perform casing pressure tests to ensure that the well construction is competent. For instance the Texas Railroad Commission requires operators to pressure test their wells to the maximum pressure allowed by the completion or, if a toe valve is used, to 80% of the toe valve's actuation pressure for a minimum of 5 minutes. See the exact wording of the regulation below:

Texas Railroad Commission Administrative Code

RULE §3.13Casing, Cementing, Drilling, Well Control, 
and Completion Requirements
(7) Additional requirements for wells on which hydraulic 
fracturing treatments will be conducted.

 (B) The operator shall pressure test the casing (or fracture tubing) 
on which the pressure will be exerted during hydraulic fracturing 
treatments to at least the maximum pressure allowed by the completion method. 
Casing strings that include a pressure actuated valve or sleeve shall be 
tested to 80 percent of actuation pressure for a minimum time period of 
five (5) minutes. A surface pressure loss of greater than 10 percent of 
the initial test pressure is considered a failed test. The casing required 
to be pressure tested shall be from the wellhead to at least the depth of 
the top of cement behind the casing being tested. The district director 
shall be notified of a failed test within 24 hours of completion of the test. 
In the event of a pressure test failure, no hydraulic fracturing treatment 
may be conducted until the district director has approved a remediation plan, 
and the operator has implemented the approved remediation plan and 
successfully re-tested the casing (or fracture tubing).

The downside of the single open design toe valve is that after performing the casing test the operator then must exceed this pressure to open the sleeve. This additional pressure could compromise the casing test. To avoid this risk, operators could choose to run an advanced toe valve. Fundamentally, an advanced toe valve technology will enable the operator to perform a casing test at the maximum pressure and open the sleeve at a lower pressure. Currently there are two categories of advanced toe valve technologies available on the market. These are time delay valves and cycling valves. 

The time delay valves enable a valve’s piston to be actuated but then held closed for a specific amount of time. These valves operate like a rupture disk piston toe valve with the addition of a fluid reservoir and an orifice. The valve will have a rupture disk, a balanced piston during run in, a fluid reservoir behind the piston, an orifice, and an atmospheric chamber. When the rupture disk is burst the pressure from the well will act against the piston, which then forces the fluid through the orifice as the piston shifts. The tool is designed such that it takes a set time for the piston to force the fluid through the orifice, delaying the opening of the sleeve. Once the fluid is forced past the orifice the sleeve will be fully opened for the pumping operation. The benefits of this design is that the rupture disk can be set at a pressure below the casing test. As the operator ramps up to their casing test pressure, the disk will burst, but the sleeve will remain closed. As the piston meters, the operator can increase their pressure beyond that of the rupture disk rating and hold as long as it takes for the piston to fully open. The operator can perform their casing test at max pressure and not exceed that pressure to open the sleeve. The downside of these sleeves is the performance is dependent on the interaction between the fluid and the orifice. If, during assembly the amount of fluid is slightly off it can affect the time it takes to open. If the temperature in the well is different than expected it can affect the fluid and change the time delay. The orifice used is very tiny. Any impurities in the fluid could clog the orifice and affect the opening of the valve. Finally, they're all time bound and your casing test is limited to the design of the tool.

The second type of cycling toe valve uses a piston that shifts back and forth until an opening configuration is reached. Typically, this involves a pressure balanced piston and an atmospheric chamber. When a rupture disk is burst, pressure acts on the piston to compress a spring. The operator can then perform their full casing test. When pressure is released, the spring will relax returning the piston to a second position. During this movement something will shift or move in a way that on the second (or third or forth) pressure cycle the sleeve will be in an opening configuration and the piston will shift fully open. Again, providing the benefit of not exceeding your casing test pressure to open the valve. The shifting toe valve eliminates the issues associated with the fluid and orifice but has other drawbacks. The spring selection for a sleeve that first compresses and then relies on the spring to relax and move the piston into another position is very difficult. It has to be weak enough to compress and then strong enough to return the piston to another position. In addition to this, relying on that spring to shift certain parts adds complexity to the tool and introduces more risk to the operation.

The Rubicon HydraSTART MTV Multi-Cycle Toe Valve is designed to take into account the issues I’ve raised above and eliminate worry from a cycling toe valve operation. The patent pending design of the MTV has a simple operation that eliminates the need for exceeding the casing test to open the valve, doesn’t rely on fluid, or a very specific spring that will compress and relax. In the opening sequence the operator will pressure up to their casing test value and hold it for any length of time. Once the test is completed, they can then bleed down the applied pressure. Upon bleed down the piston is exposed to the well pressure. To open the valve the operator can then pressure up again to shift the piston to the open position. The second shear mechanism can be custom tailored to the desires of the operator. In another configuration that valve can be set to fully open upon bleed down after the casing test. This enables the operator to run multiple valves to create a cluster type toe section to enable pumping the first frac through the valves. This simple design has been field proven to perform and is available in 4.5” and 5.5” sizes.

Regardless of what advanced toe valve you choose, knowing exactly how the valve works will provide a greater understanding of the value and risks that it will bring to your operation. If you’d like to know more about advanced toe valve technologies, please contact me at matthew_crump@hotmail.com.