Operators in the past had a fairly limited arsenal to choose from in terms of isolation tools for multistage fracturing. Cast iron plugs and packers dominated the “frac stage isolation” landscape until the composite plug was introduced to the industry. Since that time, composite plugs have become the default industry standard for multistage isolation needs. This is mostly due to the decreased time required to mill out the plug, giving the operator full production diameter within the casing.

Fast forward to the present, and the days of these limited isolation options are quickly fading. The introduction of frac sleeve technology for openhole and cemented completions has opened up a new plethora of isolation options and efficiencies for operators. In particular, i-TEC Well Solutions, the completions subsidiary of Trican Well Service, developed the i-Frac CEM completion system.

Cemented sliding sleeve technology

i-Frac CEM is a ball-drop-activated multistage fracturing system for cemented horizontal completions. The system is installed as an integrated part of the lower completion string. Multiple stages can be installed in a wellbore, and each stage can contain between one and 20 sliding sleeves that can be spaced out for optimized frac design. Once installed, the system is cemented as normal casing, and a wiper dart run ensures that the pipe inner diameter (ID) and ball seats are wiped free of cement.

For each stage one ball is pumped from surface, and it opens all sleeves in the given stage. The frac job then can be carried out in a continuous pumping operation with no preparation time between each stage. One of the main advantages of using this system over the standard plug and perf (PNP) method is time and cost savings.

By eliminating the need for a wireline system to pump down a PNP BHA, which includes significant time spent swabbing the wellbore while coming out of hole, immediate and significant time savings are realized. In addition, operators have the choice of foregoing any drill-out operations on the ball and ball seats as the well can easily produce through the restricted IDs. However, when full ID access is required, the frac balls and cast iron ball seats can be easily milled with the appropriate BHA setup.

Eagle Ford deployment

In mid-2012 a major operator inquired about a very large cemented sleeve completion in the Eagle Ford play. The operator was looking at a 15-stage completion with five perforation clusters per stage. The operator had legitimate concerns with getting a PNP BHA pumped to the desired depths in the lateral without issue as well as concerns with drilling the composite plugs back out after fracturing operations were complete.

Following a successful trial sleeve installation on another well in the Eagle Ford play, the customer wanted to prove the concept of using ball-drop-activated sliding sleeves for an entire 15-stage cemented lateral. Given the geology of the Eagle Ford play, several initiated fractures were required to produce the formation effectively. This led to the conclusion that one sliding sleeve needed to be installed on top of each casing joint throughout the lateral. This added up to a total number of 74 sleeves in the well. The well was designed with 15 frac stages, 14 of which had five sleeves per stage and one of which had four sleeves in the stage. The ports on each sleeve are configurable and therefore were sized to optimize total flow area and fracture initiation.

For space-out and handling purposes, the sleeves had been prebucked with a short pup joint on bottom and a full casing joint on top of each sliding sleeve. Each frac sleeve assembly was picked up and run in hole (RIH) in its designated RIH order.

Once the completion system was at bottom, the lateral was cemented according to standard practices. Following the cement an i-TEC-provided wiper dart was launched and displaced down by a cement-retardant fluid. The wiper dart bumped after pumping in the theoretical volume fluid, and the cement was allowed to set.

Following the rigup of the frac pumps, pressure was applied to break the rupture disks in the toe sub, and injection to the formation was established. The first frac ball was dropped to shift the sleeves in Stage 1, and the ball successfully opened all five sleeves in the stage. This process was repeated for each of the 15 stages.

All sleeves shifted open as planned with a good verification on surface. Each stage was treated at 50 bbl/min to 60 bbl/min. The first few stages went slower than anticipated due to problems with the chemical blender on surface, and several shutdowns were experienced as a result of this. Once this issue was resolved, the frac operation was carried out in a continuous pumping operation without shutdowns. Total pump time for the 15-stage job was 45 hr, including all shut-down time.

By implementing i-TEC’s cemented sliding sleeve technology in this well, the operator was able to realize significant time savings by eliminating the need to pump down a PNP gun via a wireline system for each of the 15 stages. In addition to valuable time savings, water consumption was greatly reduced compared to a standard PNP completion. With an ever-growing focus on “green initiatives and practices” in the oil and gas industry, the importance of water conservation during operations will continue to grow.