Perforating system

Sept. 1, 2003
A new state-of-the-art perforating system has been developed and used successfully on a job for Statoil, off the coast of northern Norway.

Frank Hartley • Houston

Perforating system

A new state-of-the-art perforating system has been developed and used successfully on a job for Statoil, off the coast of northern Norway. Halliburton Energy Services used its G-ForceSM Precision Oriented Perforating System.

The job required accurate orientation of the perforation planes in the direction of the maximum principle stress to ensure stable perforation tunnels to overcome a sand production problem that previously had limited production from the completion. The result was a safe onsite job execution with an initial sand-free oil production rate of 37,600 b/d, a 20% increase in the overall Norne field production potential.

This technology provides oil and gas reservoir solutions for perforating in the preferred formation stress plane to minimize sand production. It also provides methods to either reduce the likelihood of water coning into the well or increase production from wells at the same water coning likelihood.

This world's first was achieved offshore in well B-3H on Statoil's Norne field in Norway, recently. Unexpected sand production had been observed in several of the Norne field oil production wells. Due to this, combined with water breakthrough in the original perforations in the horizontal B-3H well, the well had been shut in and required a re-perforating to get it back on line. This perforating system was the best solution to use to maximize the sand-free production rate and to open new perforation channels into fresh formation in this particular well. This system allows perforating in any direction regardless of the gun's position relative to the casing.

The system can be conveyed on either wireline or pipe and does not have external upsets that are greater than the outside diameter of the gun system, so it can be used on through tubing applications as well. For the B-3H well, a 180° phasing of the shots was selected at four shots per foot with premium deep penetrating Millennium perforating charges. The tubing conveyed perforation system consisting of five 22-ft sections was deployed using a slick wireline unit combined with a well tractor pulling the guns in place.

The result of the job was an initial sand-free oil production rate exceeding 37,600 b/d. The overall operation was done with dynamically positioned drilling rig Stena Don, according to plan, with an efficiency exceeding 95% compared to original time estimates. All well objectives were met, and payback time for the operation to Statoil was approximately six days worth of production from the well.

Logging tractor

A new production services tractor developed for seamless data acquisition while tractoring in horizontal sections of complex completions has been developed. Schlumberger Oilfield Services commercially released its new MaxTrac.

In field tests in the Middle East, this production services tractor was used in horizontal, openhole completions to eliminate significant coiled tubing and nitrogen pumping costs. The record well depth logged was double that previously possible.

The tractor offers greater operational flexibility than traditional on-off systems. The look-ahead capability, while tractoring down, reduces the risk of running into problems, saving time and delivering high-quality log-down data. It works in a wide range of hole sizes and borehole conditions, and its exceptional efficiency gives higher speed and load for lower surface power on the cable.

Long horizontal sections and complex completions are the focus of this tractor technology, which can be applied to depths of more than 30,000 ft. A majority of wells in the Middle East exceed the reach of coiled tubing, and many completions fall in the complex "Y-tool" category. This provides an effective intervention solution in such situations.

Its modular design incorporating as many as four drive sections allows the tractor to pass through trouble spots such as washouts, wellbore damage, or extreme diameter changes. The tool is capable of operating in 2.4-in. to 9.625-in. internal diameter holes, can tractor through 2.2-in. restrictions, insensitive to borehole irregularities, and is compatible with standard wellsite equipment.

New sliding sleeve

A new completion component from Baker Oil Tools improves performance on frac pack and gravel pack operations by saving time and preventing fluid loss that can impair well productivity, the company says. The new tool, the CMP Defender sliding sleeve, has been run successfully in the Gulf of Mexico in both deepwater and shelf operations.

A common completion practice in Gulf of Mexico frac packed and gravel packed wells is the incorporation of a concentric string inside the sand control screen. A mechanical sliding sleeve built into the concentric string is opened with the sand control service tools to provide returns during gravel placement and then closed to control fluid loss as the service tools are removed from the well. After installing the upper well completion, slickline or coiled tubing intervention is required to open an additional mechanical sliding sleeve to allow production.

Once the upper well completion is installed in the hole, a single, remote application of surface tubing pressure releases the tool's outer housing. As the applied pressure is bled off, the spring-loaded housing shifts open to allow the well to produce. By opening when pressure is bled off, the sleeve can be used for multi-zone completions, with only one tool required per zone. After actuation, the sleeve can be mechanically manipulated to control production from the well, if required.

Oxidizer-based tool

The Expro International Group PLC recently provided stimulation services on a successful job for Unocal in the Gulf of Mexico. Unocal used the StimTube process to stimulate a previously zero production gas well back to a stable production level of 4 MMcf/d.

StimTube is an oxidizer-based tool for reservoir stimulation which, when detonated, can generate large volumes of high-pressure gas – as much as 20,000 psi at the reservoir face. These high-pressure gas pulses are effective in perforation breakdown, fracture initiation, and elimination of near wellbore damage.

The tool can be run through tubing or on slickline to stimulate existing perforations and eliminate the need for additional stimulation techniques, thus resulting in significant cost savings for clients. It can break down scale in the wellbore and displace fines from gravel pack screens. It is also an effective tool in breaking down asphaltenes and other plugging agents in heavy oil wells.

Unocal's well on Brazos block A-105 had been initially completed with 300 ft of open perforations in the low permeability Big Hum D formation. Production rates and pressures had steadily decreased over time, and large diameter tubing hindered the well's natural lifting capabilities. Over time, the well was unable to produce against a system pressure of 500 psi. A decision was made to isolate the bottom 138 ft of perforations due to water and sand production and leave 162 ft of perforations open to flow. While this successfully eliminated water and sand production, stable flow could not be initiated. Wellhead pressure would build readily to 1500 psi when shut-in, but when brought online would drop to below line pressure in a matter of minutes. It became clear to Unocal that stimulation was in order to re-establish flow from this low perm interval.

A gamma ray/casing collar locator/pressure and temperature gauge survey using their slickline depth correlation system was run. Unocal selected the best zones to stimulate based upon the original log data and simulation runs. The decision was made to run three 15-ft assemblies of StimTube and treat 75 ft of total interval.

Upon firing the tool using the slickline firing head system, an immediate pressure increase of 90 psi was observed at the surface. After the second firing, an additional increase of 20 psi was recorded. This same effect was observed following the third firing, with a total increase of 120 psi observed in surface pressures over the three runs. At this point, the well was successfully brought online and a stable flow rate of 4 MMcf/d was established. Rates as high as 5 MMcf/d have been observed.