Tech Transfer Track

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In this application, there are two challenges with conventional cement. First, there tends to be a channel at the top of the horizontal open hole. In contrast, the extra energy in foamed cement keeps the annulus full until the cement sets. Second, conventional cement is more brittle and, with pressure fluctuations during fracturing operations, cracks can tend to form. Foamed cements are more ductile (yielding, not cracking as with conventional cements). Compressive strength of foamed cements are lower, which concerns some operators. However, compressive strength is of minimal importance since the stresses during fracturing are tensile in nature.

Excerpted from “Foamed Cement Key in Woodford Shale,” The American Oil & Gas Reporter, May 2008, pp. 110-115.

Long-Term, Hydrocarbon-Activated, Active-Set Cement

There are certain environments (seismically active areas, subsidence, active faults, production/injection cycles, etc.) where frequently changing stress environments damage cement sheaths, contributing to leakage and environmental problems. These changes often occur throughout a well’s life. Schlumberger’s FUTUR formulation is one solution. FUTUR is a hydrocarbon-activated, active-set cement formulation. In plain English, this means if a crack/leak occurs and hydrocarbon starts flowing through the crack, the hydrocarbon itself “activates” the cement to swell, sealing the leak. Within reason, this can occur many times. Laboratory data support performance as do data in Canada’s foothills region (seismically active) and Europe (gas storage application).

Excerpted from “New Cement Forms Life-of-Well Seal,” Hart’s E&P, May 2008, pp. 96-97. Detailed information is available from Schlumberger online at www.slb.com/content/services
/cementing/materials/futur.asp.

Downhole Desander Increasing Life of ESP’s

Renaissance Energy, since purchased by Husky Energy, was experiencing problems getting adequate run life with electrical submersible pumps (ESPs) in its Cantuar Unit in Southwestern Saskatchewan due to sand production problems. In June 1999, with 30 operating ESPs, average run life was 406 days with some pumps running only 103 days. Renaissance wanted to run more ESPs, but needed to solve the sand production/ run life problem first. Renaissance chose to field test the Lakos PPD desander for downhole pumps, supplied by Enerscope Systems, Inc.

The desander has been widely used in groundwater wells.

The desander uses centrifugal force to move heavier particles out of the water. Sandy fluid enters through inlets at the top, and as the fluid moves down, the heavier particles are separated and forced to the periphery of the tube while the filtered fluid exits through the center and up through the vortex outlet. The sand particles then fall downward to the separator, and when maximum capacity of sand is reached, a flapper valve opens, releasing the sand downward toward the rat hole. After the sand is dumped, the ESP’s suction automatically closes the valve. With no moving parts or filters, there is no maintenance.

Over a two-year period starting in 1999, Renaissance installed 12 of the desanders. Unfortunately, only one unit was pulled and had performance data when the Husky buyout occurred, after which time data were not collected. Measures of success were lack of erosion to the ESPs and longer run lives. The test well had a history of severe sand damage—the three prior ESPs had lasted only 103, 132, and 143 days. With the desander the ESP operated flawlessly for 203 days, at which time it was pulled for inspection. Inspection showed no damage, there was no indication of sand accumulation above the packer, plus the sump was approximately 15 ft shallower than before, providing strong evidence that the desander was working. Although not formally studying the other 11 desanders, Husky has since installed a total of 30 units in its wells. In some installations, Husky is reporting average run-time increases of 110-120%. The article references other producers who have installed desanders.

Excerpted from “Downhole Desander Prevents ESP Damage in High-Watercut Well,” World Oil, June 2008, pp. 143-146.

Linear Pumps
Have Their Place

Linear pump technology combines variable speed control, simple mechanics and sophisticated software in a compact, lightweight artificial lift system. Linear pumps offer improved speed control, optimized well performance and energy efficiency, easy installation, portability and low profile/footprint. With no exposed moving parts, linear pumps are much safer in residential or urban environments. They can adapt to changing conditions without manual data input. A total system with automatic control can be purchased for a price similar to a conventional beam pump without controls. By interchanging a small number of parts, linear pumps can handle a broad range of pumping applications.

Oilfield Chemicals, A Reference Guide Hart’s E&P’s May 2008 issue contained a 36-page supplement focusing on oilfield chemicals—from drilling through production. Those relatively new to the industry should find it helpful for understanding how chemicals fit into the picture. Those of us who have been around awhile can use it as a refresher course, plus since it describes recent trends, we might get some new ideas to apply.