Water Well Journal
Issue link: http://read.dmtmag.com/i/529509
From the Archives is a look back at popular drilling content that appeared in Water Well Journal years ago, but remains important today. The quarterly column is sponsored by MARL Tech- nologies Inc., a manufacturer of drills for water well, rotary, geotechnical, environmental, sonic, geothermal, CPT, mining, and construction. More information can be found at www.marltechnologies.com. This article first appeared in the August 1995 issue of WWJ. T he cable tool or percussion method of drilling is believed to have been invented in China, perhaps as early as 2000 B.C. Even though the water well drilling industry has developed numerous other methods to install wells, there are still times when a cable tool rig is exactly the right piece of equipment for a specific job. Some cable tool methodology is in danger of being lost as experienced cable tool drillers retire. One of these endangered drilling techniques involves the use of a cable tool to aid in gravel packed, screened wells. In our area of Minnesota, almost all monitoring wells are installed using gravel packing; so are most extraction wells. However, most high-capacity production wells are developed with high-velocity jetting, mechanical surging, and air lifting process. Under most conditions, produc- tion wells provide more capacity and greater yields using natural development methods. I am a proponent of natural development for high production wells, but there will always be a place for gravel packing production wells. This article discusses the installation of a screen with gravel pack using the cable tool method. The well described was recently drilled by my company and installed for the city of Maple Grove, Minnesota. This is a high production municipal well in a gravel zone capable of 3500 to 4000 gallons per minute. The water level is about 28 feet and ex- pected drawdown is 30 to 40 feet. The outer casing of 24-inch steel pipe was drilled to 185 feet; the 18-inch-diameter inner liner was set and drilled to 300 feet. The drilling process took five weeks. Samples were taken at 5-foot inter- vals, and sieve analysis was performed on every other sample from 200 to 300 feet. An 18-inch telescopic stainless steel screen was scheduled to be in- stalled using jetting and surging as de- velopment methods. However, the sieve analysis revealed that the formation contained distinct layers of sand and gravel of different gradations. It was de- termined that an artificial gravel pack would be necessary with a 12-inch pipe size screen. The screen manufacturer recommended a 60 slot screen with a #20 U.S. sieve sand to be installed from 200 feet to 300 feet. The sand size was based on the formation and the fact that the 60 slot size would allow only 1 percent of the formation sand to pass through the screen. The 12-inch-diamater pipe size screen was chosen due to the high- capacity design of this diameter in our chosen screen type. We did have one design problem. The 12-inch-diameter riser to the surface would be too small to allow for the installation of a bowl assembly large enough to deliver 3500 to 4000 gallons per minute. How do you gravel pack a screen using a figure K-packer assembly? We determined that it would be nec- essary to first install the screen, sump, leader, and packer, then place the gravel pack in between the 12-inch screen and the 18-inch second line, remove the sec- ondary outer liner far enough to expose the screen, and complete the well with a packer assembly. After installation of the screen and gravel pack, the screen was lightly de- veloped, and a primary double-inverted J-hook figure-K packer assembly was installed to seal the 18-inch liner and the 12-inch screen assembly. Screen Assembly Components There are five components to a screen assembly: 1. The sump is made of steel that is the same diameter as the screen. It can be any length but is usually 1 to 5 feet in length. It serves two purposes: a. It provides an area for sand to accumulate during development without losing production from the screen. It allows you to fully develop the bottom of the screen area. b. It provides a way to remove the screen in future years (if neces- sary) without distorting or separat- ing the screen. An internal right hand J-hook is welded to the sump plate that will allow you to remove the screen from the bottom. 2. We usually use a stainless steel screen with a uniform slot size top to bottom. The screen can be either welded together via weld rings or joined by flush thread connections on FROM THE ARCHIVES There will always be a place for gravel packing production wells. GRAVEL PACK SCREEN DESIGN USING CABLE TOOL METHOD By Roger E. Renner, MGWC 50 July 2015 WWJ waterwelljournal.com