Packer systems

Two test wells, H-15D and LP-1, were drilled in areas known to contain other wells having high arsenic levels (Fig. 1, 2). To minimize possible contamination from drilling mud, city water (H-15D) or ground water from a nearby well (LP-1), was used to circulate rock cuttings. Water samples were collected at 15.7 m intervals using a pump and packer system, with selected zones of interest sampled in packed 1.37 m or 5.33 m intervals, using a similar protocol. 

Figure 1. Configuration of the Isothermal Test and adjacent packer systems (After, Chandler 2000).

A series of pneumatic piezometers (IRPl-10) and hydraulic piezometers (IRHl and 2) were installed within 0.9 m of the outer diameter of the borehole. Two boreholes were installed with packer systems to measure pore water pressures in the rock further from the borehole (IRW). 

They are not necessarily stand-alone methods, as coiled-tubing injection and ball sealers can be combined with isolation packer systems. 

Packer systems. Mechanical placement is the most certain method of acid diversion. Mechanical placement, or diversion, includes the use of inflatable straddle packer systems, bridge plug/packer combinations, and special wash tool packer systems, to physically isolate short sections of long treatment zones. 

Mechanical placement with isolation packer systems allows for the injection of acid within a limited treatment interval at one time. Other treatment intervals within the total zone can be treated individually in stages. Figure 6-3 depicts the treatment of a bmited interval with coiled tubing through a packer setting. 

There are a number of commercial packers and packer system manufacturers. Improvements in such treatment tool sj tems and extensions of their application are continually made. Information on packer systems and their uses, including design for specific applications, can be obtained from the major packer manufacturers or pumping service companies. 

Isolation packers for use in acid stimulation are effective in a well completion only if acid will enter perforations and continue flowing into the formation. If a poor cement job is present, acid may channel vertically along the cement/formation interface, defeating the purpose of mechanical placement. Of course, mechanical placement of add with packer systems is valid only in perforated, cemented pipe completions. As of this writing, reliable mechanical placement techniques for small-diameter, monobore (slimhole) completions do not exist. 

Packer systems for acid placement in horizontal wells do exist, however, and can be effective. The limitation that does exist with such systems is the number of placement settings or injection stages that can be applied. Typically, the rubber packer sealing elements can withstand 10-15 settings in a particular well condition before the risk of packer failure becomes high. The number of settings depends on the packer and downhole conditions. 

Another limitation to mechanical placement is cost. Packer systems often require a rig. Moreover, specialty packers may themselves be expensive. Nevertheless, mechanical placement with packers is the most reliable option and the best method for improving treatment zone coverage during add stimulation. 

Sandstone acidizing in horizontal wells is difficult because of placement limitations. Horizontal zones are typically longer than zones in vertical wells. Horizontal intervals can be many thousands of feet. Mechanical isolation with packers, which is the most effective method of placing acid in vertical wells, is not often practical in horizontal zones. Too many packer settings are required, extending beyond the limits to which current commercial packer systems can be effectively seated and reseated. 

Acidizing may be conducted successfully through certain packer systems. However, the limitation is the number of packer settings available. In long, horizontal sections, use of... 

Fig. 2. Locations of the multi-packer (MP) systems and packer systems for groundwater sampling from boreholes DH-3 and DH-4.

---