World-wide, 85 percent of oil & gas wells currently use some form of artificial lift, and nearly all wells need stimulation at some point during their production. Common artificial lift mechanisms include beam pumps, gas lift injection, submersible pumps, and hydraulic pumps—all of which require periodic optimization.
To make appropriate adjustments, well operators must record a well’s casing and tubing pressure simultaneously to inform technicians on the characteristics of the well. This helps determine when to transition from continuous to intermittent stimulation and provides a metric for judging the optimal pressure settings and duration of intervals. Several down-hole techniques exist for taking these and other measurements. However, the use of down-hole tools is expensive, and comes with a certain degree of risk to the completion, to field personnel, and to the tool itself.
Meanwhile, only imperfect tools—most commonly a two-pen chart recorder or a standard pressure gauge—have been available for measurements at the surface. A new class of tool, called a reference recorder, makes it easier to take these important measurements at the more desirable surface location.
The Goal: Safe Surface Monitoring
Using a reference recorder for measurements at the surface, in place of down-hole equipment, protects the well from damage due to a lost tool, and avoids the increased risk of a blowout or loss of seal. The risk of injury from high pressures or exposure to hydrogen sulfide gas is also lower.
Wells with high deviation, elevated bottom-hole temperatures, or an irregular borehole are especially well-suited to surface measurements. A reference recorder is easily portable, allows extended, battery-powered, Intrinsically Safe measurements without the cost of a wireline and other equipment.
How to Connect a Reference Recorder
Connecting a reference recorder for surface monitoring is straightforward. As shown in Figure 1, both the tubing and casing pressure inputs should be connected as close to the well as possible. The casing pressure input should be downstream of the input choke, and the tubing pressure input should be upstream of the choke body and any other restrictions.
In this configuration, technicians can use data from a reference recorder, in conjunction with other information, to optimize surface controls, locate surface problems, and identify down-hole problems.
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