Sarfraz Jokhio, Wood Group ESP Inc.
A magnetic bailer has been designed to capture and remove metallic compounds that gather in the wellbore and downhole operating equipment such as an ESP unit. The tool can be used as a standalone, as the part of the tubing, or can be set in the tubing as a joint that stands on Y-tool. The tool can be installed above or below the ESP unit. It can be wireline or coil tubing operated. It is, a cost effective and convenient physical way of cleaning the well. It can save significant well shut-in times that are otherwise unavoidable due to pump failure. Many producing formations produce metal compounds along with oil, gas and water. These metal compounds often are iron-associated compounds, heavy and usually settle in the wellbore. Often iron compounds combine with hydrogen sulfide (H2S) and sulfur dioxide (SO), usually present in natural gas, to form iron sulfide in the wellbore. Iron sulfide is a very hard material (SG 5.1 +). It is not malleable and has crystalline and abrasive structures. When iron sulfide enters an ESP unit, it damages the impellers, diffusers, and shaft, thereby reducing the pump run time and causing premature pump failure. Most of the time, it juggles in the fluid that is being pumped and falls back when the pump stops. It is not carried to the surface due to its high specific gravity, it instead sticks to the tubing walls above the pump, and most of the time in the first tubing joint, and with time completely plugs the tubing. Chemical treatment is usually not effective since the inhibitor is pumped out of the well. In this paper the physical properties of iron compounds in general and iron sulfide in particular, along with common contaminant compounds found in crude oil and natural gas and problems associated with iron compounds and associated scale are investigated. Second, the first indications of their presence and the unusual solids in the pump are addressed, and finally the tool design is discussed in detail.