Case History

MaxVert™ Simplifies Working Over Sub-Hydrostatic Wellbores

West Texas
Challenge

An operator had a one-year-old, 44-stage combo frac sleeve and plug and perf fractured sub-hydrostatic horizontal well, with 9,377 feet of perforations. After a year of production, scale build-up disabled several downhole pumps. In order to replace the pumps, the tubing had to be removed from the wellbore. With the tubing pulled from the wellbore, the Operator planned to re-enter the well to mill-out scale and the leftover frac hardware. During similar workovers, in adjacent sub-hydrostatic wells, the workover process typically took two weeks and only retrieved 1 – 2 m3 of scale. In an effort to safely optimize the workover process, the Operator required circulation prior to the milling operation. 

Solution

The Operator asked Impact to develop a program and utilize the MaxVert™ diverter system. The Operator wanted flow through the fractures temporarily prevented. MaxVert completely dissolves to a clear non-damaging fluid with time and temperature, and can temporarily isolate fractures. 

In two stages with a total volume of 6,700 lb, MaxVert returned circulation to the wellbore. A pump pressure increase from 115 – 145 minutes demonstrates MaxVert sealing open fractures. (A slight increase in the pressure prior to 115 minutes was simply due to friction.) In stage two, a sufficient number of the remaining open fractures were plugged to achieve the pre-job target pressure of 3,500 psi. 

Results

The mill-out time was reduced 70%, and circulation was maintained throughout the entire milling operation. During the milling process, the pump rate in was 5 BPM and the return rate never fell below 4.5 BPM. The small amount of scale typically returned to the surface (1 – 2 m3) was replaced with six, 3 m3 mounds. Previously unobserved frac parts were also returned to the surface. A substantial increase in production was measured, further enhancing the economics of the MaxVert solution. This increase in production was attributed to the prevention of formation damage from the milled up scale and frac parts. MaxVert protected the formation by temporarily isolating the fractures from the wellbore. 

A number of additional wells were treated with MaxVert in the same field, all with positive results.