This case-history paper describes methods of perforating and fracturing with coiled tubing (CT) in the South Belridge Field of California. Techniques presented in this paper allowed the operating company (OC) to fracture-stimulate multiple zones in a single trip of the CT. Each zone received fracturing treatments individually without affecting other zones. By employing a procedure developed for use in the wells of the Belridge Field that involves performing two perforating cuts (using a 5-ft tool twice) in one hydrajetting operation, using 90-mesh sand and allowing decreased circulation overflush volumes, the OC was able to double the number of perforations in each producing interval, thereby increasing the area of formation treated and the amount of proppant placed in each interval while decreasing total volume of fluid used per treatment stage.
Procedures presented are applicable in production areas where multiple pay zones require fracture stimulation. Without application of pinpoint-stimulation techniques, stimulation fluid applied to a long interval will likely enter the zone presenting the least resistance and consequently bypass other zones without stimulating them at all. Operators have solved this problem in the past by using the perf-and-plug technique, which is effective, but also slow and expensive. The CT-conveyed, pinpoint stimulation (PPS) process reduces the duration of the fracturing process for all zones from days to hours. The prominent feature of the PPS process is hydrajet-assisted fracturing (HJAF) using wellbore sand plugs immediately placed after each frac stage (Gilbert et al. 2005; Hejl et al. 2006, East et al. 2008).
Before switching to pinpoint stimulation by CT, the OC treated its wells by conventional fracturing methods, usually treating three zones with each frac stage. Interval lengths were from 150 to 250 ft, and the treating-fluid stage volume was large to deliver enough proppant for the large interval. The pumping rate was about 40 bbl/min to accommodate the interval length. However, radioactive-tracer logs run after all the frac operations showed some intervals were not treated with frac sand. With the HJAF process, the OC was able to treat each interval equally, with assurance that each pay zone was fracture-stimulated. Treating deeper zones was easier than before, and higher proppant concentrations and increased proppant volumes could then be placed in each interval. The use of the 90-mesh sand (instead of 20/40 size) for the perforating cuts allowed decreased volumes of fluid to be circulated. This method greatly reduced stage pump times and therefore, has reduced fracture-stimulation costs for the OC.