How to Perforate Challenging Wells Completed in Two Casing/Liner Overlap Sections: Mature Ecuador Field Case History

Abstract

Abstract One of the primary challenges for wellbores completed with overlap sections in prospective pay zones is determining how to establish effective communication between the wellbore and reservoir. Conventional perforations are not sufficient to initiate production. This paper presents an effective method for communication with the reservoir using cutting or slotting tools. Based on Bernoulli's energy conservation principle, an abrasive fluid, primarily composed of gel and silica sand, is forced through jets under a predetermined pressure, converting pressure energy into kinetic energy and enabling the fluid to exit the jets at velocities exceeding 1/2 Mach; this enables the abrasive cutting of the production liner/intermediate, cement sheet, and formation rock. This technique can be applied with either coiled tubing (CT) or jointed pipe, thereby achieving success in different applications, such as perforations in a single casing, overlap casing sections, and before hydraulic fractures. A value-added element of this perforation technique includes the application of a relative-permeability-modifier (RPM) additive as part of the abrasive fluid, which helps prevent formation fluid loss while jetting under high overbalance pressures in low-pressure wells. This paper describes the job design, oil-production expectations from the operator, operational data, simulations, skin analysis, and results of this case. The technique was designed and individually applied in two target sandstones, Reservoirs A and B, which are coincidentally located on both 9-5/8 × 7-in. and 7 × 5-in. overlap sections, respectively. The method enabled a customized design for each zone, which resulted in more aggressive perforations to overcome the challenge in both sections. Successful production improvement for a mature field in Ecuador was achieved using this perforation technique, which was the only available solution at the time to overcome such challenges. Advantages and lessons learned are discussed and compared to conventional gun-based perforating techniques. Another interesting factor of this case history is that Reservoir B was new, with unknown fluid and petrophysical properties.