Multistage Process Allows Pinpoint Treatment of Hard-To-Reach Pay
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90052, "Unique Multistage Process Allows Pinpoint Treatment of Hard-To-Reach Pay," by James L. Rodgerson, SPE, and Henry Lopez, BJ Services Co., and Phil Snider, SPE, Marathon Oil Co., prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September.
A new multistage treatment process optimizes perforation and treatment design. This technique, known as external casing perforating (ECP), allows the operator to perforate and isolate individual zones in as little as 30 minutes between treatment stages. As many as 17 discrete intervals have been treated within a 24-hour period. This approach minimizes total treatment volume by using the flush from the previous stage as the pad on the next stage, thus placing less fluid on the formation. Production from multiple horizons can be brought on line quickly in one rigless operation without damaging and time-consuming shut-ins.

Innovative Multizone Completion
Multizone intervals often are completed in groups or multiple stages where perforations are placed adjacent to selected pay intervals. Depending on the number of intervals and their spacing, sections of the productive horizon are grouped into bulk or gross intervals. These lumped intervals are selected by pay quality, size, and barrier development. Without extensive prejob diagnostic testing, often it is difficult to determine what constitutes a containment barrier that will group an interval. Stress intervals influence fracture growth and must be considered when planning the perforating design. Diagnostic testing can be costly and time-consuming, taking days or weeks in a multistage design, and can range from advanced log analysis to sophisticated well testing that includes extensive injection and pressure-falloff analysis. Many operators avoid performing these diagnostics because of the initial cost and time required. The benefits of diagnostic testing can be significant in terms of cost savings, enhanced production, and access to additional reserves.
Wells with minimal production or with pay zones that are stratified in multiple stringers over long intervals (i.e., several hundred feet) often are completed in the least-expensive manner. In most cases, these types of formations must be fractured hydraulically to be economically productive. A continuing practice is to fracture stimulate these often poorly connected intervals using limited-entry techniques at higher pump rates. This can be effective in stimulating sparsely populated pay over large productive intervals, but it runs the risk of leaving some zones unstimulated and unproduced. This situation was observed in the Wilshire Devonian field in Upton County, Texas. In fracture stimulation, the more-productive zone maintained higher reservoir pressure than the adjacent zones. The lower-pressured, lesser-quality zones absorbed the mass of the treatment. For several years, this Wilshire field Upper Devonian pay was left virtually unproduced until it was rediscovered in an infield recompletion program in 2002. It was later determined that the most reliable method to ensure the pay would produce was to isolate each productive interval and stimulate each in separate stages.