Abstract
Horizontal sidetracking and waterflood are part of current Wafra Ratawi reservoir management strategies. These have proven successful to arrest production decline. A comprehensive surveillance program is considered to be the key to optimize waterflood performance. Saturation profile is one of critical parameters to understand waterflood sweep efficiency. The best way to acquire saturation data is by running saturation logs in vertical wells. Since horizontal sidetracking is one reservoir management strategy, the remaining vertical wells accessible for saturation logging are becoming limited and soon will not be available. This paper discusses an innovative and cost effective approach to this surveillance challenge. A combination of permanent fullbore oriented packer and retrievable whipstock, a selective re-entry system, was chosen to complete the wells. The existing vertical wellbore was converted to an observation wellbore before sidetracking. This technique has potential to save significant capital investment by using existing vertical wellbores to serve saturation surveillance purposes.
Since the intent is to run saturation logs periodically in the vertical observation wellbore and to produce through the horizontal lateral during normal operation, there are several operational challenges that must be resolved. These mainly include: debris falling during ESP well services, re-entry jobs in horizontal lateral by work string, and effect of squeeze cement operation on cased-hole logs readings. This paper also discusses how the proposed completion techniques overcome these issues.
Three wells have been successfully completed with this system. The first time-lapse cased-hole logs were also successfully run in one of these wells, including an attempt to re-enter the horizontal lateral by work string that went smoothly. This unique concept of saturation surveillance wellbore in horizontal producers can also be extended for new drill infill producers completed with cased pilot hole. The technique is considered to be an innovative and first time application across the globe.
