Validation of C/O Log Interpretation using Fractional Flow Curve on Workover Plan of Offshore Oil Well

Abstract

RNF-1 is an oil well that has been produced since October 1975 on the offshore of the Java Sea. The well was a vertical well, until sidetrack drilling was conducted at October 2000 so RNF-1 become a horizontal well. Perforation of the horizontal segment was done at the interval 7619 – 8638 ftMD. The last production of the well is at August 2010 with 85% of water cut (WC) and the well is being suspended for the back-pressure issue. The company decided to plug the horizontal segment and design workover plan to vertical segment of the well. To minimize risk of uncertainty, an integrated and comprehensive analysis is needed in determining the next production zone target.

The analysis begins with the remaining reserve analysis of RNF-1. After that, analysis to special core analysis (SCAL) data and fluid property data is conducted to build the fractional flow curve. Then, analysis of OH Log (lithology, porosity, and resistivity tool) is done as validation to fluid saturation distribution among the well gained from C/O Log interpretation. This paper presents a novel uncertainty solution, where the value of water saturation (Sw) cut-off we get from fractional flow curve is used to validate the moveable oil saturation of C/O Log. By so, the next pay zone determination for workover plan could be done surely.

After workover plan is executed, it is proved that the production rate is increased from 607 BLPD (WC 85%) to 934.3 BLPD (WC 11.2%) with significant incremental of oil production rate as 736.6 BOPD. In this paper, we can have a view about fluid saturation distribution by C/O Log interpretation. By the validation of C/O Log using cut-off Sw, moveable oil saturation can be determined with minimum uncertainty. This, surely, will give a great feedback to the workover plan, especially for offshore well with higher cost and higher risk.