Improving Well Productivity and Sustainability in a Horizontal Exploratory Well by Multistage Fracturing - A Case Study
Authors: Almulla Sulaiman , Al-Bader Haifa , Al-Ibrahim Abdullah , Subban Packirisamy , Duggirala Vidya Sagar , Ayyavoo Mani Maran 
Published: February 2020

Abstract

Objective/Scope
The main objective is to find a way to increase the well production and sustain the production by connecting the reservoir through several stages of fractures spaced throughout the horizontal drain hole.

Method, Procedures, Process
Exploratory wells targeting Mauddud reservoir were normally drilled vertically and stimulated in a conventional way using matrix acid treatment, which proved a good hydrocarbon potential, but with low productivity. A study was conducted in one the lower cretaceous reservoir (Mauddud) which recommended the option of drilling a horizontal well in the mentioned reservoir and applying multi-stage acid frac for productivity enhancement and sustainability. The target carbonate reservoir is tight, has a porosity of approximately 12-20% and permeability between 0.05 to 2 md. The first horizontal well for Maudddud reservoir was drilled up to a measured depth of 11,171 ft MD with a horizontal section of 2,752 ft. It was completed with swell packers and seven frac sleeves for multi stage fracturing job in the horizontal section. Designing and execution of multi-stage frac in a horizontal well is technically more challenging than the conventional vertical well.
Minifrac was performed to find the fracture pressure, closure pressure and understand the net pressure needed to extend the fracture. Based on the mini-frac results, the main frac design was modified. Main Frac treatment was carried out in seven stages, each stage was performed individually and the fractured stage was isolated using frac balls with different sizes. Acid and gel mixing was performed continuously on location to enable continuous pumping operation, which minimized the time between stages. After a successful multistage frac treatment, the well was flowed back for cleanup and recovered all spent treatment fluid. Later Coiled Tubing (CT) with milling tool was used to mill the ball and seats to provide full bore access through the frac sleeves. Subsequently production logging tool (PLT) survey was carried out in horizontal section using CT to confirm the effective contribution from each stage.

Results, Observations, Conclusions
Horizontal exploratory well was drilled, completed and fractured successfully with seven stages led to a sustainable oil production after installing ESP. The flow results after the multistage frac showed that there is tremendous increase in production but with some decline. The PLT result showed the contribution profile for each stage and the cross flow status. Production enhancement and sustainability achieved from this well encouraged KOC to drill more horizontal wells for Mauddud reservoir with similar multistage completion and frac strategy to meet the production targets.

Novel/Additive Information
This paper highlights the well design, the effectiveness of multi stage fracturing, well performance analysis, lesson learned and results of the multistage completion & acid fracturing.