Production Allocation Along Long Horizontal Drains Activated by ESPs: Rising to the Challenge
Authors: Constant Stephane Alan , Foulon David Jean , Noman Rashed , Labiadh Mohamed D. , Narayanan Ramdas , Danquigny Jacques Albert 
Published: February 2016

Production allocation is of utmost importance for optimum reservoir development and production optimization. It is becoming all the more critical as fields are increasingly developed through long, often multilayer, commingled horizontal drains, either to reduce costs in offshore environments, to ensure productivity in low permeability reservoirs, or as an improved oil recovery method tapping unswept areas.

Conventional Production Logging Tools (PLTs) have been adapted to this more complex situation through optimized acquisition methodologies, and propulsion equipment using either coiled tubing or tractors. However, these tools face their limits when it comes to logging long horizontal drains produced by downhole electrical submersible pumps (ESP): the presence of a by-pass tubing at pump level makes it extremely challenging to perform a "classical" PLT in production mode. This paper describes the various attempts to rise to this production allocation challenge in a complex carbonate field located offshore Qatar.

An enhanced monitoring program was put in place over two years, to try, test, and standardize the most promising tools available in the market. Tractored production PLTs attempts were performed, enabling significant improvements in the operation methodology and tools, but highlighting the high-risk nature of such an acquisition. Injection PLTs tractored in oil producers were tested and adopted as a reliable way to get adequate information about the production allocation. Different fiber-optic distributed temperature sensors were tested in various acquisition protocols, clarifying the strategy for optimum acquisition and the corresponding potential for production allocation.

Overall, more than fifteen production allocation-related acquisitions were performed, including several world "firsts", resulting in an improved knowledge of the production split along the well bore, the identification of the most reliable tools-tractors combinations, successful reperforation operations, and a clear assessment of the way forward.

Introduction

The typical well on Al Khalij is a sub-horizontal drain of 2500 to 3000 m, which is crossing several layers with various petrophysical characteristics and productivity potential (Fig. 1). The drain is drilled in 8-1/2 and cased with a cemented 6–5/8 or 7" liner. The zones of interest are perforated and massively stimulated with Emulsified Acid. The diversion is obtained through high pump rate, viscosity and the use of bioballs. (Ref. 1).

Due to the field depletion and low gas associated to the oil, all the wells are currently activated by Electrical Submersible Pump (ESP) and produce through a 4-1/2 tubing.

One of the key uncertainties at the well scale is to confirm that the production distribution along the wellbore is consistent with the petrophysical characteristics of the perforated intervals in order to validate our well architecture and completion strategy with long multi-layered drain with cemented liner and acidized perforated intervals.

Another key uncertainty at field scale is to understand the water production mechanism: bottom coning vs. edge coning; possible active fracture corridor, vertical vs. lateral water sweeping.

The ideal acquisition to obtain a maximum of informations is a Production Logging (PLT) associated with a S log acquisition (for cased-hole saturation evaluation in Al-Khalij salted formation water environment) in production mode.

Due to the difficulty linked with this type of acquisition, alternative solutions were put in place over two years: PLT in injection mode, Distributed Temperature Sensors (DTS) and inwell tracing.

This paper will present the performed acquisitions with their success, limitations and sometimes failure.

It will highlight the impact of the results in our field behaviour understanding and their application.