Reduced Risk Alternatives for Water Entry Detection in High Water Producing Horizontal Wells
Authors: Ojonah Okenufowo , Kohring James 
Published: February 2016

Maximising the potential of a producing well requires knowledge of the fluid types and flow rates entering the wellbore. Optimum and accurate determination of multiple phase fluid entry requires two primary measurements:holdup, or the cross-sectional area in the well occupied by the phase of interest, andvelocity, or the speed at which the available phase is flowing.

Recent industry developments in production logging have addressed these fundamental requirements of measurement with multiple probe technology that differentiate between Oil Holdup (Yo), Gas Holdup (Yg) and Water Holdup (Yw), as well as providing multiple spinners for revealing stratified velocities travelling inside highly deviated completions.

Pulsed-neutron (PNL) technology provides two services related to measuring water production:the Water Flow Log (WFL) measures the speed of the water flow, whilethe Three-Phase Holdup Log (TPHL) confirms the available multi-phase holdups.

When water velocity and water holdup are measured and when changes in phase behaviour due to variations in wellbore deviation are factored, water inflow quantification is attainable. The conclusions and claims of this technique are validated against the results of an advanced production logging tool (APLT) utilizing multiple spinners and multiple probes, and comparisons of the advantages and disadvantages of each technology as a standalone water entry recognition solution are offered.

The results of this research, along with the inclusion of two Niger Delta case studies, address the viability of a possible lower cost alternative for water entry quantification in near-horizontal wells that potentially have a higher risk of encountering sensor damage due to loose sand and/or debris. Other candidate wells that would benefit from these concepts include those producing with large water cut where high water holdup and water velocity would likely be encountered downhole. Once the water producing zones are identified, water shut-off solutions can be subsequently designed for the purpose of restoring the well's oil producing capabilities.

Introduction

It is common knowledge that oil production declines are often associated with increases in unwanted water production and this is particularly universal in brown fields. Production logging provides a viable means of detecting and measuring downhole oil, gas and water entry, especially with the recent technological advances that significantly augment confident answers. The determination of the water entry locations then provides a target for a water shut-off program with the objective of restoring oil inflow.

Difficulties in acquiring quality data in horizontal flow environments, specifically wells with loose sand and/or debris that potentially damage sensitive spinner and probe sensors, are not uncommon. Producing horizontal wells completed in unconsolidated and poorly sorted formation sands can be particularly perilous to production measurements. Although some of the more sophisticated production detecting tools such as the APLT provide optimum answers of flow distribution, it is necessary to consider technology and technique that functions with a high degree of reliability in these often times hostile environments.

This paper examines an alternative flow detection solution and provides recommendations for the identification of water entry in horizontal flow environments. Two Niger Delta case study wells validate the precision of the measurements against the results of the APLT multi-probe, multi-spinner production logging tool.

The Challenge

Skepticism towards attempting to acquire Production Logging Tool (PLT) data in Nigeria horizontal wells is commonplace. Some of the issues are related to lack of knowledge and trust in the sensors due to previous failed experiences in attempting to identify oil, gas and water inflow with tools and utilizing flow models that are designed for vertical wells. Even with the evolution of advanced PLT technology that now offers tools designed specifically for highly deviated wells and three-phase flow, resistance to deploying these new tools remains high mainly due to one notorious issue: loose sand.