Production Logging Tool Developments for Horizontal Wells and Hostile Environments
Authors: Gardner Dave , Fallet Truls , Nyhavn Fridtjof 
Published: December 2007

Abstract
The purpose of production logging is to describe the flowing characteristics of a well, however, it is only in the simpler well and fluid configurations that conventional measurement technology is in general adequate. In addition, the challenge of obtaining useful measurements is further complicated by the rapid advancement of completion technology resulting in increasingly complex well configurations.
As a part of a Norwegian research program new technology is being developed with the objective of improving the diagnostic capability of production logging in especially horizontal wells. Sensor developments include a downhole sand detection tool and an ultrasonic flowmeter. Complimentary developments in the field of high temperature electronics are improving tool reliability and extending the capability of downhole instrumentation to deeper (hotter) reservoirs.
This paper describes the technology taken into use and reviews laboratory and field experience.

Introduction
Production logging attempts, from bottomhole measurements, to describe the flowing characteristics of a well. Well problems can thus be diagnosed/repaired and reservoir management is assisted. However in general it is only in the simpler well and fluid configurations that conventional production logging measurement technology is adequate. This reflects that developments in production logging have not kept pace with completion technology which in contrast is resulting in increasingly complex well configurations and associated bottomhole flowing conditions.
A program of production logging tool development is in progress also as a part of a Norwegian research program in well technology. The production logging developments include new sensor technology for sand detection, flow metering and fluid compositional measurements, high temperature electronic design and integration with complementary systems such as the well tractor. This paper reviews those developments that have reached field testing including a downhole sand detector, an ultrasonic flowmeter and high temperature electronics.
Sand production problems can represent a limiting factor for well and field production potentials. Identifying sand producing zones and measuring their production characteristics can assist in choosing the correct sand control strategy. A downhole sand detection tool has been developed based on established surface sand detection technology. The tool is in use in the North Sea and Middle East.
For multiphase flow in highly deviated and horizontal wells the simple designs of contemporary flow metering devices are generally insufficient to provide an adequate description of the fluid flow. In addition, due to their mechanical nature flowmeters often prove to be unreliable in the harsh bottomhole environment. A solid state ultrasonic flowmeter is under development based on medical doppler velocimetry which potentially can provide an improved description of the flow velocities. Field testing has proven the viability of using the technique downhole The most recent prototype tool makes multiple velocity measurements across the wellbore cross section.
As oil exploration drills deeper, reservoir temperatures are increasing and HPHT wells are planned with bottomhole temperatures as high as 230 C. Conventional high temperature production logging tool technology is normally rated to a maximum operating temperature of 175 C and for a limited period of time. As a part of an advanced production logging tool development, high temperature electronic circuits are being developed to replace conventional logging tool electronics. Laboratory testing indicates reliable high temperature operation is achievable at 230 C. The resulting downhole electronics are very compact, taking as little as 1/20th of the space of conventional electronics.
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