Integrating Advanced Production and Image Logging in a High-GOR Horizontal Well
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 93473, "Integration of Advanced Production and Image Logging in a High-GOR Horizontal Well With Assessment of Remedial Actions," by A.A. Al-Fawwaz, SPE, and H.K. Mubarak, Saudi Aramco, and M. Zeybek, SPE, Schlumberger Oilfield Services, prepared for the 2005 SPE Middle East Oil & Gas Show and Conference, Bahrain, 12-15 March.
Production logging in high gas/oil ratio (GOR) horizontal wells is difficult because of complicated multiphase-flow regimes in long undulating wellbores. Accurate diagnosis of gas-entry points is important to understand well performance and the reservoir dynamics and characterization and, if possible, to plan remedial shutoff action. This paper summarizes a case study of a high-GOR horizontal well from which oil production decreased significantly because of gas entry. An integrated production-logging tool was used to detect gas-entry points and determine the flow profile.

Introduction
Increased gas production can reduce oil-well performance significantly. Generally, a drop in reservoir pressure or gas break-through could cause an increase in GOR. Detecting gas-entry intervals, in the case of early increases in GOR, provides valuable information for understanding reservoir dynamics and optimizing well placement. Well-performance evaluation is crucial for maximum productivity and choosing well trajectories. The integration of reservoir and geological data yields a more accurate characterization.
Conventional production-logging tools, developed for vertical wells, often do not perform well in horizontal wells because multiphase flow in horizontal sections is highly segregated. In this case, high-GOR production began during the first year. Detection of gas-entry intervals was the primary objective. An integrated production-logging tool string, including a gas-holdup optical-sensor tool, was run. The tool detected gas and oil entry accurately. The integration with static data from openhole and image logs showed coherent results by identifying high- and low-permeability facies where the gas entries were observed from high-permeability zones crossing the wellbore. A fine-grid numerical-simulation model was developed with a commercial simulator to assess remedial-action plans.

Gas/Liquid Flow and Integrated Production-Logging Tool String
It is known that, generally, oil/water flow regimes in horizontal wells are stratified. It is important that fluid-flow regimes be understood for interpretation and measurement accuracy. Fig. 1 shows the flow regimes in horizontal wells having gas/liquid flow. Mostly stratified or wavy-stratified flow regimes are observed when the deviation is 90° or greater. However, the stratified-flow domain is limited when the deviation is less than 90°. Plug or slug flow becomes dominant at this deviation, indicating the complexity of the flow. Considering the small changes in well deviation and fluctuations in the well performance, real-time gas-holdup measurements during each pass would improve the results.