Production and Video Logging in Low-Permeability Horizontal Gas Wells
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 108084, "Production and Video Logging in Horizontal Low- Permeability Gas Wells," by D. Sask, SPE, Consultant; C.D. Hundt, SPE, and J.M. Slade, SPE, EnCana Corp.; and P. Daly, Consultant, prepared for the 2007 SPE Rocky Mountain Oil & Gas Technology Symposium, Denver, 16–18 April.
Effective production-logging (PL) techniques are available for low-rate horizontal gas wells. Between June 2005 and September 2006, eight Sierra-field wells were evaluated with either traditional PL tools or downhole-video-logging tools. Pressure, temperature, nuclear-fluid-density, single-capacitance, capacitance-array, fullbore-spinner, caliper, and gamma ray data were acquired with traditional PL tools. Video logging collected wellbore images as well as pressure and temperature information. The PL data indicated liquid accumulations; however, the different logging tools showed varying degrees of detail. Video-logging data provided definitive images of gas bubbles and slugs flowing through liquid.

Introduction
In the past, operations in the Sierra field consisted of drilling, completing, and commissioning a large number of wells during the winter when the muskeg is frozen and land access is available. The initial focus was to bring on new production with very little engineering or research applied to mature wells. Incorrect assumptions resulted from this lack of engineering data. One such assumption was that the reservoir contained undersaturated gas and that, therefore, liquid-loading problems should be minimal.
The greater Sierra area is approximately 90 km east of Ft. Nelson, British Columbia. Approximately 700 producing wells have been drilled into the carbonate Devonian Jean Marie formation. The horizontal wells are drilled underbalanced to limit formation dam-age to the underpressured reservoir. Gas is produced from openhole completions. While drilling horizontally, well trajectory is steered on the basis of gas rate while drilling. The inclination is varied up and down until a good permeability streak is indicated by a spike in gas flow rate on the gas-rate-while-drilling chart. After total depth is reached, tubing is installed and the well is brought on production. Typical gas-production rates decline from an initial rate of 1125 m3/d to 281 m3/d after 12 months and 221 m3/d after 36 months.

Equipment and Processes
Two types of equipment were used. The first was a typical full suite of PL tools run in memory mode, and the second was a downhole-video tool run in real-time-data mode.
The following options for conveyance and operation were considered for the PL program.Wireline-with-tractor conveyance and real-time data collection.Coiled-tubing (CT) conveyance with electric line inside and real-time data collection.Continuous-sucker-rod conveyance with memory-mode data collection.
Factors that influenced decisions on equipment selection and conveyance included the following.The cost to conduct the program— the largest factorThe need to pull the tubing to run a wireline-tractor assemblyThe helical-buckling and lockup limitations of smaller CT