Evaluating Production-Log Data From Horizontal Organic-Shale Wells
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 144326, ’Evaluation of Production-Log Data From Horizontal Wells Drilled in Organic Shales,’ by Camron Miller, SPE, George Waters, SPE, and Erik Rylander, Schlumberger, prepared for the 2011 SPE North American Unconventional Gas Conference and Exhibition, The Woodlands, Texas, 14-16 June. The paper has not been peer reviewed.

Production logs from more than 100 horizontal shale wells in multiple basins were interpreted. The evaluation confirmed that production is highly variable along the length of the wellbores. In some basins, two-thirds of gas production comes from only one-third of the perforation clusters. Further, when looking at all basins, almost one-third of all perforation clusters are not contributing to production. This finding highlights a significant opportunity to improve overall completion effectiveness and economics in these high-profile projects.

Introduction

Not all horizontal wells drilled in organic shale have been a complete success. With the heightened risk of exploring for and developing unconventional gas, success rates are scrutinized closely. This study reviewed more than 100 production logs run in horizontal shale-gas wells and attempted to explain the variability in production in terms of reservoir quality (RQ), completion quality (CQ), and operational efficiency (OE). RQ is defined by petrophysical parameters of organic shales including organic content, thermal maturation, effective porosity, fluid saturations, pore pressure, and gas in place. CQ is defined by geomechanical parameters required to stimulate organic shales effectively. The key geomechanical parameters are near-wellbore and far-field stresses; mineralogy (specifically, clay content and type); and the presence, orientation, and nature of natural fractures. OE is the improvement in the connection between the reservoir and the wellbore. The goal was to better understand the parameters that control completion effectiveness and corresponding productivity in horizontal organic-shale wells.

While 3D seismic, offset-well logs, logging-while-drilling gamma ray logs, and mud logs all have application, they do not address the small-scale vertical variability that exists within shale reservoirs. To optimize productivity, reservoir heterogeneity must be accounted for during drilling or stimulation.

The authors suggest that well placement and stimulation with respect to RQ and CQ will result in more-uni-form production across perforation stages and better overall well performance. Formations having superior RQ and CQ should be targeted because they will provide better drilling and completion efficiency.

Horizontal Production Logging

Production logging is used often in shale reservoirs to determine the success of horizontal-well placement and reservoir stimulation. Often, a flow-scanning/-imaging tool is used for production logging in multiphase horizontal wells. One such tool provides a phase-area measurement (holdup) and phase-velocity measurements of gas, oil, and water in the wellbore by use of probe and micro-spinner technologies. The end product is a direct, downhole calculation of multiphase production.