Optimized Shale-Resource Development: Well Placement and Hydraulic-Fracture Stages
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 162534, ’Optimized Shale-Resource Development: Proper Placement of Wells and Hydraulic-Fracture Stages,’ by Robert L. Kennedy, SPE, Rajdeep Gupta, SPE, Sergey Kotov, SPE, W. Aaron Burton, SPE, William N. Knecht, SPE, and Usman Ahmed, SPE, Baker Hughes, prepared for the 2012 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11-14 November. The paper has not been peer reviewed.

Europe and Australia have joined the US in expanding recoverable hydrocarbons from unconventional resources, and initial activities are on the rise elsewhere. However, not all wells are producing commercially, and not all hydraulic-fracture stages contribute within the producing wells, suggesting that it is important to target the field’s sweet spots when dealing with shale resources. Therefore, unconventional-resource development based on the current concepts of geometric placement of hydraulic-fracture stages may not be appropriate.

Introduction

Although significant advancements in technology for the development of shale gas/oil plays in North America (particularly in the US) have been made in recent years, a number of these shale wells still experience relatively low initial productivity. There are two possible reasons for this: Fracture placement does not intersect the natural fractures in the well, and reservoir quality [i.e., total-organic-carbon (TOC) levels, thermal maturity, and remaining hydrocarbon in the source-rock reservoir] is low or nonexistent at the locations where fracture stages have been placed.

Many US operators do not invest in methods of reservoir characterization along the horizontal lateral to assess reservoir quality (i.e., no logs run, drilling cuttings not analyzed, and advanced mud logging with addition of gas chromatography not used). However, international operators in China, Latin America, Saudi Arabia, and India, who are just beginning to explore and exploit shale reservoirs, are eager to consider new technologies that have been shown to reduce cost or increase recovery.

Well-by-well production data indicate that shale formations have small spots of very productive wells—sweet spots—surrounded by large areas of wells that produce far less gas/oil. Sweet spots are a function of TOC, thermal maturity, thickness, natural fractures, mineralogy, and geomechanical stresses in the area. The first step in identifying sweet spots is from information collected during a basin screening study. It is recommended that such studies be conducted in a new basin or in a different part of a basin than that being developed currently.

To begin initial characterization of the reservoir, it is recommended that 3D seismic be conducted over the potential play area. Data from exploration and appraisal wells are used to pinpoint the location of sweet spots through further formation assessment consisting of detailed mineralogical, structural, and geomechanical characterization (pulsed neutron spectroscopy, nuclear magnetic resonance, and acoustic logs). These data are more location-specific, while information gathered through seismic is broad, spread out, and not as accurate as that obtained from an actual wellbore penetrating the formation.