Fracturability Index is a Mineralogical Index: A New Approach for Fracturing Decision
Authors: Alzahabi Ahmed , AlQahtani Ghazi , Soliman Mohamed Y. , Bateman Richard M. , Asquith George , Vadapalli Ravi 
Published: June 2015

Shale has ultra-low matrix permeability, and consequently requiring the creation of hydraulic fracturing to maximize the contact area with the reservoir. The key to successful fracturing treatment in shale formation is the identification of the sweet spots. Productive shale consists of quartz, feldspar or carbonate and clays, in addition to organic matter (Kerogen). Thus it is challenging process to map the best zones to fracture and locate horizontal wells. A new Fracturability Index based on mineralogy has been developed to locate the best areas along horizontal wells to fracture. A good Mineralogical Index would prolong production plateau for shale plays.

Current technology follow two schools, first one through equally spaced fracturing, and the more fractures the better production, second; guide through brittleness index, which distinguish brittle versus ductile zones along the well path, supporting the second school, we have a better correlation of Fracturability index, the new correlation indicates the most brittle parts of the reservoir (MI&gt;0.6) versus the most ductile parts (MI &lt;0.6), it became easier to map the producing shale with sweet or unattractive spots leading to the effective fracture locations. It is a new sweet spot identifiers, which guide the fracture design and fracture allocation along horizontal wellbore path, it may optimize well placement and hydraulic fracturing positioning in unconventional resources.

A new Minerological Index is developed ranging from 0 to 1 which helps optimize the fracturing and shale development, in addition to guaranteeing fracture treatments are in the right place. This will facilitate connectivity with natural fracture network, priority of guiding fracture design start with High FI which corresponds to higher mineralogy index. MI value of 0.6 is a good starting point to map sweet spots. This may enhance far field Fracturing Complexity and help getting a branched fracture. Based on a sub category of quartz, type of treatment may be recommended.

Introduction

With the increased demand on oil and gas resources from shale plays, it has become profitable developing these resources. Many successful shale plays such as Baken, Eagle Ford, Barnnet, have been developed through horizontal wells and multi stage fracturing. The recent big shale resources added to these common successful plays are Wolfcamp across Permian basin in Midland (West Texas). Wolfcamp formation lies beneath Spraberry and dean formation. Over the last 20 years, companies were developing over 10 formations using vertical wells. The Wolfcamp is over 1000 feet, subdivided into A, B, C, and D. They are principally shale rich, except the upper part is more carbonate rich. They key on placing wells in sand rich intervals.

Considering an unconventional gas reservoir for which gas production totals over the entire reservoir area are given (or estimated). We are interested in the Wells Placement Problem (WPP), i.e., maximizing the total gas production of the reservoir while minimizing the cost and subject to certain constraints such as number of non-conventional wells and distances between well. Spacing between wells and fractures wells are also constrained by stress regime and by a new Fracturability index FI. The new Minerological index serve as a quality map to guide the selection of non-conventional wells hydraulic fracture locations.