Integration of Petrophysical and Geomechanical Properties for Enhanced Fracture Design
Authors: Al-Kharraa Hamad , Al-Ameer Ahmed , Al-Qahtani Faris , Al-Sultan Ali , Al-Abbad Mustafa , Al-Obaid Osama 
Published: June 2015

Shale reservoirs retain significant natural gas reserves, which are more challenging to recover than in conventional reservoirs. Production from these unconventional resources became economically feasible as a result of advances in both horizontal drilling and hydraulic fracturing technologies. Stimulation technologies continue to improve through the combining of advanced logging, geomechanics, microseismic and frac fluids. This has led to further optimization of hydraulic fracture treatments and higher recovered unconventional reserves.

Petrophysical and geomechanical models are built using advanced well logging, special core analysis (SCAL), and rock mechanical properties. Within the petrophysical evaluation, special care must be taken when transferring the dynamic values of Poisson’s ratio and Young modulus, obtained from acoustic data, to static values, to reduce the uncertainty of stress and fracture width estimations. Additionally, one of the key parameters in improving hydrocarbon production is choosing a suitable fluid type and associated chemicals to be used in reducing damage to the formation. Geomechanically, utilizing “Drilling-Induced Tensile Fractures” (DITFs) analysis is crucial to estimate fracture half-length, number of fracture stages, closure pressure of the frac and designing the appropriate pump rates.

This paper presents a case study from a Saudi Arabian shale formation. The described workflow is designed to help optimize both reservoir characterization and design of hydraulic stimulation treatments. It will be shown that engineered completions are more effective and yield higher ultimate recoveries than geometric spaced completions. Simulating a hybrid fracture design comparing both geometrically spaced clusters and petrophysically engineered clusters showed a 38 percent increase in conductivity within the engineered design. Particular attention has been given to the effects of natural fractures on the stimulation both in size and direction of extension.

Introduction

Growing energy demand has forced the oil and gas industry to develop unconventional resources, including shale and tight sand reservoirs. Saudi Aramco has shown that reservoir potential for shale gas plays is promising. However, developing shale gas plays has many recognized challenges. High formation heterogeneity, clay laminations, types of clays will all play a major role in the petrophysical interpretation as well as Completion Quality (CQ or fracability) of the reservoirs. Any petrophysical interpretation should be processed using a deterministic method. This will yield a reservoir quality (RQ) quotient. Equally important is combing the geomechanical completion quality (CQ) with the petrophysical evaluation. These will both be necessary when working with ultra-low permeability rocks that require engineered stimulations. Combining the RQ and the CQ will allow us to better answer whether or not a stimulation treatment will be contained or propagate out of zone. After combing the RQ and CQ, advanced stimulation tools can then be used to incorporate that data and further improve the ultimate fracture design.