SHALE GAS PETROPHYSICS – MONTNEYAND MUSKWA,ARE THEY BARNETT LOOK-ALIKES?

摘要

Shale gas reservoirs have rapidly become thefocus of exploration and production throughoutthe Continental USA and Canada. These shale gasreservoirs invariably have two factors in common,namely, the need for quality petrophysical workand the implementation of innovative drilling andcompletion technology. In the past 5 years theBarnett shale has become the benchmark for bothpetrophysical and completion technology work, ahuge success story for the United States. Withthis, there has almost been a requirement tocompare “your” shale with the Barnett shale, toprovide a comfort level for both management andnon industry financiers.This work compares two shales of very differentcharacter. They are both in British Columbia,Canada and are themselves the focus ofexponential growth, associated land prices havingincreased 10 fold in 2008 alone. In addition, theyhave both at one time, been cited by industrycommentators as Barnett look-alikes.Net pay mapping of the shales is key topurchasing the best land and drilling the bestwells. First and foremost, it is important tounderstand the geological environment ofdeposition of each of the shales. We demonstratethat the depositional setting for the Montney andMuskwa shales is very different, giving rise toequally different rocks. Both are fundamentallydeep basinal environment, however the Montneyhas well sorted sediment influx in the form ofsubmarine flows or turbidites. Once this isunderstood, the rock work, including thinsections, XRD, SEM and core analysis (TOC,porosity, permeability, Dean-Stark saturation andgrain density) can be effectively integrated intothe petrophysical evaluation and more reliable netpay maps can be produced.This paper illustrates the predictive capability of awell calibrated wireline log in estimatingpetrofacies, porosity, and TOC. Net pay, porosityand TOC maps are presented in the paper.Further, we show that although both are prolificgas producing formations, only one, the Muskwa,can truly be called a Barnett look alike. TheMontney can be termed a hybrid shale,comprising thinly laminated shale, organicmaterial and siltstone. The Montney has muchlower TOC than the Muskwa, 1 to 3 percentcompared to 5 to 10 percent, but has intrinsicallyhigher permeability than the Muskwa because ofits coarser, more granular siliciclasticcomposition. In this regard, the Muskwa is similarto the Barnett shale. An understanding of therock fabric and the differing petrophysicalproperties of the two shales leads to differentcompletion strategies for optimum gasproduction.