Distribution and Relationship of Key Properties of Different Fine-grained Facies

Shu Jiang¹, Thomas Anderson¹, Steven Osborne¹, Jinchuan Zhang², and Xian Shi^3
1Energy & Geoscience Institute, University of Utah, Salt Lake City, UT, USA
²China University of Geosciences, Beijing, China
³China University of Petroleum, Qingdao, China

The study of producing shale plays in North America and emerging shale plays in China and South America shows that the tight rock of so-called “shale” reservoirs are defined as shale due to their fine-grained property, their lithologies include siliceous shale (i.e. Mississippian Barnett shale in US, Silurian Longmaxi shale in China, Jurassic Los Molles shale in Argentina), carbonate rich shale (i.e. Cretaceous Eagle Ford in US), clay rich shale (i.e. Triassic Yanchang7 shale and Paleogene Shahejie3 shale in China), chalk and marl (i.e. Niobrara), dolomite (i.e. middle Bakken, Paleogene Kongdian2 and Shahejie1 dolomite in China) (Figure 1.) The facies differentiation, organic matter distribution and mineralogy variation of fine-grained deposits are controlled by tectonic setting, sea level change, sediment source, depositional setting, etc. The fine-grained rocks widely occur in marine, transitional (coastal swamp) and lacustrine settings. Regionally extensive shales were generally formed during high sea or lake level and/or rapid basin subsidence periods. The lithofacies vary in locations, e.g. the Niobrara formation has a higher component of clastics (clay and sand/silt) towards the west Orogenic Belt, and it is chalk rich in open and shallow warmer water to the east that is away from clastic influx. Regional study in Paleozoic marine shale basins and Mesozoic lacustrine shales in China, marine shale basins in US and marine shale basins in South America reveals: From basin margin facies to basinal or depositional center facies, the sediments become finer and less influenced by sediment source, and total organic content (TOC) usually increase with the decreasing of depositional energy (Figure.2). If the fine-grained depositional systems in a basin are mainly controlled by clastic influx (i.e. Cretaceous Vaca Muerta equivalent formation in Neuquen Basin in Argentina), the clay content will increase away from sediment source since larger and dense sediments are deposited first, followed by fine-grained sediments. If the fine-grained depositional systems in a basin are far away from classic dilution area (i.e. Devonian Marcellus shale in US Appalachian Basin), the biogenic quartz will elevate the high brittle mineral content. The sample test of China shales shows the rough trend of quartz or brittle mineral content in shales of different depositional settings is Marine>lacustrine>transitional. The geomechanical property e.g. strength, Young’s Modulus or fracability also follows this trend. The key mineralogical, geochemical, petrophysical, geomechanical properties and log response of fine-grained rocks are correlatable, e.g. the calcite rich interval of Niobrara has higher porosity, higher resistivity and lower gamma ray. The potential typical shale reservoir intervals of Silurian Longmaxi marine shale, Triassic Yanchang7 lacustrine shale, Jurassic Dongyuemiao lacustrine shale, Paleogene Shahejie3 lacustrine shale in China and Vaca Muerta marine shale in South America have the characteristics of high gamma, high TOC, high resistivity, high acoustic transit time, high gas shows from mud logs, relatively high porosity, high quartz or brittle mineral content and high Young’s Modulus.

AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013