A Technique For The Measurement Of Dynamic Mechanical Properties Of Oil Sands
Authors: Hsu T.R. , Chen G.G. , Gong Z.L. 
Published: March 2010

This paper describes a special technique for the measurement of Young's modulus and maximum compressive strength of Alberta oil sand specimens under confining pressure. A modified split Hopkinson bar facility with a pressure chamber was used to provide the source of dynamic loading. Measured strain data were recorded and processed by a high-speed digital oscilloscope and a microcomputer. Mechanical properties of oil sand specimens at strain rates of up to 2000/s were measured. Results indicated strong sensitivity of these properties to the loading (strain) rates.

Introduction

As the conventional oil reserves in the world are being depleted at an alarming rate and more exploration of new sources has been initiated in offshore and frontier regions, the vast reserve of oil sand deposits in this country presents a very attractive and viable alternative to make up this shortage. It is estimated that the total in-place volume of heavy hydrocarbons in oil sand deposits is in the order of 3 trillion barrels, which is roughly equal to the total discovered conventional oil reserve in the world. Unfortunately over 80% of the deposits in Alberta are situated at depths of over 150 metres from the ground surface, which makes in-situ processes the only practical production method(1).

Oil sand is a densely packed material with a density exceeding 2 Mg/m3. It is usually comprised of four distinct phases: mineral solids, water, bitumen and gases. The extremely high viscosity of the entrapped bitumen makes conventional recovery by pumping virtually impossible. Most in-situ processes thus involve heating the oil sand with pressurized steam or by controlled combustion. Two common problems associated with these processes however, appear to be the poor sweep efficiency and communication between the injection and production wells. Pre-injection in-situ fracture of the oil sand pay zone is considered to be a partially effective method to improve the permeability and hence increase the sweep efficiency for the subsequent steam injection.

There are two fracture methods commonly being used in reservoir engineering, namely hydraulic fracturing by pressurized water or steam and dynamic fracturing by explosives. The hydrofracture method is a more commonly used method but was found to be less controllable and often resulting in undesirable fracture patterns. The technology of dynamic in-situ fracture is not as widely used but has been found to be effective in similar applications for hard rock(2). The present authors believe that by introducing proper loading rates and fracture starters at the wellbore, dynamic fracturing can be both effective and controllable. Better understanding of the behaviour of oil sands under dynamic loading conditions is thus necessary.

A literature review has failed to reveal any previous measurement of dynamic mechanical properties of oil sand under various loading rates. These properties are a necessary input to the analytical models for the dynamic in-situ fracture design and imulation. This paper will describe the construction of a split Hopkinson bar facility used to measure some key mechanicalroperties of pressurized oil sand specimens. Results have clearly indicated the sensitivity of these properties to the applied loading (or strain rates).