EXPERIMENTAL INVESTIGATION OF MICHANICAL MECHANISM OF HYDRAULIC
FRACTURING IN ULTRA-HEAVY OILSAND FROM XINJIANG OILFIELD
Botao Lin1*, Yan Jin1, Mian Chen1, Huiwen Pang1, Bing Hou1
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing,
102249, China
*
Corresponding author: PhD, M.ARMA, SPE, Assistant Professor, email: linbotao@vip.163.com
1
ABSTRACT
Steam Assisted Gravity Drainage (SAGD) has become the mainstream technology for ultra-heavy oil
recovery in Xinjiang oilfield, the success of which depends significantly on shortening of preheating period
as well as forming homogeneous and highly permeable zone in land-facies oilsand layer. Towards this aim
a special hydraulic fracturing process is required, which is accomplished through controlled water injection
to a pair of horizontal wells in order to create homogenously distributed microcracks in the zone between
the two wells. The associated mechanical response of this fracture zone, however, is unclear for land-facies
oilsand that is loose in texture. In this regard, this research utilizes high-pressure, high temperature triaxial
test system (Figure 1) on field-collected oilsand cores. The test system is able to simulate temperature,
confining stress and injection pressure the in-situ oilsand is under, so as to assess the two possible
mechanisms, known as shear-dilation and tensile parting, during the fracturing activities. Moreover, the
integrated ultrasonic, acoustic emission and fast pulse-decay permeability apparatuses are applied for
monitoring wave velocity, crack development and transient permeability during various loading stages.
Based on these comprehensive studies, the principles of microcrack initiation and propagation in oilsand
are investigated, so are the stress-strain relations and the permeability evolution. In addition, scanning
electron microscopy (SEM) and micrometer computer topography (CT) are used to image the
microstructure of core samples before and after triaxial tests. Combining the aforementioned experimental
and analytical results, a conceptual model for the fracture mechanics of land-facies ultra-heavy oilsand is
established, which can provide theoretical and technical support for evaluating the permeation effects of
fracture zone over the entire SAGD recovery process. The model also provides theoretical basis for
numerical simulation of oilsand behavior taking place during hydraulic fracturing.
Figure 1 – High temperature high pressure rapid triaxial rock testing system and associated apparatuses
KEYWORDS
SAGD, Oilsand, Land-facies, Hydraulic fracturing, Microcrack, Shear dilation, Tensile parting