Abstract
Water injection can effectively improve the reservoir porosity and permeability by shear dilation in the vicinity of wellbores. In this paper, shear dilation and permeability improvement capability/potential are proposed to describe the evolutions of porosity and permeability under water injection-induced shear. The mathematical models based on Karamay oil sand microstructures derived from ESEM (environmental scanning electron microscope) are established to predict the shear dilation effects based on the particle packing theory. Triaxial compression and permeability experiments are conducted to validate the theoretical models, and the experimental data is consistent with model results. Also, the study compares shear dilation capabilities evaluated from three scales: ESEM (μm), laboratory triaxial compression tests (cm), and field injection tests (m). Major conclusions through an application on the wellpair A-2 in area A of the Karamay oil field showed that the oil sands have an excellent shear dilation potential. The larger arrangement angle results in stronger shear dilation and permeability, which means a lower arrangement angle provides a higher potential for improvement. The shear dilation capabilities predicted by ESEM, triaxial compression experiments, and field injection data descend in turn, which indicates that the actual shear dilation capability is difficult to be utilized by present field operations.
Highlights
Oil sands have been defined as a kind of porous media that contain an extremely viscous hydrocarbon which is not recoverable in its natural state by conventional EOR methods [1]
The end significance of this paper is to find the shear dilation effects quantitatively represented by shear dilation capability (SDC) and permeability improvement capability (PIC) under actual field operations, and to see how much residual effective shear dilation potentials quantitatively described by SDP and permeability improvement potential (PIP) are for further utilization
This paper proposed a method of evaluating the shear dilation effects of the Karamay oil sand reservoir under water injection by particle packing theory
Summary
Oil sands have been defined as a kind of porous media that contain an extremely viscous hydrocarbon which is not recoverable in its natural state by conventional EOR (enhanced oil recovery) methods [1] They are highly dilatant materials which possess common characteristics of very dense sands. Oil sands in Karamay, Xinjiang, have a terrestrial unconsolidated and interlocked structure like but not as dense as Alberta oil sands [6], which are formed in deep burial depth and elevated temperature over geological time [2]. These special structures make it possible for oil sands to expand in volume by shear dilation and tensile parting dilation during thermal stimulations [7]. The use of geomechanics in enhancing the SAGD (steam-assisted gravity drainage) process, especially for the startup phase (i.e., water injection and steam circulation prior to the oil production phase), has drawn widespread attention and resulted in extensive research, technical discussions, and field applications, mostly focusing on the oil sands in Alberta, Canada [8]
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