Abstract

Thermal production is an important heavy oil recovery method. While production, Steam injection triggers complex thermal and hydraulic processes which can dramatically alter the formation pressure and temperature leading to various changes within the reservoir as well as in the surrounding rock. This study is conducted to experimental research on the thermal cracking characters of mudstone barriers induced by heavy oil thermal production.

In this research, a thermal-mechanical coupling experimental device was developed. It can impose triaxial stresses and local wellbore high temperature to the rock sample. The temperature sensor was used to record the temperature change in the rock sample. Industrial computerized tomography (CT) technology was employed to scan the rock sample before and after the experiments, compared the changes of CT images and observe the thermal cracking characters of mudstone.

Mudstone of our laboratory studies were coring from the heavy oil reservoirs of Xinchun Oilfield (Xinjiang, China). The experimental results are listed as follows: (1) The thermal cracking developed with heating temperature increase. It's observed that the micro-fissures developed and connected to form larger fractures under 260°C. (2) The fractures propagate along the maximum/minimum horizontal stress direction on the surface of rock sample. CT images indicated that fractures propagation along the horizontal stress direction inside the sample. The propagating patterns also affected by the rock lithology, natural fissures and formation heterogeneity, etc. (3) The width of thermal cracking change with temperature, and the fractures closure during cooling from the growth temperature of 260°C to room temperature.

The above works show that thermal production affect the deformation and failure behavior of the mudstone barriers, it may cause the thermal cracking during multiple steam stimulation process. This will be instructive for optimizing the parameters of thermal production.

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