In order to evaluate the risk(s) of formation damage from well operations, laboratory core flood tests are commonly performed to closely mimic wellbore conditions. Analysis is required on the core samples in order to identify formation damage mechanism(s) which may be difficult due to the microscopic scale, opacity of rock and fluids. An already established approach of using cryogenic scanning electron microscopy (CryoSEM) at cryogenic conditions would be advantageous to observe the fluids contained within the pores of core samples to help identify formation damage mechanism(s). Other analysis (e.g. X-rays, acoustic velocity, nuclear magnetic resonance imaging) although useful fail to offer the same level of detail. This paper illustrates the method(s) to obtain the required detail by using additional techniques in conjunction with CryoSEM analysis this is referred to as "CryoSEM technique" from here on. In the past ten years CryoSEM has been revived in conjunction with the developed techniques which enables direct imaging of rock, pore space and fluids. Although quite commonly used and referenced in other papers there has never been a comprehensive description of the CryoSEM technique and its current abilities.
This paper describes in detail the CryoSEM technique and outlines some of the core sample preparation techniques and analysis procedures developed. The use of the CryoSEM technique in the description of critical formation damage mechanisms will be described. Examples of the use of CryoSEM as an aid to interpretation of formation damage mechanism(s) will be presented with some case histories with associated of formation damage mechanisms never previously observed will be presented.
The advantages and disadvantages of CryoSEM and other techniques will be discussed and the authors will also present some potential future developments in this area.