Initial Skin Determination
An initial skin determination can be performed by Smarts32 on the matrix flow component of a step rate test. Generally these type test are ran prior to performing a fracturing or matrix acidizing stimulation. The ranges of rate steps are dependent upon the formation type. From this analysis one can determine from the actual pressure versus rate plot versus the master curves generated based on the actual formation properties, the initial skin of the well. Typically this type test is ran prior to the actual matrix acidizing treatment to insure that the evolving skin during the acid treatment is within an accurate range.
Real-time Matrix Acidizing Evolving Skin Analysis
Evolving Transient Skin Determination
An evolving transient skin versus time or volume/height analysis can also be used real-time for matrix acidizing treatments when utilizing the Matrix Acidizing modes of Smarts32. The acid treatment is performed below the breakdown pressure of the formation. Generally matrix acidizing is performed for the following reasons.
As a stimulation process to increase well production by removal of near well bore damage.
To remove near well bore damage in waste disposal wells in an effort to lower treatment pressures.
If the treatment is chemically successful, the evolving skin should be diminishing during treatment as compared to the initial skin. If the treatment does not show a diminishing skin, then the treatment chemicals used should probably not be considered for use in that formation within that area for future treatments. Also, if a major skin decline occurs and later stages of other chemical do not change the evolving skin further, then one can save money by not pumping the non-reactive stages! An example of a Smarts32 generated graph for a monitored matrix acidizing job on a waste disposal well is as follows.
As can be seen very little skin removal occurred after half of the 15% HCL stage was introduced on formation. Therefore the matrix acidizing treatments of other offset wells in the area ended after about half of the volume of the original designs 15% HCL stage was pumped. This resulted in significant cost savings as compared to the original design.