Proppant is used to keep hydraulic fractures open and to maintain the conductivity of the fracture. This helps operators produce the well economically. It is normal for well productivity to decline as reservoir pressure declines. However, steeper rates of decline are often observed, which have been attributed to additional damage mechanisms, such as proppant crushing, embedment, and fines migration.
Proppant diagenesis may also be a contributing factor affecting production decline. Proppant diagenesis has been discussed previously (Weaver and Rickman 2010), where pressure solution and the compaction mechanisms are proposed to be responsible for causing diagenesis of proppant. This concept has gained momentum and has been the subject of other recent studies and discussions, particularly in the hydrothermal industry.
Choosing the correct proppant for a given formation at the reservoir temperature and stress becomes an important factor. Selection of proppant should not be based solely on the crush strength of the proppant at the applied stress value, but should also depend on the overall integrity of the proppant after being exposed to the reservoir conditions. Choosing the proper proppant for the job should be more economical for the long-term stability of the well.
This paper provides details of the testing protocols developed to provide improved understanding of proppant diagenesis under different reservoir conditions. The discussion should help operators understand the importance of the procedures used to obtain accurate results, as well as shed light on the process of selecting the correct proppant for long-term fracture stability.