Abstract
Mobilization of fines can severely damage a well's productivity and is one of the more costly sources of well damage identified to date. Termed fines migration, the phenomenon is complex but governed largely by mineralogy, permeability, salinity and pH changes as well as drag forces created by flow velocity, turbulence and fluid viscosity1–10 .
Over the years various mixtures containing hydrogen fluoride (HF) acid or its precursors have been used to dissolve fines and increase permeability in sandstones. However, it has been noted in considerable prior literature11–21 that these treatments can result in relatively shallow penetration due to the rapid spending of HF. Frequently the treatment is limited to a few inches in the formation beyond the wellbore region and this allows future fines re-invasion into the near well bore. Also fines acidizing alone is merely treating the symptom rather than the underlying cause and it can be assumed that the duration of the benefit is limited to how long it takes for fines to be released and begin to restrict flow again. Thus, a concern for operators is the fact that the benefit of HF acid treatments for fines can be short-lived. Other treatments were developed to fix fines in place21–22 however these systems have not been widely used.
The optimum treatment for fines would integrate techniques to dissolve fines, enlarge pore-throat size to diminish near wellbore particle bridging, and finally to "lock-in-place" those fines that are not removed by the treatment. Furthermore, a long-term, integrated solution must address the mechanism of fines migration so that a comprehensive approach to the problem may be employed.
This paper reviews fines damage mechanisms and presents a fluid system to correct fines damage and prevent fines migration in a single treatment, while keeping acidizing risk at a minimum. The new system uses an organo-phosphonic acid (HV) to generate and moderate HF for deep penetration and an organosilane fines-fixing agent (FFA).
