6. Introduction to Acid Treatment Design.

Wells that have skin or zonal damage are good candidates for well stimulation
treatments. Major increases in productivity or injectivity can result. The well and the
treatment, however, should be selected with care, and reservoir conditions should
be adequate to assure economic pay-out. Misapplied stimulation treatments are
costly and ineffective, often creating more problems than they solve.
Selecting the correct treatment is often not a simple matter. With an engineering
approach to any well problem however, the chance of success is generally
increased. The following information should be considered in the selection of a well
treatment:

• · Type of formation and mineral composition of the formation.
• · Type and amount of damage.
• · Contact time available for chemical treatment.
• · Physical limitations of well equipment.
• · Bottom hole pressure and temperature.
• · Possible contaminants such as water, mud, cement filtrate and bacteria.
• · Treating fluid compatibility with contaminants present and reservoir fluids.
• · Formation properties such as acid solubility, permeability and porosity.
• Various damage mechanisms and treatment design criteria are considered in the following sections.

6.1 Geographic Probability.

If no information other than well location and T.V.D. is available, then the only
design criteria will be geographic probability. For some areas of the U.S.A. BJServices
has developed an indexing system based on geographic probability. This
system provides geological data such as clay technology and treatment response
data including: PI performance, emulsion tendencies, sludging, clean-up rates, type
of particles solubilised, precipitates etc.