Matrix Acidization Analysis

As ECW specifically has asked to look into the effects and consequences of acidization, we put a strong emphasis on this technique. Although other techniques might be considered. We’ll review the technique in relation to the different scenarios of the well damage.
5.1 Acidization
In this chapter, the process of Matrix Acidizing is considered to stimulate the limited flow in the ECW Middenmeer geothermal well (MDM-GT-03). Different potential matrix acidizing processes are described per formation damage scenario: mud cake, scaling and lead precipitation. Matrix acidizing is probably the most widely performed job because of its relative low cost, compared to other techniques and because it is a relatively simple stimulation technique to improve

Amorphous silica Clay and silicate dissolution in HF. Amorphous silica results from both secondary and tertiary HF acidizing reactions.
Sodium and potassium fluosilicates Feldspar and illite clay dissolution in HF produce these primary reaction products. They can also form if seawater or sodium or potassium brines are mixed with spent HF.
Sodium and potassium fluoaluminates Silico-aluminate dissolution in HF. Fluoaluminates, like fluosilicates, occur when spent mud acid (H2SiF6) reacts with the formation. They can also form if seawater or sodium or potassium brines are mixed with spent HF.
Aluminium hydroxides and fluorides Clay and feldspar dissolution in HF can cause these precipitates.
Iron compounds Iron minerals or iron oxides (rust) can react with HCl-HF to produce these compounds.
Table 3. Possible precipitates in sandstones acidizing based on Schlumberger report (Portier, André, & Vuataz, 2007).
Acid additives could be used as a precautionary or corrective measure to the well problem outlined above. Acid additives normally used in practice

Geothermal fields are often near populated areas, and wells are tested and flowed to the atmosphere. Noise and odours affecting the local population are of concern for the geothermal operators when flowing back wells after stimulation.

• Limited Information — Geothermal operation practices differ from oilfield operations in that most geothermal operators do not take steps to obtain, store, analyse and track individual well information and performance trends. Coring, production tests, injection tests, build-up and drawdown tests, and other information that could be important and useful is usually partially or totally missing. A change in the mind of the geothermal industry is necessary in this regard. The benefit of acid stimulation of geothermal wells is apparent even with the minimal information available. Imagine the potential if the gathering of such information were standard