1. Access the spreadsheet and gather the relevant data.

2. Use the appropriate equation (Oddo and Tomson) to compute the scale saturation index, in a spreadsheet.

3. Run a sensitivity on pH.

4. Prepare charts showing the sensitivities.

5. Write a short report, as for Phase 1, with the same sections. You can join the two reports together.

6. Give a conclusion on the scaling risk for calcite scaling and recommend a suitable course of action

Calcite Scale Model from Oddo & Tomson (1994) modified.

SI = log (Ca)(HCO₃)
+ pH - 2. 76

+ (9.88*10-3)T + (0.61*10-6)T2

- (3.03 *10-5)P

- (2.348 *(IS0.5) ) + (0.77*IS)

Where: SI is the Saturation Index of calcite (Ca) and (HCO₃) are the molar concentrations of Ca and HCO₃ ions in mol/L.
The molecular weight of Ca is 40, HCO₃ is 61.
T = temperature in degrees F

P = pressure in psi

IS = ionic strength of the produced water. This should be converted to mol/L by dividing by an average molecular weight (53.4) and converting to litre (outcome is to divide IS by 53400)

Sensitivity Analysis: use the range of temperature and pressure shown on the Well Data worksheet to calculate the SI for a range of T, P and pH. Produce charts of these relationships.

Your report could include one or two pages of text and one page of tables and figures. The text should include the following:

Discussion : You may want to address the following in your discussion:

(a) Explain the mechanism for production of calcite scale?

(b) Describe the relevance of the Saturation Index and the meaning of a negative or positive value?

(c) What are major limitations of your evaluation and what can be measured?

(d) The well is scheduled as part of a large field development, what would you recommend to the Project Manager?

(e) When the well is in operation and producing, how would you monitor the process to ensure the scale risk was minimised.