To estimate the Net Debt/EBITDA ratio for ENI S.P.A. for the year 2022, we follow the S&P methodology, which defines Net Debt as Total Debt (short-term and long-term borrowings) minus Cash and Cash Equivalents, and EBITDA as Profit/Loss from Operating Activities plus Depreciation, Amortization, and Impairment losses/reversals.

**1. Calculate Net Debt for 2022 (as of 2022-01-01):**
*   Short-term Borrowings: 2,299,000,000 EUR
*   Current Portion of Long-term Borrowings: 1,781,000,000 EUR
*   Long-term Borrowings: 23,714,000,000 EUR
*   Total Debt = 2,299,000,000 + 1,781,000,000 + 23,714,000,000 = 27,794,000,000 EUR
*   Cash and Cash Equivalents: 8,254,000,000 EUR
*   Net Debt = 27,794,000,000 - 8,254,000,000 = 19,540,000,000 EUR

**2. Calculate EBITDA for 2022 (for the period 2021-01-01 to 2022-01-01):**
*   Profit/Loss from Operating Activities: 12,341,000,000 EUR
*   Depreciation and Amortisation Expense: 7,063,000,000 EUR
*   Impairment Loss/Reversal (Recognised in Profit/Loss): 167,000,000 EUR
*   EBITDA = 12,341,000,000 + 7,063,000,000 + 167,000,000 = 19,571,000,000 EUR

**3. Calculate Net Debt / EBITDA Ratio:**
*   Ratio = 19,540,000,000 / 19,571,000,000 ≈ 0.9984

Rounding this based on standard financial reporting practices:

<answer>0.9984</answer>