Sure! Below is the test case generator for the given problem "Problem G: Oil Company".

```python
import random

def tcgen():
    # Number of test cases
    N = random.randint(1, 10)
    test_cases = []
    
    for _ in range(N):
        W = random.randint(1, 20)
        H = random.randint(1, 20)
        
        # Generate the grid map with random oil reserves
        grid = [[random.randint(0, 9999) for _ in range(W)] for _ in range(H)]
        
        test_cases.append((W, H, grid))
    
    return N, test_cases

# Generate a sample test case
N, test_cases = tcgen()

# Print the generated test case
print(N)
for i, (W, H, grid) in enumerate(test_cases):
    print(W, H)
    for row in grid:
        print(' '.join(map(str, row)))
```

Here is an explanation of the code:

1. **Importing the `random` module**: This is used to generate random numbers.

2. **Define the `tcgen()` function**: This function generates random test cases for the problem.

    - **Generate `N`**: The number of test cases. It's a random integer between 1 and 10.
    
    - **Loop for each test case**:
        - **Generate `W` and `H`**: Random integers between 1 and 20, representing the width and height of the grid.
        - **Generate the grid map**: A list of lists where each integer is a random number between 0 and 9999.
        
    - **Store each generated test case** in a list called `test_cases`.
    
3. **Return `N` and `test_cases`**: The function returns the number of test cases and the list of test cases.

4. **Generate a sample test case**: Call the `tcgen()` function to generate a sample test case.

5. **Print the generated test case**: Print the number of test cases and the details of each test case in the required format.

You can run the above script to generate random test cases for the problem "Problem G: Oil Company". Each time you run the script, it will produce different test cases due to the randomness.

Feel free to adjust the ranges and limits according to your specific needs or constraints.