Mobil Germany's pilot-project Soehlingen Z10 had the objective to make the large gas potential of the Main Sandstone of the gasfield Soehlingen (more than 40 Billion m3 of gas-in-place) producable at economic production rates. Due to the presence of Illite, the Main Sandstone has a reduced permeability of only 10 to 20 jxD. Offset wells had proven that economic production rates are achievable by means of hydraulic fracturing.

The drilling phase was completed in July 1994 following an extensive completion and stimulation phase with four hydraulic fracs in the horizontal section of the well. A 5750 m well with a 630 m horizontal section at a TVD of 4780 m under 92 degrees inclination was drilled. Drilling the well broke several records, being the deepest horizontal well drilled and logged with the deepest liner run to TD, cemented, completed and stimulated. In the horizontal section, the deepest plug back and sidetracking operation was carried out successfully.

To ensure the operational success, several long-term plan-ning and designing steps concerning the location of the wellsite, optimization of the wellpath, required minimum mud weight for the pay zone, secure drilling of the depleted Wustrow sandstone in the Rotliegendes above the payzone and proper running and cementing of the 7" liner in the horizontal section of the well took place in MEEG's drilling group to reach the high set goals of the project. Also a number of adjustments in the plan were implemented based on the actual conditions encountered in the well.

After finishing drilling operations the completion and stimulation works were performed successfully until the first production tests began at the end of January. Production from all four fracs yielded a rate of more than 20,000 m3 (Vn)/h, in comparison to the expected rate of 15,000 m3. These production statistics indicate the overall success of this highly difficult pilot project, which hopefully may lead to success of similar projects in the future on a worldwide basis.

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