Soehlingen Z10: Drilling Aspects of a Deep Horizontal Well for Tight Gas
- G. Pust (Mobil Erdgas-Erdoel GmbH) | J. Schamp (Mobil Erdgas-Erdoel GmbH)
- Document ID
- Society of Petroleum Engineers
- Offshore Europe, 5-8 September, Aberdeen, United Kingdom
- Publication Date
- Document Type
- Conference Paper
- 1995. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 4.1.2 Separation and Treating, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.6.1 Drilling Operation Management, 1.10 Drilling Equipment, 1.2.3 Rock properties, 1.12.1 Measurement While Drilling, 1.6.9 Coring, Fishing, 1.14.4 Cement and Bond Evaluation, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.1 Well Planning, 5.1.2 Faults and Fracture Characterisation, 1.6 Drilling Operations, 1.6.6 Directional Drilling, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.2.2 Perforating, 1.14 Casing and Cementing, 4.1.5 Processing Equipment, 3 Production and Well Operations, 5.8.1 Tight Gas, 1.4 Drillstring Design
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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 D. 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 planning and designing steps concerning the location of the wellsite, optimization of the wellpath, required minimum mud weight for the payzone, 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.
The Mobil operated gasfield Soehlingen is located in the northwestern part of Germany between the cities of Hamburg, Hannover and Bremen. Partners are BEB Erdgas und Erdoel GmbH (30%), RWE-DEA (30%) and Wintershall AG (10%). Producing horizons are the Wustrow, Munster and Schneverdingen sandstones of the Permian Rotliegendes formations. A large volume of Gas-in-Place in the Main Sandstone is not producable at economic rates due to a reduced permeability of only 10 to 20 microDarcies because of the presence of Illite in the reservoir rock. However offset wells have shown, that this formation can be produced if the sandstone is fraced hydraulically (Table 1).
It was the basic concept of the pilot project Soehlingen Z10, to combine the two existing technologies of hydraulic fracturing and horizontal drilling. The objective was to drill a well with a 1000 m long horizontal section in a TVD of 4780 m, cased with a 7" cemented liner. The gas should be produced through six hydraulic fracs performed perpendicular to the wellbore axis.
The boundary conditions of great depth, high temperatures and pressures and a complex geological situation underneath the Soehlingen saltdome led to a number of different drilling challenges which only could be solved by a team effort of all disciplines.
-Location of the wellsite in respect of drilling cost, wellbore azimuth, in-situ rock stresses and fracture orientation.
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