Simulation of a Tight Gas Reservoir with Horizontal Multifractured Wells
- E. Ehrl (Mobil Erdgas-Erdoel GmbH) | S.K. Schueler (Mobil Erdgas-Erdoel GmbH)
- Document ID
- Society of Petroleum Engineers
- SPE European Petroleum Conference, 24-25 October, Paris, France
- Publication Date
- Document Type
- Conference Paper
- 2000. Society of Petroleum Engineers
- 5.8.1 Tight Gas, 4.3.4 Scale, 5.8.8 Gas-condensate reservoirs, 2.5.1 Fracture design and containment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6.6 Directional Drilling, 5.1.5 Geologic Modeling, 4.1.5 Processing Equipment, 2.5.4 Multistage Fracturing, 2.2.2 Perforating, 2 Well Completion, 1.6.9 Coring, Fishing, 5.5.8 History Matching, 5.1 Reservoir Characterisation, 5.1.2 Faults and Fracture Characterisation, 5.1.1 Exploration, Development, Structural Geology, 1.6 Drilling Operations, 5.6.4 Drillstem/Well Testing, 3.3.1 Production Logging, 5.5 Reservoir Simulation, 4.1.2 Separation and Treating
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The concept of multiple fractured horizontal wells has been successfully used for the development of a deep, ultra-tight Rotliegendes gas reservoir. Because of extremely low permeabilities (0.01 - 0.02 md) conventionally fractured vertical wells produced at uneconomically low gas rates. The pilot well Soehlingen Z10 combined the methods of horizontal drilling and multiple fracturing and proved an economic technique for developing the significant gas resources in the tight gas reservoir.
An integrated 3-D geologic model and a field-scale reservoir simulation model were used to optimize future field development. The wells were modelled with a system of local grid refinements (LGR) around the horizontal wells. Adjusting permeabilities and cell sizes of the hydraulic fractures and the surrounding reservoir area helped solve the numerical stability problems without affecting simulation of long-term production performance. The history match for the existing multiple fractured horizontal well, Soehlingen Z10, was based on a five-year production period. Previous analytical studies were confirmed by numerical results. A multi-well program was developed with up to eight wells of 1,000 to 1,500 m long horizontal sections. Each well will be stimulated by 5 to 7 hydraulic fractures depending on the horizontal section length. Timing and sequence of the planned tight gas wells were analyzed using an integrated subsurface-surface study. The development plan incorporates the spare capacity of existing surface facilities and the actual production decline of other producing horizons in the field. Following this study, the Soehlingen Z13 well was drilled, stimulated and brought on production in 1999.
The Soehlingen field, located onshore Northwest Germany, was discovered in 1980. Mobil Erdgas Erdoel GmbH is the operator of a consortium that includes BEB Erdgas und Erdoel GmbH, RWE-DEA AG and Wintershall AG. The field comprises three major Rotliegendes-age gas reservoirs: the Wustrow and Havel sandstones with moderate permeability (above 1 md) and the massive but ultra-tight Dethlingen sandstone.
After discovery, 12 further producing wells were drilled in the Soehlingen field. Main production to date has been from Havel and Wustrow reservoirs. Both of these reservoirs have reached an advanced depletion stage and field capacity will start to decline in the near future.
Development of the Dethlingen reservoir also started in the early 80's with three vertical wells, Soehlingen Z3, Z4 and Z5. All three wells were stimulated with massive hydraulic fracture treatments. Typical post-fracture rates were in the range of 5,000 m3/h but declined significantly within the first five years. For economic gas production three to five times the rate of a fractured vertical well is required. This could only be achieved by using multiple fractured horizontal wells. This technology was proven by the Soehlingen Z10 well, which was drilled to a TD of 5,750 m with a 640 m horizontal section and four hydraulic fractures. Initial production rate was set at a constant plateau of 20,000 m3/h. Cumulative gas production to date is 600 MM m3 (see Figure 1). The technical and economical success of the Soehlingen Z10 well was a milestone for the tight gas development and a multi-well program started with the Soehlingen Z13 well, drilled and completed in 1999. The well was stimulated with 5 hydraulic fractures placed along the 1,000 m horizontal section. In January 2000 the well produced at a maximum gas rate of 29,000 m3/h. Currently the Soehlingen Z14 well is in the drilling phase with a projected horizontal length of 1,500 m and 7 hydraulic fractures.
To optimize the field development, reservoir simulation studies were made to predict future performance of the reservoir based on a full-field development plan. This paper describes the methods used and the results obtained from the numerical model.
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