Coal Bed Reservoir and Continuity Evaluation, Ibbenbueren Mine Cores, Germany: Analog for NW Germany CBM wells

Kissner, Ewa P.¹; Snedden, John W.¹
(1) Exploration, ExxonMobil Production Deutschland GmbH, Hannover, Germany.

Sedimentologic and stratigraphic interpretation of 2 km of core from 3 wells located in the Ibbenbueren mine area in Germany provide a well documented analog for the coalbed methane (CBM) play in northern Germany. Lateral continuity and vertical thickness trends of coals and carbonaceous shales as well as variation in cleat sets were investigated. The German Westphalian (Carboniferous) CBM interval has experienced a complex tectonic history. The Ibbenbueren mine area is an inversion structure located in the Osning fault zone, bordering the Ruhr Basin to the south and the Lower Saxony Basin to the north. Analyzed data include core from 2 vertical well and 2 sidetracks with varying offset distances up to 1 km. The major coal-bearing depositional environments are upper and lower delta plain.

Correlation of coal beds between wells is based on mining data, core observations and a high-resolution regional sequence stratigraphic framework.

Sedimentological observations show lateral changes from carbonaceous mudstone to coal over distances of about 900m and in other areas, coal bed continuity up to 1km. Lateral continuity is limited by fluvial erosion of coals as indicated by thickness changes and coal clasts in channel fills. Variations in coal bed thickness depend on depositional environment and accommodation trends. In upper delta plain genetic facies, generally thinner coals were deposited indicated by a vertical thinning trend; in the lower delta plain, thicker coals are developed signaled by a vertical thickening trend.

The accommodation controls are interpreted from a stratigraphic framework and stacking patterns. Maximum coal bed thickness is developed in the lowstand system tracts; thin coals are developed in the transgressive system tracts.

Success of a CBM play is also related to the permeability of the coal. This is is a function of number of cleat sets, cleat-cement fill and orientation of the cleats in each coal seam. Analysis of the cleat trends demonstrates variations in cleats over comparable offset distances.

This analog work has guided operational decisions in the CBM drilling campaign as well as development modeling of potential pilot areas in Northwest Germany.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.