Bunter Reservoir Quality for Geothermal Applications in the Zuid Holland Area.

With the continued growth of world population comes the need for more energy resources to quench the thirst of the energy insatiable world we live in. Geothermal energy is green and is a sustainable way of providing our energy needs. Formation water at depths greater than 3,000m in the Netherlands is a potential source of energy to generate electricity. Over the study area observed formations are buried deep enough to reach water temperatures in excess of 1000C, and this could conceivably be used for the generation of electricity with very low CO2 emissions. Four seismic surveys L3NAM1985P (146.6km2), L3NAM1991A (414.5km2), Z3NAM1990D (762.2km2) and Z3AMC1989A (544.6km2) were interpreted and integrated with well data including well tops to help in this evaluation. The Detfurth and Volpriehausen (Triassic) of the West Netherlands Basin in the Zuid Holland area are established to be potentially good reservoirs for geothermal development. This is due to the fact that stratigraphically, they are the deepest sandstones and consequently most likely to reach sufficient depths. These objectives are too deep to be visible and adequately interpretable on seismic due to the low impedance contrast and because it is overlain by the strong reflectors of the evaporates of the Upper Germanic Triassic. Therefore, surfaces for these objectives were generated based on formation markers in the wells that intersected the Triassic using 3D gridding in Jewel Suite. Generally, the reservoir interval from the top of the Detfurth to the base of the Volpriehausen contains enough thick sequences of porous sands. The gross thickness ranges from 95m in well VAL-01 to 163m in P15-14. Two porosity/permeability relationships have been used for calculating N/G at various permeability cut-offs of 0.1mD, 1mD, 10mD and 100mD. Net sand ranges from 0.14m to 58.04m for 10mD and 0.1mD permeability cut-offs respectively. The zone in and around Wells MON-03, P18-A-02, P15-01 and P15-14 show the best reservoir intervals based on average porosity and N/G values. Based on different scenarios the average porosity ranges from 6.5% to 16.2% and N/G ranges from 0.6% to 30.8%. Primary porosity and permeability are generally low in the mapped area, but it is expected that permeability and connectivity are enhanced locally through fracturing. The objective is highly faulted, and hence this will serve as conduit for water leading to a higher level of connectivity and water production. Heterogeneity remains an issue of concern due the high level of Vcl is some of the intervals. But it is believed that they will generally not serve as a barrier or baffle to flow, i.e. it will reduce the vertical permeability but not the important horizontal permeability. The objectives in the mapped area suggest that aeolian and fluvial facies occupy more than 50% of the rock unit. Aeolian sandstones are known for their excellent reservoir qualities. They are well sorted with good porosity and permeability. This means that a larger part of the rock unit within the mapped area is of good reservoir quality. The focus of the oil industry is on the structural highs. Prospective areas for geothermal exploitation occur in lows. The lows have no well penetrations and are usually considerably deeper than the much shallower oil fields. It is, however, suspected that structuration and formation of highs and lows is relatively late and that diagenesis predates structuration. This would imply that the shallow oil fields have porosities representative of much greater depths. This is borne out by the fact that there is hardly any relationship of porosity against depth. When this proves to be accurate it would have a very positive effect on the development of geothermal energy, since this reduces the uncertainties involved in a project like this.Petroleum Engineering and GeosciencesSection Petroleum GeosciencesCivil Engineering and Geoscience