Over the past decade in the Netherlands, most operators have only developed a single doublet. The learning effect from these single events is suboptimal, and operators have only been capable of developing doublets in areas with relatively low exploration risk. This ‘stand-alone’ approach can be significantly improved by a collective approach to derisk regions with similar subsurface characteristics. Such a play-based portfolio approach, which is common in the oil and gas industry, can help to accelerate the development of the geothermal industry through unlocking resource potential in areas marked by high upfront geological risk, effectively helping reduce costs for the development. The basis of the methodology is to deploy new information to the play portfolio by trading off with the risk of the first wells, resulting in a strong geological risk reduction. The added value of the portfolio approach is demonstrated for the Netherlands in this paper through a comparison with a ‘stand-alone’ development. In the stand-alone approach, each new project will be equally risky, and therefore relatively unprofitable. In the case of a portfolio approach, all experience about the play is used optimally for derisking. In case of success, subsequent projects will have a higher chance of being successful, due to the experience gained in previous projects. Even if a project fails, this may help in increasing the probability of success for subsequent projects. For plays that are initially considered too risky for the market to start developing, the value of information (VoI) of a play-based portfolio approach will help by derisking the play to such an extent that it becomes attractive for the market to develop, even at high initial risk. It can be demonstrated for several geothermal plays in the Netherlands that by adopting the portfolio approach, the probability of a play being developed becomes higher, the number of successfully developed projects increases and the average profitability of the project will also be higher. Five more advantages are: (1) continuous improvement by integrated project development, (2) cost reduction through synergy, efficiency and standardisation, (3) optimisation of the surface heat demand and infrastructure, (4) the possibility of structural research and development (R&D) and innovation, and (5) financing advantages. The advantages reinforce each other. A preliminary estimate of the geothermal potential of the Netherlands adopting the portfolio approach is between 90 and 275 Petajoules (PJ). For about 350 doublets being developed, producing about 70 PJ, the value of the advantage of the play-based portfolio approach is €2 billion for the three main plays: Rotliegend, Triassic and Jurassic/Cretaceous. The learning effects of synergy, efficiency and standardisation are expected to be significant.

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The potential for the exploration and exploitation of geothermal energy for greenhouses in Franekeradeel in the north of the Netherlands has been investigated. Available borehole and seismic data have been used for the evaluation of the subsurface. These data show that the Slochteren Formation sandstone reservoirs are very likely present at a depth of ca 3,000 m. These reservoirs are deemed to be suitable for the production of hot water. From interpreted 2D seismic lines could be inferred that the Slochteren Formation is around 200 m thick at the proposed location. Based on the local geothermal gradient, the temperature at the top is estimated to be around 100 ºC. At the surface location a fault zone is present in the subsurface complicating the siting of the injection and production wells. Towards the northeast the proposed reservoir is seemingly less faulted. A minimum transmissivity of 11 Dm is expected, based on the measured porosity in nearby boreholes and porositypermeability relationships in the surrounding area. A potential flow rate of 160 m 3 /h is hence inferred, leading to a thermal capacity of 11 MW t which can be delivered with one doublet. Different well configurations were studied. The conclusion is that deviated wells from the edge of the surface location towards the northeast carry the lowest risk at still acceptable costs. From financial analyses taking different options into account, it was concluded that geothermal energy can deliver significant amounts of renewable energy for heating of greenhouses. In the optimum situation, the cost price of heat amounts to 6,20 Euro/GJ delivering annual 202 TJ of energy. This price is below the current price (January 2008) of natural gas at 0,20 Euro/m 3 .