The impact of reduction of doublet well spacing on the net present value and the life time of fluvial hot sedimentary aquifer doublets

This paper evaluates the impact of reduction of doublet well spacing, below the current West Netherlands Basin standard of 1000–1500 m, on the Net Present Value (NPV) and the life time of fluvial Hot Sedimentary Aquifer (HSA) doublets. First, a sensitivity analysis is used to show the possible advantage of such reduction on the NPV. The parameter value ranges are derived from West Netherlands Basin HSA doublet examples. The results indicate that a reduction of well spacing from 1400 to 1000 m could already improve NPV by up to 15%. This effect would be larger in more marginally economic HSA doublets compared to the West Netherlands Basin base case scenario. The possibility to reduce well spacing is supported by finite element production simulations, utilizing detailed facies architecture models. Furthermore, our results underline the necessity of detailed facies architecture models to assess the potential and risks of HSA doublets. This factor significantly affects doublet life time and net energy production of the doublet

Interference between geothermal doublets across a fault under subsurface uncertainty: Implications for field development and regulation

Direct Use Geothermal Systems (DUGS) are increasing their installed capacity worldwide and denser developments with multiple doublets are becoming more common. Interference between doublets therefore becomes an additional concern to subsurface uncertainties. Faults can be either barriers or conduits to flow and can affect the fluid pathways inside the reservoir. The interference between two doublets that are separated by a fault has not been previously studied for DUGS. In this work considering subsurface uncertainty in a full factorial design using 5184 3D reservoir simulations we show that a fault can reduce the system lifetime of a two-doublet system by more than 40 % if one doublet is at close proximity to it. Further, we identify that the fault can also improve both the system lifetime and generated Net Present Value (NPV) with appropriate development decisions. Contrary to previous results that did not consider reservoir architecture, a tramline well configuration is preferable when the doublets have the fault in the centre, while a checkerboard configuration is preferable as the distance to the fault decreases. The Heat In Place (HIP) recovery shows a linear relationship with flow rate and well spacing that is not affected by the fault distance or flow properties. The dimensions of the Influence Area (IA) previously considered are insufficient to capture the temperature drop at the producer wells and the fault position can increase this discrepancy. Our results show the importance of fault characterisation and well positioning with respect to a fault considering subsurface uncertainty and how this can affect denser field development of DUGS. Our findings suggest to integrate faults and the relative positioning of well doublets with respect to a fault more strongly in field development plans. Such considerations should also be included in future optimization plans of multi-well geothermal systems. Moreover, the regulatory framework should be revised to achieve a better match between the IA boundary and the production well temperature drop to enable better planning for denser development of DUGS

Coupled modeling of well and reservoir for geo-energy applications

The energy transition is inevitable since approximately two-thirds of the current global GHG emissions are related to energy production. Subsurface can provide a great opportunity for innovative low-carbon energy solutions such as geothermal energy production, hydrogen storage, carbon capture, and sequestration, etc. Well and borehole operations play an important role in all these applications. In order to operate wells intelligently, there must be a robust simulation technology that captures physics and the expected production scenario. In this study, we design a numerical framework for predictive simulation and monitoring of injection and production wells based on the general multi-segment well model. In our simulation model, wells are segmented into connected control volumes similar to the finite-volume discretization of the reservoir. Total velocity serves as an additional nonlinear unknown and it is constrained by the momentum equation. Moreover, transforming nonlinear governing equations for both reservoir and well into linearized equations benefits from operator-based linearization (OBL) techniques and reduce further the computational cost of simulation. This framework was tested for several complex physical kernels including thermal compositional multiphase reactive flow and transport. The proposed model was validated using a comparison with analytic and numerical results.</p

Nonlinear solver based on trust region approximation for CO₂ utilization and storage in subsurface reservoir

Simulation of CO2 utilization and storage (CCUS) in subsurface reservoirs with complex heterogeneous structures requires a model that captures multiphase compositional flow and transport. Accurate simulation of these processes necessitates the use of stable numerical methods that are based on an implicit treatment of the flux term in the conservation equation. Due to the complicated thermodynamic phase behavior, including the appearance and disappearance of multiple phases, the discrete approximation of the governing equations is highly nonlinear. Consequently, robust and efficient techniques are needed to solve the resulting nonlinear system of algebraic equations. In this study, we present a powerful nonlinear solver based on a generalization of the trust-region technique for compositional multiphase flows. The approach is designed to embed a newly introduced Operator-Based Linearization technique and is grounded on the analysis of multi-dimensional tables related to parameterized convection operators. We split the parameter space of the nonlinear problem into a set of trust regions where the convection operators preserve the second-order behavior (i.e., they remain positive or negative definite). We approximate these trust regions in the solution process by detecting the boundary of convex regions via analysis of the directional derivative. This analysis is performed adaptively while tracking the nonlinear update trajectory in the parameter space. The proposed nonlinear solver locally constrains the update of the overall compositions across the boundaries of convex regions. We tested the performance of the proposed nonlinear solver for various scenarios. In many cases, our approach yields an improved behavior of the nonlinear solution in comparison to state-of-the-art solvers.</p

Hydraulic-mechanical properties of microfaults in granitic rock using the Punch-Through Shear test

Fault zones are key features in crystalline geothermal reservoirs or in other subsurface environments due to the fact that they act as main fluid pathways. An adequate experimental description of the evolution of permeability of a realistic microscopic fault zone under in-situ reservoir and fracture parallel flow conditions is required. To address this topic, we demonstrate a novel experimental set up (Punch-Through Shear test) that is able to generate a realistic shear zone (microfault) under in-situ reservoir conditions while simultaneously measuring permeability and dilation. Three samples of intact granite from the Odenwald (Upper Rhine Graben) were placed into a MTS 815 tri-axial compression cell, where a self-designed piston assembly punched down the inner cylinder of the sample creating the desired microfault geometry with a given offset. Permeability was measured and fracture dilation was inferred from an LVDT extensometer chain, as well as the balance of fluid volume flowing in and out of the sample. After fracture generation, the shear displacement was increased to 1.2 mm and pore pressure changes of ± 5 or ± 10 MPa were applied cyclically to simulate injection and production scenarios. Formation of a microfault increased the permeability of the granite rock by 2 to almost 3 orders of magnitude. Further shear displacement led to a small increase in permeability by a factor of 1.1 to 4.0, but permeability was reduced by a factor of 2.5 to 4 within 16 h due to compaction and fault healing. Effective pressure cycling led to reversible permeability changes. CT images showed that the fracture network is rather complex, but depicts all features commonly observed in larger scale fault zones.</p

Reservoir Modelling of Lower Cretaceous West Netherlands Basin Aquifers for Geothermal Energy Production

This project aims to predict Lower Cretaceous reservoir architecture and reservoir properties of the graben blocks in the West Netherlands Basin for low enthalpy district heating geothermal energy. Horst and pop-up structures in the study area were targets of oil and gas production in the last 60 years. For the recent upcoming geothermal energy production the focus lays on the deeper and warmer graben structures in between the oil and gas fields. Reservoir property predictions like thickness and permeability are currently based on interpolations between oil and gas well measurements on horst and pop-up structures. In order to successfully produce from the current 45 geothermal licences in the province of Zuid-Holland, detailed reservoir models and associated uncertainty maps of the Lower Cretaceous sandstones are required. Goals of the project are to model the reservoir architecture in order to simulate production and determine optimal well placement of geothermal doublets and predict possible doublet interference. Reservoir architecture of these sandstones will be studied by re-evaluating the existing lithostratigraphically based well log correlations, in combination with seismic interpretation and core studies. A palinspastic reconstruction is carried out on a cross section to indicate the paleotopography and the complex reservoir architecture

Clogging mechanisms in geothermal operations: a case-study of a geothermal field in the Netherlands

The number of geothermal operations worldwide has been actively growing over the last decades. To increase their efficiency, prevent reservoir depletion and avoid environmental issues, produced water is commonly reinjected. Despite these benefits of fluid reinjection, various clogging problems resulting in injectivity decline have been reported by field operators. Research on individual clogging mechanisms is published in various studies. However, fluid injectivity problems are still widely faced, leading to decreased overall productivity and even abandonment of some wells. Therefore, it is essential to better understand reasons of fluid pathway clogging processes and especially their interactions to efficiently predict and prevent them. In this research, we present a theoretical analysis of different clogging mechanisms. The influence of various parameters on different clogging mechanisms from existing experimental studies and field reports has been reviewed and summarized. Additionally, we compared these experimental literature concepts with a real case study of a running geothermal field facing clogging problems in the Netherlands. The study includes a detailed analysis of production data, as well as fluid and filter sample analyses. Results show correlation patterns between concentration changes of chemical species in the fluid, as well as influence of injection parameters (temperature, flow rate) on injectivity. The outcomes were compared to literature examples to generalize the conclusions. This will allow an improved understanding of processes occurring in geothermal fluids during fluid production and reinjection. As a next step of this research, more field data will be analyzed to identify similar trends and correlations as well as the interdependency of injectivity problems

Interference between geothermal doublets across a fault under subsurface uncertainty: Implications for field development and regulation

Direct Use Geothermal Systems (DUGS) are increasing their installed capacity worldwide and denser developments with multiple doublets are becoming more common. Interference between doublets therefore becomes an additional concern to subsurface uncertainties. Faults can be either barriers or conduits to flow and can affect the fluid pathways inside the reservoir. The interference between two doublets that are separated by a fault has not been previously studied for DUGS. In this work considering subsurface uncertainty in a full factorial design using 5184 3D reservoir simulations we show that a fault can reduce the system lifetime of a two-doublet system by more than 40 % if one doublet is at close proximity to it. Further, we identify that the fault can also improve both the system lifetime and generated Net Present Value (NPV) with appropriate development decisions. Contrary to previous results that did not consider reservoir architecture, a tramline well configuration is preferable when the doublets have the fault in the centre, while a checkerboard configuration is preferable as the distance to the fault decreases. The Heat In Place (HIP) recovery shows a linear relationship with flow rate and well spacing that is not affected by the fault distance or flow properties. The dimensions of the Influence Area (IA) previously considered are insufficient to capture the temperature drop at the producer wells and the fault position can increase this discrepancy. Our results show the importance of fault characterisation and well positioning with respect to a fault considering subsurface uncertainty and how this can affect denser field development of DUGS. Our findings suggest to integrate faults and the relative positioning of well doublets with respect to a fault more strongly in field development plans. Such considerations should also be included in future optimization plans of multi-well geothermal systems. Moreover, the regulatory framework should be revised to achieve a better match between the IA boundary and the production well temperature drop to enable better planning for denser development of DUGS.Petroleum Engineerin

Interdependencies between physical, design and operational parameters for direct use geothermal heat in faulted hydrothermal reservoirs

Interest in direct use geothermal systems is increasing due to their ability to supply renewable, environmentally friendly heat. Such systems are mostly developed in conduction dominated geological settings where faults are often encountered. Interdependencies between physical, design and operational parameters make it difficult to assess the performance of such systems. Interaction with faults could potentially have adverse effects on system lifetime, generated Net Present Value (NPV) and produced energy. In this work a single doublet system in the enthalpy range of 140 kJ/kg to 350 kJ/kg is analysed using COMSOL Multiphysics. A choice of design (well spacing and placement), physical (layered reservoir, fault flow properties, fault throw) and operational (injection and production flow rates) parameters are considered in a full factorial design that includes 2430 3D reservoir simulations. Results show that fault flow properties characterization is more significant than fault throw structural characterization. For the considered reservoir properties, increasing the flow rate four times results in an NPV increase of a factor seven, despite the shorter system lifetime. A sealing fault renders the system lifetime less sensitive to the doublet positioning. Synthetic model results shown can serve as guidelines to reducing full scale field models. Importance and relevance of these results remains very high for horizontally homogeneous, layered reservoirs. The analysis expands the understanding of interdependencies for direct use geothermal systems and informs on their further development.Petroleum Engineerin