Summary Saline aquifers represent the type of geological carbon storage unit with the highest CO2 storage potential worldwide. Considering remote locations without the availability of a suitable pipeline infrastructure, transportation by ship paired with a cyclic (intermittent) injection scheme is a viable option. The combination of high injection rates, the interplay of viscous, gravity and capillary forces and the salt precipitation phenomenon resulting from water evaporation, makes cyclic CO2 injection a challenging operation. This numerical study puts emphasis on investigating the relationship between injectivity and salting-out effect under cyclic injection regime, considering typical North Sea reservoir conditions. The results showed that the distribution and magnitude of halite deposition within the reservoir varies influenced by the prevalent driving forces. Shut-in periods create favorable conditions for upward migration of the CO2 due to buoyancy and formation of high gas saturation channel below the top which is then preferentially used by CO2 during next injection cycles. The strongest impact of salting the out effect occurs at the tail of the CO2 plume, where the equilibrium between water removal by evaporation and capillary brine backflow persist close to the well, generating an increasing reduction in porosity and permeability and the subsequent loss of injection capacity.

Summary The Mahalanobis distance is a statistical distance and is often used in various machine learning tasks to perform clustering analysis. This paper presents its application to history matching. This new extension, so-called rock typing coupled with the adjoint method, is proposed to maintain the geological consistency between model parameters of different rock types. The rock types have different porosity and permeability ranges, relative permeability curves, and different connate water and residual oil saturation. In general, most gradient-based history matching tools honour the minimum and maximum geological constraints, but the link between the different rock type-dependent parameters may not be maintained. This leads to questionable geological admissibility of the entire model and, thus, calls for the necessity of removing or minimising inconsistencies. This paper shows how the use of Mahalanobis distance calculation can suggest better and more plausible results. It presents the theory, applied methodology and the applicability of Mahalanobis distance calculation in a new history matching workflow that improves geological consistency, including the rock types. The rock type is changed with corresponding parameters at the grid-block level based on the porosity and horizontal permeability change with the rock typing history matching workflow. The so-called rock-typing extension of the history matching workflow allows parameters to be modified co-dependently according to the rock type definition based on the porosity and the permeability adjustments suggested by adjoint-based sensitivity calculations. The Mahalanobis distance is associated with the rock types through their porosity and permeability correlations. Therefore, it guides the correction step and determines the appropriate rock type based on the underlying statistical information. History matching was performed on a simple synthetic model, a quarter of a five-spot pattern with the standard and the rock-typing extended workflow. Comparison results show significant improvements in history matching quality in terms of geological consistency with fewer iterations or within the same number of iterations but with favourable objective function values. With the help of Mahalanobis distance, the novel approach has successfully preserved the geological consistency of the models during the history matching process.

Summary The prospecting of geothermal energy in depleted gas reservoirs is considered the environmentally friendly and low cost. The aim of this paper is to present a workflow that utilizes the legacy data modeling the potential geothermal reservoir, make a comprehensive evaluation and feasibility study of geothermal development. With this idea, the Wealden formation of the Burgwedel area (North Germany) are been modeled by using the legacy geo- data from the local depleted gas field. The integrated analysis, assessment, and decision- making work will be based on structural and properties modeling result which indicates that: there were 4 coarse sandstone layers have geothermal energy potential due to their well petrophysical properties and connectivity; sand layer two maybe the most priority target and it expected 71 - 82 °C hot water production; the surface map combine with reservoir model will help the surface facility design.

Summary The relative permeability and capillary pressure are interdependent characteristics of two phase flow which can be most accurately evaluated by performing flooding and centrifuge experiments on the same core sample. The presented approach allows to history match the results of both experiments at the same time with synchronous determination of optimal parameters for capillary pressure and relative permeability curves. The accuracy and robustness of the approach are ensured by NURBS representation of the curves and by adjoint method for calculation of sensitivity coefficients, meaning derivatives of the data which we are trying to match with respect to the model parameters. Numerical modeling takes into account interference of both viscous and capillary forces which makes the interpretation of experimental results more accurate compared to well-known analytical approaches. During the history matching process not only shape parameters of the above-mentioned curves is important to match, but also due to the uncertainty of residual oil saturation and connate water saturation, these values can be calculated more accurately by simulation as well. In this paper, in-house made tool based on publicly available MRST simulator is presented. Simulated cases are based on synthetic data and include several scenarios with various combinations of experiments.

The remarkable increase of greenhouse gases in the atmosphere, particularly carbon-dioxide (CO2) is often assumed as one of the main causes of the climatic changes. A potential short-term mitigation to these is a reduction of anthropogenic CO2 emissions into the atmosphere via capture and geological storage, a process that has been studied over the last two decades. An important aspect of understanding the migration process is the simulation of large-scale projects. The aim of this paper is to examine the effects of the relevant processes occurring in the second phase of CCS on the storage capacity and on the behaviour of CO2 plume in the reservoir: influence of thermal processes on the spreading of CO2, phase transfer (the amount of CO2 in free gas form and dissolved in brine), leakage and the impacts of these processes on the pressure distribution in the field. For this purpose, three subcases were introduced where CO2 is injected into a deep saline aquifer of the Johansen Formation.