Assessing the potential for Compressed Air Energy Storage using the offshore UK saline aquifer resource

In the context of the development of renewable energy sources in the U.K., and of the increase in anthropogenic atmospheric CO2, it is important to develop alternative ways of providing energy to the community. The shift to renewable sources of electricity comes to a cost: variable generation. At present, an important part of the renewable electricity capacity is being curtailed during low demand periods. One way to ensure that electricity supply matches demand is to store excess energy when it is available and deliver it when demand cannot be met by primary generation alone. Compressed Air Energy Storage (CAES) allows this storage. The aim of this project is to build upon existing knowledge on CAES using porous rocks (PM-CAES) to assess the technical feasibility for this storage technology to be developed offshore of the UK. The focus is on inter-seasonal storage. This assessment is undertaken by developing geological and power plant models to calculate the storage potential of offshore UK formations. Modelling of a conceptual aquifer air store enables approximations of the subsurface pressure response to CAES operations. These pressure changes are coupled with surface facilities models to provide estimates of both load/generation capacity and roundtrip efficiencies. Algebraic predictive models can be developed from the results of a sensitivity analysis of the store and plant idealised models. Screening of the CO2 Stored database, containing data on geological formations offshore of the UK (initially developed for CO2 storage), was then performed to estimate PM-CAES potential using the predictive models. The results suggest that there is substantial PM-CAES potential in the UK. Results indicate an energy storage potential in the range of 77-96 TWh, which can be released over 60 days. A geographic information system (GIS) study was then performed to identify the portion of the identified storage potential colocated with offshore windfarm. 19 TWh of the storage potential identified is colocated with windfarm and would be achievable at an average levelised cost of electricity of 0.70 £/kWh

Cyclical hydraulic pressure pulses reduce breakdown pressure and initiate staged fracture growth in PMMA

Using unique experimental equipment on large bench-scale samples of Polymethylmethacrylate, used in the literature as an analogue for shale, we investigate the potential benefits of applying cyclical hydraulic pressure pulses to enhance the near-well connectivity through hydraulic fracturing treatment. Under unconfined and confined stresses, equivalent to a depth of up to 530 m, we use dynamic high-resolution strain measurements from fibre optic cables, complemented by optical recordings of fracture development, and investigate the impact of cyclical hydraulic pressure pulses on the number of cycles to failure in Polymethylmethacrylate at different temperatures. Our results indicate that a significant reduction in breakdown pressure can be achieved. This suggests that cyclic pressure pulses could require lower power consumption, as well as reduced fluid injection volumes and injection rates during stimulation, which could minimise the occurrence of the largest induced seismic events. Our results show that fractures develop in stages under repeated pressure cycles. This suggests that Cyclic Fluid Pressurization Systems could be effective in managing damage build-up and increasing permeability. This is achieved by forming numerous small fractures and reducing the size and occurrence of large fracturing events that produce large seismic events. Our results offer new insight into cyclical hydraulic fracturing treatments and provide a unique data set for benchmarking numerical models of fracture initiation and propagation

Basin Analysis and Petroleum Systems Modeling of the Lokichar Basin (Kenya)

International audienceA first wave of exploration of the Cenozoic half graben basins of the East African Rift System in the early 1990's resulted in the acquisition of 2D seismic in the Turkana area (northern Kenya) and the drilling of well Loperot-1 in the eastern part of the Lokichar Basin. The well turned out to be a commercial failure, and a second dry hole further north marked the end of the exploration activities. Recently, exploration has been revived in East Africa and revealed major discoveries in the vicinity of Loperot-1 and in particular along the western bounding fault of the Lokichar Basin. This play is currently drilled out, and first appraisal wells will reveal the commerciality of the discoveries. We will present a regional synthesis, seismic interpretation and derived isopach maps, and a series of structural restoration sequences and petroleum systems models. Using this information, we first review the failure of Loperot-1. This wildcat well encountered the organic-rich and oil-mature Lokhone and Loperot shale members and good reservoir facies in the Auwerwer and Lokhone sandstones, with oil shows. However, late tectonic activity of the trap-bounding fault is interpreted to have a destructive impact on the modeled pre-existing oil accumulation. Based on a serious of 2D and 3D petroleum systems models, we will then discuss the elements (source, reservoir and seal rocks) and dynamic processes (trap formation, charge and preservation) of the petroleum systems to discuss the success of the recent drilling activities in the Lokichar Basin. Finally, we will point out potential areas for future exploration. The analysis of the unconformities and the orientation of spatial trends in the isopach maps suggest 3 distinct periods of tectonic activity, from which only the most recent can be accurately dated (starting approximately Late Oligocene). The directional trend of the deepest identifiable basin fill is interpreted to be aligned with the extensional direction of the Cretaceous Central African Rift System (NW to SE). This suggests that the Lokichar Basin might have been formed already during Cretaceous as part of the Central African Rift System, which hosts major oil reserves in the neighboring Soudan. Sandstones of Cretaceous age are observed in the Lapur Range in the northern Turkana area, and similar sediments might be present below the Cenozoic basin