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Africa (Sub-Sahara) Bowleven began drilling operations at its Zingana exploration well on the Bomono permit in Cameroon. Located 20 km northwest of Douala, Cameroon's largest city, the well will target a Paleocene (Tertiary) aged, three-way dip closed fault block. The company plans to drill the well to a depth of 2000 m and will then spud a second well in Moambe, 2 km east of Zingana. Bowleven is the operator and holds 100% interest in the license. Asia Pacific China National Offshore Oil Company (CNOOC) has brought its Dongfang 1-1 gas field Phase I adjustment project on line ahead of schedule. The field is located in the Yinggehai basin of the Beibu Gulf in the South China Sea and has an average water depth of 70 m. The field is currently producing 53 MMcf/D of gas and is expected to reach its peak production of 54 MMcf/D before the end of the year.
A new methodology for a "Level 2" Seismic Hazard Assessment has been developed for a geothermal project. Geomechanical models were created to understand the thermo-mechanical effects in the lifetime of a specific geothermal operation. Two types of geomechanical models are used, a 3-D Mohr-Coulomb model using both a deterministic and a probabilistic methodology, and a 2-D elastoplastic finite element model, simulating the lifetime and the associated mechanical changes caused by the geothermal operation. The simulated results show that, under maximum production conditions, there is a 1% likelihood of induced seismicity. Using published correlations, the movement along a fault is used to calculate the maximum magnitude of the unlikely seismicity, projected to be the order of 1.5 to 2 M w . As a mitigation method, a Traffic Light System is proposed. This allows the geothermal operation to continue while staying within the expected safety margins.
Bowleven began drilling operations at its Zingana exploration well on the Bomono permit in Cameroon. Located 20 km northwest of Douala, Cameroon's largest city, the well will target a Paleocene (Tertiary) aged, three-way dip closed fault block. The company plans to drill the well to a depth of 2000 m and will then spud a second well in Moambe, 2 km east of Zingana. Bowleven is the operator and holds 100% interest in the license. China National Offshore Oil Company (CNOOC) has brought its Dongfang 1-1 gas field Phase I adjustment project on line ahead of schedule.
ABSTRACT: Rock salt formations are a common reservoir seal worldwide with excellent sealing capacity. Restoring the sealing capacity of rock salt caprocks penetrated by wells using the same rock salt as plugging material is therefore an attractive, safe and environmentally friendly option. The concept is based on the removal of a section of casing over a part of a formation consisting of rock salt and creation of a sealing well barrier (plug) by the creep of rock salt. Geomechanical numerical simulations were conducted to estimate wellbore closure times for a range of conditions representative of the Zechstein evaporites overlying Rotliegend reservoirs in the Northwestern Europe. Results showed that the salt creep largely depends on the salt properties, differential stress and in-situ temperature. Estimated closure times of a reamed interval, for the maximum underbalance, were in the range of a few weeks for a depth of 3100 m, a few months for a depth of 2500 m and a few years for a depth of 2000 m. Reamed intervals should be at least 10 m long to avoid slowing down the process of creep that occurred for shorter reamed intervals.
The most common caprock lithologies are shales, evaporites and in particular rock salt (halite). These natural sealing materials have held hydrocarbons over geological timescales and are generally regarded as proven hydraulic seals. Using the same caprock material for well plugging and abandonment (P&A) is therefore an attractive option as the initial sealing capacity of caprocks penetrated by wells could be restored by well plugs made of the native caprock lithology. However, this option of using natural formation sealing for well isolation and P&A is currently underutilized.
The use of creeping formation for annular sealing of oil and gas wells has been encouraged by the regulatory agency in Norway. Creeping formation has been accepted as a new well barrier element (NORSOK Standard D-010, 2013). In practice, creeping formation was mainly used for annual sealing of oil and gas wells (Williams et al., 2009). An example is Green Clay or Green Shale, found in the Norwegian Central Graben. This creeping shale incorporates several stratigraphic units of the Tertiary Hordaland Group. The shale is usually over-pressured, contains high amounts of smectite and exhibits fast creep strain rates. The green shale has been relatively unaffected by diagenesis and preserved its ductility despite burial depths of 3 km.
Teatini, P. (University of Padova) | Ferronato, M. (University of Padova) | Franceschini, A. (University of Padova) | Frigo, M. (University of Padova) | Janna, C. (University of Padova) | Zoccarato, C. (University of Padova) | Isotton, G. (M3E Srl)
ABSTRACT: Underground gas storage (UGS) is a practice that is becoming widely implemented to cope with seasonal peaks of gas consumption. When the target reservoir is located in a faulted basin, a major safety issue concerns the reactivation of pre-existing faults, possibly inducing (micro-) seismicity. Faults are reactivated when the shear stress exceeds the limiting acceptable strength. It has been observed in The Netherlands that this occurrence can happen “unexpectedly” during the life of a UGS reservoir, i.e. when the actual stress regime is not expected to reach the failure condition. A numerical analysis by a 3D FE-IE elasto-plastic geomechanical simulator has been carried out to cast light in this respect, by investigating the mechanisms and the critical factors that can be responsible for a fault reactivation during the various stages of UGS in reservoirs located in the Rotliegend formation. The model outcomes show that the settings (in terms of reservoir and fault geometry, geomechanical parameters, and pressure change distribution) more prone to fault activation during primary production are also the most critical ones during cushion gas injection and UGS cycles.
Because of the importance of natural gas for energy production, the interest to develop underground gas storage (UGS) projects is continuously increasing worldwide. In May 2015, 268 UGS facilities existed or were planned in Europe and over 400 in the USA. UGS is traditionally used to ensure a relatively smooth delivery from gas reservoirs to the gas consumption pattern dictated by daily and seasonal oscillations. The hazard and risk associated with subsurface gas storage are a recurrent issue whenever a new UGS is planned. Many different aspects are involved, such as formation integrity, health and safety as related to public perception, economic risk, and environmental impacts. Among the latter, the geomechanical effects induced by seasonal gas injection and withdrawal may play a very important role.
The Slootdorp field has a complex structure with most reserves in Rotliegend sandstone, which is communicating with gas bearing Zechstein carbonates. The Rotliegend reservoir is bounded by a large fault, which might become seismogenic during depletion. A 3D geomechanical model was built, based on the faults and horizons in the geological model. Both the Rotliegend and Zechstein reservoirs were included in the model. The model was populated with geomechanical properties derived from logs, LOT's (leak off tests) and regional data on the stress field. Also, overburden properties from previous studies on nearby fields were used.
The pressure input was obtained from reservoir simulation. It is important to include the water leg pressure in the pressure input since the Rotliegend gas reservoir is in contact with an active aquifer. Pressure reduction drives the compaction of the reservoir, which induces stresses on the faults causing slippage. Since the water is quite incompressible, a large pressure reduction in the water leg may be caused temporarily by a rising gas water contact.
It turned out that slippage is not expected at the lowest gas pressure using a conservative estimate of the critical friction coefficient on the fault of 0.55. Sensitivity analysis on the most important input parameters was performed with a range that can be expected for such a field. The result was that the maximum critical stress ratio could range between 0.46 and 0.53 for the expected uncertainty of input parameters. The geomechanical modeling shows that an active aquifer has a dominant, mitigating effect on seismic risk, which can explain why many reservoirs show no seismicity in the Netherlands, although other effects could also play a role.
Quantitative integrated ground models are a requirement for proper cost optimal site characterization, for offshore renewables, coastal activities and O&G projects. Geotechnical analyses and interpretations often rely on isolated 1D boreholes. On the other hand, geophysical data are collected in 2D lines and/or 3D volumes. Geophysical data therefore provides the natural link to re-populate geotechnical properties found in the 1D boreholes onto a larger area and thereby build a consistent and robust ground model. The geophysical data can be used to estimate geotechnical data and, as of today, there are a few methods available that can reliably map the dynamic properties from the seismic data (stratigraphic information,
We have developed a workflow to build quantitative ground models following three approaches: (i) a geometric model in which the seismic data interpretations guide the prediction of geotechnical properties; (ii) a geostatistical approach in which in addition to the structural constraints, we used the seismic velocities to guide the prediction; and (iii) a multi-attribute regression using an artificial neural network (ANN). We apply it to a set of publically available data from the Holland Kust Zuid wind farm site in the Dutch sector of the North Sea. The result of the workflow yields maps or sub-volumes of geotechnical or geomechanical properties across the development site that can be used in further planning or engineering design.
In this study, we use the tip resistance from a CPT as an example. The tip resistance derived using all methods generally give good results. Validation against randomly selected CPT shows good correlation between predicted and measured tip resistance. The ANN performs better than the geostatistical approach. However, these two approaches require good data quality and a rather large dataset to be effective. Therefore, using a global dataset not restricted to the Holland Kust Zuid site may improve the prediction. Moreover, using existing empirical correlation and calibration through laboratory testing or by training another ANN model, the geotechnical stiffness/strength parameters such as angle of friction or undrained shear strength could be derived.
The next step is to use the results and their uncertainty into a cost assessment for the given foundation concepts.
Stoljarova, Anastasia (Freie Universität Berlin / Institute for Chemistry and Biochemistry) | Regenspurg, Simona (German Research Centre for Geosciences) | Bäßler, Ralph (BAM Federal Institute for Materials Research and Testing)
Geothermal wells are a feasible energy source to replace fossil fuel supply. Hence, many technologies have been developed to take advantage of geothermal energy. Nevertheless, service conditions in geothermal facilities are due to the chemical composition of hydrothermal fluids and temperatures, in many cases, extreme in terms of corrosion. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities. However, some additional aspects might rise.
During circulation tests at the geothermal research facility in Groß Schönebeck (Germany), massive copper precipitation has been observed downhole clogging the production well. Occurring mechanisms and measures to prevent copper precipitation or scaling needed to be investigated.
This contribution deals with the evaluation of the corrosion behavior of different metals ranging from carbon steel via stainless and duplex steels to titanium in a copper containing artificial geothermal water, simulating the conditions in the Northern German Basin, using electrochemical measurements and exposure tests. While carbon steel exhibits copper deposition (scaling) and copper precipitation, higher alloyed materials show different response to Cu-species in saline geothermal water. Here, no relevant formation of insoluble Cu-species could be detected.
Based on these results, the suitability of the investigated high alloyed materials and Ti-alloy can be concluded for use in such conditions, as long as no crevice conditions in combination with non-metallic parts occur. Carbon steel is not recommended to be used.
Since geothermal reservoirs are a feasible energy source to replace fossil fuel supply, many technologies have been developed to take advantage of geothermal energy. Nevertheless, due to the chemical composition of hydrothermal fluids and temperatures, service conditions in geothermal facilities are demanding in many cases in terms of corrosion. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities.
Since operational conditions in geothermal power plants are crucial in terms of corrosion special attention is paid to materials selection1-3
The democratization of artificial intelligence began with the collection of large datasets and the ability to consume them for inferences and prediction by leveraging exponentially increasing computational power. This was further enhanced by the ability to parallel process datasets by breaking them up into independent units and applying fast computation to those units using Graphical Processing Units (GPUs). We discuss one such application in the area of seismic interpretation in the oil and gas sector. Seismic interpretation is particularly suitable since seismic datasets’ characteristics make them inherently amenable to parallel processing in post-stack format.
True big data in the oil and gas sector exists in the seismic arena, where up to one terabyte of data or more can be collected per hour. We show that while preprocessing is required for cleansing and quality checking the data, novel techniques can be applied from the medical and healthcare sectors, namely radiology, for image processing and anomaly detection in images. Further, we also show methods of preprocessing the seismic data, development of seismic images, and novel denoising techniques that lead to the construction of seismic cubes.
3D and 4D seismic cubes post-stack are today amenable to a plethora of neural network based parallel processing methods for anomaly detections. Using such techniques, the achievable speeds to detect anomalies are effectively above ten times what an experienced human being can do. These methods, at their very best, go far beyond human capabilities in terms of processing terabytes to petabytes of data. Such image processing is in use in image recognition, for example, in border control for person identification and verification, and satellite image analysis to discover the minutest of details. We showcase novel techniques based on Convolutional Neural Networks and Deep Neural Networks being utilized for subsurface geological and geophysical properties identification. Further developments of our current and future work are also discussed.
Our presentation specifically describes methods based on Convolutional and Deep Neural Networks to predict faults and salt domes in seismic images. The ability of Deep Neural Networks to continuously learn and self-optimize is the basis of our novel approach. A common criticism of machine learning methods is that most reported results describe results on field data where part of the field data has been used in training the neural network algorithms being used. In the work reported here, we describe the results of our algorithm on two completely blind field data sets – where none of the field data has been used in training the algorithms.
Compartmentalized reservoirs are often segmented by a sealing fault acting as a barrier to pressure communication between neighboring reservoirs. However, changes in reservoir pressure, due to either fluid withdrawal or injection, can induce changes in local stresses that can lead to fault slip and associated alteration of fault permeability, which can transform the initially sealing fault into partially conductive. This paper examines the transient pressure response to a sudden change in anisotropic fault permeability as an indicator of fault seal breakdown. Analytical solutions for pressure-transient response for a linesource, constant-rate well in a compartmentalized reservoir where fault permeability is rapidly enhanced, are presented. The fault is modeled as a linear interface between semi-infinite homogeneous and isotropic formation layers. Laplace-Fourier transform technique is used to solve the governing equations analytically. Pressure-transient solutions are presented as type curves for the scenarios of across-fault and simultaneous across-along-fault permeability enhancement. Characterization of enhanced fault transmissibility using asymptotic late-time solutions is discussed.