In the land known for the midnight sun, beautiful snow-clad mountains, and the green sky lights, there is a place where the "black gold" shines. The oil capital of Norway, the southwest coastal city of Stavanger has grown into one of the major international oil and gas hubs. As the importance of North Sea oil and gas production has increased for Europe, Stavanger has welcomed the world to its doorstep. The personality of Stavanger is not only oil and gas; in 2008, it was chosen as one of two European cultural capitals. A lively city, Stavanger embraces the diversity of the world's professionals who call Norway home.
The last decade has spotted a tremendous upsurge in casing failures. The aftermaths of casing failure can include the possibility of blowouts, environmental pollution, injuries/fatalities, and loss of the entire well to name a few. The motivation behind this work is to present findings from a predictive analytics investigation of casing failure data using supervised and unsupervised data mining algorithms. Scientists and researchers have speculated the underlying causes but to date this type of work remains unpublished and unavailable in the public domain literature.
This study assembled comprehensive data from eighty land-based wells during drilling, fracturing, workover jobs, and production. Twenty wells suffered from casing failure while the remaining sixty offset wells were compiled from well reports, fracturing treatment data, drilling records, and recovered casing data. The failures were unsystemic but included fatigue failure, bending stresses from excessive dogleg, buckling, high hoop stress on connections, and split coupling. The failures were detected at various depths, both in cemented and uncemented hole sections. Failures were spotted at the upper and lower production casing.
Using a predictive analytics software from SAS, twenty-four to twenty-six variables were evaluated through the application of various data mining techniques on the failed casing data sets. The missing data was accounted for using multivariate normal imputation. The study outcome addressed common casing sizes and couplings involved with each failure, failure location, hydraulic fracturing stages, cement impairment, dogleg severity, thermal and tensile loads, production-induced shearing, and DLS. The predictive algorithms used in this study included Logistic Regression, Hierarchal Clustering, and Decision Trees. While the descriptive analytics manifested in visual representations included Scatterplot Matrix, and PivotTables. Failure causes were identified. A total of five statistical techniques using the aforementioned algorithms were developed to evaluate the concurrent effect of the interplay of these variables. Nineteen variables were believed to possess the highest contribution to failure. Scatterplot matrix suggested a complex correlation between the total base water used in fracturing simulation and casing thickness. Logistic Regression suggested nine variables were significant including: TVD, operator, frac start month, MD of most severe DL, heel TVD, hole size, BHT, total proppant mass, cumulative DLS in lateral and build sections variables as significant failure contributors. PivotTables showed that the rate of casing failure was highest during the winter season.
This investigation is aimed to develop a thorough understanding of casing failures and the myriad of contributing factors to develop comprehensive predictive models for future failure prediction via the application of data mining algorithms. These models intend to provide a theoretical and statistical basis for cost-effective, safe, and better drilling practices.
Sun, Zhuang (The University of Texas at Austin) | Tang, Hewei (Texas A&M University) | Espinoza, D. Nicolas (The University of Texas at Austin) | Balhoff, Matthew T. (The University of Texas at Austin) | Killough, John E. (Texas A&M University)
The reduction of pore pressure caused by depletion can induce significant reservoir compaction, especially in unconsolidated reservoirs. Experiments using unconsolidated core samples are often sparse and costly. We develop a numerical approach based on computer-based simulations of rock samples and mechanical tests. The numerical sample consists of crushable grains simulated with the discrete element method (DEM) and the bonded-particle model (BPM). Model parameters are calibrated through numerical single-grain-crushing tests which reproduce the experimentally-measured sand strength. Grain crushing induced by the uniaxial strain stress path results in a pronounced reduction of porosity and permeability, which manifests more readily for samples with large grain size. The change of particle size distribution indicates that the high effective stress causes grain crushing and produces a significant amount of fines. We perform numerical uniaxial strain tests on numerical samples comprising stiff and soft mineral grains. Simulation results indicate that the presence of soft grains and inclusions (e.g. shale fragments) facilitates the grain crushing. Reservoir simulations, incorporating the change of porosity and permeability as a compaction table, show that the upscaled compaction can enhance production due to compaction drive but also reduces production rate by impairing the reservoir permeability. This multiscale numerical workflow bridges particle-scale compaction behavior and field-scale reservoir production. In this paper, (a) DEM simulations provide a useful tool to investigate compaction effects and complement laboratory experiments; (b) the multi-scale numerical approach can predict the depletion-induced evolution of reservoir production.
Fluid injection into the subsurface perturbs the pore pressure and alters the effective stress quasi-statically, inducing seismicity on fractures of certain orientations (we hereinafter do not distinguish between a fracture and a fault in this study). This process is traditionally considered as a decoupled hydroshear process: the effective normal stress on a fracture simply decreases by the amount of fluid overpressure, whereas the shear stress remains unchanged (e.g., Byerlee, 1978; Scuderi & Collettini, 2016; Mukuhira et al, 2016), resulting in a direct increase in the Coulomb stress, which, when driven from negative to zero, signifies the occurrence of seismicity. Such a decoupled mechanism remains as the basis of some prevalent statistical models of induced seismicity in a permeable porous medium (e.g., Shapiro et al., 2005; Rothert & Shapiro, 2007). In this class of models, a statistically random critical pore pressure is used as a proxy of the frictional strength of a preexisting fracture and the pore pressure evolution is governed by simple linear fluid diffusion; the modeled spatialtemporal distribution of seismicity, however, is often inconsistent with observations. As a remedy, some nonlinear diffusion models have been developed by adding a pressure-dependent diffusivity (Hummel & Shapiro, 2012; Johann et al., 2016; Carcione et al., 2018). The diffusion-based seismicity models can be further extended by incorporating, e.g., random stress heterogeneity (Goertz-Allmann & Wiemer, 2012), fractures following distributions derived from field observations (Verdon et al., 2015), and even empirical seismic emission criteria for generating synthetic seismograms (Carcione et al., 2015). This decoupled mechanism also underlies some studies that invert for distributions of permeability (Tarrahi & Jafarpour, 2012) and pore pressure (Terakawa et al., 2012; Terakawa, 2014) from induced seismicity data. However, the decoupled mechanism inherently cannot explain the remoting triggering of seismicity in areas not subjected to pressure perturbation (Stark & Davis, 1996; Megies & Wassermann, 2014; Yeck et al., 2016); it also directly contradicts the commonly observed depletioninduced faulting (Zoback & Zinke, 2002).
Homburg, Janelle (ExxonMobil Upstream Research Company) | Crawford, Brian (ExxonMobil Upstream Research Company) | Fernandez-Ibanez, Fermin (ExxonMobil Upstream Research Company) | Freysteinson, Jordan (ExxonMobil Upstream Research Company) | Reese, William (ExxonMobil Upstream Research Company)
ABSTRACT: Natural fractures in fine grained carbonate reservoirs can modify reservoir behavior during hydrocarbon production because they increase both porosity and permeability of the host formation. These fractures, and their associated porosity and permeability, will respond to pore pressure changes associated with hydrocarbon production. The aim of this study is to evaluate this response using natural, partially cemented fractures. To this end a series of experiments was undertaken on fracture carbonate samples from Dry Canyon, NM. Fractures geometries were characterized via micro-CT imaging and petrographic analysis. Samples were then tested to determine their mechanical and hydraulic stress dependence. Results were fit with a semi-logarithmic closure model that relates fracture aperture change to applied stress and good agreement was found with the results of other studies. These findings support the use of this closure model in predicting the behavior of some naturally fractured carbonate reservoirs.
Produced water chemical compositional data are collected from a carbonate reservoir which had been flooded by North Seawater for more than 20 years, so there is an opportunity to analyse the large amount of produced water data collected, understand the brine/brine and brine/rock interactions and explore the impact factors behind them. In some publications, core flood experimental tests were performed with chalk cores or carbonate columns in order to make an understanding of possible chemical reactions occurring triggered by injected water with different composition (Seawater, low salinity water or any other brine). However, most of the time the laboratory conditions where core flooding experiments are implemented cannot fully simulate the real reservoir conditions. Therefore, in this study, with the help of the valuable produced water dataset and some basic reservoir properties, a one-dimensional reactive transport model is developed to identify what in situ reactions were taking place in the carbonate reservoir triggered by seawater injection.
From the perspective of reservoir mineralogy, calcite, as the dominant mineral in the carbonate reservoir, is relatively more chemically reactive than quartz and feldspar which are usually found in sandstone. Whether calcite is initially and dominantly present in the carbonate reservoir rock is dissolved under seawater flooding or not is the first key issue we focused on. The effects of calcite dissolution on the sulphate scaling reactions due to incompatible brine mixing and the potential occurrence of carbonate mineral precipitation induced by calcite dissolution are investigated and discussed in detail. The comparison of simulation results from the isothermal model and the non-isothermal model show the important role of temperature during geochemical processes. The partitioning of CO2 from the hydrocarbon phase into injected brine was considered through calculation of the composition of reacted seawater equilibrated with the CO2 gas phase with fixed partial pressure (equivalent with CO2 content), then subsequently the impact of CO2 interactions on the calcite, dolomite and huntite mineral reactions are studied and explained. We also use calculation results from the model to match the observed field data to demonstrate the possibility of ion exchange occurring in the chalk reservoir.
Schutjens, P. M. T. M. (Shell Global Solutions International B.V.) | Fokker, P. (Shell Global Solutions International B.V.) | Rai, B. B. (Shell Global Solutions International B.V.) | Kandpal, J. (Shell Global Solutions International B.V.) | Cid Alfaro, M. V. (Shell Global Solutions International B.V.) | Hummel, N. D. (Shell Global Solutions International B.V.) | Yuan, R. (Shell Global Solutions International B.V.) | Klever, F. (Shell Global Solutions International B.V.) | De Gennaro, S. (Shell Global Solutions International B.V.) | Vaibav, J. (Shell Global Solutions International B.V.) | Bourgeois, F. (Mærsk Oil) | Calvert, M. (Mærsk Oil) | Ditlevsen, F. (Mærsk Oil) | Hendriksen, P. (Mærsk Oil) | Derer, C. (Mærsk Oil) | Richards, G. (Rockfield Software) | Price, J. (Rockfield Software) | Bere, A. (Rockfield Software) | Cain, J. (Rockfield Software)
ABSTRACT: Multi-scale numerical geomechanical models for reservoir and overburden deformation in the Tyra chalk field (Denmark) were made, and calibrated by laboratory deformation tests and field data. The mechanical interaction between the compacting and deforming formation, cement and casing was 1) modeled as a function of well orientation, cement distribution, and mechanical properties, 2) followed by probabilistic analysis of the model results in well-failure risking models to gain insight in the effects of rock deformation on well failure, both in space and time, and then 3) used as input in fluid-flow models to forecast the impact of well-failure on production. The risk analysis revealed that, whilst further Tyra compaction will probably lead to more well failure, its impact on production is probably low. Our geomechanical modeling helped to reduce uncertainty in the high-cost multi-year Tyra Future field upgrade planned for the next years to support Tyra production over the next decades.
1.1 Problem definition
About five meters of maximum subsidence has occurred so far in the Tyra chalk field (Denmark), significantly reducing the gap between wave crest and platform base (see Figures 1a, b). In addition, well deformations in reservoir and overburden have been measured and inferred by caliper data and hold-up-depth incidents (HUD) during logging and work-overs (Figures 1c, d). In the overburden, these have been interpreted mainly from the Upper Lark to Sele-Lista formation, 120 m to 400 m above the top reservoir at about 1950 m TVDss.
With the remaining 35% of the total depletion planned for the next decades, some 8 meters of total subsidence may occur by the end of Tyra field life (about 2042). Also, in view of the increasing reservoir compaction strains, there is concern that wells could catastrophically fail (and thus stop producing, i.e. terminally fail) as a result of the accumulated deformation and/or a possible acceleration of reservoir/overburden deformation. In the framework of the multi-year “Tyra Future” project (in which the Tyra production facilities are adapted to the subsiding sea-bed) field-wide and well-scale finite-element geomechanical models were built to 1) describe the compaction and subsidence, 2) study the mechanical effects of the compacting reservoir and its deforming overburden on cement and casing as function of well inclination, cement distribution, and mechanical properties of formation, cement and casing, and 3) provide input to reservoir fluid-flow simulations to assess the impact of Tyra well failure on production.
The Jasmine field is one of several ConocoPhillips-operated assets in the UK North Sea. ConocoPhillips is preparing to sell its fields in the North Sea, according to a Reuters report. Citing sources in the oil and gas industry and in banking, the news agency said the operator’s decision is part of an overall effort to focus on US shale operations.
The Jasmine field is one of several ConocoPhillips-operated assets in the UK North Sea. ConocoPhillips is preparing to sell its fields in the North Sea, according to a Reuters report. Citing sources in the oil and gas industry and in banking, the news agency said the operator’s decision is part of an overall effort to focus on US shale operations. While ConocoPhillips has not launched a formal process or appointed a bank to manage a potential sale, the report said that the company’s executives have had discussions with a number of North Sea operators and bankers in the region to test the waters. Reuters said that the sale could net as much as $2 billion, though it was not clear how much of ConocoPhillips’ portfolio would be available, or if the company would put its Norwegian North Sea assets up as well.
Tariq, Zeeshan (King Fahd University of Petroleum & Minerals) | Abdulraheem, Abdulazeez (King Fahd University of Petroleum & Minerals) | Elkatatny, Salaheldin (King Fahd University of Petroleum & Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum & Minerals) | Muqtadir, Arqam (King Fahd University of Petroleum & Minerals) | Murtaza, Mobeen (King Fahd University of Petroleum & Minerals)
In a quest to reduce the greenhouse gasses, geologic sequestration of carbon dioxide (CO2) in an underground hydrocarbon rock formation or aquifer is one of the most promising alternative to reduce the amount of CO2 release in an open environment. However, long-term storage of CO2 effects the geomechanical and geochemical properties of the host rock. In carbonate aquifers, water dissolves the injected CO2 gas forming carbonic acid which has the tendency to dissolve calcium compounds present in the formation. The dissolution of calcium is particularly worrying since it contributes to the matrix of the rock. Thus, the mechanical properties of the rock are altered, which left unattended could result and in compaction of the formation and surface subsidence.
This paper aims to study the degradation of the petrophysical and mechanical properties of two types of rocks namely limestone and sandstone due to the storage of supercritical CO2 for desired amount of time. Supercritical CO2 has low viscosity but high density and has ability to store in large amount within the same space and with the high pumping efficiency. Two different carbonate rocks and one sandstone rock were exposed to a CO2-brine solution at a pressure of 1200 psi and at 120 °C for durations ranging from 10 to 120 days. The mechanical properties were then examined by both static and dynamic mechanical tests along with the routine core analysis (RCA).
Results showed that long term CO2 storage affected the mechanical, acoustic and petrophysical parameters of rocks examined in this study, viz., Khuff limestone, Berea Sandstone, and ordinary limestone. The duration of solubility time brine-CO2-rock has a considerable impact on the petrophysical and mechanical parameters of the rock samples. Outcomes of this study also shows that the rock mechanical and petrophysical properties significantly affected when CO2 store for the longer period of time. CO2, rock, and brine interaction is dependent on time consequently the rock mechanical and petrophysical parameters changes are also time dependent. The potential candidate found for geological sequestration of CO2 studied is limestone because of its minimal rock properties altered.
Release of CO2 gas in the environment is one of the main concern and reason for the rise in the global warming because CO2 has the tendency to trap heat. Although about half of the greenhouse gasses are absorbed naturally (into deeper seas), the rest stays in the Earth's atmosphere for centuries.