Because of the metastable character of natural gas hydrate-bearing sediments (GHBS), they can be easily affected by drilling operations, thereby inducing the wellbore instability risk. This issue is ...studied in this paper by means of numerical simulations based on the first exploration well performed in the Shenhu area of the South China Sea in 2007. The corresponding simulated results were compared against the field caliper logging curve. Besides this analysis, the effects of both drilling mud properties (i.e., temperature, density, and salinity) and initial reservoir conditions (i.e., permeability, and saturation) on the wellbore stability were further investigated under the condition of drilling mud invasion into the GHBS. It is anticipated that the coupled multiphysics phenomena triggered under operation conditions can lead to wellbore instability and may also trigger the formation of fractures. The simulation results show that the predicted yield region around the borehole of well SH2 conforms to the borehole enlargement observed in the field. The sensitivity analyses indicate that a local increase in the pore pressure is likely to be generated in the wellbore vicinity, triggered by the large amount of free gas to be released during hydrate dissociation, which is in turn induced by heating (i.e., coming from the drilling-friction effects) and the high salinity of the drilling muds typically used. This study shows that by engineering the salinity of the drilling mud, the amount of free gas to be produced from marine GHBS can be controlled, preventing in this way further wellbore instability issues. This research also shows that an increase in the drilling-mud density not only impact on the development of pore pressures near the borehole, but it also affects the extent of drilling-mud invasion. This effect will extend the hydrate dissociation to a wider area and will also reduce the resistance of the formation, leading to further deformation and potential failure. The analyses also show that the increase in the initial hydrate saturation is associated with a stronger sediment and a more stable wellbore. The model also predicts that GHBS with higher absolute permeability will dissipate faster the excess of pore pressure in the surrounding sediment, contributing to wellbore stability; however, the extent of the hydrate dissociation zone will expand and thereby will increase the yield region.
•A coupling method was proposed for analyzing wellbore stability drilling in GHBS.•The latest function between mechanical properties and SH was used in our model.•The model was demonstrated by the field caliper logging results.•The effect of drilling mud properties on wellbore stability was reported.•Wellbore stability affected by hydrate reservoir conditions was analyzed.
This paper summarizes historical asbestos exposure data collected during the handling of short-fiber chrysotile asbestos that was used as an additive to drilling fluid in oil and gas exploration. A ...total of 1171 industrial hygiene (IH) personal and area air samples were collected and analyzed from more than 20 drilling rigs between 1972 and 1985. The dataset consists of 1097 short-term samples (<240 min) with more than 80% having sample durations less than 30 min. Average airborne fiber concentrations measured during asbestos handling activities ranged from 0.62 f/cc to 3.39 f/cc using phase-contrast microscopy (PCM). An additional 14 samples were considered long-term samples (>240 min) and there were 60 samples with no reported sample duration. Eight-hour time-weighted average (8-h TWA) results, calculated using short-term samples, along with long-term samples greater than 240 min, did not exceed contemporaneous Occupational Safety and Health Administration (OSHA) permissible exposure limits (PELs). This analysis fills a data gap in the evaluation of asbestos exposures from the use of drilling mud additives (DMAs) that contained chrysotile asbestos.
This paper evaluates current and historical drilling and completion costs of oil and gas wells and compares them with geothermal wells costs. As a starting point, we developed a new cost index for US ...onshore oil and gas wells based primarily on the API Joint Association Survey 1976–2009 data. This index describes year-to-year variations in drilling costs and allows one to express historical drilling expenditures in current year dollars. To distinguish from other cost indices we have labeled it the Cornell Energy Institute (CEI) Index. This index has nine sub-indices for different well depth intervals and has been corrected for yearly changes in drilling activity. The CEI index shows 70% higher increase in well cost between 2003 and 2008 compared to the commonly used Producer Price Index (PPI) for drilling oil and gas wells. Cost trends for various depths were found to be significantly different and explained in terms of variations of oil and gas prices, costs, and availability of major well components and services at particular locations.
Multiple methods were evaluated to infer the cost-depth correlation for geothermal wells in current year dollars. In addition to analyzing reported costs of the most recently completed geothermal wells, we investigated the results of the predictive geothermal well cost model WellCost Lite. Moreover, a cost database of 146 historical geothermal wells has been assembled. The CEI index was initially used to normalize costs of these wells to current year dollars. A comparison of normalized costs of historical wells with recently drilled ones and WellCost Lite predictions shows that cost escalation rates of geothermal wells were considerably lower compared to hydrocarbon wells and that a cost index based on hydrocarbon wells is not applicable to geothermal well drilling. Besides evaluating the average well costs, this work examined economic improvements resulting from increased drilling experience. Learning curve effects related to drilling multiple similar wells within the same field were correlated.
•Current and historical drilling costs of oil, gas, and geothermal wells are evaluated.•Despite the differences in lithology and well design, their average costs are similar.•A new cost index for 1976–2009 US onshore oil and gas wells was developed.•Oil and gas well cost increased by over 250% between 2003 and 2008.•Learning curve effects for oil and gas well drilling were correlated.
When drilling deep wells and high-temperature high-pressure (HTHP) formations, the solids sagging and inconsistent drilling mud properties are widely encountered and exhibit severe technical and ...operational challenges. The aim of this work is to provide a new novel solution using “vermiculite” for sagging prevention and enhancing the mud stability. The vermiculite was introduced as anti-sag additive for water-based drilling fluid at elevated temperature. Various quantities of vermiculite were added (0, 1, 2, 3, and 4 lb./bbl) and the mud stability was accordingly evaluated by conducting the static and dynamic sagging measurements. The effects of vermiculite on mud properties were thoroughly investigated by assessing the mud density, alkalinity, rheology, viscoelasticity, and filtration behavior. The practical elevated temperature was simulated experimentally by conditioning the tests up to 250 °F. The results of this work showed an improvement on mud stability as the sag tendency was reduced by adding vermiculite. The amount of 4 lb./bbl vermiculite was enough to mitigate the solids sag at elevated temperature and bring the sag tendency factors to the safe values. The rheological and viscoelastic properties were notably improved with vermiculite. The 14% reduction on plastic viscosity and the increment of yield point by 36% with better gelling structure confirmed the ability of vermiculite to enhance the mud stability. In addition, the 4 lb./bbl-vermiculite contributed to the outperformed filtration performance with less filtrated volume and affinity to formation damage. The vermiculite containing drilling fluid yielded better filter cake characteristics with less thickness, weight, and permeability by 34, 35, and 66%, respectively.
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•Vermiculite was introduced as a novel anti-sag agent for water-based mud.•New mud formulation was investigated for high-temperature high-pressure applications.•Mud stability was enhanced by adding vermiculite.•Adding vermiculite results in better rheological and viscoelastic properties.•The filtration performance was improved with vermiculite.
The logging-while-drilling (LWD) acoustic technology has been developed to measure formation velocities/slownesses for rig time saving and real-time applications such as seismic-tie, pore pressure ...determination and/or deep-sea drilling exploration. The formation compression-wave velocity is often hard to determine because of the drilling environment and wave dispersion effects. We develop a new model-based dispersive processing (MDP) method to accurately determine wave slowness from the LWD acoustic data. Two specific steps are included during the MDP procedure. In the first, the effective collar parameters are determined using the collar-wave from the measurements. The second step is the inversion for the wave slowness by minimizing the difference between the theoretical curve and dispersion data. We have validated the result of the MDP inversion with synthetic data testing and applied it to the acoustic LWD data of the Ocean Drilling Program (ODP) 808I hole. Applications of the corrected slowness results to synthetic seismogram and porosity prediction analyses demonstrate the effectiveness of the correction method.
During industrial offshore deep-water drilling process, gas kick event occurs frequently due to extremely narrow Mud Weight (MW) window (minimum 0.01sg) and negligible safety margins for the well ...control purposes. Further, traditional gas kick detection methods in such environments have significant time-lag and can often lead to severe well control issues, and occasionally to well blowouts or borehole abandonment. In this study, firstly, the raw field data is processed through data collection, data cleaning, feature scaling, outlier detection, data labeling and dataset splitting. Additionally, a novel data labeling criterion for gas kick risks is proposed where five kick risks (Indicated by different colors in this study) are defined based on three key indicators: differential flow out (DFO), kick gain volume (Vol), and kick duration time (Time). Kick risk status represents one of the following cases: Case 0 - No indicators are activated (Green), Case 1 - Multi-drilling parameters deviation or DFO is activated (Orange), Case 2 - DFO and Vol are simultaneously activated (Light Red), Case 3 - DFO and Time are simultaneously activated (Light Red), Case 4 - DFO, Vol and Time alarms are simultaneously activated (Dark Red). Then, a novel data mining method using Long Short-Term Memory (LSTM) Recurrent Neural Network (RNN) is presented for early detection of gas kick events by analyzing time series data from field drilling process. The network parameters such as number of hidden layers and number of neurons are initialized to build the LSTM network. The learned LSTM model is evaluated using the testing set, and the best LSTM model (six (6)-layers eighty (80)-nodes (6 L*80 N)) is optimally selected and deployed. The accuracy of deployed LSTM model is 87 % in the testing dataset, which is reliable enough to identify the kick fault during the deep-water drilling field operation. Lastly, the LSTM model detected the gas kick events earlier than the “Tank Volume” detection method in several representative case studies to conclude that the application of LSTM model can potentially improve well control safety in the deep-water wells with narrow MW windows.
The vertical and directional drilling are the key technologies for the exploration and exploitation of oil and gas resources in deep formations. Meanwhile, they are also the very important ways to ...exploit deep geothermal energy and geo-resources, conduct international continental scientific drilling program. The aim of the present overview is to review and discuss the vertical and directional drilling technologies and their recent developments since the pioneering work in 1890s. It starts with the historical development and classification of main drilling methods for petroleum extraction, such as the vertical drilling, directional drilling and horizontal drilling, and the main application scopes of these methods are also discussed. Then, the developments of the directional techniques, the main directional tools (deflection tools, down-hole motor, rotary steerable drilling system and vertical drilling system), the directional survey techniques (measuring and transmission techniques), the main drill bits (roller cone bits, fixed cutter bits and hybrid bits), and the main drilling fluids (gas-base drilling fluid, water-based drilling fluid and oil-based drilling fluid) are summarized and analyzed. The top 15+ deepest and top 20+ longest wells all over the world are collected from related literatures to analyze the achievements of vertical and directional drilling in petroleum industry, the challenges of vertical and directional drilling are also discussed. Finally, a brief summary and prospect of vertical and directional drilling are presented.
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•Drilling wastes are between the main residues generated by the E & P industry.•Several environmental impacts are related to incorrect drilling wastes disposal.•Treatment methods ...presented promising results to remediate drilling wastes.•New treatment methods applied on large scale needs to be developed.
The oil Exploration & Production (E&P) industry provides an important energy source for the world. However, there is a worldwide concern about the environmental impacts of E&P activities. Spent drilling fluid is one of the drilling wastes generated by the oil and gas industry’s activities. Drilling fluid and drill cuttings together form the second-largest volume of residues generated by the E&P industry. Drilling fluids are responsible for many important functions in the well drilling process. They are recirculated between the well and the platform several times during the drilling of an oil well. When the drilling reaches the reservoir phase, spent drilling fluid return to the surface contaminated with oil. The resulting residue has several compounds containing potential pollutants, which if incorrectly disposed of can pose several risks to terrestrial, aquatic, and aerial environments, including reducing soil fertility, affecting negatively the flora and fauna and causing health problems due to the volatilization of hazardous oil components such as benzene, toluene, ethylbenzene and xylene into the atmosphere. In this sense, regulators have established that the disposal of non-water based and water-based drilling fluid containing free oil is not allowed above 1% in volume. Therefore, the treatment of oily residues generated in E&P activities is an essential task.
Studies around the world presented a variety of physical, chemical, and biological methods to treat drilling waste: bioremediation, thermal, physicochemical, supercritical fluid, electrokinetic and stabilization/solidification treatment. All these methods showed promising results while presenting a series of advantages and limitations. It is also important to note that most treatment methods can recover and/or recycle oil, the main contaminant of the wastes generated. In choosing the best method, some relevant factors need to be considered, such as the drilling waste’s characteristics and the costs to implement the process on a large scale. It was observed that only bioremediation and stabilization/solidification proved to be easy to apply on a large scale. However, the bioremediation treatment process is of long duration, and high biodegradation efficiency is difficult to be achieved in uncontrolled environments. In the stabilization/solidification treatment, in turn, encapsulating all contaminants from the waste is difficult. Therefore, the development of new physicochemical methods for the large-scale treatment of drilling waste have been proposed, as the physicochemical treatment presented the highest treatment efficiency when compared with other methods, while also enabling the recovery and reuse of all separated phases.
Deepwater drilling involves complex operations and equipment, so it is faced with various operational challenges including well control accidents. This paper proposes a dynamic risk assessment model ...for evaluating the safety of deepwater drilling operations. The dynamic risk assessment process includes three key steps: constructing fault tree models to analyze risk factors leading to a blowout accident, developing dynamic Bayesian network model based on the constructed fault trees, and performing dynamic risk analysis to evaluate the safety of well control operation. The proposed model includes risk factors about kick cause, kick detection, shut-in operation and kill operation, which covers the full process of a blowout. The proposed model could analyze the risk of blowout more comprehensively and the influencing degree of these four phases could also be clarified. Besides, the modular modelling method could update the structure and parameters of the developed model easily if new factors or data are added. The results show kick cause has the greatest impact on blowout accidents, followed by shut-in operation, kill operation and kick detection. Mutual information analysis and uncertainty analysis is performed to investigate the effects of risk factors on blowout. Finally, some corresponding preventive measures for blowouts are proposed.
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