Loss Circulation Research Articles

Geomechanics impact due to in-situ and induced stresses during drilling of horizontal and highly deviated coal bed methane wells

Hydrocarbon exploration is the arduous task. Urgency of hydrocarbon and avengement of technology push operators to recover the unexplored unconventional hydrocarbon like coal bed methane (CBM) which has been discontinued. Limitations such as misunderstanding of geomechanical stress, formation behaviours- abrasiveness, mud properties etc; impaired the drilling performance and leads to well failure. Therefore, wellbore stability due to geomechanical stresses is considered as one of the major stages in well planning and required extensive study. The dominant elements of fascinating the CBM extraction are cost and the currently available technology and poor understanding of reservoir as compare to conventional reservoir. CBM wells fails due to exceeding the limit of tensile and shear strength which includes wellbore collapse, pipe sticking, caving, loss circulation and leads to ruin the operator’s money and time. The stress regimes in induced, in-situ stresses are natural and cannot be change; however study of these stresses and implementation of findings are essential to implement while planning the well and monitoring stresses behaviour during drilling of highly deviate or horizontal wells are key element to successfully develop the coal bed methane reservoir. Effect of geomechanical stresses are experienced while drilling horizontal and highly deviated wells. By considering the effects of in-situ and induced stresses; suitable operational window can be design to reduce the CBM wellbore failure. The present work analyse the geomechanical in-situ and induced stresses which are contributing towards instability of wellbore along with matrix shrinkage effect, outcome of this study can be utilized for the efficient planning of failure-free wellbore operating envelopes for CBM wells.

Modelling of cohesive expandable LCMs for fractures with large apertures

The problem of loss circulation in geothermal wells is inherently challenging due to high temperatures, brittle rocks, and presence of abundant fractures. Because of the inherent challenges in geothermal environments, there are limitations in selecting proper lost circulation materials (LCMs). Traditional LCMs such as calcium carbonates that are commonly used in the oil and gas drilling may be softened and prone to failure during geothermal drilling. Moreover, evaluating the performance of different LCMs for geothermal drilling requires unique testing setups, which is expensive, and complicated to run due to harsh environmental conditions of geothermal systems. Herein, we present a numerical approach to simulate LCM transport and bridging through fractures in downhole conditions. By discrete element methods, each individual particle trajectory, and their interactions with the fluid and surrounding particles are incorporated into the analysis. To validate the model, we used experimental results acquired from a high-temperature flow loop system built specifically for this purpose. We took a further step in this work and considered LCM particles that are made from a shape memory polymer (SMP). These particles start expanding and adhering to each other in downhole conditions. The use of SMP is shown to be advantageous in sealing large fractures (3 mm aperture). We demonstrated how numerical modelling may supplement laboratory tests to show initiation of the bridging process, fracture plugging or even its failure. Using the proposed methodology may significantly reduce the number of experiments needed to find an effective LCM recipe, hence drillers can save time and costs by assessing different LCM systems numerically.

Subpolar Atlantic Ocean mixed layer heat content variability is increasingly driven by an active ocean

Cold conditions in the upper layer of the subpolar North Atlantic Ocean, at a time of pervasive warming elsewhere, have provoked significant debate. Uncertainty arises both from potential causes (surface heat loss and ocean circulation changes) and characteristic timescales (interannual to multidecadal). Resolution of these uncertainties is important as cold conditions have been linked to recent European weather extremes and a decline in the Atlantic overturning circulation. Using observations, supported by high resolution climate model analysis, we show that a surprisingly active ocean regularly generates both cold and warm interannual anomalies in addition to those generated by surface heat exchange. Furthermore, we identify distinct sea surface temperature patterns that characterise whether the ocean or atmosphere has the strongest influence in a particular year. Applying these new insights to observations, we find an increasing role for the ocean in setting North Atlantic mixed layer heat content variability since 1960.

Characterizing shallow subsurface using 3D seismic while drilling with a downhole pilot

Seismic while drilling (SWD) can provide high-resolution subsurface information and characterize near-surface geology. We present a case study of SWD analysis using a data set from a desert environment acquired over a complex overburden. The data were acquired with a system composed of wireless surface geophones as well as top-drive and downhole sensors. The drill-bit noise data were reprocessed using a specialized workflow with two essential elements. First, a downhole pilot from a near-bit sensor was used for deconvolution, which led to improved data quality, particularly in the shallow subsurface. Second, nonlinear beamforming leveraged the 3D carpet of geophones to enhance signal quality and enable picking 3D traveltimes. A simple workflow for building a 1D velocity model used 3D traveltimes from an offset of 180 to 500 m. We vertically projected and averaged all 3D traveltimes to obtain a robust checkshot profile for the section from 190 to 1855 m. For the shallow subsurface (0–800 m), we further applied an advanced workflow with 3D traveltime inversion that more accurately handled mid- and far-offset data using a ray-tracing engine. More than 100,000 offset traveltime picks were inverted for a 1D velocity model. The model closely ties with the geology of the near surface, namely the formation tops associated with major impedance and lithologic contrasts. Amplitude signatures of 3D SWD gathers also correlate with the velocity model and lithologic changes, showing weak energy associated with soft formations and higher-energy first-arrival waveforms associated with compacted formations. Finally, we used the data extracted from a 2D line to reconstruct a migrated image of the back-propagated drill-bit sources. Joint use of kinematic and dynamic signatures helps characterize markers associated with loss circulation zones and target layers.

Dynamically Evaluating the Performance of Naturally Occurring Additives to Control Lost Circulation: On the Effect of Lost Circulation Material Type, Particle-Size Distribution, and Fracture Width

Summary Lost circulation is one of the most challenging problems during drilling of oil and gas wells. This issue leads to significant loss of drilling fluid, increase of nonproductive time as well as dictating additional costs to drilling companies. Lost circulation may also lead to other consequences, including stuck pipe, poor hole cleaning, and well control issues. How to efficiently control lost circulation have been traditionally depending on the type of the used lost circulation material (LCM). Injection of commonly available materials (without any further process on their chemical properties) into the thief zone is a common method of lost circulation control. These nonmodified materials are named as conventional LCMs against the unconventional LCMs which are designed/produced just for fluid lost control. The objective of this paper is to comparatively investigate the performance of cane, oak shell, wheat, and mica as LCM of water-based drilling fluid exposed to fractured formations. These materials were chosen because of their low cost, easy access, and compatibility with the environment. The sealing efficiency of these materials was assessed at different particle-size distributions (PSDs) for proper treatment of loss circulation. To do so, an experimental setup containing a cell with adjustable fracture size was designed. Among the LCM formulations made of each of the materials, oak shell formulations are better than the others, followed by mica and cane blends, respectively. The results reveal that combining the materials together is a better treatment than the separate use of them. As it will be seen in detail later, high diversity in particle size (broad PSD) causes more efficient control of fluid loss. Also, to reduce the dependency of sealing ability of LCM formulation on fracture size, mixing of the materials with different particle sizes and shapes is recommended.

Characterizing Permeability from Geological and Geochemical Data in the Olkaria Domes Field in Kenya

Olkaria geothermal field is located in the Kenyan Rift Valley that is a part of the Great East Africa Rift System (EARS). The geothermal field continues to be associated with a high geothermal gradient that arises from shallow magmatic activities which are ongoing in the enormous igneous province. Exploration and drilling of wells that were undertaken in the past revealed the existence of exploitable geothermal steam. The Olkaria field is divided into seven sections namely; Olkaria East field, Olkaria North East field, Olkaria North West field, Olkaria South East field, Olkaria South West field, Olkaria Central field, and Olkaria Domes field. The productivity of the geothermal wells continues to be influenced by factors such as subsurface permeability. Permeability is one of the parameters used for the characterization of geothermal fields. Other parameters used for characterization are associated with geotechnical weak zones and include features such as; fractures, vein bodies, and deformational fault systems. The research work involved geoscientific characteristics of the Olkaria Domes field based on the geological and geochemical factors to characterize the permeability of the field. The research involved studying rock types in the area by analysing drill cuttings obtained from six drilled wells in the Olkaria Domes field. Three of the six drill wells were considered for correlative description for the purpose of this paper. Correlation of the main lithologies and zones for loss of circulation in the field was also undertaken as well as the creation of mineralogical maps to capture the distribution of the minerals that were derived from hydrothermal weathering processes. The depths and formation for major loss circulation zones in the reservoir section of the field were identified and included in the description. Analysis of soil gas survey using radon as a geochemical tool in the Domes field was also carried out successfully. The relatively high levels of the soil gas ratios that were analysed captured the ratio distribution of carbon dioxide to radon at various reservoir depths. The detection of the two gases at the surface showed the existence of permeable zones which facilitated the movement of the gases through the fault-controlled structural systems of the studied Olkaria Domes field.

Lost circulation mitigation using modified enzyme induced calcite precipitation technique

Circulation loss is a very common and undesirable non-productive time (NPT) event that happens during the oil and gas well drilling operations. Many loss circulation materials (LCM) have been formulated and implemented in the process of gas and oil wells drilling to minimize or mitigate this problem. In-situ calcite precipitation in effective pores can restrict the movement of the water flow between the grains by forming bridges. In this study, different mixes of Enzyme-induced calcite precipitation (EICP) solution are studied and tested in the laboratory to mitigate lost circulation problem. EICP solution is primarily composed of urea, calcium chloride, magnesium chloride, Xanthan Gum, and urease enzyme. Different concentrations and compositions of reagents were tested. The properties of the created precipitates were examined through different techniques such as X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The combination that produced the highest amount of thermally stable calcite with a minimal amount of aragonite, along with the highest precipitation efficiency was further selected for lost circulation application. A solution containing 1M Urea, 0.9M CaCl 2 , 0.1M MgCl 2 , 1 g/L Xanthan Gum, and 3 g/L urease was considered as an optimum combination for an EICP process. Lost circulation experiments were carried out in core flooding experiments on a high permeable Indian Limestone sample at room and elevated temperature conditions with the optimum combination of EICP reagents. The permeability of the samples was measured before and after the treatment. Nuclear Magnetic Resonance (NMR) scan was also run before and after the treatment to determine the pore size redistribution. Results showed that the permeability of the samples was reduced by 99%, NMR results showed that the porosity of the samples was also reduced by 20%. • Investigation of the modified enzyme induced calcite precipitation as a lost circulation technique. • Investigation of incorporating magnesium in an EICP process to precipitate dolomite mineral. • Investigation of incorporating Xanthan Gum as a temperature stabilizer for an EICP reaction. • Coreflooding and NMR experiments with optimized EICP solution as a potential lost circulation material. • 99% reduction in permeability achieved with modified EICP process.

Development of cost-effective drilling fluid from banana peel pectin and fly ash for loss circulation control

The global demand for energy has increased the petroleum operations mutlifolds and the challenges associated with it. The loss circulation is often problematic and cost intensive. The Banana Peel Pectin (BPP) and Fly Ash (FA) provides an efficient control to loss circulation. The rheological properties viz, Plastic viscosity, gel strength suggest the increases in viscosity and gelation with increase in %BPP. The SEM analysis was performed to asses the meshing and bridging performance of BPP and FA. Theconsistencyof drilling fluid confirms its pumpability for a 4.5 h. The present work provides an efficient control of mud filtrate loss at extremely low cost.

3D numerical modeling of the effect of the drill string vibration cyclic loads on the wellbore natural fracture growth

The maintenance of wellbore stability remains one of the major sources of Non-Productive Time in the oil industry. During drilling process, the drill string vibration cyclic loads which are applied on the wellbore progressively affect the initial parameters of the fractured formation (such as its length and width), finally resulting into wellbore instability. In this research, a three-dimensional poro elasto plastic finite element model was built using a non-linear finite element software ABAQUS purposely to investigate the effect of drill string vibration cyclic loads on the wellbore natural fracture growth. The main conclusions exhibited that the dependency of the fracture width profiles with the time followed an oscillating comportment analogous to the vibration cyclic loads profiles. For distinct cyclic load magnitudes and constant number of cyclic loads, the biggest percentage augmentation of the fracture width after integration of cyclic loads was 64.77%. Interestingly, the aperture of the fracture increased with the length of the fracture in the region neighboring the wellbore while it globally declined when going farther aside the wellbore. But for constant magnitude of cyclic load and distinct cyclic loads number, the highest rate of fracture aperture augmentation after incorporation of cyclic loads was moderately smaller representing 63.12% while the sinusoidal period of the fracture aperture grew with the number of cyclic loads number. The alternate studies demonstrated that the vibration cyclic loads were approximately unrelated to the fracture length development and the bottom hole pressure evolution. However, the fracture aperture and the loss circulation rate were significantly influenced by the vibration and the biggest percentage augmentation of the loss circulation rate after implementation of cyclic loads was 14.3%. This study broadens the understanding of the coupling between the drill string vibration cyclic loads and the wellbore natural fracture rock development which is a thematic that has been seldom examined in the literature.

Application of Spectral Decomposition Technique to Delineate the Evolution of Karst on Carbonate Platforms of Central Luconia, Offshore Sarawak, Malaysia

Karstification in carbonate platforms of the Miocene age in Central Luconia province, offshore Sarawak, Malaysia, has been discussed since the onset of exploration and initial discoveries in the region, with over 200 mapped platforms to date. An extensive drilling program over the last decade confirmed the existence of karst during the drilling process where issues such as total loss circulation and bit drops were common. Karst in Central Luconia has been proposed by several authors; however, detailed quantitative description of the observed features have not yet been conducted. This study involves systematic mapping of loss circulation depths, chalkified/rubble/vuggy zones described from cores, and vugs of >2 mm in size and moldic porosity observed on thin sections of the Jintan platform. These data supplement the interpretation of karst from multiple 3D seismic attributes. Seismic interpretation of the Jintan and M1 platforms revealed an extensive dendritic pattern which is on average 70–100 m deep and 3–5 km long, and circular geobodies of 1 km in width that exist on the upper part of the platform. Spectral decomposition, also known as time-frequency analysis, was used to enhance the interpretation of karst features on seismics within a specific wavelength. In this study, a comparison of three spectral decomposition methods applied on the 3D seismic cube of the Jintan and M1 platforms was undertaken to determine the method which allowed for better delineation of the karst features. The results show that the short-time Fourier transform (STFT) method using frequencies of 46, 54, and 60 Hz delineated most of the karst features compared to the continuous wavelet transform (CWT) Morlet and CWT Ricker wavelet methods. This paper aims to discuss the dimensions, evolution and geometry of the karst features quantitatively on three selected karst horizons named “K1”, “K2”, “K3”. Interpretation revealed that the dendritic karst features were found to be most prominent on the K2 horizon which lies below a conspicuous change of the external geomorphology of the platform. Backstepping of the platform margin by 12 km is observed in both platforms. Quantitative seismic interpretation shows that the karst observed in M1 platform is approximately 70–100 m deep, and the dendritic features are around 1–2 km in length and approximately 500 m wide; whereas, in the Jintan platform the dendritic features observed are up to 5 km in length with several 1 km wide circular/sinkhole features. More than 20 dendritic features orientated SE and NS were mapped mainly in the transitional area as well as the center of both platforms. The nature of the karst morphology in Central Luconia remains controversial; however, it is proposed to be of mixing zone karst origin.

Development and field application of downhole crosslinking plugging agent

There were mainly cement slurry, bridge plugging and polymer gel plugging materials for fracture loss circulation and fractured/caved loss circulation. The downhole crosslinking plugging agent was researched for the plugging agents’ respective limitations leaded to low success rate of plugging and longer construction period. This kind of plug agent is consistent with emulsion, phase inversion agent and crosslinking agent. It could form a high strength elastomer when the plug agent is pumped into the leaking layer and mixed with a certain amount of water. The elastomer with strong ability could offer good resident ability to reduce cement slurry thickening by underground water and plugging mud, and increased the ratio of success. The experimental results showed that crosslinking time wasn’t affected by temperature, salt water, drilling cuttings, bentonite mud and other pollutants. The plug agent has been successfully used in several wells of the sixth block in Sudan.

Evaluating sealability of blended smart polymer and fiber additive for geothermal drilling with the effect of fracture opening size

Geothermal formations often contain extensive fracture networks. These fracture networks contribute to the significant loss of drilling fluids during geothermal drilling. Multiple loss circulation materials (LCM) such as fiber, granules, and pills have been proposed to tackle this problem but with only limited success. Recent advances in materials science have led to the development of thermoset shape memory polymers (SMP) to address the lost circulation problem. In this paper, we evaluate a thermoset SMP performance in sealing near wellbore fractures of different sizes in geothermal wells. The SMP performance was assessed using granite disks and cylindrical granite cores having fracture sizes of 1000 μm and 3000 μm. A static filtration test was performed using cedar fiber, CaCO3, and SMP. Results showed cedar fiber performed better than the CaCO3., reducing fluid loss by 89% and improving sealing pressure by 200 psi. A novel dynamic testing unit that allows for high-temperature testing under flowing conditions was used in this study. The analysis showed that 3% by weight SMP and fiber blends could bridge and plug the 1000 μm fracture. For a larger fracture of 3000 μm width, there was a need to increase the weight concentration of the SMP to 6% to plug the fracture opening effectively. We showed the influence of key parameters such as the type of LCM, concentration, and particle size distribution in optimizing the performance of drilling fluid loss treatment.

Characterizing Permeability from Geological and Geochemical Data in the Olkaria Domes Field in Kenya.

Olkaria geothermal field is located in the Kenyan Rift Valley that is a part of the Great East Africa Rift System (EARS). The geothermal field continues to be associated with a high geothermal gradient that arises from shallow magmatic activities which are ongoing in the enormous igneous province. Exploration and drilling of wells that were undertaken in the past revealed the existence of exploitable geothermal steam. The Olkaria field is divided into seven sections namely; Olkaria East field, Olkaria North East field, Olkaria North West field, Olkaria South East field, Olkaria South West field, Olkaria Central field, and Olkaria Domes field. The productivity of the geothermal wells continues to be influenced by factors such as subsurface permeability. Permeability is one of the parameters used for the characterization of geothermal fields. Other parameters used for characterization are associated with geotechnical weak zones and include features such as; fractures, vein bodies, and deformational fault systems. The research work involved geoscientific characteristics of the Olkaria Domes field based on the geological and geochemical factors to characterize the permeability of the field. The research involved studying rock types in the area by analysing drill cuttings obtained from six drilled wells in the Olkaria Domes field. Three of the six drill wells were considered for correlative description for the purpose of this paper. Correlation of the main lithologies and zones for loss of circulation in the field was also undertaken as well as the creation of mineralogical maps to capture the distribution of the minerals that were derived from hydrothermal weathering processes. The depths and formation for major loss circulation zones in the reservoir section of the field were identified and included in the description. Analysis of soil gas survey using radon as a geochemical tool in the Domes field was also carried out successfully. The relatively high levels of the soil gas ratios that were analysed captured the ratio distribution of carbon dioxide to radon at various reservoir depths. The detection of the two gases at the surface showed the existence of permeable zones which facilitated the movement of the gases through the fault-controlled structural systems of the studied Olkaria Domes field.

Overpressure’s top and generating mechanism in “APR” block, North Sumatra offshore area

The offshore North Sumatra Basin is one of the hydrocarbon-prone basins in Indonesia. The Malacca Formation acts as the reservoir in this basin. However, there are some drilling problems caused by abnormal pore pressures. Overpressure analysis is carried out so that drilling activities are avoided from drilling problems such as kicks, blowouts, stuck pipes, loss circulation, and collapse. This study aims to analyze the overpressure in the “APR” block, offshore North Sumatra Basin, which includes determine the depth of the top overpressure and the mechanism of overpressure formation. In the research area, analysis of 3 exploration wells was carried out. Overpressure is analyzed based on well log data, and pressure test data using the Eaton method (1975) supported by other data such as LOT (Leak-Off Test) data, drilling reports, mudlogs. At Well A, top overpressure depth is ± 3235 ft TVDSS (true vertical depth sub sea). At Well P, top overpressure depth is ± 3065 ft TVDSS, and at Well R, top overpressure depth is ± 2901 ft TVDML (true vertical depth mud line). The overpressure generating mechanism in the study area is caused by the loading mechanism (disequilibrium compaction) and caused by the nonloading mechanism (hydrocarbon buoyancy).

Research on an Lost Circulation Zone Location Method Based on Transient Pressure Wave.

Accurately identifying the location of loss zone after lost circulation is the key to subsequent plugging operation. In view of the difficulty of identifying the location of lost circulation zone, a method of identifying the location of loss zone by transient pressure wave signal is proposed. When lost circulation occurs, transient back pressure is applied to the wellhead at the surface choke manifold to produce transient pressure wave. The transient pressure wave propagates downward from the wellhead. The propagation process of transient pressure wave in an annulus system is analyzed, and the position of loss zone is determined according to the change of pressure signal at the choke manifold. Based on the simulation of this method, relevant experiments are also carried out. Aiming at the problem of excessive noise of the pressure wave signal collected in the experiment, variational modal decomposition (VMD) is used to decompose the signal into multiple band-limited intrinsic mode function (BIMF) components. Combined with a Hilbert spectrum, the time–frequency characteristics and energy distribution of each BIMF component are analyzed in turn. The main frequency component is selected to reconstruct the signal to achieve the denoising effect. On this basis, a wavelet modulus maxima method is used to decompose the denoised signal, extract the characteristic points of the signal, identify the loss circulation information in the signal, and then identify the thief zone position by a time–domain method. Through experimental verification, the existence of loss zone will affect the change trend of pressure wave; a VMD–wavelet modulus maxima algorithm can effectively remove the noise of the pressure wave signal and locate the pressure change point. The experimental recognition error range of this method is 0.10–9.22%, which has certain guiding significance for field application.

The application of deep learning algorithms to classify subsurface drilling lost circulation severity in large oil field datasets

In this paper, we present how precise deep learning algorithms can distinguish loss circulation severities in oil drilling operations. Lost circulation is one of the costliest downhole problem encountered during oil and gas well construction. Applying artificial intelligence can help drilling teams to be forewarned of pending lost circulation events and thereby mitigate their consequences. Data-driven methods are traditionally employed for fluid loss complexity quantification but are not able to achieve reliable predictions for field cases with large quantities of data. This paper attempts to investigate the performance of deep learning (DL) approach in classification the types of fluid loss from a very large field dataset. Three DL classification models are evaluated: Convolutional Neural Network (CNN), Gated Recurrent Unit (GRU) and Long-Short Term Memory (LSTM). Five fluid-loss classes are considered: No Loss, Seepage, Partial, Severe, and Complete Loss. 20 wells drilled into the giant Azadegan oil field (Iran) provide 65,376 data records are used to predict the fluid loss classes. The results obtained, based on multiple statistical performance measures, identify the CNN model as achieving superior performance (98% accuracy) compared to the LSTM and GRU models (94% accuracy). Confusion matrices provide further insight to the prediction accuracies achieved. The three DL models evaluated were all able to classify different types of lost circulation events with reasonable prediction accuracy. Future work is required to evaluate the performance of the DL approach proposed with additional large datasets. The proposed method helps drilling teams deal with lost circulation events efficiently.Article HighlightsThree deep learning models classify fluid loss severity in an oil field carbonate reservoir.Deep learning algorithms advance machine learning a large resource dataset with 65,376 data records.Convolution neural network outperformed other deep learning methods.

Application of Empty Oil Palm Bunches as CMC to Prevent Loss Circulation

Drilling is an activity carried out to obtain the desired target. Furthermore, drilling mud a very significant material involved in the drilling process, and must, therefore, obtain a rational value from the rheology. A suitable technique to achieve this goal is the use of additives, for instance, Carboxymethyl Cellulose (CMC) to improve the viscosity and air binding. This study, therefore, uses CMC produced from organic oil palm bunches as an alternative for industrial CMC. CMC of Oil Palm Empty Bunches have been tested by Energy Dispersive X-ray Spectroscopy (EDS) to determine its composition. The Empty Oil Palm Oil which uses Tenera type was taken from Riau Province, Rokan Hulu Regency, Kunto Darussalam District. In this study, this experiment used CMC Empty Oil Palm and industrial CMC to find the value of viscosity, plastic thickness, melting point, gel strength, mud cake, and filtering volume of drilling mud and prevent the loss circulation with adding each CMC composition to mud samples with amount of 2 gr, 4 gr, 6 gr, 8 gr and 10 gr. According to the EDS analysis, the Carbon (C) and Oxygen (O) content of CMC from empty oil palm bunches were 58.85% and 41.15%, respectively. In addition, the industrial standard for plastic viscosity and yield point were not attained by using 8 gr and 10 gr of this CMC.

Detection of Loss Zones While Drilling Using Different Machine Learning Techniques

Abstract Fluid loss into formations is a common operational issue that is frequently encountered when drilling across naturally or induced fractured formations. This could pose significant operational risks, such as well-control, stuck pipe, and wellbore instability, which, in turn, lead to an increase of well time and cost. This research aims to use and evaluate different machine learning (ML) techniques, namely, support vector machines (SVMs), random forests, and K-nearest neighbors (K-NN) in detecting loss circulation occurrences while drilling using solely drilling surface parameters. Actual field data of seven wells, which had suffered partial or severe loss circulation, were used to build predictive models, while Well-8 was used to compare the performance of the developed models. Different performance metrics were used to evaluate the performance of the developed models. Recall, precision, and F1-score measures were used to evaluate the ability of the developed model to detect loss circulation occurrences. The results showed the K-nearest neighbors classifier achieved a high F1-score of 0.912 in detecting loss circulation occurrence in the testing set, while the random forests was the second-best classifier with almost the same F1-score of 0.910. The support vector machines achieved an F1-score of 0.83 in predicting the loss circulation occurrence in the testing set. The K-nearest neighbors outperformed other models in detecting the loss circulation occurrences in Well-8 with an F1-score of 0.80. The main contribution of this research as compared with previous studies is that it identifies losses events based on real-time measurements of the active pit volume (APV).

Technical research on realizing remote intelligent diagnosis of petroleum drilling loss circulation under smart city strategy

In recent years, smart energy has become an important part of smart city construction. For the oil industry, exploring how to apply enabling technologies such as data transmission, internet of things, big data analysis in the energy field can fill the gap of applying intelligent technologies to energy facilities system. For the petroleum field, one of the biggest threats to safe drilling operations during oil and gas exploration is loss circulation. In the study, based on a new assessment framework that integrates intelligent energy into smart cities, an improved fuzzy evaluation method of drilling risk based on cloud method is proposed to realize the transformation of drilling risk from quantitative to qualitative. The theory proposed in this paper considers the subjective engineering experience of experts and the information contained in objective data, which make the judgment results more objective. The cloud theory proposed can clearly show the result of risk assessment, which fully reflects the fuzziness and randomness of the drilling system. The model is embedded in the evaluation framework of smart cities, which realizes the online remote online assessment of risks by city office workers.

\u2018Level-off\u2019 cement plugging method to cure lost circulation verified with case studies

Controlling lost circulation during drilling operations in a reservoir prone to fluid losses is typically remedied by cement squeezing or plug setting as the last resort. The aim being to minimize or stop drilling fluid losses and to regain full returns at surface, and to maintain wellbore integrity. Different placement methods of cement plugs have been discussed in detail in the literature, except for the ‘level-off’ method, which can be effective for curing complete loss circulation cases. Following modeling and calculations of this cement plug placement method, its design and execution procedures are discussed, together with two successful field cases in highly fractured carbonate reservoirs in the Middle East. Using drill pipe and a Retrievable-Test-Treat-Squeeze (RTTS) packer, set with some spacing from the loss zone, the method entails that the cement slurry is allowed to drop by gravity in order to cure lost circulation. As the column of fluid, mud and slurry in the well exceeds formation pore pressure, i.e., overbalanced conditions, a volume of acid-soluble cement slurry is allowed to slowly drop and freely penetrate the formation, i.e., through its fractures or caverns. During the penetration of this viscous slurry into the loss zone, the cement slurry can set and the fracture or fissure openings are plugged. Presented are detailed design calculations for the level-off placement technique, determination of required cement slurry and displacement volumes, and recommended displacement and RTTS packer setting depths. The expected depth of the top of cement plug is estimated. The design parameters are compared with field cases and explanations are given for possible discrepancies. Success of the operation is discussed in terms of final mud loss after cement plugging and Non-Productive Time mitigation. Detailed field procedures and execution are also presented. The level-off job is already practiced by the industry, but it is not published in the literature, in some cases they have different methods with causing some errors. To the best of authors’ knowledge, this is the first detailed description and stepwise calculation of the level-off cement placement technique in the literature.