Loss Circulation Research Articles

Shape memory polymers as new advanced loss circulation materials for drilling applications

Shape memory polymers as new advanced loss circulation materials for drilling applications

Effect of swab and surge pressure on the time-dependent wellbore natural fracture development

Drilling engineers continue to grapple with the persistent challenge of maintaining wellbore stability. Throughout the drilling process, the wellbore pressure experiences fluctuations induced by various factors such as swab and surge pressure, leading to potential instability. This study employs a numerical approach, utilizing Abaqus software, to investigate the impact of swab and surge pressure on the natural fracture growth within the wellbore and the evolving pore pressure. A computational tool developed with MATLAB is then utilized to ascertain a safe operational mud window by assessing the time-dependent collapse and fracture pressures. The findings illustrated a notable increase in fracture width as a function of time in response to swab and surge pressure, with the most significant percentage increase reaching 69.92%. Notably, a 69.16% augmentation in fracture width is observed in the immediate vicinity of the wellbore following the application of swab and surge pressure. However, parameters such as fracture length, loss circulation rate, and pore fluid pressure exhibited marginal changes post-integration of swab and surge effects. The examination of the time-dependent wellbore stability after integration of swab and surge pressure indicated a narrowing of the initial mud window as a function of time, with a 14.33% increase in collapse pressure and a 13.80% decrease in fracture pressure. The numerical model verification against analytical solutions demonstrated good agreement, highlighting its potential utility in optimizing particle size for wellbore reinforcement and mitigating lost circulation through natural fracture sealing.

Design and experimental study on rheological behavior and sealing performance of shear sensitive fluids to control lost circulation during drilling

Loss circulation is considered as a time-consuming, costly, and challenging issue while drilling or cementing jobs, which ought to be treated and resolved promptly. The choice of a treatment that quickly plugs the loss zone and helps to restore the circulation is critical. Cross-linkable polymer gels play a significant role in mitigating drilling fluid loss, but controlling the gelation time and pumpability are the main challenges of these gels. This research aims to evaluate a novel smart fluid that has high flexibility in design. The shear sensitive fluid (SSF) is an oil-based fluid containing a polymer, gelation agents, and multi-crosslinkers. After passing through the drilling bit, the SSF is crosslinked with time to produce a high strength gel. The designed shear sensitive fluid is one of the possible solutions for severe loss circulation.The overall purpose of this research was to scrutinize the gelation behavior and SSF performance as a smart lost circulation treatment, which was followed in two sections including experimental analysis and empirical modeling. The effect of various factors including the type of crosslinker, shear rate, emulsifier concentration, temperature, shear history, salinity, etc. on the performance of the formed gels was studied. Furthermore, the maximum sealing pressure of formed gels in the highly permeable porous medium and fractured core as well as the probability of formation damage was evaluated.In order to determine the correlations required to predict the ultimate gelation time of SSF, the response surface methodology was utilized according to the central composite design. The considerable values of correlation coefficients (R2 = 0.91) prove the validity of estimated models for the fit enough responses with the experimental data. For the designed SSFs, depending on the operating conditions, the appropriate gelation time can be adjusted by emulsifier concentration and shear rate values. Also, the minimum gelation time and the highest crosslinking rate occur approximately at the shear rate of 45,000 1/s. At high shear rates, the effect of temperature on the functionality of the formed gels decreases, which is due to the high rate of crosslinking. Based on dynamic sealing pressure tests, the SSFs have a high potential in mitigation of lost circulation during drilling. The maximum sealing pressure was measured above 1000 psi in highly permeable porous medium and up to 600 psi in fractured core, which indicate the high strength of the formed gels against drilling fluid pressure. The designed SSFs could be easily removed from reservoir by 15 vol% hydrochloric acid, indicating the non-damaging properties of the formed gels.

Anomaly detection in multivariate time series of drilling data

Different clusters of abnormal activities often arise within same temporal domain of drilling operations. This contrasts with employing simplified scenarios, such as anomaly detection models for specific issues like stuck pipe or loss circulation. The dynamic nature of drilling environments demands a holistic framework that can adapt to evolving conditions and detect anomalies beyond predefined categories. There exists a need to evaluate the performance of various data-driven models and achieve a broader applicability of anomaly detection instead of focusing on a single abnormal activity type. This study presents a generalized framework designed to detect anomalous events in drilling operations. Three different unsupervised learning algorithms, principal component analysis (PCA), isolation forest (IF) and lstm-autoencoder (LSTM-AE), are used to determine abnormal patterns and irregularities in the drilling data. PCA is chosen for its interpretability and efficiency in handling high-dimensional data by reducing the dimensionality. IF is selected for its effectiveness in isolating anomalies, making it robust for scenarios where anomalies exhibit distinct patterns. LSTM-AE is employed due to its capability to capture temporal dependencies and nonlinear patterns in time series data. A multivariate time series of drilling data from an offshore well is collected to use in this work. The dataset comprises approximately six months of drilling operations, including drilling and non-drilling periods. The input variables are chosen from the common controllable parameters continuously monitored by the drilling crew. The pre-processed drilling data with input features is organized into groups based on each drilling section. These unlabeled data is split into train, validation and test sets. Cross-validation (CV) is applied into train and validation sets to prevent overfitting and tune the hyperparameters. The test data is used to evaluate the generalizability and robustness of each model. Evaluation metrics such as precision, recall, F1 score, and receiver operating characteristic (ROC) curve are used to select the best-performing model. The thresholds for anomaly identification are determined by analyzing the reconstruction errors from PCA and LSTM-AE models, as well as anomaly scores from the IF algorithm. Subsequently, evaluation metrics are calculated using these thresholds, assigning true and false predictions to each data point. These predictions are then compared with the ground truth data labels obtained from the daily reports. Experimental results show that the proposed approach can effectively predict anomalous events in drilling operations. It is observed that there is a causal link between irregularities in time series drilling data and the occurrence of anomalous events in drilling operations. Implementing the proposed approach in real-time monitoring systems may improve overall efficiency and minimize risks in drilling operations. The presented methodology can be tested with diverse drilling datasets to enhance the generalizability and reduce bias, leading to a more comprehensive and reliable assessment across various scenarios.

Complex fuzzy-probabilistic analysis of information on drilling mud losses

In recent years, classification and clustering have been widely used for processing and analyzing information for the purpose of structuring, ordering, summarizing, and sorting. Classification and clustering are used when working with information processes both in enterprises (large and medium-sized) and in various fields of scientific activity, which is especially important in the context of the constant growth of processed information. At the same time, during cluster analysis, an important task is to assess its quality. In this work, cluster analysis was used to identify loss circulation zones when drilling wells and classify them by severity (intensity). To determine the quality of the cluster analysis, the entropy value was calculated, which should tend to a minimum. In our case, it was 0.23, which allows us to judge the fairly high quality of the cluster solution.

A new detection method of co-existence of well kick and loss circulation based on thermal behavior of wellbore-formation coupled system

Accurately obtaining wellbore-formation temperature distribution during drilling in fractured carbonate formations is the basis for effectively solving the problem of the well kick and loss circulation coexisting (WK-LC). Therefore, based on the energy conservation law and considering the convective heat transfer and variable mass flow caused by well kick and loss circulation, this paper developed a full transient heat transfer model of wellbore-formation coupled system under the WK-LC. The reliability of model was verified by field measured temperature data. Based on field well, the thermal behavior of wellbore-formation coupled system under normal condition, well kick, loss circulation and WK-LC were compared and studied.The results showed that the bottom-hole temperature of well kick and Case1-2 is higher than that of normal condition, while the bottom-hole temperature of loss circulation and Case3-4 is lower than that of normal condition. The temperature difference between annulus and drill string (TD-AD) shows a “wavy line” trend of increasing-decreasing-increasing-decreasing along the well depth. The TD-AD of wellhead is about 6 °C in normal and WK-LC conditions. The traditional wellhead temperature monitoring method can only distinguish well kick and leakage, and it is difficult to judge whether WK-LC occur.In addition, the influence of the distance and well kick/leakage rate difference between the well kick region and the leakage region on thermal behavior of wellbore-formation coupled system was discussed. Finally, a new auxiliary method is proposed to identify the well kick, the loss circulation and the WK-LC. Which will have a significant implication for well killing and leaking stoppage operations.

Magnesium Oxychloride and Magnesium Oxysulfate Cements as Temporary Plugging Agents in Geothermal Drilling.

The development and utilization of geothermal resources are effective ways to alleviate the current haze situation, adjust the energy structure, and achieve energy conservation and emission reduction. Geothermal formations typically contain extensive fracture networks, with fracture openings. These fracture networks can result in substantial losses of the drilling fluid and increased costs for geothermal drilling. Temporary plugging cements are used to solve the problem of lost circulation due to their high strength and high acid solubility. In this paper, two types of temporary plugging materials, magnesium oxysulfate (MOS) cement and magnesium oxychloride (MOC) cement, were prepared. The influence of the plugging agent on the flow field and the force exerted on the solid under the action of the fluid was analyzed using fluid-solid coupling software. The simulation results show that when subjected to a flow rate of 10 m/s, the edge of the cement experiences a significant force, while the stress is not widely transmitted to the middle and rear of the cement. This indicates that the cement has a strong resistance to the fluid flow. The fundamental characteristics of MOC cement and MOS cement, such as compressive strength and setting time, were investigated. The test results show that adjusting the molar ratio of the two types of cements can shorten the setting time by 60% and increase the compressive strength to up to 23 MPa. In addition, the acid solubility of the cement with different ratios of raw materials is above 95%. The plugging performance of these two cements as loss circulation materials was evaluated by using a physical simulation device. The pressure bearing capacity of the MOC cement with different MgO/MgCl2·6H2O/H2O molar ratios ranged between 13.4 and 23.6 MPa. The maximum bearing capacity of the MOS cement can reach up to 18.6 MPa. The results showed that both cements possess excellent plugging and pressure bearing capacity.

Investigating the suitability of North Dakota fly ash as fluid loss reducing additive in densified water-based drilling fluid

Fluid loss circulation control during drilling operations is becoming more challenging as exploration moves from conventional to unconventional energy resources. The process of controlling filtrate loss during drilling operation necessitates the right design of drilling fluid that is capable to build an impermeable thin filter cake layer and permit a loss of a reasonable amount of filtrate volume into the formation. It is essential to understand the dynamics that play out between particle morphology of drilling mud additives to assess the sealing efficiency of the loss-reducing additives. As a result, a lot of materials were suggested as fluid loss-reducing materials, which also give thin filter cake thickness. This study investigates the suitability of a coal-fired plant waste (fly ash), as an alternative supplement for filtration agents to improve the quality of the filter cake layer that is built using ilmenite (FeTiO3) derived densified drilling fluid. The ilmenite-derived densified water-based mud samples containing 0, 1, 2, and 3 lb./bbl of fly ash were investigated. To gain an understanding of the pozzolanic influence of class C fly ash on ilmenite-weighted water-based mud, tests were conducted at reservoir conditions according to API specifications. The results from drilling fluid tests were benchmarked against the API standard range of values and contrasted with a control drilling fluid with no-fly ash added. It has been found that mud samples that include fly ash have better filtration properties. The openings in the filter cake were sealed by the amorphous structured fly ash particles, which created an impermeable filter cake. In Mud-4 and Mud-5, where the filtrate volume was reduced by 75% and 79%, respectively, the influence of particle size distribution to form a good sealant and a further reduction in filtrate loss was observed.

The Development and Evaluation of Novel Self-Degrading Loss-Circulation Material for Ultra-Deepwater Drilling in South China Sea

Focusing on the problem of drilling fluid loss circulation due to fractured granite formation in ultra-deepwater drilling in the research area, a novel self-degrading loss-circulation material is developed with polymer resin as the core material, according to the principles of loss-circulation prevention and reservoir and environmental protection. The relevant properties of the novel self-degrading loss-circulation material are evaluated by using tests or experiments. The pressure-bearing properties are evaluated by using a sealing capability test; the self-degrading properties are evaluated by using a self-degrading performance test; the pressure-bearing capability and reservoir protection properties are tested by measuring pressure sealing and gas permeability. The results of the tests and experiments show that the grinding rate of the loss-circulation material is less than 6% under 25 MPa, indicating that the novel loss-circulation material is of high compressive strength. The degradation process of the novel self-degrading loss-circulation material can be accelerated by increasing temperature and pH, and the degradation of the self-degradable polymer composite can be accomplished within 5 days under 95 °C and pH = 14. After self-degrading, the permeability recovery values of the highly permeable reservoir and the fractured reservoir are more than 96.9% and 99.15%, respectively, which indicates outstanding reservoir protection capability. Therefore, the novel self-degrading loss-circulation material has excellent temporary plugging and reservoir protection performance and can be used for plugging while drilling in ultra-deepwater drilling.

Recent Advances and Challenges of the Application of Artificial Intelligence to Predict Wellbore Instabilities during Drilling Operations

Summary Artificial intelligence (AI) is revolutionizing several businesses across the world, and its implementation in drilling engineering has enhanced the performance of oil and gas companies. This paper reviews and analyzes the successful application of AI techniques to predict wellbore instabilities during drilling operations. First, a summary of the implementation of AI for the prediction of loss circulation, pipe stuck, and mud window is highlighted. Then, the recent innovations and challenges of the AI adoption in major drilling companies is presented. Finally, recommendations are provided to improve the integration of AI in the drilling industry. This analysis gives deep insight into the main publications and recent advances of the application of AI in drilling engineering and is expected to contribute to the further development of the drilling industry.

Experimental investigation of magnetized-Cocos nucifera husk supported Citrullus lanatus peel microparticles as loss circulation agent in water-based drilling fluids

Lost circulation agents (LCAs) are usually added to drilling fluids (DFs) for fluid loss control into formation. This improves their filtration and rheological properties that are advantageous for well drilling operation. This study conducted experimental investigation of Cocos nucifera husk (CNH) and Citrullus lanatus peel (CLP) as fluid loss additive in water-based drilling fluids (WB-DFs). The effect of magnetizing 50 and 100 μm CNH and CLP microparticles (MPs) on the effectiveness of WB-DFs was investigated. Prototype core samples of uniform dimension were prepared from unconsolidated sandstone. The rheological, filtration, and petrophysical properties of samples were evaluated. Scanning electron microscope (SEM) and Fourier transform infrared spectrophotometer (FTIR) were used to characterize drilling fluid samples. Plastic viscosity (PV), gel strength (GS), yield point (YP), mud cake thickness (MCT), and mud density (MD) of magnetized CNH supported CLP microparticles in WB-DF (mMp-CNH-CLP-WB-DF) increased by 44.44%, 14.29%, 60.71%, 16.08%, and 26.64%, respectively, when the weight was increased from 5 g to 20 g. The filtrate volume (FV) reduced by 56.38% when the weight of CNH and CLP was increased from 5 g to 20 g. The drilling fluid was less alkaline at this condition. The formation damage (FD) percentage of mMp-CNH-CLP-WB-DF decreased from 12.57% to 7.31% at 100 psi and 100 µm particle size. SEM and FTIR showed smooth particle arrangement and presence of active functional groups. In conclusion, presence of mMp-CNH-CLP-WB-DF in WB-DF improved its suitability for use in drilling operation.

Analysis of Fluid Flow Pathways in the Mount Meager Volcanic Complex, Southwestern Canada, Utilizing AMT and Petrophysical Data

AbstractDefining the spatial distribution of geological structures and rock properties is important for understanding how fluid flow is controlled in a geothermal reservoir. Here, we present a procedure to examine the potential fluid pathways. By combining 3‐D resistivity models derived from audio‐magnetotelluric (AMT) data with available rock properties (porosity and permeability) and fluid sample data (fluid resistivity, salinity, and temperature), we investigated the relationship between electrical resistivity and fluid flow in an active volcanic system. Different petrophysical models and empirical relations are evaluated to determine the relationship between the fluid flow system at Mount Meager, British Columbia, and the resistivity model. In addition, we utilized porosity and permeability measured in the laboratory to define the porosity‐permeability relationship. The porosity of the volcanic core samples showed a range of 2.6%–23.2% and the permeability was in a range of 0.001–5,186.57 mD. The results showed the potential of 3‐D inversion of AMT data to map the fluid pathways at Mount Meager. These pathways are correlated with loss circulation zones in boreholes and can account for porosity up to 8.5%, which using the porosity‐permeability relationship translates to permeability of the order 0.249 mD. Not only are the fault and fracture zones important for reservoir exploitation, but they also provide permeability for the circulation of meteoric water. Our studies suggest that a set of fractures with 0.1 m spacing and 20 mm aperture can keep 40% fluid in pores and transmit fluid with possible permeability of 666 mD.

Performance of Perlite as viscosifier in manganese tetroxide water based-drilling fluid

The rheological properties of drilling fluids are considered critical criteria in mud design and selection. Rheological parameters greatly impact various drilling fluid functions, including the ultimate workover, carrying capacity, cuttings transportation, minimizing the loss circulation, etc. Therefore, different additives were used to control the rheological properties and improve the other drilling fluid parameters such as filtration and filter cake properties. In this work, amorphous glass rock known as Perlite was examined as an additive for manganese tetroxide water based-drilling fluids. Two dosages of manganese tetroxide were prepared namely 250 and 350 lb/bbl. The rheological properties were evaluated and implemented to assess the fluid behavior using four different models including Bingham plastic, power-law, Herschel-Bulkley and Robertson-Stiff models. In addition, the impact of Perlite on the manganese tetroxide drilling mud at varied densities were investigated in term of pH value and the sagging tendency. The obtained results showed that as function of adding the Perlite, the plastic viscosity was reduced while the yield point increased. The three parameters’ models including Herschel-Bulkley and Robertson-Stiff models were the best in describing the drilling fluid with and without the Perlite. It was also observed that the Perlite has negligible effect on pH and the sagging factor was maintained in the safe window. Moreover, the filtration and the filter cake characteristics were enhanced upon the Perlite addition in both mud densities.

Evaluation of shape memory polyurethane as a drilling fluid lost circulation and fracture plugging material

In a previous work, we developed shape memory polyurethane lost circulation materials (SMPU LCMs) programed to recover at wellbore temperature and plug fractures. Further testing and characterization of SMPU LCMs under various conditions and in the presence of different drilling fluid additives promote their field applicability. In this work, SMPU LCMs with 13/12/1, 18/17/1, and 25/24/1 M ratio of (hexamethylene diisocyanate/1,4 butanediol/polycaprolactone diol) were synthesized. Mechanical property testing indicated that SMPU13121 had the highest shape recovery (98.3%) and shape fixity (99%) and wellbore activation temperature of 59.1 °C. SMPU13121 was selected as the medium size SMPU LCMs to build the bridge. SMPU25241, with the highest Young's modulus (48 MPa), tensile strength (8.9 MPa) at 80 °C, and compression resistance (85.4 MPa), was selected as the fine SMPU LCMs to maximize the plug mechanical strength. A specifically designed particle permeability apparatus paired with a series of stainless-steel discs was utilized to investigate SMPU loss circulation attributes in cracked impermeable formation with varying fracture metrics, including fracture thickness and fracture wall angle. Different weighting materials and drilling fluid densities were employed. In straight slot discs, the bridging occurs largely near the fracture mouth and is independent of disc thickness, whereas in tapered discs, SMPU LCMs sealing pressure improved by 9% and 146% with increasing fracture depth, from 13.07 mm to 52.3 mm, and decreasing wall angle, from 3.5° to 1.15°. Furthermore, increasing drilling fluid density from 1442 kg m−3 to 1762 kg m−3 increases the fracture sealing pressure by 11%. Different weighting materials also increase the fracture sealing pressure, depending on the particle size distribution and the morphology of the weighting material. The barite-WBM had the highest sealing pressure at 8.97 MPa, while the limestone-WBM had the lowest sealing pressure at 8.05 MPa. Limestone larger particle size distribution and lack of particle size in the range 63 μm–100 μm may explain the limestone-WBM lower pressure sealing ability.

Plugging efficiency of flaky and fibrous lost circulation materials in different carrier fluid systems

Lost circulation is one of the most significant contributors to wellbore instability and causes an increase in drilling operation costs. It is also a major contributor to the nonproductive time and must be minimized for improved economic and operational performance. The objective of this research is to provide tools and information about specific loss circulation management techniques that drillers can use to minimize lost circulation. This study involves comprehensive approaches to test the plugging efficiency of three different lost circulation materials (LCMs) from two groups of materials (flaky and fibrous). It also highlights the carrier fluids (drilling fluids) and the determination of the optimum drilling fluid properties. Different fracture sizes and the effect of the various LCM are analyzed. The impact of LCM’s shape, size, and physical and chemical properties along with the fracture sizes is discussed. Examining the particle size distribution before and after mixing with the fluids shows the capability of the materials in plugging the fracture while maintaining the minimum porosity and permeability of the plug. It also helps to strengthen the fracture gradient of the formation by knowing the actual particle sizes. The primary objective of this work is to precisely study and analyze these factors on the three LCMs along with different carrier fluids to investigate their plugging efficiency and potentially resolve or minimize the severity of the lost circulation problem.

Research and Practice of Risk Early Warning Technology for Lost Circulation with Drilling under the Conditions of Geological Engineering Information Fusion: The Example of the Yuanba Area

In the Yuanba area, many lost circulation accidents occur due to the complex geological structure, broken strata, and developed fractures, which seriously affect construction safety and drilling costs. Therefore, the Yuanba district is the focus of this paper. Firstly, a three-dimensional geomechanical model is established through multi-source information fusion to identify the main geological risk factors of lost circulation, according to the data on drilling and well logging in the operation area. Then a risk warning model and evaluation methods for loss circulation, based on geological engineering data fusion, are established, through which the characteristic parameters of various loss of circulation risks can be calculated in real time, parameters along the well trajectory can be extracted and compared, and thus, the risk of lost circulation is warned and analyzed in real time. The early warning of lost circulation risk can be achieved during drilling operations, which can improve the drilling efficiency and shorten the drilling cycle as a result.

Development and application of guar gum crosslinked gel with adjustable gelation time for total loss treatment

To remediate the problem of severe or total losses, and meet the requirements of borehole plugging and pumping at different well depths, a novel crosslinked polymer gel (named HPG/Zr gel) with controlled gelation time and high gel strength was developed as loss circulation material, which mainly comprised hydroxypropyl guar gum, zirconium compound and triethanolamine. The influence of hydroxypropyl guar gum concentration, zirconium compound concentration, triethanolamine concentration and temperature on the gelation time of HPG/Zr gel was evaluated. In addition, the performance of HPG/Zr gel was investigated in terms of temperature resistance and shear resistance property, plugging ability and supporting cement slurry ability. According to the results, HPG/Zr gel can form a viscoelastic body with a network structure, and its gelation time can be practically adjustable. The results of the plugging experiment at different temperatures, pressures and pore sizes of quartz sand revealed that HPG/Zr gel could effectively plug sand pores at 150°C, and its pressure-bearing capacity can be up to 5 MPa. Employing its flow resistance and ability of supporting cement slurry, HPG/Zr gel was successfully applied in two geological boreholes by combining with cement slurry. Overall, the results of laboratory research and field tests indicate that HPG/Zr gel is useful for mitigating the lost circulation, and it is of huge importance to engineering applications.

Eco-Friendly Bridging Material: Experimental Characterization of Eggshells as an Affordable Natural Waste Non-Damaging Lost Circulation Material to Reduce Drilling Fluid Cost in Reservoir Drill-In-Fluid System

Lost circulation nowadays became one of the major problems in many drilling operations worldwide. This problem is complicated for it can significantly cause non-productive time during drilling operations. This research aims to study eggshells as a LCM and to provide further insight about the reliability and cost analysis of eggshells as a potential drilling fluid additive. Moreover, the research successfully identified the usage of an abundant natural waste, i.e. eggshells, as an environmentally friendly fluid additive. This research also investigated the technical feasibility of the eggshells and also its economics impact on drilling operations. In addition, it is found that the eggshells can also act as a non-damaging LCM for production zone that is more affordable as compared to other natural waste loss circulation materials and current commercially chemical. Series of laboratory tests were conducted such as mud balance for the density test, rheological test using viscometer Fann Vg, filtration loss test with filter press, and also alkalinity (pH) test. An excellent result from filtration loss test i.e. decreased fluid losses and showed great improvement almost same as commercially CaCO3 result in the filter cake thickness. The research proves great potential of the utilization of eggshells as a multi-purpose additive in a drilling fluid. Economic analysis also suggests that it can possibly be implemented and to be further developed for a large-scale field operations. Finally, it is found that using eggshells as LCM can reduce the cost up to 72.2 % cheaper than commercial CaCO3. It is also safe for drilling in the production zone (pay-zone) because of its solubility on acid that it can disappear during the acidizing job. If this paper can be implemented on a wide-range scale it will be very beneficial to reduce other commercial additives usage without losing its reliability.

Performance evaluation of nanosilica derived from agro-waste as lost circulation agent in water-based mud

Seepage or loss of the mix-water from the drilling muds into the porous and permeable formations is a common problem during drilling operation. The drilling mud design requires a good knowledge of sealing integrity and all the factors influencing the mud to bridge through fractures or pore throat of exposed rocks. Loss circulation materials (LCMs) are commonly introduced into the drilling mud to prevent or minimize filtrate loss. This study investigates silica nanoparticle (SNP) derived from rice husk (RH) termed RH-SNP using the wet-milling method as an LCM in water-based mud (WBM). The impact of the RH-SNP in the enhancement of rheology and filtrate loss control properties of WBM was studied. Subsequently, the sealing integrity of the RH-SNP in a 1 mm and 2 mm simulated fracture for 7 min was determined using a stainless-steel slotted filter disk. The performance of the developed RH-SNP was compared with the widely applied nutshell. The synthesized RH-SNP at amount of 2.0 wt% significantly enhanced the yield point and plastic viscosity of the WBM by 75% and 386%, respectively, and minimized the fluid loss of the WBM by 47% at 80 °F. The enhancement is due to the particles ability to spread and interact efficiently with the WBM. With the use of 1 mm and 2 mm simulated fracture for 7 min, the mud loss volume of the base mud reduced by 50%, 66.7%, 86%, and 90% (for 1 mm) and 40%, 65.7%, 77.1%, and 80% (for 2 mm) with the inclusion of 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt% of RH-SNP, respectively. Overall, the results showed that RH-SNP enhanced the seal integrity of the drilling mud and was more resistant to deformation compared to the nutshell. The findings of this study can help for better understanding of the application of RH-SNP as a loss circulation agent owing to its superior ability to seal fractured formation compared with the often used nutshell.

Solution and Analysis of Wellbore Temperature and Pressure Field Coupling Model under Lost Circulation.

The fluid in the annulus is in a variable mass flow state under the lost circulation condition, significantly affecting wellbore pressure distribution and the heat transfer efficiency between wellbore and formation. Therefore, based on the hydrodynamics and energy conservation law, a coupling model of transient wellbore temperature and pressure field under lost circulation conditions is established, which fully considers the casing program, bottom hole assembly, and heat source generated in drilling, as well as the influence of the temperature and pressure coupling in wellbore on the physical parameters of drilling fluid. The calculation results of the model in this paper are in good agreement with the field measured data and the previous research results, which verifies the rationality and accuracy of the model in this paper. The effects of the loss rate and the lost circulation zone location on the wellbore temperature and pressure distribution are analyzed, and the variation rule of the physical parameters of drilling fluid under the lost circulation condition is studied. The numerical simulation results show that the density and viscosity of drilling fluid in the annulus and bottom hole pressure increase with the increase in the circulation time; the annulus temperature decreases gradually with the increase in cycle time and tends to become stable after 8 h of the cycle. The annulus temperature and bottom hole pressure decrease with the increase in loss rate and closeness of the loss zone to the well bottom. When the loss zone is in the upper open-hole section, an inflection point consistent with the location of the loss zone appears on the annular temperature difference curve between the loss circulation and the nonloss circulation, and the position of the loss zone can be judged according to the inflection point.