Bottom Hole Research Articles

Distributed model for the drill-string system with multiple regenerative effects in the bit-rock interaction

In this paper, an integrated model is presented to study the axial–torsional dynamics of a distributed drill string. The coupled axial and torsional drill string dynamics typically lead to severe phenomena such as bit-bounce and stick–slip, which are the main causes of failure and efficiency reduction. The top-drive dynamics and the Bottom Hole Assembly (BHA) dynamics are interconnected through the drill pipes. In order to preserve the infinite-dimensional feature of the drill pipes in the mathematical modeling, a distributed model in terms of Delay Differential Algebraic Equations (DDAE) is proposed to represent the dynamics of the drill string. The bit-rock interaction, which consists of the cutting and the frictional components, is responsible for the coupling between the axial and torsional dynamics. A rate-independent bit-rock interaction law is employed for both cutting and frictional components. In order to capture the global bit motion, including multiple regenerative effects, the well-bottom depth function is used to determine the depth of cut. The well-bottom pattern evolution is formulated through algebraic equations rather than Partial Differential Equations (PDEs). A new formulation for the linearized drill string system in terms of Neutral-type Delay Differential Integral Equations (NDDIEs) is proposed to investigate the initiation of the oscillations around the nominal operation. By this formulation, the local stability of the distributed system is studied by determining the right-most eigenvalue of the linearized dynamics. A simulation-based case study reflecting real-life scenarios is presented to investigate the dynamical behavior of the system under different operating conditions.

Utility of fluid inclusion paleo-temperature in petroleum system modelling: A case study from western offshore, India

The paleo-temperature (Th) data from fluid inclusions are utilized for thermal history modelling using PetroMod software. Generally, bottom hole temperature (BHT) and vitrinite reflectance (Ro) measurements are widely used in petroleum system modelling (PSM) in the oil industry for calibration purposes. Th representing the minimum temperature of fluid entrapment estimated from fluid-inclusion study provides extra support to build the thermal models for PSM. Fluid inclusion parameters along with Rock-Eval pyrolysis analysis have been used to predict the maturity of oil in terms of API gravity as well as the maturity of source rocks respectively. Two exploratory wells RV-1 (Mumbai Offshore Basin) and KK4C-A-1 (Kerala-Konkan Offshore Basin), India were examined and the Th from most of the fluid inclusions of wells RV-1 and KK4C-A-1 fell in the oil window range of 60–140 °C suggesting thermal conditions favourable for oil generation in both of the wells. Th of coeval aqueous inclusions along with the Hydrocarbon Fluid inclusions (HCFIs) was used to calibrate PSM. Vital parameters show that source rocks of well RV-1 are mature and that of well KK4C-A-1 are immature. Two sets of PSM are created in terms of generation and expulsion for the dry wells RV-1 and KK4C-A-1 and calibrated each well using fluid inclusion Th and BHT. From the fluid inclusion analysis method, it is evident that hydrocarbon generation happened in both wells and the paleo-temperature indicates that the formations of both wells were subjected to temperatures in the oil window range, even though it was designated as dry wells in the present scenario. The present study highlights the application of fluid inclusion paleo-temperature (Th) during calibration instead of commonly used methods. We could obtain desirable and accurate data output from PSM using Th calibration.

An approach for optimization of controllable drilling parameters for motorized bottom hole assembly in a specific formation

This study focuses on optimizing drilling parameters when using Positive Displacement Motors (PDMs). In drilling operations involving mud motors, weight-on-bit (WOB) alterations lead to variations in the system's parasitic pressure drop. Consequently, this affects the optimum flow rate and the hydraulic power of the bit. Also, if the flow rate changes, the bit's rotations per minute (RPM) also change. In other words, using PDMs creates a link between the hydraulic system and the drilling speed, such that changing drilling parameters such as the WOB causes changes in the hydraulic system's performance. Therefore, one possible way to optimize the drilling parameters is to consider the drilling rate and hydraulic system simultaneously using a multi-objective approach. This study used an integrated approach encompassing data mining and mathematical modeling, employing a multi-objective framework to identify optimal parameters. The approach was applied to Dariyan Formation drilling data. The data mining approach revealed a well-distributed data set covering optimal and suboptimal zones suitable for optimization. In data mining, the identification of optimal conditions included a WOB of 11500 lb, a rotation speed of 105.8 rev/min, and a flow rate of 843 gpm, leading to an ROP of 44.23 ft/h. In multi-objective optimization, the optimal parameters consisted of a WOB of 14480 lb, a rotation speed of 115 rev/min, and a flow rate of 920.8 gpm, resulting in an ROP of 40.49 ft/h. Comparing optimal results with the drilling data shows a substantial MSE reduction of over 35 %. The results show the good performance of this approach in detecting the optimal and non-optimal drilling variables.

Detection of Barely Visible Impact Damage in Composite Structures Using Backward Sweep Vibro-thermography Technique Utilizing Asymmetry in Local Defect Resonance

ABSTRACT In this article, local defect resonance-based vibrothermography has been studied for different sweep direction and ranges. Two different carbon fiber-reinforced polymer (CFRP) composite plate has been fabricated from vacuum assisted resin transfer molding. In the first plate, a flat bottom hole has been made and two barely visible impact damages are created in other plate. The area of delamination has been determined from phased array ultrasound testing. Laser doppler vibrometry (LDV) has been performed first for different sweep ranges and directions. The CFRP plate is excited with a piezoelectric element at 150 Vpp and the vibration over defect area is captured using a single point laser doppler vibrometer, operating in scanning mode. It has been found that vibration amplitude at local defect resonance (LDR) frequency increases in narrow sweep range compared to a wideband excitation. Again, in both cases, it has been found that backward sweep produces more amplitude compared to forward one due to softening nonlinearity. An asymmetry in LDR frequency is also been observed when the sweep range is further narrowed. An uncooled microbolometer camera is used for reception in case of vibrothermography. Backward sweep is found to be more effective as compared to the forward one and the temperature increment increases in case of narrowband excitation range.

Simulation study of drilling fluid cooling in long horizontal wells based on phase change heat absorption

ABSTRACT The shale gas resources found in deep formations are abundant and represent a crucial area for current and future shale gas development. However, as shale gas exploration and development intensify in China, an increasing number of high-temperature formations are being encountered during drilling, presenting significant challenges to drilling engineering and severely constraining the development of deep shale gas exploration. In this study, the stability of PCM (phase change material) combined with drilling fluid as a coolant was discussed, and the influence of PCM on wellbore temperature field in drilling fluid was considered. A calculation model of temperature field of drilling fluid containing PCM was established, the cooling characteristics of PCM under the influence of different parameters were simulated, and the cooling effect of PCM integrated with drilling fluid on ultra-deep and high-temperature Wells was analyzed. The investigated PCM has a phase change temperature range of 120 ~ 130°C and a latent heat of 264.15 ~ 265.53 kJ/kg. Our results showed that the cooling impact of PCM exhibits an upward trend as the quantity of PCM utilized increases. Assuming the drilling temperature limit is 135°C, after adding 5% PCM to the drilling fluid, the drilling length of the horizontal section increased by approximately 500 m. With 15% PCM added, the horizontal section could be extended by about 1000 m. We conducted a simulation analysis on a well in southern Sichuan, and found that adding 12% PCM had the best cooling effect, reducing the bottom hole temperature by 12.3°C and extending the horizontal section by 700 m. Compared with conventional drilling fluid cooling methods, incorporating PCM as cooling agents within the drilling fluids provided better cooling effects. It effectively addressed the problem of excessive bottom-hole temperatures in deep wells, extended the drilling length of horizontal sections, and prolonged the service life of downhole instruments. Our research lays the groundwork for the future investigation of cooling techniques for high-temperature deep well drilling fluids.

Deep eutectic solvent modified graphene as a lubricant for water-based drilling fluid

ABSTRACT Deep and ultra-deep drilling technology development is critical to the exploitation of ultra-deep oil and gas deposits. As the number of ultra-deep wells increases, the bottom hole temperature of certain ultra-deep wells approaches 250°C. The high-temperature and high-pressure environment can influence the stability and longevity of drilling instruments, as well as the density, rheology, and stability of drilling fluid, making wellbore stability difficult to maintain. Problems such as high torque and high friction affect the safety of downhole drilling and drilling efficiency. Adding lubricant to drilling fluid is an effective way. In this study, choline chloride (ChCl) and polyethylene glycol (PEG) were used to synthesize a deep eutectic solvent (DES), and an environmentally friendly water-based drilling fluid lubricant DES/G was prepared by compounding the DES with graphene (G). Infrared spectrum, particle size analysis, and electron microscope tests were used to characterize the structure of the lubricant. At the same time, the effect of lubricant was evaluated by extreme pressure lubricity tester and friction and wear tester, and the adhesion coefficient of filter cake was tested. At temperatures below 200°C, DES/G demonstrated a significant enhancement in the lubricating properties of drilling fluids and filter cakes. The adhesion coefficient was controlled within 0.1, and the reduction rate was exceeding 30%. With increasing dosage of the lubricant, DES/G consistently maintained a low adhesion coefficient value of 0.03803 to 0.06253 (at 180°C) and 0.0414 to 0.07337 (at 200°C). Furthermore, it exhibited higher values of reduction rate, reaching a maximum of 64%. The lubricant can increase lubricating performance by adsorbing on the metal surface to generate a strong lubricating coating and converting the sliding friction between drilling tools to rolling friction.

Geomechanical Response in Energy Transition Applications: Assessing its Role with Data Assimilation

The subsurface is characterized by significant uncertainties that pose challenges for geothermal energy production, CO2 sequestration, and hydrocarbon field development. To handle this uncertainty, engineers often use ensembles of models with different porosity and permeability distributions. In addition, history-matching procedures can further reduce uncertainty. However, traditional methods using well bottom hole pressures as observations can be challenging for geothermal or CO2 sequestration projects with a limited number of wells. To overcome this limitation, additional observation data can be used. In this study, we propose using vertical displacements to evaluate the subsidence/uplift of the model. Pressure depletion, for example, leads to surface subsidence due to rock compaction. We suggest measuring subsidence during field development and using it as an objective function to minimize the difference from measured data. Our approach provides a more reliable and accurate way to evaluate the model's subsurface behavior, helping to reduce uncertainties in geothermal energy production, CO2 sequestration, or hydrocarbon field development.
 We used a state-of-the-art simulator called DARTS [1] to simulate fluid flow in the subsurface, and computed geomechanics response using a physics-based proxy. We then performed history matching using ensemble smoother with multiple data assimilation (ES-MDA) of the reservoir subsidence to better understand the reservoir properties, such as permeability [2]. Our workflow involved generating an ensemble of models with varying permeability and computing vertical displacements using the physics-based proxy model for geomechanics [3]. We then applied ES-MDA to find the model with permeability that fits best to the reference subsidence surface. Flow pattern in heterogeneous reservoir determines in-situ stress changes, which could induce seismicity in a presence of natural faults. We used fault slippage criteria for each scenario. Data assimilation procedure provide us history matched model, and, therefore, more reliable assessment of induced seismicity risk. We used 2.5D extruded mesh with heterogeneous permeability and uniform geomechanical properties.

Reservoir Analysis for A Low Recovery Factor Mature Reservoir with A Gas Cap and Large Aquifer: A Proposed Coning Correlation

With the development of reservoir engineering and management, enhanced oil recovery (EOR) techniques are becoming increasingly sophisticated. Generally, the recovery factor (RF) for a conventional reservoir can range from around 10% to 60% after four decades of production, with an average recovery factor of around 35%. While the RF of the NGJ field with high porosity (0.25) and permeability (300 to 600 md) is 6.11% after producing for over 40 years, which is rare in such good reservoir conditions. In this work, some classic techniques and several advanced methods were utilized to investigate the reason behind the low RF for this reservoir.A dynamic reservoir simulation was constructed on the basis of a statics petrophysical model. Based on the preliminary simulation study, it was found that gas coning is a common problem in the reservoir. Therefore, a concept of coning correlation function (CCF) is proposed, and the procedures for developing the CCF are explained. The critical oil rate was estimated using the Addington correlation and modified through the proposed coning correlation that varies as a function of time. The estimated critical rate through CCF is used to control flowing bottom hole pressure (FBHP) in the prediction scenarios.

Analysis of Well Performance Based on Bottom Hole Pressure Calculations for Gas Lift Application

This paper focuses on optimizing gas lift techniques in four wells located in the North Sea to overcome the common issue of low reservoir pressure. Gas lift is a common artificial lift technique used in wells with low reservoir pressure where the natural pressure of the reservoir is insufficient to bring the oil to the surface. The success of gas lift optimization depends on identifying the deepest injection point, gas injection rate, and pressure of the gas injected. The paper proposes the deepest injection points for wells A-03, A-09A, A-10T2, and A-12BT2 as 3809.38 ft, 6649.7 ft, 3559.88 ft, and 3979.04 ft, respectively. The injection rates analyzed in this paper range from 1-10 mmscf/day, and injection pressures of 500 psia, 1000 psia, and 1500 psia were used. The response of each well to gas lift was analyzed, and increasing injection rate and pressure were found to increase oil production rate. The optimal gas injection rate and pressure for wells A-03, A-09A, and A-12BT2 were found to be 10 mmscf/day and 1500 psia, while for well A-12BT2, the best oil recovery was obtained at an injection rate of 3 mmcsf/day and injection pressure of 1500 psia. Tubing size within the range of 1-5.5 inch was examined, and it was found that increasing tubing size enhances oil flow rate. The optimal tubing size for the wells was found to be 5.5 inch, taking into consideration factors such as flow rate, pressure, temperature requirements, and fluid type.

Identification of resistance torque on the roller cone bit in the drill rod rotation drive

There is a problem of increasing the durability of the roller cone bit of the drilling rigs used in the quarries of Ukraine. One of the effective ways to solve it is to apply the control method of maintaining a constant flow of mechanical power in the bottom hole zone. The implementation of such a control method leads to the necessity of controlling and limiting the resistance torque on the roller cone bit. To solve the problem of determining the resistance torque, we used methods of parameter identification: the Luenberger observation device with adaptation to external influences; estimation of the resistance torque using an extended observation object; the theory of regulators adapting to perturbations. It has been established that the most rational method of identifying the resistance torque on a roller cone bit is an astatic monitoring device, which allows to implement a method of controlling the rotation of the drill rod by a drive mechanism that maintains a constant flow of mechanical energy through the roller cone bit and increases the durability of the roller cone bit.

A new strategy for eliminating bottom hole defects during aluminum droplet printing within a broad temperature range

A new strategy for eliminating bottom hole defects during aluminum droplet printing within a broad temperature range

Swab – Surge Pressure Investigation, and the Influence Factors, Prediction and Calculation (Review)

Surge pressure is supplemental pressure because of the movement of the pipes downward and the swab pressure is the pressure reduction as a result of the drill string's upward movement. Bottom hole pressure is reduced because of swabbing influence. An Investigation showed that the surge pressure has great importance for the circulation loss problem produced by unstable processes in the management pressure drilling (MPD) actions. Through Trip Margin there is an increase in the hydrostatic pressure of mud that compensates for the reduction of bottom pressure due to stop pumping and/or swabbing effect while pulling the pipe out of the hole. This overview shows suggested mathematical/numerical models for simulating surge pressure problems inside the wellbore with adjustable cross-section parts. The developed models require simple input data that may be gotten from the rig location. Pressure variations due to Swabs and surge has been a major concern in the oil industry for numerous years. If the pressure variations become moreover extraordinary, this leads to formation fracture, and formation influx principal to a kick. In the worst circumstances and situations that kick principal on the blowout and put crew life in hazard. By using theoretical investigation and experimental consequences, it established that the surge pressure is a function of the well depth, the drilling tools combination, the diameter of the wellbore, drilling mud properties, drilling pipe operation speed, and acceleration of the drill pipe movement, etc. This review focuses and investigates the essential theory and on software that computes the pressure variations in different flow conditions to predict surge and swab pressure values.

Study on development methods of different types of gas wells in tight sandstone gas reservoirs

Reasonable production allocation of tight sandstone gas reservoirs is an important basis for efficient development of gas wells. Taking Block XX in Ordos Basin as an example, the modified flowing material balance equation was established considering the variation of gas viscosity and compression coefficient, the advantages and disadvantages of the method were discussed, and a reasonable production allocation process for gas wells was developed. The results show that: ① The commonly used flow material balance method ignores the change of natural gas compression coefficient, viscosity and deviation coefficient in the production process. The slope of the relationship curve between bottom hole pressure and cumulative production and the slope of the relationship curve between average formation pressure and cumulative production are not equal After considering this change. Compared with the results calculated by the material balance method, the results calculated by the flow material balance method are smaller. ② The production of 660 gas wells in the study area during stable production period is verified. Compared with the open flow method, the dynamic reserve allocation method is better, with an error of 0.06%. ③ The new method in this paper is used to allocate production for different types of gas wells. The cumulative production of different types of gas wells shows different degrees of increase. The I, II, III and IV types of gas wells increase by 32.26%, 30.29%, 23.58% and 25.07% respectively. This study provides technical support for dynamic reserve calculation and reasonable production allocation of gas wells in the study area, and has important guiding significance for the formulation of reasonable development plan and economic and efficient development of tight sandstone gas reservoirs.

A coupled matrix-fracture productivity calculation model considering low-velocity non-Darcy flow in shale reservoirs

The flow behavior of shale reservoirs is extremely complex. The mainly used development method of large-scale volume fracturing of horizontal wells is associated with a series of problems such as low productivity in general, fast decrease in productivity, and difficulty to increase productivity. Therefore, it is necessary to evaluate the productivity of shale oil wells and determine the key control factors. Considering low-velocity non-Darcy flow, this paper establishes an analytical solution model for productivity calculation of multi-fracture shale oil horizontal wells with coupled matrix-fracture flow. Calculating the oil production rate by considering low-velocity non-Darcy flow in shale oil reservoirs obtains values closer to the actual oil production rate on site. The average relative error of the oil production rate of the H8 shale oil well is 4.27%. The average relative error of the oil production rate of the TMS shale oil wells is 34.97%, which exceeds the rate of the semi-analytical model by 47.84%. Sensitivity analysis shows that the oil production rate of multi-fracture shale oil horizontal wells is most sensitive to fracture cluster spacing and flowing bottom hole pressure. With decreasing fracture cluster spacing and flowing bottom hole pressure, both the matrix pressure gradient and the apparent permeability of the matrix increase. These increases not only increase the oil production rate but also reduce the influence of the non-Darcy effect on the oil production rate caused by boundary effect. In addition, the limits of the impact of non-Darcy effects caused by boundary effect on oil production rate have been clarified. The results enable not only the prediction of the oil production rate, cumulative oil production, and recovery factor of multi-fracture horizontal shale oil wells, but also the finding of the shale oil sweet spot according to the influence of matrix permeability and crude oil viscosity on the oil production rate.

Synergistic CH4 hydrate recovery and CO2 storage by coupling depressurization with CO2/N2 injection: A pilot-scale investigation

To ensure sustainable energy supply while mitigating climate change, combining CH4 recovery with CO2 storage in marine natural gas hydrate (NGH) reservoirs is a promising carbon–neutral technology. In this study, a pilot-scale reactor (V = 22 L) was used to study the combined processes of CH4 recovery from the methane hydrate-bearing sediment by using depressurization followed by in-situ CO2/N2 injection to form mixed CH4/CO2/N2 hydrate (Mix-H) at marine NGH reservoir conditions (T = 283.8 K and P = 11.0 MPa). The bottom hole pressure (BHP = 3.2 MPa, 5.3 MPa, and 6.8 MPa) during depressurization and the setting of horizontal wellbore (HW), were systematically investigated to optimize the synergistic CH4 recovery and CO2 storage. The CH4 recovery ratio (55.4–80.6%) and the CH4 production rate (5.15–134.98 mol/d) increased as BHP decreased. After CO2/N2 injection, Mix-H formed first in the CH4-rich region in the upper section of the reactor and propagated downward to the lower. The Mix-H formation kinetics were significantly enhanced with an increase in BHP, leading to a decrease in CO2 composition in the Mix-H. The use of a horizontal wellbore (HW) facilitates a more even distribution of the CO2/N2 within sediments, resulting in a 13.5% increase in CO2 composition of Mix-H compared with no HW setting. The CO2 conversion ratio and hydrate restoration ratio reaches 52.8% and 69.4% at BHP = 5.3 MPa with HW, respectively. The technical feasibility of CO2 storage in exploited marine NGH reservoirs was first proved at pilot-scale. The results provided insights into the synergistic method of NGH exploitation and CO2 storage at the marine NGH reservoirs.

Detection of Over Normal Pore Pressure Intervals by Using Well Logs

Pore pressure is very important parameter that impacting on drilling, production planning and operations. Drilling and production processes cannot be beginning if pore pressure is not estimated. There is a limit of difference between hydrostatic pressure of mud column and pore pressure during drilling to ensure that the layers are preserved from fracturing, as well as that kicking does not occur inside the well. Difference between pore pressure and bottom hole flowing pressure is a key for production process. Over (Abnormal) pressure intervals are causing many problems during drilling. In present study, pore pressure is estimated firstly as a hydrostatic pressure, and secondly, after determination of shale flag, two methods of Eaton slowness and Bowers original are used for detecting of over (Abnormal) pressure shale intervals. Compressional and density logs of three wells (X3, X4, and XD) located at Y oil field and producing from Asmari formation are used to perform the present study. Density log is linearly extrapolated to estimate bulk density from zero depth to last depth point at reservoir. Vertical stress is predicted for these three wells. The vertical stress gradients were 1.03, 0.99, and 0.93 psi/ft for XD, X3, and X4 wells respectively. Results are reveals that Bowers original better than Eaton slowness in detection of over (abnormal) pressure intervals where the last did not cut all shale intervals by compressional slowness shale base line that equal to 80 us/ft so, Eaton slowness method provided either very high over pressure in some shale intervals or subnormal pressure to other shale intervals and that inaccurate while Bowers original method approximately provided all shale intervals as over pressure in reasonable values. Modular dynamic tester measurements for pore pressure of these three wells are used for calibration. Maximum percent error between predicted and measured pore pressure of wells (X3, X4, and XD) are 1.2%, 0.89% and 3% respectively where these percent are very acceptable. Maximum over pressure values in Asmari formation zones at wells are as follows: 6328 psi at depth 3225 m in well X3, 7538 psi at depth 3080 m in well X4, and 6731 psi at true vertical depth 3067 m in well XD.

Real-time rate of penetration prediction for motorized bottom hole assembly using machine learning methods

Drilling rate of penetration (ROP) is one of the most important factors that have their significant effect on the drilling operation economically and efficiently. Motorized bottom hole assembly (BHA) has different applications that are not limited to achieve the required directional work but also it could be used for drilling optimization to enhance the ROP and mitigate the downhole vibration. Previous work has been done to predict ROP for rotary BHA and for rotary steerable system BHA; however, limited studies considered to predict the ROP for motorized BHA. In the present study, two artificial intelligence techniques were applied including artificial neural network and adaptive neurofuzzy inference system for ROP prediction for motorized assembly in the rotary mode based on surface drilling parameters, motor downhole output parameters besides mud parameters. This new robust model was trained and tested to accurately predict the ROP with more than 5800 data set with a 70/30 data ratio for training and testing respectively. The accuracy of developed models was evaluated in terms of average absolute percentage error, root mean square error, and correlation coefficient (R). The obtained results confirmed that both models were capable of predicting the motorized BHA ROP on Real-time. Based on the proposed model, the drilling parameters could be optimized to achieve maximum motorized BHA ROP. Achieving maximum ROP will help to reduce the overall drilling cost and as well minimize the open hole exposure time. The proposed model could be considered as a robust tool for evaluating the motorized BHA performance against the different BHA driving mechanisms which have their well-established models.

Chaotic Effect-Based Array Duffing Systems with Improved Nonlinear Restoring Force for Weak Signal Detection in Dynamic MWD.

In the process of dynamic Measurement While Drilling (MWD), the strong vibration and rapid rotation of the Bottom Hole Assembly (BHA) lead to multi-frequency and high-amplitude noise interference in the attitude measurement signal. The weak original signal and extremely low signal-to-noise ratio (SNR) are always the technical difficulties of dynamic MWD. To solve this problem, this paper uses the chaotic effect of the Duffing system, which takes the expression (-x3 + x5) as a nonlinear restoring force to detect the weak characteristic signal of downhole dynamic MWD. First of all, in order to meet the limit condition of the chaotic phase transition of the system output, the frequency value of the characteristic signal is reconstructed and transformed based on the variable scale theory. Then, in order to solve the influence of the initial phase of the characteristic signal on the detection accuracy, a detection model based on the array Duffing system is presented, and a frequency-detection scheme with all-phase coverage is given. Finally, another array Duffing system is designed for the parameter estimation of the characteristic signal. The critical value of chaotic phase transition is determined by adjusting the amplitude of the driving signal of the array Duffing system, and then the amplitude and phase parameters of the characteristic signal are synchronously estimated. The experimental results show that the proposed method can effectively extract the weak characteristic signal within the strong noise, and the SNR of the characteristic signal can be as low as -21 dB. Through the attitude calculation for the extracted characteristic signal, it can be seen that the proposed method can improve the accuracy of the inclination of the drilling tool significantly, which proves the feasibility and effectiveness of the method proposed in this paper.

Superior crack propagation inhibitory effectiveness of MWCNT reinforced SBS toward improving oil/gas well cement integrity

The brittleness and low cracking resistance of oil- and gas-well cement threaten its integrity, specially under the high stress concentrations at bottom-hole conditions. Fortunately, the excellent mechanical properties of carbon nanotubes and elastomers motivate researchers to utilize them as versatile candidates that can positively modify the breakage behaviors of cement-based materials. Herein, we investigated the hybridization effects of multi-walled carbon nanotubes (MWCNTs) and styrene–butadiene–styrene (SBS) on the mechanical properties and breakage behaviors of oil- and gas-well cements. MWCNTs and SBS were synthesized and then, characterized with a wide range of techniques, signifying successful syntheses of these two materials. Afterward, SBS was dry mixed with cement powder and then added to the aqueous suspension of MWCNT prepared via sonication method. The mechanical testing (e.g., uniaxial, triaxial, and Brazilian tests), numerical simulation, and imaging analysis showed that incorporation of the SBS into the cement matrix promoted the ductility and macro-scale cracking resistance. The introduction of MWCNTs improved the cohesion, micro-scale cracking resistance, and strength properties of the cement matrix. Thereupon, the hybridization of 0.075 wt% of MWCNT and 9 wt% of SBS endowed great mechanical behavior and cracking resistance to the conventional oil-well cement in both micro and macro structures. These specifications can maintain cement’s durability under the critical thermal and mechanical stress concentrations at various bottom hole conditions. This improvement contains the increasing of strain energy, tensile strength, cohesion, and Poisson’s ratio by 219.27%, 141.17%, 750% and 100%, respectively and reducing the elastic modulus by 41.67%. Fourier Transform Infrared Spectroscopy (FTIR) analysis exhibited that these enhancements can be attributed to favorable interactions between MWCNT and SBS in the cement matrix.

ANALYSIS OF MUD DENSITY BY USING CUTTING CAPACITY ANNULUS METHOD

Drilling mud has an important role in drilling operations, as well as lifting the cutting to the surface, controlling the pressure of the formation, and preventing the collapse of the borehole. Therefore, the drilling operations can be continued without obstacles. The function of the drilling mud depends on the conditions of the formation to be drilled for optimal results. One of the main functions is to lift cutting from a bottom hole to the surface. In the annulus, the minimum speed for lifting the cutting to the surface was calculated. The Cutting Capacity Annulus (CCA) is the value of the level of solids in the annulus. The proper concentration of cutting in the annulus is not more than 5%, to avoid drilling problems, such as decreased rate of penetration (ROP), increased drag and torque, and stuck pipe related to hole cleaning problems. In analyzing the lifting ability of cutting, CCA is very suitable to be used because it accounts for the parameters of ROP value. This study conducted a comparison of two types of natural polymers that have a function to help the hole cleaning in the drilling process. The two types of polymers are cellulose polymers (drispac) and polysaccharide polymers (starch). Furthermore, it also had been tested on a field scale using the cutting transport ratio (CTR) method to find out how much ratio is obtained in the two types of polymer mud. Based on the test of the two mud samples on the cutting removal process in the CCA method at a temperature of 150oF, the mud samples containing starch ranged from 1.0731% to 1.0792%, while the mud samples containing drispac ranged from 1.0730% to 1.0793%. At 200oF the mud samples containing starch ranged from 0.7357% to 1.3604%, while the mud samples containing drispac ranged from 0.7357% to 1.3603%. At a temperature of 250oF, the mud samples containing starch ranged from 0.2652% to 0.4903%, while the mud samples containing drispac ranged from 0.265178% to 0.4907%. Although the density of the starch-containing mud sample was greater than drispac, the CCA value did not have much effect due to the difference in density of the two mud samples of 0.1 ppg. Both samples were able to optimally lift the cutting above the surface because the CCA value was less than 5%.